Prepare the v0.11.2 release

AGENTS.md

@@ -1,2 +1,6 @@
-Please review `docs/development.md` for initial orientation in this repository
-and follow its task-specific reading guide.
+Start with `docs/development.md` for orientation and use its policy reading guide
+to select the policies applicable to the task. Do not read the entire suite by
+default.
+
+Read and follow `docs/policy/agents.md` before recommending, planning, or
+implementing repository changes.

COPYRIGHT

@@ -0,0 +1,23 @@
+PromptKit
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: LGPL-3.0-or-later
+
+This library is free software: you can redistribute it and/or modify it
+under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+The GNU Lesser General Public License version 3 is provided in LICENSE.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Lesser General Public License for more details.
+
+Policy documents copied or adapted from Standard Repository Policies remain licensed
+under CC-BY-SA-4.0. See docs/oss/attribution.md for the affected material,
+upstream credit, and license links.
+
+Third-party code and assets are subject to their respective license terms.

README.md

@@ -31,4 +31,52 @@ Contributors should start with the [development guide](docs/development.md).
 The [architecture policy](docs/policy/architecture.md) defines the library
 boundary and constraints that framework work must preserve.
 
-Promptkit is licensed under the [GNU General Public License version 3](LICENSE).
+## Release Guidance
+
+The [v0.11.2 release notes](docs/releases/v0.11.2.md) cover policy alignment
+and copied-policy attribution updates.
+
+The [v0.11.1 release notes](docs/releases/v0.11.1.md) cover the MIT-licensed
+catalog updates and licensing documentation improvements.
+
+Consumers upgrading to `v0.11.0` should read the
+[v0.11.0 changelog and migration guide](docs/releases/v0.11.0.md), particularly
+the default retry behavior and license change.
+
+Consumers upgrading to the `v0.10.0` profile-policy transition
+should read the [v0.10.0 transition guide](docs/releases/v0.10.0.md).
+
+Consumers upgrading from `v0.8.0` to `v0.9.0` should read the
+[v0.9.0 changelog and migration guide](docs/releases/v0.9.0.md).
+
+Consumers upgrading from `v0.7.0` to `v0.8.0` can consult the
+[v0.8.0 changelog and migration guide](docs/releases/v0.8.0.md).
+
+Earlier adopters can consult the
+[v0.7.0 changelog and migration guide](docs/releases/v0.7.0.md).
+
+Consumers upgrading from `v0.5.0` to `v0.6.0` can consult the
+[v0.6.0 changelog and migration guide](docs/releases/v0.6.0.md).
+
+Consumers upgrading from `v0.4.0` to `v0.5.0` can consult the
+[v0.5.0 changelog and migration guide](docs/releases/v0.5.0.md).
+
+Consumers upgrading from `v0.3.0` to `v0.4.0` should read the
+[v0.4.0 changelog and adoption guide](docs/releases/v0.4.0.md).
+
+Consumers upgrading from `v0.2.0` to `v0.3.0` should read the
+[v0.3.0 changelog](docs/releases/v0.3.0.md).
+
+Consumers moving from `v0.1.0` to `v0.2.0` should read the
+[v0.2.0 changelog and migration guide](docs/releases/v0.2.0.md).
+
+## Related Project
+
+[Scriptorium](https://gitea.maximumdirect.net/eric/scriptorium) is the CLI and
+HTTP application built on Promptkit.
+
+## License
+
+Promptkit is licensed under the [LGPL v3.0 or later](COPYRIGHT).
+
+[Open Source attribution notices](docs/oss/attribution.md) are available.

appended_messages_contract_test.go

@@ -0,0 +1,145 @@
+package promptkit_test
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"sync/atomic"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+func TestAppendedMessageRoleConstantsAreStrings(t *testing.T) {
+	var (
+		developer string = promptkit.RoleDeveloper
+		system    string = promptkit.RoleSystem
+		user      string = promptkit.RoleUser
+		assistant string = promptkit.RoleAssistant
+	)
+	if developer != "developer" || system != "system" || user != "user" || assistant != "assistant" {
+		t.Fatalf("unexpected role constants: %q %q %q %q", developer, system, user, assistant)
+	}
+}
+
+func TestAppendedMessagesComposeFrozenEffectivePrompt(t *testing.T) {
+	cacheControl := &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}
+	appended := []promptkit.RenderedMessage{
+		{Role: " \tAsSiStAnT\n", Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: cacheControl},
+	}
+	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "output"}}
+	engine, err := promptkit.NewEngine(
+		promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "configured prompt"), "."),
+		promptkit.WithProfiles(promptkit.Profile{ID: "profile", Endpoint: "http://example.test/v1", Model: "model"}),
+		promptkit.WithLLMClient(client),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+	request := promptkit.RunRequest{PromptID: "prompt", AppendedMessages: appended}
+
+	plain, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("prepare plain request: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), request)
+	if err != nil {
+		t.Fatalf("prepare appended request: %v", err)
+	}
+	expected := []promptkit.RenderedMessage{
+		{Role: promptkit.RoleUser, Content: "configured prompt"},
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}},
+	}
+	if !reflect.DeepEqual(prepared.Messages, expected) || prepared.PromptHash != plain.PromptHash || prepared.RenderedPromptHash == plain.RenderedPromptHash {
+		t.Fatalf("prepared effective prompt = %#v, plain = %#v", prepared, plain)
+	}
+
+	equivalent, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: &promptkit.CacheControl{Type: promptkit.CacheControlEphemeral, TTL: "1h"}},
+	}})
+	if err != nil || equivalent.RenderedPromptHash != prepared.RenderedPromptHash {
+		t.Fatalf("normalized-equivalent request = (%#v, %v), want matching rendered hash %q", equivalent, err, prepared.RenderedPromptHash)
+	}
+
+	for _, variant := range []promptkit.RunRequest{
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{{Role: promptkit.RoleAssistant, Content: "changed"}, expected[2]}},
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{expected[2], expected[1]}},
+		{PromptID: "prompt", AppendedMessages: []promptkit.RenderedMessage{{Role: promptkit.RoleAssistant, Content: "previous response"}, {Role: promptkit.RoleUser, Content: "corrective request"}}},
+	} {
+		variantPrepared, prepareErr := engine.Prepare(context.Background(), variant)
+		if prepareErr != nil || variantPrepared.RenderedPromptHash == prepared.RenderedPromptHash || variantPrepared.PromptHash != prepared.PromptHash {
+			t.Fatalf("variant preparation = (%#v, %v)", variantPrepared, prepareErr)
+		}
+	}
+
+	result, err := engine.Run(context.Background(), request)
+	if err != nil || result.RenderedPromptHash != prepared.RenderedPromptHash || !reflect.DeepEqual(client.requests[0].Prompt.Messages, expected) {
+		t.Fatalf("run result = (%#v, %v), request = %#v", result, err, client.requests)
+	}
+
+	execution, err := engine.PrepareExecution(context.Background(), request)
+	if err != nil {
+		t.Fatalf("prepare execution: %v", err)
+	}
+	appended[0].Content = "changed caller content"
+	cacheControl.TTL = ""
+	firstDetails := execution.Details()
+	firstDetails.Messages[1].Content = "changed details content"
+	firstDetails.Messages[2].CacheControl.Type = "changed details cache"
+	secondDetails := execution.Details()
+	if !reflect.DeepEqual(secondDetails.Messages, expected) || secondDetails.RenderedPromptHash != prepared.RenderedPromptHash {
+		t.Fatalf("prepared execution details = %#v, want frozen %#v", secondDetails, expected)
+	}
+
+	result, err = engine.RunPrepared(context.Background(), execution)
+	if err != nil || result.RenderedPromptHash != prepared.RenderedPromptHash || !reflect.DeepEqual(client.requests[1].Prompt.Messages, expected) {
+		t.Fatalf("prepared result = (%#v, %v), requests = %#v", result, err, client.requests)
+	}
+}
+
+func TestInvalidAppendedMessagesFailBeforeSourceOrModelWork(t *testing.T) {
+	promptSource := &inspectionCountingFS{}
+	var modelCalls atomic.Int64
+	engine, err := promptkit.NewEngine(
+		promptkit.Config{},
+		promptkit.WithPromptFS(promptSource, "."),
+		promptkit.WithLLMClient(countingLLMClient{calls: &modelCalls}),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+	request := promptkit.RunRequest{
+		PromptID: "unreached",
+		AppendedMessages: []promptkit.RenderedMessage{{
+			Role:    "unsupported-role",
+			Content: "sensitive appended content",
+		}},
+	}
+
+	operations := []struct {
+		name string
+		run  func() error
+	}{
+		{name: "Prepare", run: func() error { _, err := engine.Prepare(context.Background(), request); return err }},
+		{name: "PrepareExecution", run: func() error { _, err := engine.PrepareExecution(context.Background(), request); return err }},
+		{name: "Run", run: func() error { _, err := engine.Run(context.Background(), request); return err }},
+	}
+	for _, operation := range operations {
+		t.Run(operation.name, func(t *testing.T) {
+			err := operation.run()
+			if !errors.Is(err, promptkit.ErrInvalidRequest) {
+				t.Fatalf("error = %v, want ErrInvalidRequest", err)
+			}
+		})
+	}
+	if promptSource.opens.Load() != 0 {
+		t.Fatalf("invalid appended message opened prompt sources %d times", promptSource.opens.Load())
+	}
+	if modelCalls.Load() != 0 {
+		t.Fatalf("invalid appended message invoked the model %d times", modelCalls.Load())
+	}
+}

backends.go

@@ -0,0 +1,107 @@
+package promptkit
+
+import (
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+// BackendOpenRouter is the reserved ID of Promptkit's built-in OpenRouter
+// backend.
+const BackendOpenRouter = backend.OpenRouterID
+
+// BackendRakestrawHome is the reserved ID of Promptkit's built-in
+// Rakestrawhome backend.
+const BackendRakestrawHome = backend.RakestrawHomeID
+
+// BackendLocal is the case-sensitive conventional ID used by [LocalBackend].
+// It is not a built-in or reserved backend and must be registered with
+// [WithBackend].
+const BackendLocal = "local"
+
+// Backend configures one engine-scoped OpenAI-compatible backend.
+//
+// Backend has no stable JSON representation. Use keyed literals so additions
+// to this configuration value do not break source compatibility.
+type Backend struct {
+	// ID is the stable, case-sensitive registry key. NewEngine trims it and
+	// requires a non-blank value. Built-in backend IDs are reserved.
+	ID string
+	// Endpoint is the OpenAI-compatible base endpoint. NewEngine trims it and
+	// requires an absolute HTTP or HTTPS URL with a host and without user
+	// information, a query string, or a fragment. Paths are allowed.
+	Endpoint string
+	// APIKeyEnv optionally names an environment lookup source for an API key.
+	// NewEngine trims it and requires the portable form [A-Za-z_][A-Za-z0-9_]*.
+	// A direct RunRequest.APIKey takes precedence. When no usable credential is
+	// available, the built-in client omits Authorization; injected clients own
+	// their own credential-resolution behavior. Store only the name, never a
+	// credential value.
+	APIKeyEnv string
+	// ExtraParams contains backend-wide request defaults. Values must be
+	// JSON-compatible, finite, acyclic, and keyed by non-empty strings. Keys
+	// must not be model, session_id, messages, temperature, max_tokens, top_p,
+	// service_tier, reasoning_effort, or response_format. An empty map supplies
+	// no defaults. NewEngine deeply copies the map and rejects excessively deep
+	// or large values for safety.
+	ExtraParams map[string]any
+	// ConcurrencyLimit is the maximum number of simultaneous model-generation
+	// calls allowed for this backend within one Engine. Zero leaves the backend
+	// unlimited. A negative value makes NewEngine fail with ErrInvalidConfig.
+	ConcurrencyLimit int
+	// QueueCapacity controls how many additional Run or RunPrepared calls may
+	// be admitted beyond ConcurrencyLimit. Nil uses 1024 when ConcurrencyLimit
+	// is positive; a pointer uses its exact value, including zero. The pointed-to
+	// value must be non-negative, and QueueCapacity must be nil when
+	// ConcurrencyLimit is zero. Their sum must fit in an int. WithBackend copies
+	// the value and does not retain the pointer.
+	QueueCapacity *int
+}
+
+// LocalBackend returns a caller-owned Backend for a conventional local
+// OpenAI-compatible endpoint. It sets ID to BackendLocal and copies endpoint
+// and concurrencyLimit into Endpoint and ConcurrencyLimit without
+// normalization or validation. APIKeyEnv, ExtraParams, and QueueCapacity keep
+// their zero values.
+//
+// LocalBackend does not read environment variables, register the value, or
+// mutate engine or package state. Supply the returned value through
+// [WithBackend]; [NewEngine] then applies the ordinary backend validation and
+// concurrency semantics, including default queue capacity for a positive
+// limit, unlimited behavior for zero, and ErrInvalidConfig for a negative
+// limit.
+func LocalBackend(endpoint string, concurrencyLimit int) Backend {
+	return Backend{
+		ID:               BackendLocal,
+		Endpoint:         endpoint,
+		ConcurrencyLimit: concurrencyLimit,
+	}
+}
+
+// WithBackend adds one Backend registration to the constructed Engine.
+//
+// Registrations accumulate in option order. Every normalized ID must be unique
+// across consumer registrations and built-ins; a duplicate or invalid
+// definition makes NewEngine fail with ErrInvalidConfig. Built-in IDs,
+// including [BackendOpenRouter] and [BackendRakestrawHome], cannot be
+// replaced. The immutable registration is scoped to the resulting Engine and
+// cannot be enumerated, replaced, removed, or mutated after construction.
+// WithBackend does not install package-global state.
+func WithBackend(backend Backend) Option {
+	queueCapacity := 0
+	queueCapacitySet := backend.QueueCapacity != nil
+	if queueCapacitySet {
+		queueCapacity = *backend.QueueCapacity
+	}
+	return optionFunc(func(options *engineOptions) error {
+		options.internal.AddBackend(domain.Backend{
+			ID:               backend.ID,
+			Endpoint:         backend.Endpoint,
+			APIKeyEnv:        backend.APIKeyEnv,
+			ExtraParams:      backend.ExtraParams,
+			ConcurrencyLimit: backend.ConcurrencyLimit,
+			QueueCapacity:    queueCapacity,
+			QueueCapacitySet: queueCapacitySet,
+		})
+		return nil
+	})
+}

capacity_contract_test.go

@@ -0,0 +1,409 @@
+package promptkit_test
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+func TestEngineLimitsInjectedClientConcurrency(t *testing.T) {
+	release := make(chan struct{})
+	client := newCapacityGateClient(release, 8)
+	engine := newBackendCapacityEngine(t, client, 2, capacityInt(4), nil)
+
+	results := make(chan capacityRunResult, 6)
+	for i := 0; i < 6; i++ {
+		go runCapacityRequest(engine, context.Background(), promptkit.RunRequest{
+			PromptID: "prompt",
+			Execution: &promptkit.ExecutionTargetOverride{
+				Endpoint: "http://request.example/v1",
+			},
+		}, results)
+	}
+
+	first := awaitCapacityRequest(t, client.started)
+	second := awaitCapacityRequest(t, client.started)
+	if first.Target.BackendID != "limited" || second.Target.BackendID != "limited" {
+		t.Fatalf("endpoint override changed backend pool: first=%q second=%q",
+			first.Target.BackendID, second.Target.BackendID)
+	}
+	if active, peak, _ := client.snapshot(); active != 2 || peak != 2 {
+		t.Fatalf("client concurrency before release=(active=%d peak=%d), want 2", active, peak)
+	}
+
+	close(release)
+	for i := 0; i < 6; i++ {
+		outcome := awaitCapacityRun(t, results)
+		if outcome.err != nil || outcome.result == nil {
+			t.Fatalf("run outcome=(%+v, %v), want success", outcome.result, outcome.err)
+		}
+	}
+	if _, peak, calls := client.snapshot(); peak > 2 || calls != 6 {
+		t.Fatalf("client observations=(peak=%d calls=%d), want peak <= 2 and 6 calls", peak, calls)
+	}
+}
+
+func TestEngineRejectsRunBeforeCompletionWhenAdmissionIsFull(t *testing.T) {
+	artifactRelease := make(chan struct{})
+	reader := &capacityArtifactReader{
+		entered: make(chan struct{}, 2),
+		release: artifactRelease,
+	}
+	client := newCapacityGateClient(closedCapacityChannel(), 2)
+	engine := newBackendCapacityEngine(t, client, 1, capacityInt(0), reader)
+	firstResult := make(chan capacityRunResult, 1)
+	go runCapacityRequest(engine, context.Background(), capacityInputRequest("http://first.example/v1"), firstResult)
+
+	awaitCapacitySignal(t, reader.entered, "first artifact read")
+
+	canceledContext, cancel := context.WithCancel(context.Background())
+	cancel()
+	result, err := engine.Run(canceledContext, capacityInputRequest("http://canceled.example/v1"))
+	if result != nil || !errors.Is(err, context.Canceled) {
+		t.Fatalf("canceled capacity admission=(%+v, %v), want context cancellation", result, err)
+	}
+	var canceledCapacityErr *promptkit.CapacityError
+	if errors.Is(err, promptkit.ErrCapacityExceeded) || errors.As(err, &canceledCapacityErr) {
+		t.Fatalf("canceled admission exposed capacity rejection: %v", err)
+	}
+
+	result, err = engine.Run(context.Background(), capacityInputRequest("http://second.example/v1"))
+	if result != nil {
+		t.Fatalf("capacity rejection returned partial result: %+v", result)
+	}
+	if !errors.Is(err, promptkit.ErrCapacityExceeded) {
+		t.Fatalf("capacity rejection=%v, want ErrCapacityExceeded", err)
+	}
+	if errors.Is(err, promptkit.ErrInvalidRequest) || errors.Is(err, promptkit.ErrLLMGenerate) {
+		t.Fatalf("capacity rejection had an unrelated category: %v", err)
+	}
+	var capacityErr *promptkit.CapacityError
+	if !errors.As(err, &capacityErr) || capacityErr == nil {
+		t.Fatalf("capacity rejection=%v, want CapacityError", err)
+	}
+	if capacityErr.BackendID != "limited" {
+		t.Fatalf("capacity backend ID=%q, want limited", capacityErr.BackendID)
+	}
+	capacityErr.BackendID = "changed"
+
+	result, err = engine.Run(context.Background(), capacityInputRequest("http://third.example/v1"))
+	var subsequentCapacityErr *promptkit.CapacityError
+	if result != nil || !errors.As(err, &subsequentCapacityErr) ||
+		subsequentCapacityErr == nil || subsequentCapacityErr.BackendID != "limited" {
+		t.Fatalf("subsequent capacity rejection=(%+v, %v), want independent limited CapacityError", result, err)
+	}
+	if calls := reader.callCount(); calls != 1 {
+		t.Fatalf("artifact calls=%d, want only the admitted run", calls)
+	}
+	if _, _, calls := client.snapshot(); calls != 0 {
+		t.Fatalf("client calls=%d before admitted run was released, want 0", calls)
+	}
+
+	close(artifactRelease)
+	outcome := awaitCapacityRun(t, firstResult)
+	if outcome.err != nil || outcome.result == nil {
+		t.Fatalf("first run outcome=(%+v, %v), want success", outcome.result, outcome.err)
+	}
+}
+
+func TestBackendCapacityIsIndependentBetweenEngines(t *testing.T) {
+	firstRelease := make(chan struct{})
+	firstClient := newCapacityGateClient(firstRelease, 1)
+	firstEngine := newBackendCapacityEngine(t, firstClient, 1, capacityInt(0), nil)
+	secondClient := newCapacityGateClient(closedCapacityChannel(), 1)
+	secondEngine := newBackendCapacityEngine(t, secondClient, 1, capacityInt(0), nil)
+
+	firstResult := make(chan capacityRunResult, 1)
+	go runCapacityRequest(firstEngine, context.Background(), promptkit.RunRequest{PromptID: "prompt"}, firstResult)
+	awaitCapacityRequest(t, firstClient.started)
+
+	result, err := secondEngine.Run(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil || result == nil {
+		t.Fatalf("second engine run=(%+v, %v), want independent success", result, err)
+	}
+	if _, _, calls := secondClient.snapshot(); calls != 1 {
+		t.Fatalf("second engine client calls=%d, want 1", calls)
+	}
+
+	close(firstRelease)
+	outcome := awaitCapacityRun(t, firstResult)
+	if outcome.err != nil || outcome.result == nil {
+		t.Fatalf("first engine run=(%+v, %v), want success", outcome.result, outcome.err)
+	}
+}
+
+func TestUnlimitedBackendsRetainInjectedClientConcurrency(t *testing.T) {
+	tests := []struct {
+		name      string
+		configure func(*testing.T, promptkit.LLMClient) *promptkit.Engine
+	}{
+		{
+			name: "custom backend",
+			configure: func(t *testing.T, client promptkit.LLMClient) *promptkit.Engine {
+				return newBackendCapacityEngine(t, client, 0, nil, nil)
+			},
+		},
+		{
+			name: "endpoint-only profile",
+			configure: func(t *testing.T, client promptkit.LLMClient) *promptkit.Engine {
+				engine, err := promptkit.NewEngine(promptkit.Config{},
+					promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "message"), "."),
+					promptkit.WithProfiles(promptkit.Profile{
+						ID: "profile", Endpoint: "http://endpoint.example/v1", Model: "model",
+					}),
+					promptkit.WithLLMClient(client),
+				)
+				if err != nil {
+					t.Fatalf("construct endpoint-only engine: %v", err)
+				}
+				return engine
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			release := make(chan struct{})
+			client := newCapacityGateClient(release, 2)
+			engine := tc.configure(t, client)
+			results := make(chan capacityRunResult, 2)
+			for i := 0; i < 2; i++ {
+				go runCapacityRequest(
+					engine,
+					context.Background(),
+					promptkit.RunRequest{PromptID: "prompt"},
+					results,
+				)
+			}
+
+			awaitCapacityRequest(t, client.started)
+			awaitCapacityRequest(t, client.started)
+			if active, peak, _ := client.snapshot(); active != 2 || peak != 2 {
+				t.Fatalf("unlimited concurrency=(active=%d peak=%d), want 2", active, peak)
+			}
+			close(release)
+			for i := 0; i < 2; i++ {
+				outcome := awaitCapacityRun(t, results)
+				if outcome.err != nil || outcome.result == nil {
+					t.Fatalf("run outcome=(%+v, %v), want success", outcome.result, outcome.err)
+				}
+			}
+		})
+	}
+}
+
+func TestCapacityExceededSentinelContract(t *testing.T) {
+	if promptkit.ErrCapacityExceeded == nil {
+		t.Fatal("ErrCapacityExceeded is nil")
+	}
+	var nilCapacityErr *promptkit.CapacityError
+	zeroCapacityErr := &promptkit.CapacityError{}
+	populatedCapacityErr := &promptkit.CapacityError{BackendID: "limited"}
+	for _, capacityErr := range []error{nilCapacityErr, zeroCapacityErr} {
+		if !errors.Is(capacityErr, promptkit.ErrCapacityExceeded) {
+			t.Fatalf("capacity error=%v, want ErrCapacityExceeded", capacityErr)
+		}
+	}
+	var discoveredCapacityErr *promptkit.CapacityError
+	if !errors.As(populatedCapacityErr, &discoveredCapacityErr) || discoveredCapacityErr != populatedCapacityErr {
+		t.Fatalf("populated capacity error is not discoverable: %v", populatedCapacityErr)
+	}
+
+	for _, unrelated := range []error{
+		promptkit.ErrInvalidConfig,
+		promptkit.ErrInvalidRequest,
+		promptkit.ErrLLMGenerate,
+		promptkit.ErrValidation,
+	} {
+		if errors.Is(promptkit.ErrCapacityExceeded, unrelated) ||
+			errors.Is(unrelated, promptkit.ErrCapacityExceeded) ||
+			errors.Is(populatedCapacityErr, unrelated) {
+			t.Fatalf("ErrCapacityExceeded aliases unrelated sentinel %v", unrelated)
+		}
+	}
+}
+
+type capacityRunResult struct {
+	result *promptkit.RunResult
+	err    error
+}
+
+func runCapacityRequest(
+	engine *promptkit.Engine,
+	ctx context.Context,
+	request promptkit.RunRequest,
+	results chan<- capacityRunResult,
+) {
+	result, err := engine.Run(ctx, request)
+	results <- capacityRunResult{result: result, err: err}
+}
+
+func newBackendCapacityEngine(
+	t *testing.T,
+	client promptkit.LLMClient,
+	limit int,
+	queueCapacity *int,
+	reader promptkit.ArtifactReader,
+) *promptkit.Engine {
+	t.Helper()
+	promptFS := contractPromptFS("prompt", "profile", "message")
+	if reader != nil {
+		promptFS = contractInputPromptFS()
+	}
+	options := []promptkit.Option{
+		promptkit.WithPromptFS(promptFS, "."),
+		promptkit.WithBackend(promptkit.Backend{
+			ID:               "limited",
+			Endpoint:         "http://backend.example/v1",
+			ConcurrencyLimit: limit,
+			QueueCapacity:    queueCapacity,
+		}),
+		promptkit.WithProfiles(promptkit.Profile{
+			ID: "profile", BackendID: "limited", Model: "model",
+		}),
+		promptkit.WithLLMClient(client),
+	}
+	if reader != nil {
+		options = append(options, promptkit.WithArtifactReader(reader))
+	}
+	engine, err := promptkit.NewEngine(promptkit.Config{}, options...)
+	if err != nil {
+		t.Fatalf("construct capacity engine: %v", err)
+	}
+	return engine
+}
+
+func capacityInputRequest(endpoint string) promptkit.RunRequest {
+	return promptkit.RunRequest{
+		PromptID: "input-prompt",
+		Inputs: map[string]promptkit.ArtifactRef{
+			"input": promptkit.Inline("input"),
+		},
+		Execution: &promptkit.ExecutionTargetOverride{Endpoint: endpoint},
+	}
+}
+
+type capacityGateClient struct {
+	mu      sync.Mutex
+	active  int
+	peak    int
+	calls   int
+	started chan promptkit.GenerateRequest
+	release <-chan struct{}
+}
+
+func newCapacityGateClient(release <-chan struct{}, buffer int) *capacityGateClient {
+	return &capacityGateClient{
+		started: make(chan promptkit.GenerateRequest, buffer),
+		release: release,
+	}
+}
+
+func (c *capacityGateClient) Generate(
+	ctx context.Context,
+	request promptkit.GenerateRequest,
+) (*promptkit.GenerateResponse, error) {
+	c.mu.Lock()
+	c.calls++
+	c.active++
+	if c.active > c.peak {
+		c.peak = c.active
+	}
+	c.mu.Unlock()
+	defer func() {
+		c.mu.Lock()
+		c.active--
+		c.mu.Unlock()
+	}()
+
+	c.started <- request
+	select {
+	case <-c.release:
+		return &promptkit.GenerateResponse{Content: "ok"}, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+func (c *capacityGateClient) snapshot() (active, peak, calls int) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.active, c.peak, c.calls
+}
+
+type capacityArtifactReader struct {
+	mu      sync.Mutex
+	calls   int
+	entered chan struct{}
+	release <-chan struct{}
+}
+
+func (r *capacityArtifactReader) Read(
+	ctx context.Context,
+	_ promptkit.ArtifactRef,
+) (*promptkit.Artifact, error) {
+	r.mu.Lock()
+	r.calls++
+	r.mu.Unlock()
+	r.entered <- struct{}{}
+	select {
+	case <-r.release:
+		return &promptkit.Artifact{Body: []byte("input")}, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+func (r *capacityArtifactReader) callCount() int {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.calls
+}
+
+func awaitCapacityRequest(
+	t *testing.T,
+	requests <-chan promptkit.GenerateRequest,
+) promptkit.GenerateRequest {
+	t.Helper()
+	select {
+	case request := <-requests:
+		return request
+	case <-time.After(5 * time.Second):
+		t.Fatal("timed out waiting for client invocation")
+		return promptkit.GenerateRequest{}
+	}
+}
+
+func awaitCapacityRun(t *testing.T, results <-chan capacityRunResult) capacityRunResult {
+	t.Helper()
+	select {
+	case result := <-results:
+		return result
+	case <-time.After(5 * time.Second):
+		t.Fatal("timed out waiting for Run")
+		return capacityRunResult{}
+	}
+}
+
+func awaitCapacitySignal(t *testing.T, signal <-chan struct{}, name string) {
+	t.Helper()
+	select {
+	case <-signal:
+	case <-time.After(5 * time.Second):
+		t.Fatalf("timed out waiting for %s", name)
+	}
+}
+
+func capacityInt(value int) *int {
+	return &value
+}
+
+func closedCapacityChannel() <-chan struct{} {
+	channel := make(chan struct{})
+	close(channel)
+	return channel
+}

capacity_error.go

@@ -0,0 +1,40 @@
+package promptkit
+
+import (
+	"fmt"
+	"strings"
+)
+
+// CapacityError reports bounded admission rejected for a selected backend.
+//
+// Engine-produced values identify only rejection at Promptkit's bounded
+// [Engine.Run] or [Engine.RunPrepared] admission boundary. BackendID is the
+// normalized registered backend ID used for routing and capacity; endpoint
+// overrides do not change it. Every engine-produced value is nonnil and has a
+// nonblank BackendID. Provider errors, active-generation waiting, and caller
+// cancellation are not represented by this type.
+//
+// Callers own returned values and may mutate BackendID without affecting engine
+// state or another error. CapacityError and its default Go encoding have no
+// stable JSON contract. Consumer-constructed values do not establish that an
+// engine rejected work.
+type CapacityError struct {
+	// BackendID is the normalized registered backend ID whose admission was
+	// rejected.
+	BackendID string
+}
+
+// Error returns diagnostic wording that is not a parsing contract. It is safe
+// to call on a nil receiver or a value with a blank BackendID.
+func (e *CapacityError) Error() string {
+	if e == nil || strings.TrimSpace(e.BackendID) == "" {
+		return ErrCapacityExceeded.Error()
+	}
+	return fmt.Sprintf("backend %q admission: %v", e.BackendID, ErrCapacityExceeded)
+}
+
+// Unwrap returns ErrCapacityExceeded so errors.Is and errors.As can be used
+// together. It is safe to call on a nil receiver or a zero value.
+func (e *CapacityError) Unwrap() error {
+	return ErrCapacityExceeded
+}

convert.go

@@ -1,9 +1,12 @@
 package promptkit
 
 import (
+	"fmt"
 	"reflect"
+	"unicode/utf8"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
 )
 
 func toDomainRunRequest(req RunRequest) (domain.RunRequest, error) {
@@ -11,19 +14,59 @@ func toDomainRunRequest(req RunRequest) (domain.RunRequest, error) {
 	if err != nil {
 		return domain.RunRequest{}, err
 	}
+	appendedMessages, err := toDomainAppendedMessages(req.AppendedMessages)
+	if err != nil {
+		return domain.RunRequest{}, err
+	}
+	var observer domain.ExecutionObserver
+	if req.Observer != nil {
+		callback := req.Observer
+		observer = func(event domain.ExecutionEvent) { callback(fromDomainExecutionEvent(event)) }
+	}
 	return domain.RunRequest{
-		PromptID:      req.PromptID,
-		PromptVersion: req.PromptVersion,
-		ProfileID:     req.ProfileID,
-		APIKey:        req.APIKey,
-		Inputs:        toDomainArtifactRefMap(req.Inputs),
-		Vars:          copyStringMap(req.Vars),
-		Execution:     execution,
-		Validation:    toDomainOutputContractPtr(req.Validation),
-		Metadata:      copyStringMap(req.Metadata),
+		PromptID:         req.PromptID,
+		PromptVersion:    req.PromptVersion,
+		ProfileID:        req.ProfileID,
+		SessionID:        req.SessionID,
+		APIKey:           req.APIKey,
+		Inputs:           toDomainArtifactRefMap(req.Inputs),
+		Vars:             copyStringMap(req.Vars),
+		Execution:        execution,
+		Validation:       toDomainOutputContractPtr(req.Validation),
+		AppendedMessages: appendedMessages,
+		TransientRetries: copyIntPtr(req.TransientRetries),
+		Observer:         observer,
 	}, nil
 }
 
+func toDomainAppendedMessages(messages []RenderedMessage) ([]domain.RenderedMessage, error) {
+	if messages == nil {
+		return nil, nil
+	}
+
+	converted := make([]domain.RenderedMessage, len(messages))
+	for index, message := range messages {
+		if !utf8.ValidString(message.Content) {
+			return nil, fmt.Errorf("appended message %d content must be valid UTF-8", index)
+		}
+		role, err := domain.NormalizeMessageRole(message.Role)
+		if err != nil {
+			return nil, fmt.Errorf("appended message %d role: %w", index, err)
+		}
+
+		cacheControl, err := domain.NormalizeCacheControl(toDomainCacheControl(message.CacheControl))
+		if err != nil {
+			return nil, fmt.Errorf("appended message %d cache_control: %w", index, err)
+		}
+		converted[index] = domain.RenderedMessage{
+			Role:         role,
+			Content:      message.Content,
+			CacheControl: cacheControl,
+		}
+	}
+	return converted, nil
+}
+
 func fromDomainPreparedRun(prepared *domain.PreparedRun) *PreparedRun {
 	if prepared == nil {
 		return nil
@@ -33,6 +76,7 @@ func fromDomainPreparedRun(prepared *domain.PreparedRun) *PreparedRun {
 		PromptVersion:        prepared.PromptVersion,
 		PromptHash:           prepared.PromptHash,
 		SelectedProfileID:    prepared.SelectedProfileID,
+		SelectedBackendID:    prepared.SelectedBackendID,
 		EffectiveModelParams: fromDomainExecutionTarget(prepared.EffectiveModelParams),
 		OutputContract:       fromDomainOutputContract(prepared.OutputContract),
 		StructuredOutput:     fromDomainStructuredOutputSpec(prepared.StructuredOutput),
@@ -58,8 +102,10 @@ func fromDomainRunResult(result *domain.RunResult) *RunResult {
 		PromptID:             result.PromptID,
 		PromptVersion:        result.PromptVersion,
 		PromptHash:           result.PromptHash,
+		SessionID:            result.SessionID,
 		RenderedPromptHash:   result.RenderedPromptHash,
 		SelectedProfileID:    result.SelectedProfileID,
+		SelectedBackendID:    result.SelectedBackendID,
 		ModelName:            result.ModelName,
 		Endpoint:             result.Endpoint,
 		EffectiveModelParams: fromDomainExecutionTarget(result.EffectiveModelParams),
@@ -86,8 +132,22 @@ func toDomainGenerateResponse(resp *GenerateResponse) *domain.GenerateResponse {
 		return nil
 	}
 	return &domain.GenerateResponse{
-		Content: resp.Content,
-		Usage:   toDomainTokenUsage(resp.Usage),
+		Content:       resp.Content,
+		Usage:         toDomainTokenUsage(resp.Usage),
+		UsagePresence: toDomainTokenUsagePresence(resp.UsagePresence),
+	}
+}
+
+func toDomainTokenUsagePresence(presence *TokenUsagePresence) *domain.TokenUsagePresence {
+	if presence == nil {
+		return nil
+	}
+	return &domain.TokenUsagePresence{
+		PromptTokens:     presence.PromptTokens,
+		CompletionTokens: presence.CompletionTokens,
+		TotalTokens:      presence.TotalTokens,
+		CachedTokens:     presence.CachedTokens,
+		CacheWriteTokens: presence.CacheWriteTokens,
 	}
 }
 
@@ -132,7 +192,7 @@ func toDomainExecutionTargetOverride(override *ExecutionTargetOverride) (*domain
 	if override == nil {
 		return nil, nil
 	}
-	extraParams, err := copyPublicJSONMap(override.ExtraParams)
+	extraParams, err := jsonvalue.CopyMap(override.ExtraParams)
 	if err != nil {
 		return nil, err
 	}
@@ -144,7 +204,7 @@ func toDomainExecutionTargetOverride(override *ExecutionTargetOverride) (*domain
 		TopP:            copyFloat64Ptr(override.TopP),
 		TimeoutSeconds:  copyIntPtr(override.TimeoutSeconds),
 		ServiceTier:     override.ServiceTier,
-		ReasoningEffort: override.ReasoningEffort,
+		ReasoningEffort: copyStringPtr(override.ReasoningEffort),
 		APIKeyEnv:       override.APIKeyEnv,
 		ExtraParams:     extraParams,
 	}, nil
@@ -152,6 +212,7 @@ func toDomainExecutionTargetOverride(override *ExecutionTargetOverride) (*domain
 
 func fromDomainExecutionTarget(target domain.ExecutionTarget) ExecutionTarget {
 	return ExecutionTarget{
+		BackendID:       target.BackendID,
 		Endpoint:        target.Endpoint,
 		Model:           target.Model,
 		Temperature:     target.Temperature,
@@ -165,6 +226,40 @@ func fromDomainExecutionTarget(target domain.ExecutionTarget) ExecutionTarget {
 	}
 }
 
+func fromDomainProfileInspection(inspection *domain.ProfileInspection) *ProfileInspection {
+	if inspection == nil {
+		return nil
+	}
+	return &ProfileInspection{
+		ProfileID:            inspection.ProfileID,
+		EffectiveModelParams: fromDomainExecutionTarget(inspection.EffectiveModelParams),
+		APIKeyRequired:       inspection.APIKeyRequired,
+	}
+}
+
+func fromDomainPromptInspection(inspection *domain.PromptInspection) *PromptInspection {
+	if inspection == nil {
+		return nil
+	}
+	inputs := make([]PromptInputDefinition, len(inspection.Inputs))
+	for i, input := range inspection.Inputs {
+		inputs[i] = PromptInputDefinition{
+			Name:        input.Name,
+			Required:    input.Required,
+			ContentType: input.ContentType,
+			Description: input.Description,
+		}
+	}
+	return &PromptInspection{
+		PromptID:         inspection.PromptID,
+		PromptVersion:    inspection.PromptVersion,
+		PromptHash:       inspection.PromptHash,
+		DefaultProfileID: inspection.DefaultProfileID,
+		Inputs:           inputs,
+		OutputContract:   fromDomainOutputContract(inspection.OutputContract),
+	}
+}
+
 func fromDomainExecutionTargetPresence(presence domain.ExecutionTargetPresence) ExecutionTargetPresence {
 	return ExecutionTargetPresence{
 		Temperature:    presence.Temperature,
@@ -246,6 +341,16 @@ func fromDomainRenderedMessages(messages []domain.RenderedMessage) []RenderedMes
 	return out
 }
 
+func toDomainCacheControl(cacheControl *CacheControl) *domain.CacheControl {
+	if cacheControl == nil {
+		return nil
+	}
+	return &domain.CacheControl{
+		Type: domain.CacheControlType(cacheControl.Type),
+		TTL:  cacheControl.TTL,
+	}
+}
+
 func fromDomainCacheControl(cacheControl *domain.CacheControl) *CacheControl {
 	if cacheControl == nil {
 		return nil
@@ -397,6 +502,14 @@ func copyFloat64Ptr(src *float64) *float64 {
 	return &v
 }
 
+func copyStringPtr(src *string) *string {
+	if src == nil {
+		return nil
+	}
+	v := *src
+	return &v
+}
+
 func copyIntPtr(src *int) *int {
 	if src == nil {
 		return nil

convert_appended_messages_test.go

@@ -0,0 +1,108 @@
+package promptkit
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+func TestToDomainAppendedMessages(t *testing.T) {
+	tests := []struct {
+		name        string
+		messages    []RenderedMessage
+		want        []domain.RenderedMessage
+		wantErr     string
+		privateRole string
+		privateText string
+	}{
+		{
+			name: "normalizes supported roles",
+			messages: []RenderedMessage{
+				{Role: " DeVeLoPeR ", Content: "developer"},
+				{Role: "SyStEm", Content: "system"},
+				{Role: "\tUsEr\n", Content: "user"},
+				{Role: "assistant", Content: "assistant"},
+			},
+			want: []domain.RenderedMessage{
+				{Role: domain.RoleDeveloper, Content: "developer"},
+				{Role: domain.RoleSystem, Content: "system"},
+				{Role: domain.RoleUser, Content: "user"},
+				{Role: domain.RoleAssistant, Content: "assistant"},
+			},
+		},
+		{
+			name:     "invalid role UTF-8",
+			messages: []RenderedMessage{{Role: string([]byte{0xff}), Content: "private-content"}},
+			wantErr:  "appended message 0 role",
+		},
+		{
+			name:     "invalid content UTF-8",
+			messages: []RenderedMessage{{Role: "private-role", Content: string([]byte{0xff})}},
+			wantErr:  "appended message 0 content",
+		},
+		{
+			name:        "unsupported role",
+			messages:    []RenderedMessage{{Role: "private-role", Content: "private-content"}},
+			wantErr:     "appended message 0 role",
+			privateRole: "private-role",
+			privateText: "private-content",
+		},
+		{
+			name:        "invalid cache control",
+			messages:    []RenderedMessage{{Role: RoleUser, Content: "private-content", CacheControl: &CacheControl{Type: "private-cache"}}},
+			wantErr:     "appended message 0 cache_control",
+			privateText: "private-content",
+		},
+		{
+			name: "empty and whitespace content",
+			messages: []RenderedMessage{
+				{Role: RoleUser, Content: ""},
+				{Role: RoleAssistant, Content: " \t\n "},
+			},
+			want: []domain.RenderedMessage{
+				{Role: domain.RoleUser, Content: ""},
+				{Role: domain.RoleAssistant, Content: " \t\n "},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got, err := toDomainAppendedMessages(test.messages)
+			if test.wantErr != "" {
+				if err == nil || !strings.Contains(err.Error(), test.wantErr) {
+					t.Fatalf("error = %v, want %q", err, test.wantErr)
+				}
+				for _, privateValue := range []string{test.privateRole, test.privateText} {
+					if privateValue != "" && strings.Contains(err.Error(), privateValue) {
+						t.Fatalf("error exposed appended message data %q: %v", privateValue, err)
+					}
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("toDomainAppendedMessages() error = %v", err)
+			}
+			if !reflect.DeepEqual(got, test.want) {
+				t.Fatalf("toDomainAppendedMessages() = %#v, want %#v", got, test.want)
+			}
+		})
+	}
+}
+
+func TestToDomainAppendedMessagesCopiesCacheControl(t *testing.T) {
+	cacheControl := &CacheControl{Type: CacheControlEphemeral, TTL: "1h"}
+	messages := []RenderedMessage{{Role: RoleUser, Content: "content", CacheControl: cacheControl}}
+	request, err := toDomainRunRequest(RunRequest{AppendedMessages: messages})
+	if err != nil {
+		t.Fatalf("toDomainRunRequest() error = %v", err)
+	}
+
+	messages[0].Content = "changed"
+	cacheControl.TTL = ""
+	if request.AppendedMessages[0].Content != "content" || request.AppendedMessages[0].CacheControl.TTL != "1h" {
+		t.Fatalf("domain request did not retain an independent appended-message copy: %#v", request.AppendedMessages)
+	}
+}

doc.go

@@ -1,8 +1,71 @@
 // Package promptkit provides an embeddable engine for preparing and executing
 // prompt-defined LLM workflows.
 //
-// Applications construct an Engine with NewEngine, select filesystem or
-// in-memory definition sources with options, and use Prepare or Run to execute
-// requests. Concrete repositories, validators, and outbound clients remain
-// internal implementation details.
+// Applications construct an [Engine] with [NewEngine], select filesystem or
+// in-memory sources and optional engine-scoped [Backend] registrations, and
+// call [Engine.InspectPrompt], [Engine.InspectProfile], [Engine.Prepare],
+// [Engine.PrepareExecution], [Engine.Run], or [Engine.RunPrepared]. Concrete
+// registries, repositories, validators, and the built-in OpenAI-compatible
+// client remain internal implementation details.
+//
+// # Concurrency and ownership
+//
+// An Engine supports concurrent InspectPrompt, InspectProfile, Prepare,
+// PrepareExecution, Run, and RunPrepared calls. Engine-local backend policies
+// bound admitted Run and RunPrepared calls and model generations where
+// configured, while different backend pools and unlimited backends continue
+// independently. An injected [LLMClient] or [ArtifactReader] can therefore
+// still receive concurrent calls and must be safe for that use.
+//
+// NewEngine copies in-memory profiles and backend definitions. Prepare,
+// PrepareExecution, and Run copy request maps, slices, pointer values, and
+// JSON-compatible extra parameters before using them. InspectPrompt and
+// InspectProfile return copied inspection values. Returned values and values
+// passed to extension interfaces are likewise isolated from engine state.
+// Callers own those copies and may mutate them after the call that supplied or
+// returned them. [CapacityError] values are caller-owned and may be mutated
+// without affecting engine state or another error. Immutable [GenerationError]
+// values are also caller-owned and do not retain shared engine state.
+//
+// # Security and sensitive data
+//
+// The default artifact reader treats [File] paths as caller-selected operating
+// system paths. It does not restrict them to an application root or impose an
+// inbound request-size policy. Promptkit is not an inbound request or
+// untrusted-input security boundary. Applications must validate and restrict
+// untrusted input before constructing a request, or install an [ArtifactReader]
+// that enforces their filesystem, authorization, and size policies.
+//
+// Rendered messages, input and output [Artifact] bodies, [RunResult.RawOutput],
+// and [ValidationResult.Errors] may contain sensitive data. Credential
+// exclusion and redaction do not sanitize those values. Applications and
+// injected collaborators are responsible for access control, retention,
+// logging, and secret handling appropriate to their data.
+//
+// # JSON
+//
+// Stable JSON representations are provided for [PreparedRun], [RunResult],
+// [Artifact], [ExecutionTarget], [OutputContract], [ValidationResult],
+// [TokenUsage], [RenderedPrompt], [RenderedMessage], [CacheControl],
+// [StructuredOutputSpec], [StructuredOutputJSONSpec], [GenerateRequest],
+// [GenerateResponse], [ExecutionTargetPresence], and the string value types
+// used by those values.
+//
+// Construction, inspection, handle, and error values, including [Config],
+// [Backend], [RunRequest], [ArtifactRef], [ExecutionTargetOverride], [Profile],
+// [OpenAICompatibleProfileConfig], [ProfileInspection],
+// [PromptInputDefinition], [PromptInspection], [PreparedExecution],
+// [CapacityError], [GenerationError], [RetryExhaustedError], and
+// [ExecutionEvent], do not have stable JSON
+// representations. Direct API keys are nevertheless excluded from JSON for
+// every public value.
+
+// Provider-derived [GenerationError] accessor values are untrusted and can
+// contain sensitive request or schema fragments. Applications must apply their
+// own disclosure policy before logging, displaying, or returning them.
+//
+// JSON timestamps use time.Time's RFC 3339 encoding and are omitted when zero.
+// PreparedRun and RunResult durations are encoded as integer milliseconds in
+// duration_ms and omitted when zero. Run IDs and all exposed hashes are opaque:
+// their spelling, length, character set, and algorithm are not API contracts.
 package promptkit

docs/consumers/pkg-promptkit.md

@@ -1,151 +1,637 @@
 # Package `promptkit`
 
-Import path:
+## Purpose
+
+This guide helps Go consumers assemble Promptkit and choose the main
+preparation or execution workflow. The declarations and GoDoc in the
+[root package](../../doc.go) own exact field, option, serialization,
+concurrency, ownership, failure, and cancellation semantics. The
+[framework format reference](../formats.md) owns prompt, profile, and schema
+file contracts.
+
+Import the package as:
 
 ```go
 import "gitea.maximumdirect.net/eric/promptkit"
 ```
 
-Package `promptkit` is the supported Go contract for in-process prompt
-preparation and execution. The declarations and their GoDoc in the
-[root package](../../doc.go) own the exact API; this guide explains how the
-pieces are used together. The [framework format reference](../formats.md) owns
-prompt, profile, and schema file contracts.
+The following Go fragments are illustrative and omit surrounding package,
+import, and error-handling code. Use the maintained examples for complete
+programs.
 
-## Engine Construction And Sources
+## Construct An Engine
 
-Construct an engine with [`NewEngine`, `Config`, and
-`Option`](../../engine.go). `PromptDir` is required unless a prompt source
-option is supplied. `ProfileDir` optionally overlays built-in profiles, and an
-empty `SchemaDir` uses the current directory. `Timeout` is the transport-wide
-safety cap for the built-in OpenAI-compatible client. An optional `HTTPClient`
-is cloned; its positive timeout takes precedence.
+Create an engine with
+[`NewEngine`](../../engine.go). A directory-backed setup supplies a prompt
+directory and may supply profile and schema directories:
 
-Nil options are ignored. Invalid construction, including a nil injected client
-or artifact reader, returns an error matching `ErrInvalidConfig`.
+```go
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir:  "prompts",
+	ProfileDir: "profiles",
+	SchemaDir:  "schemas",
+})
+```
 
-The [source options](../../engine.go) replace their matching directory source:
-
-- `WithPromptFS` and `WithPromptFile` select prompt definitions;
-- `WithProfileFS` and `WithProfileFile` overlay built-in profiles;
-- `WithProfiles` adds in-memory profiles ahead of file and built-in profiles;
-- `WithSchemaFS` and `WithSchemaFile` select JSON Schema documents;
-- `WithLLMClient` replaces the built-in model client; and
-- `WithArtifactReader` replaces the default reader for every input.
-
-Source selection, path resolution, strict decoding, profile overlays, and
-file-to-request precedence are defined in the
+Options support single-file or `fs.FS` sources, in-memory profiles,
+engine-scoped backends, and injected artifact or model clients. Consult the
+[constructor and option GoDoc](../../engine.go) for composition, precedence,
+validation, and default transport behavior. Source discovery, format
+validation, and profile precedence are defined by the
 [framework format reference](../formats.md).
 
-Per-generation timeout values from profiles or requests are independent of
-the transport cap and caller context. An explicit request value of zero
-disables only the per-generation deadline. The
-[outbound integration contract](../integrations/openai-compatible-chat.md#timeout-and-cancellation)
-defines the complete timeout layering.
+## Supply Embedded Application Defaults
 
-## Preparation And Execution
+Use `WithFallbackProfileFS` when an application packages profile definitions
+that should apply unless an operator provides an ordinary configured profile
+with the same ID. For example, an application can embed its defaults while
+continuing to use `ProfileDir` for operator overrides:
 
-[`Engine.Prepare` and `Engine.Run`](../../engine.go) accept the public
-[`RunRequest`](../../types.go). `Prepare` resolves the prompt, profile, input
-artifacts, validation contract, and rendered messages without calling an LLM.
-`Run` performs the same preparation, calls the configured client, and validates
-the generated content. The maintained
+```go
+//go:embed profiles/*.yaml
+var applicationProfiles embed.FS
+
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir:  "prompts",
+	ProfileDir: operatorProfileDir,
+},
+	promptkit.WithFallbackProfileFS(applicationProfiles, "profiles"),
+)
+```
+
+Keep application-owned profile IDs and definitions in the embedded source.
+Use the ordinary configured profile source for operator overrides. Leave
+`operatorProfileDir` empty when the operator did not configure an override
+directory; a non-empty path names an authoritative higher-precedence source,
+so an unavailable or unreadable directory is an error rather than a reason to
+fall back. The
+[framework format reference](../formats.md#source-and-profile-precedence)
+owns the exact profile format and lookup order; the
+[`WithFallbackProfileFS` GoDoc](../../engine.go) owns its option contract and
+validation rules.
+
+## Inspect A Prompt Before Preparation
+
+Use [`Engine.InspectPrompt`](../../engine.go) to check one configured prompt's
+declared inputs and output workflow without creating placeholder inputs or
+resolving a profile:
+
+```go
+inspection, err := engine.InspectPrompt(ctx, "meeting.summary", "")
+if err != nil {
+	return err
+}
+
+for _, input := range inspection.Inputs {
+	// Compare the declared input with application configuration.
+}
+```
+
+Use this configuration-time boundary when the application needs only the
+declared prompt interface. Use `InspectProfile` separately when it must also
+check a configured profile. Use `Prepare` when it needs inputs, schemas, or
+rendered messages, and use prepared execution when that work must remain tied
+to later execution. The method's [GoDoc](../../engine.go) owns exact fields,
+hash, ownership, and error semantics.
+
+## Prepare Without Model Execution
+
+[`Engine.Prepare`](../../engine.go) resolves the selected prompt and profile,
+loads inputs and any structured-output schema, and renders messages without
+calling a model client. Choose it when the prepared value is the final
+inspection or persistence result and no later execution must be tied to that
+exact snapshot:
+
+```go
+prepared, err := engine.Prepare(ctx, promptkit.RunRequest{
+	PromptID: "meeting.summary",
+	Inputs: map[string]promptkit.ArtifactRef{
+		"note": promptkit.Inline("Synthetic meeting notes"),
+	},
+})
+```
+
+The maintained
 [offline preparation example](../../examples/go-library/prepare/main.go)
-provides a complete runnable workflow using a prompt file, in-memory profile,
-and inline input.
+shows a complete runnable setup with a prompt file, in-memory profile, and
+inline input. Exact request requirements and prepared-result fields belong to
+the [`RunRequest` and `PreparedRun` GoDoc](../../types.go).
 
-[`PreparedRun` and `RunResult`](../../types.go) expose copied public values.
-Preparation returns effective settings, hashes, rendered messages, selected
-profile, structured-output information, and timing without resolved secrets or
-model output. Execution adds the generated artifact and raw output, validation
-state, model metadata, usage, run ID, and duration.
+## Prepare Now And Execute The Same Snapshot Later
 
-A generated-content validation failure returns a result with
-`Validation.Status == ValidationFailed`. An inability to perform validation
-returns an error matching `ErrValidation`.
+Use [`Engine.PrepareExecution`](../../engine.go) when an application must
+inspect or persist preflight details before deciding whether to start model
+work, while ensuring that later execution uses those exact rendered messages,
+inputs, target settings, and validation resources:
 
-## Requests, Inputs, And Overrides
+```go
+preparedExecution, err := engine.PrepareExecution(ctx, promptkit.RunRequest{
+	PromptID: "meeting.summary",
+	Inputs: map[string]promptkit.ArtifactRef{
+		"note": promptkit.Inline("Synthetic meeting notes"),
+	},
+})
+if err != nil {
+	return err
+}
+defer preparedExecution.Discard()
 
-The [request and value declarations](../../types.go) own the available fields,
-serialized constants, and result shapes. Use `File`, `Inline`, or
-`InlineWithURI` to construct artifact references. The
-[framework format reference](../formats.md) defines declared inputs, template
-references, output contracts, and the relationship between file values and
-request overrides.
+details := preparedExecution.Details()
+// Inspect or persist an application-selected safe subset of details.
 
-`ExecutionTargetOverride` uses pointers for numeric settings so an explicit
-zero remains distinct from no override. `ExtraParams` accepts JSON-compatible
-strings, booleans, finite numbers, string-keyed objects, arrays or slices, and
-nil. Unsupported values, non-string map keys, non-finite numbers, and cycles
-match `ErrInvalidConfig` in profiles or `ErrInvalidRequest` in request
-overrides.
+result, err := engine.RunPrepared(ctx, preparedExecution)
+```
 
-Returned requests, profiles, prepared values, results, artifacts, maps, and
-slices are isolated from internal engine state. Consumers and injected
-extensions should not retain or mutate values owned by another caller.
+Preparation does not call the model or reserve backend capacity.
+`RunPrepared` executes from the retained snapshot rather than reloading
+consumer sources. The handle is opaque in-process state, while `Details`
+contains rendered content and remains subject to the application's data
+handling policy. The
+[`PreparedExecution` and method GoDoc](../../prepared_execution.go) and
+[engine operation GoDoc](../../engine.go) own exact lifecycle, engine-binding,
+credential, cancellation, timing, and error semantics.
 
-## Profiles And Credentials
+If the request supplied `Observer`, successful preparation retains that
+function for `RunPrepared`; preparation itself emits nothing. Observation
+starts only when the owning engine successfully claims the handle. Reused,
+discarded, foreign, and invalid handles emit nothing. `Discard` clears the
+retained callback without invoking it. The function's closure is retained by
+identity, so synchronize any shared state it uses. Prepared start events can
+include identities already resolved in the frozen snapshot.
 
-[`OpenAICompatibleProfile`](../../profiles.go) constructs an ordinary
-in-memory profile for an OpenAI-compatible chat-completions endpoint.
-`WithProfiles` rejects duplicate IDs in one call and gives in-memory profiles
-precedence over explicit file sources and built-ins.
+## Execute And Validate
 
-Raw API keys do not belong in profiles. File-backed profiles may name an
-environment variable, while an in-memory profile can require a request key.
-A direct `RunRequest.APIKey` is request-scoped and takes precedence over an
-environment lookup for the built-in client. Profile fields, ranges, built-ins,
-precedence, and credential rules are owned by the
-[framework format reference](../formats.md).
+[`Engine.Run`](../../engine.go) performs the same preparation, invokes the
+configured model client, classifies the generated artifact, and validates the
+content in one call. Choose it when the application does not need a preflight
+boundary tied to the eventual execution. A completed content check may return
+`ValidationFailed` in the result; an operational inability to validate returns
+an error.
 
-API keys are excluded from JSON, prepared values, and results. The public
-`String` and `GoString` methods report only whether a direct key is present.
-Avoid reflection-based dumps of request structs, which can bypass that
-redaction.
+The maintained
+[offline execution example](../../examples/go-library/run/main.go) injects a
+deterministic model client and exercises `Run` without credentials, network
+access, or paid calls. It is intentionally separate from the preparation
+example so each workflow and its small prompt fixture can be copied and run on
+its own.
+
+Use the [`RunResult` and `ValidationResult` GoDoc](../../types.go) for the
+returned data and the `Engine.Run` GoDoc for failure and cancellation
+semantics. The
+[OpenAI-compatible integration contract](../integrations/openai-compatible-chat.md)
+owns the built-in client's outbound HTTP behavior.
+
+### Observe An Ordinary Run
+
+Set `RunRequest.Observer` to receive synchronous metadata events from `Run`:
+
+```go
+request.Observer = func(event promptkit.ExecutionEvent) {
+	// Translate selected metadata into an application-owned record.
+}
+result, err := engine.Run(ctx, request)
+```
+
+An ordinary run emits `started` before request conversion, followed by any
+attempt and retry-delay completions, then one `finished` event on a normal
+return. `Prepare` and `PrepareExecution` emit no events. A start event has no
+resolved prompt, profile, or model; later events gain identities only as
+selection succeeds. The terminal event has dispatched-attempt, transient-retry,
+repair-call, duration, and presence-aware usage totals. Its usage is an
+aggregate, not an additional billable attempt. A known zero differs from an
+unknown count, and incomplete totals must not be treated as complete cost
+accounting. A failed operation still returns no partial `RunResult`.
+An injected client that leaves `UsagePresence` nil can report known nonzero
+counts, but its zero counts remain unknown to observations; supply explicit
+presence when measured zeros matter. Existing `RunResult.Usage` sums returned
+values independently of observation presence.
+
+Callbacks run synchronously, in order for one operation, and can overlap for
+different operations. Synchronize shared callback state and avoid blocking on
+work that needs the same run's admission slot. Callback panics propagate;
+there is no durable event history or promise of a terminal event after panic.
+Events omit content and error objects, but selected identifiers may still be
+sensitive. See the [observation GoDoc](../../observations.go) for exact fields.
+The [offline proposal and assessment example](../../examples/go-library/observe/main.go)
+shows application-owned event collection and a separate semantic acceptance
+decision using the built-in HTTP path without network access.
+
+### Repair A Structured Result
+
+Set a small additional-call budget when a structurally invalid result can be
+corrected automatically:
+
+```go
+request.Validation = &promptkit.OutputContract{
+	Format:         promptkit.FormatJSON,
+	ValidationMode: promptkit.ValidationJSONSchema,
+	SchemaPath:     "events.schema.json",
+	RepairAttempts: 1,
+}
+```
+
+Each repair attempt is another model generation, so it can increase latency and
+usage; `RunResult.Usage` is cumulative and `Validation.RepairAttempts` reports
+repair generations rather than transient HTTP attempts. Exhaustion still
+returns the final failed validation result. `basic` validation can also repair
+an empty candidate, but structural
+validity is not evidence of factual or domain correctness. See the
+[output-contract format reference](../formats.md#output-contract) and
+[`OutputContract` GoDoc](../../types.go) for the exact budget and eligibility
+rules.
+
+The built-in client also retries eligible temporary HTTP statuses. By default,
+each generation can make two additional attempts; a repair generation receives
+its own budget. Set `Config.TransientRetries` to a pointer to zero for the
+previous single-attempt behavior, or set `RunRequest.TransientRetries` to
+override one execution. A custom HTTP transport still uses this policy;
+injected `LLMClient` implementations retain their own retry policy. Application
+semantic retries are separate runs and can multiply provider traffic further.
+The caller context covers capacity and retry waiting as well as attempts;
+without a deadline a valid provider delay can be long. Promptkit does not
+infer exactly-once or complete cost accounting from a retry outcome.
+See the [provider integration contract](../integrations/openai-compatible-chat.md#transient-status-retries)
+for eligible statuses, waits, timeouts, and provider timing.
+
+### Append Already-Rendered Messages
+
+An application can include an earlier assistant response and its own corrective
+instruction in a fresh request without changing the configured prompt:
+
+```go
+request.AppendedMessages = []promptkit.RenderedMessage{
+	{Role: promptkit.RoleAssistant, Content: previousResponse},
+	{Role: promptkit.RoleUser, Content: correction},
+}
+result, err := engine.Run(ctx, request)
+```
+
+These messages are already rendered: Promptkit does not template or resolve
+files in them, and they can contain sensitive model output or application
+feedback. Promptkit remains stateless; every `Run` call re-resolves its current
+sources and the application owns any semantic retry budget. When a
+pre-execution equality check is required, use `PrepareExecution` and compare
+its opaque rendered-prompt hash before invoking `RunPrepared`.
+
+## Inputs, Profiles, And Overrides
+
+Use `File`, `Inline`, or `InlineWithURI` to construct request inputs. A request
+can select a profile explicitly or use the prompt's default profile, and can
+replace execution settings or the complete output contract.
+
+The [public value GoDoc](../../types.go) defines nil, empty, zero, replacement,
+copy, and credential behavior. The
+[framework format reference](../formats.md) defines how those request values
+interact with prompt definitions, file-backed and application fallback
+profiles, built-ins, schemas, and framework defaults.
+
+For programmatic profiles,
+[`OpenAICompatibleProfile`](../../profiles.go) converts ordinary
+OpenAI-compatible settings into a value accepted by `WithProfiles`.
+
+### Choose A Profile Ownership Model
+
+Choose the profile source that matches the application's continuity needs:
+
+- Select `promptkit-openrouter-standard` or `promptkit-openrouter-auto` when
+  the maintained literal name is the desired consumer contract. Their current
+  selections are in the [format reference](../formats.md#built-in-profile-catalog).
+- Select an external catalog profile directly when the application accepts that
+  profile's catalog volatility. The selected external inventories are linked
+  from the [format reference](../formats.md#external-profile-inventories).
+- Define a complete application-owned profile with an explicit backend or
+  endpoint, model, and settings when the application owns those choices.
+
+An application profile that inherits an external base follows later changes to
+that base and fails if the base disappears; it is not a frozen copy. Promptkit
+tests the catalog versions selected in its module graph. Independently advancing
+a catalog dependency can remove an inherited base and produce an untested
+combination. Pinning the resolved module graph preserves the embedded data for
+a build, but cannot preserve provider availability. Running binaries neither
+download catalog updates nor automatically replace withdrawn models. See the
+[release policy](../policy/release.md#catalog-profile-compatibility) for the exact
+cross-version guarantees.
+
+### Alias A Built-In Profile
+
+Give an application-owned profile ID a built-in base when prompts should select
+the application ID while inheriting the built-in target. The child can override
+only the setting it owns:
+
+```go
+promptkit.WithProfiles(promptkit.Profile{
+	ID:              "weather-light",
+	BaseProfileID:   "promptkit-openrouter-standard",
+	ReasoningEffort: "high",
+})
+```
+
+Select `weather-light` in a prompt or `RunRequest.ProfileID`; it remains the
+reported selected profile. See the [profile inheritance format
+reference](../formats.md#profile-inheritance) and the
+[`Profile` GoDoc](../../types.go) for exact lookup, merging, and validation
+behavior. If the base is an external profile, apply the volatility guidance
+above when deciding whether to use an application-owned complete definition
+instead.
+
+### Use The Rakestrawhome Built-In Profile
+
+Set `RAKESTRAWHOME_INFERENCE_API_KEY` in the application environment, then
+select `rakestrawhome-gemma-4-31b` as an ordinary profile ID. For example, a
+prepared result identifies the selected built-in through
+`BackendRakestrawHome`:
+
+```go
+prepared, err := engine.Prepare(ctx, promptkit.RunRequest{
+	PromptID:  "meeting.summary",
+	ProfileID: "rakestrawhome-gemma-4-31b",
+	Inputs:    inputs,
+})
+if err != nil {
+	return err
+}
+if prepared.SelectedBackendID != promptkit.BackendRakestrawHome {
+	return fmt.Errorf("unexpected backend %q", prepared.SelectedBackendID)
+}
+```
+
+Do not register `rakestrawhome` manually. When adopting this built-in, remove
+an existing `WithBackend` registration with that exact ID; retaining it causes
+the intentional duplicate-ID configuration error. Direct request credentials
+and runtime endpoint overrides remain supported under their ordinary GoDoc and
+format contracts.
+
+### Inspect A Profile Before Prompt Work
+
+Use [`Engine.InspectProfile`](../../engine.go) to validate one configured
+profile without constructing a synthetic prompt or placeholder inputs. It
+resolves the profile's effective target but does not prepare or execute a
+prompt:
+
+```go
+inspection, err := engine.InspectProfile(ctx, profileID)
+if err != nil {
+	return err
+}
+
+target := inspection.EffectiveModelParams
+if target.APIKeyEnv != "" {
+	// This is a configured optional environment lookup source.
+} else if inspection.APIKeyRequired {
+	// Arrange a direct credential before later execution.
+}
+```
+
+Use this configuration-time boundary when only the profile and its target need
+checking. Use `Prepare` when the application also needs prompt, input, schema,
+or rendering work; use prepared execution when that work must remain tied to a
+later execution. A reported `APIKeyEnv` is a configured optional source, while
+`APIKeyRequired` is the explicit local requirement. The
+[credential format reference](../formats.md#credentials) and the method's
+[GoDoc](../../engine.go) own the exact precedence, timing, result, and error
+contracts.
+
+### Set A Per-Run Session And Reasoning
+
+Supply a direct session ID when one prompt should be correlated with a
+consumer-managed conversation or workflow without changing prompt variables:
+
+```go
+reasoning := "high"
+result, err := engine.Run(ctx, promptkit.RunRequest{
+	PromptID: "meeting.summary",
+	SessionID: "conversation-42",
+	Inputs: map[string]promptkit.ArtifactRef{
+		"note": promptkit.Inline("Synthetic meeting notes"),
+	},
+	Execution: &promptkit.ExecutionTargetOverride{
+		ReasoningEffort: &reasoning,
+	},
+})
+```
+
+A nil reasoning pointer inherits the selected profile, a pointer to a
+nonblank string replaces it, and a pointer to a blank string disables
+reasoning for that run. Session IDs are correlation metadata, not credentials;
+use stable, non-secret values that are safe to expose to collaborators and
+providers. The
+[`RunRequest` and `ExecutionTargetOverride` GoDoc](../../types.go) owns the
+exact normalization, precedence, error, copying, and exposure contract.
+
+### Configure A Local OpenAI-Compatible Endpoint
+
+Choose the smallest configuration that fits how the endpoint will be reused.
+
+#### Use An Endpoint-Only Profile
+
+Put the endpoint directly on an in-memory profile when only that profile needs
+it and shared backend identity or capacity policy is unnecessary:
+
+```go
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir: "prompts",
+},
+	promptkit.WithProfiles(promptkit.Profile{
+		ID:       "local-summary",
+		Endpoint: "http://localhost:8000/v1",
+		Model:    "example-model",
+	}),
+)
+```
+
+Endpoint-only profiles have an empty backend ID and remain unrestricted by
+backend capacity policy.
+
+#### Use The Conventional Local Backend
+
+Use `LocalBackend` when profiles should share the conventional `local`
+identity, endpoint, and concurrency limit:
+
+```go
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir: "prompts",
+},
+	promptkit.WithBackend(
+		promptkit.LocalBackend("http://localhost:8000/v1", 2),
+	),
+	promptkit.WithProfiles(promptkit.Profile{
+		ID:        "local-summary",
+		BackendID: promptkit.BackendLocal,
+		Model:     "example-model",
+	}),
+)
+```
+
+The helper is explicit: it does not pre-register a backend or read environment
+variables. Supplying a positive limit leaves queue capacity omitted, so normal
+backend registration selects the existing default waiting capacity of 1024.
+The returned value still enters the engine through `WithBackend`.
+
+#### Configure A Complete Backend
+
+Use a keyed `Backend` value for authentication, extra request parameters, an
+explicit queue capacity, a custom ID, or multiple local endpoints:
+
+```go
+noWaiting := 0
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir: "prompts",
+},
+	promptkit.WithBackend(promptkit.Backend{
+		ID:               "local-gpu",
+		Endpoint:         "http://gpu-host:8000/v1",
+		APIKeyEnv:        "LOCAL_GPU_API_KEY",
+		ExtraParams:      map[string]any{"provider_option": "enabled"},
+		ConcurrencyLimit: 2,
+		QueueCapacity:    &noWaiting,
+	}),
+	promptkit.WithProfiles(promptkit.Profile{
+		ID:        "gpu-summary",
+		BackendID: "local-gpu",
+		Model:     "example-model",
+	}),
+)
+```
+
+Use distinct custom IDs when registering multiple local endpoints.
+Registrations belong to one engine and custom IDs cannot replace built-ins.
+The [`Backend`, `LocalBackend`, and `WithBackend` GoDoc](../../backends.go)
+defines exact construction, validation, copying, uniqueness, concurrency, and
+request-default behavior.
+
+Both file-backed and in-memory profiles select a registration through
+`backend` or `Profile.BackendID`. Profile and request endpoint overrides retain
+that routing and capacity identity. `PreparedRun.SelectedBackendID`,
+`RunResult.SelectedBackendID`, and the effective `ExecutionTarget.BackendID`
+expose it to consumers and injected model clients. Endpoint-only profiles
+remain supported and expose an empty backend ID.
+
+### Limit Backend Concurrency
+
+Set `Backend.ConcurrencyLimit` when a backend needs protection from too many
+simultaneous model calls. Leaving `QueueCapacity` nil, as in the local-backend
+example above, selects the default waiting capacity of 1024.
+
+To accept no waiting backlog beyond the active calls, provide an explicit
+zero:
+
+```go
+noWaiting := 0
+backend := promptkit.Backend{
+	ID:               "local-gpu",
+	Endpoint:         "http://gpu-host:8000/v1",
+	ConcurrencyLimit: 2,
+	QueueCapacity:    &noWaiting,
+}
+```
+
+The pointer distinguishes an explicit zero from omission. Keep using keyed
+`Backend` literals so additive configuration fields remain source-compatible.
+Capacity belongs to one engine and the selected backend ID; endpoint-only
+profiles and custom backends without a configured limit remain unrestricted.
+Exact validation, defaulting, ownership, and concurrency semantics belong to
+the [`Backend` GoDoc](../../backends.go).
+
+## Credentials
+
+File-backed profiles name an environment variable; in-memory profiles can
+require a direct request key. Direct keys are request-scoped and are excluded
+from supported JSON values and the package's `String` and `GoString`
+summaries. The exact precedence and redaction guarantees belong to
+[`RunRequest`, `GenerateRequest`, and the profile GoDoc](../../types.go).
+
+## Protect Files And Generated Data
+
+The default artifact reader opens a `File` reference as a caller-selected
+operating-system path. It does not constrain paths to an application root,
+impose an inbound request-size policy, or establish an untrusted-input security
+boundary. Applications must validate and restrict untrusted paths and payloads
+before constructing a request, or inject an artifact reader that enforces
+their filesystem, authorization, and size policies.
+
+Rendered messages, input and output artifact bodies, raw model output, and
+validation diagnostics can contain sensitive data. API-key redaction does not
+sanitize those values. Treat prepared values, results, collaborator requests,
+errors, and logs according to the application's data-access, retention, and
+secret-handling policies.
 
 ## Extension Interfaces
 
-The [`LLMClient`, `GenerateRequest`, and
-`GenerateResponse`](../../types.go) boundary lets a consumer replace model
-generation. Injected clients receive copied rendered messages, effective
-settings, explicit numeric-setting presence, structured-output constraints,
-and the request-scoped key. They return generated content and token usage.
+Inject an [`LLMClient` or `ArtifactReader`](../../types.go) when the built-in
+behavior does not fit the application. Their GoDoc defines concurrent use,
+context handling, ownership of copied values, nil responses, and preservation
+of collaborator errors. Implementations must honor cancellation, safely manage
+copies they retain, avoid unsafe logging of content or credentials, and enforce
+the application policy that motivated the injection.
 
-The [`ArtifactReader`](../../types.go) boundary replaces the default inline and
-file reader for every input. Readers provide artifact content and metadata; the
-engine fills an empty artifact name from the input-map key. A reader error
-matches `ErrArtifactLoad` while preserving the original identity for
-`errors.Is`. A nil artifact with a nil error is also an artifact-load failure.
+## Handle Errors
 
-Extensions should honor context cancellation and avoid logging raw prompts,
-artifacts, or credentials.
+Use `errors.Is` with the
+[public error sentinels and operation GoDoc](../../engine.go). The declarations
+distinguish invalid construction, invalid requests, absent sources,
+source-loading failures, collaborator failures, and operational validation
+failures. Specific request conditions may also match the broader
+`ErrInvalidRequest`, and injected collaborator identities are preserved where
+documented. Invalid or duplicate backend registrations match
+`ErrInvalidConfig`; selecting an unknown backend matches `ErrProfileLoad`.
 
-## Errors
+When a limited backend has admitted all active and waiting calls, handle
+`ErrCapacityExceeded` separately from request errors and provider failures:
 
-The [public error declarations](../../engine.go) and
-[mapping](../../errors.go) preserve these sentinel checks through `errors.Is`:
+```go
+result, err := engine.Run(ctx, request)
+if errors.Is(err, promptkit.ErrCapacityExceeded) {
+	var capacityErr *promptkit.CapacityError
+	if errors.As(err, &capacityErr) {
+		// Record capacityErr.BackendID using application-owned diagnostics.
+	}
 
-- `ErrInvalidConfig`
-- `ErrInvalidRequest`
-- `ErrPromptNotFound`
-- `ErrProfileNotFound`
-- `ErrProfileRequired`
-- `ErrPromptLoad`
-- `ErrProfileLoad`
-- `ErrAPIKeyEnvMissing`
-- `ErrArtifactLoad`
-- `ErrPromptRender`
-- `ErrLLMGenerate`
-- `ErrValidation`
+	// Apply application policy: shed work, report overload, or retry later.
+}
+```
 
-`ErrProfileRequired` and `ErrAPIKeyEnvMissing` also match
-`ErrInvalidRequest`, allowing either broad request handling or a specific
-condition. Wrapped collaborator errors retain their identity where the public
-contract promises it.
+A rejected call returns no partial result and does not invoke the model
+client. Promptkit does not prescribe retries or map this error to an HTTP
+status; those choices remain with the consuming application. The
+[`CapacityError` GoDoc](../../capacity_error.go) owns the exact typed-error
+contract, while the [`Engine.Run` and error GoDoc](../../engine.go) owns broad
+error and cancellation identities.
 
-## Consumer Boundary
+For a non-2xx response from the built-in OpenAI-compatible client, inspect the
+status and deliberately selected provider diagnostic when useful:
+
+```go
+var generationErr *promptkit.GenerationError
+if errors.As(err, &generationErr) {
+	status := generationErr.StatusCode()
+	message := generationErr.ProviderMessage()
+	_, _ = status, message // Apply application presentation policy.
+}
+```
+
+All provider fields are untrusted and can contain sensitive request or schema
+fragments. Do not log, display, or return them without an application-specific
+disclosure policy. Promptkit does not assign presentation behavior.
+The [`GenerationError` GoDoc](../../generation_error.go) owns the exact typed
+error contract.
+
+Generation failures also match `ErrTransport` when the built-in HTTP request
+fails, or `ErrMalformedResponse` when a successful provider response cannot be
+decoded or an injected client returns a nil successful response. Both retain
+`ErrLLMGenerate`; transport failures retain their original causes for
+`errors.Is` and `errors.As`. Caller cancellation and deadlines retain their
+standard context identities. Arbitrary injected-client errors retain their own
+identities without Promptkit guessing a failure category from their text.
+An eligible built-in status that consumes a positive retry budget additionally
+matches `ErrRetriesExhausted`; use `errors.As` to read
+`RetryExhaustedError.Attempts()` and the final `GenerationError` status. With
+explicit zero retries, the first eligible status is an ordinary generation
+error, not exhaustion. Completed structural rejection remains a normal result
+with failed validation, while an operational error returns no partial result.
+
+## Application Boundary
 
 Promptkit is an importable library. It does not own a command, inbound HTTP
-API, process configuration, or deployment policy. Scriptorium is one
-downstream application that maps this root package contract into those
-application concerns.
+API, process configuration, or deployment policy. Applications map the root
+package's results and errors into those concerns, including inbound size and
+trust policy.

docs/development.md

@@ -1,8 +1,7 @@
 # Development
 
-This is the contributor entry point for Promptkit, a reusable Go library. All
-contributors must read the
-[architecture policy](policy/architecture.md) before making changes.
+This is the contributor entry point for Promptkit, a reusable Go library.
+Use the Policy Reading Guide below to select policies applicable to the task.
 
 ## Initial Orientation
 
@@ -15,17 +14,27 @@ Before starting work:
 4. keep documentation limited to implemented behavior unless an accepted
    decision or temporary roadmap explicitly owns future work.
 
-Start with:
+## Policy Reading Guide
 
-- the [architecture policy](policy/architecture.md) for library boundaries,
-  dependency direction, invariants, and non-goals;
-- the [internal component overview](internal/overview.md) for the current
-  package and component inventory;
-- the [documentation policy](policy/documentation.md) before changing
-  documentation;
-- the [testing policy](policy/testing.md) before adding, rewriting, or deleting
-  tests; and
-- the [release procedure](release.md) for version and publication work.
+| Policy | Read before… |
+| --- | --- |
+| [Policy set provenance](policy/meta.md) | Adopting policies, checking upstream revisions, or updating the adopted policy set. |
+| [Agents](policy/agents.md) | Recommending, planning, or implementing repository changes. |
+| [Architecture](policy/architecture.md) | Planning or changing library code or its structure. |
+| [Testing](policy/testing.md) | Selecting validation for code changes, or adding, changing, removing, or evaluating tests. |
+| [Documentation](policy/documentation.md) | Writing, revising, or reorganizing documentation. |
+| [OSS](policy/oss.md) | Adding or updating dependencies or incorporated third-party material, or changing licensing or attribution. |
+| [Release](policy/release.md) | Preparing or publishing a release, changing release procedures, or making versioning and compatibility decisions. |
+
+- Read applicable policies before making decisions they govern; multiple policies
+  may apply.
+- Select policies using the task triggers above. Follow cross-references to
+  relevant sections when needed to resolve a concrete question.
+- Reuse policies already available in context; reread when changed or no longer
+  available.
+- Expand reading when the task's scope expands.
+- When revising a policy itself, read that policy and any provisions elsewhere
+  affected by the revision.
 
 ## Task-Specific Reading Guide
 
@@ -34,108 +43,55 @@ Start with:
 | Root public API | The [architecture policy](policy/architecture.md), [consumer guide](consumers/pkg-promptkit.md), [testing policy](policy/testing.md), and existing GoDoc. |
 | Prompt, profile, or schema formats | The [framework format reference](formats.md), owning parser or validator package, and [documentation policy](policy/documentation.md). |
 | Source loading or validation | The [framework format reference](formats.md), [internal source document](internal/sources.md), and owning package tests. |
+| Maintained external catalogs or built-ins | The [internal source document](internal/sources.md), [framework format reference](formats.md), [testing policy](policy/testing.md), both catalog module repositories, each catalog's release procedure, and the selected module versions in `go.mod`. |
 | Model-client behavior | The [OpenAI-compatible integration contract](integrations/openai-compatible-chat.md), [internal model-client document](internal/llm.md), and owning package tests. |
 | Internal package implementation | The [architecture policy](policy/architecture.md), [internal component overview](internal/overview.md), and focused internal document listed for that package. |
 | Tests or test fixtures | The [testing policy](policy/testing.md), owning package, and focused internal document listed by the component overview. |
-| Maintained example | The [example](../examples/go-library/prepare/main.go), [consumer guide](consumers/pkg-promptkit.md), [framework format reference](formats.md), and [documentation policy](policy/documentation.md). |
+| Maintained example | The [preparation](../examples/go-library/prepare/main.go), [execution](../examples/go-library/run/main.go), and [observation](../examples/go-library/observe/main.go) examples, [consumer guide](consumers/pkg-promptkit.md), [framework format reference](formats.md), and [documentation policy](policy/documentation.md). |
 | Documentation | The [documentation policy](policy/documentation.md) and canonical owner of every affected contract. |
-| Release preparation or publication | The [release procedure](release.md). |
+| Licensing, dependencies/catalog updates, copied material, or attribution | The [OSS policy](policy/oss.md), [project grant](../COPYRIGHT), [license texts](../LICENSE), and [attribution entries](oss/attribution.md); inspect the selected upstream source's notices. |
+| Release preparation or publication, including release notes | The [release policy](policy/release.md), [release procedure](release.md), and [OSS discoverability rules](policy/oss.md#discoverability). |
 
 For cross-cutting changes, follow every applicable row. Do not create
 placeholder documents for packages, APIs, or integrations that do not yet
 exist.
 
-## Maintainer-Run Validation
+## Maintainer Validation
 
-Promptkit does not currently use hosted CI. Maintainers are responsible for
-running the documented checks before accepting changes. Run the default Go
-validation from the Promptkit repository root:
+For ordinary work, select validation proportionate to the change. Do not repeat
+successful checks for unchanged content merely to create a commit. The full
+release-candidate checks have one executable entry point from the repository root:
 
 ```sh
-go test ./...
-go test -race ./...
-go vet ./...
-go build ./...
-go run ./examples/go-library/prepare
+./scripts/release-check.sh
 ```
 
-Check formatting across every tracked Go file:
+The [script](../scripts/release-check.sh) owns the executable checks:
+race-enabled tests, vet, the three offline consumer examples with semantic output
+assertions, tracked Go formatting, local Markdown links, module/workspace
+hygiene, whitespace, and the credential-pattern scan. It does not publish,
+change files, validate release-note structure, or retire roadmaps. It requires Go,
+Git, a POSIX shell, and Python 3. Tests and examples require no provider
+credentials or live inference calls.
 
-```sh
-gofmt -l $(git ls-files '*.go')
-```
+The script can run on intended uncommitted changes during development.
+Formatting and documentation checks use tracked files; stage intended new
+files before final validation so those checks include them. The release
+procedure separately enforces a clean, committed candidate.
 
-The formatting command must produce no paths. Follow every added or changed
-Markdown link and confirm its target exists. Finally, check whitespace:
+### Change Review
 
-```sh
-git diff --check
-```
+Inspect `git status --short --untracked-files=all` and the complete diff before
+accepting a change. Reject unintended files, credentials, private data,
+generated binaries, test output, downloaded assets, and template residue.
+The automated credential scan does not replace review of the actual change.
 
-Documentation-only work does not require unrelated new tests, but it still
-requires link validation and `git diff --check`. Run the Go validation whenever
-documentation changes commands, examples, generated output, or another
-behavior checked by the module.
+For releases, follow the [release procedure](release.md). Its publication
+command runs the full local checks once on the final committed candidate and
+automates release-note structure and Git checks. Do not repeat ordinary change
+review as a release sign-off. Roadmap retirement remains preparation housekeeping.
 
-## Focused Validation
-
-Use focused checks while iterating, then run the complete validation sequence
-before accepting the change. The root package supports:
-
-```sh
-go test .
-go vet .
-go build .
-```
-
-Filter tests by name without assuming a fixed internal package layout:
-
-```sh
-go test ./... -run 'TestName'
-```
-
-Replace `TestName` with a useful regular expression. Target only paths that
-exist, and consult the internal component overview for their owning
-documentation. A filtered or package-specific run does not replace the
-complete repository validation.
-
-## Coordinated Work With Scriptorium
-
-Promptkit and Scriptorium must remain independently valid. For temporary local
-integration, use either a Go workspace outside both repositories or an
-uncommitted replacement in the consuming module.
-
-If the repositories are sibling directories, run the workspace commands from
-their parent directory:
-
-```sh
-go work init ./promptkit ./scriptorium
-go work sync
-```
-
-Use the workspace only for coordinated local checks. From the same parent
-directory, remove it when finished:
-
-```sh
-rm -f go.work go.work.sum
-```
-
-Alternatively, from the Scriptorium repository root, temporarily point its
-Promptkit dependency at the sibling checkout:
-
-```sh
-go mod edit -replace gitea.maximumdirect.net/eric/promptkit=../promptkit
-```
-
-After coordinated checks, remove the replacement and reconcile module
-metadata:
-
-```sh
-go mod edit -dropreplace gitea.maximumdirect.net/eric/promptkit
-go mod tidy
-```
-
-Never commit `go.work`, `go.work.sum`, or a local filesystem `replace`
-directive. Before committing in either repository, inspect its module files and
-working tree independently. Published consumer versions must depend on a tagged
-Promptkit version, not a workspace, local replacement, or unpublished commit.
+Follow the [agent commit policy](policy/agents.md#git-commit-policy) for local
+commits. Ordinary commits may leave unrelated work in the workspace; preserve
+and report it. A clean worktree and index are required for release candidates,
+as enforced by the publication command, not for every ordinary commit.

docs/formats.md

@@ -9,9 +9,10 @@ explains how to select these sources and invoke the engine. The
 owns the resulting outbound wire behavior.
 
 Prompt and profile sources recursively discover files ending in `.yaml` or
-`.yml`. YAML decoding is strict: unknown fields are errors for the selected
-definition. Definitions are selected by their YAML `id`, not their file name
-or directory.
+`.yml`. Each prompt-definition and profile file contains exactly one YAML
+document; comments and trailing whitespace are allowed. YAML decoding is
+strict: unknown fields are errors for the selected definition. Definitions are
+selected by their YAML `id`, not their file name or directory.
 
 ## Prompt Definitions
 
@@ -58,6 +59,11 @@ When a request omits a version, the selected prompt ID must identify exactly
 one definition. When it supplies a version, the ID and version pair must be
 unique.
 
+Exact prompt inspection uses this same configured source, strict decoding,
+referenced content-file resolution, and ID/version selection. It reports the
+selected definition's declared metadata without changing the prompt format or
+executing the definition.
+
 ### Inputs
 
 Each `inputs` item has these fields:
@@ -76,14 +82,27 @@ allowed.
 
 ### Messages And Templates
 
-Each message has a non-empty `role` and exactly one of:
+Each message has a `role` that Promptkit trims and lowercases. It must then be
+exactly one of `developer`, `system`, `user`, or `assistant`; blank, custom,
+`tool`, and `function` roles are invalid. This intentionally tightens the
+previous nonblank-string rule. Consumers migrating to the next minor release
+must update any nonstandard prompt-definition roles before upgrading.
+
+Each message also has exactly one of:
 
 - `content`, containing an inline Go template; or
 - `content_file`, naming a file whose contents are the Go template.
 
-For directory and `fs.FS` prompt sources, `content_file` resolves relative to
-the prompt file and remains within the source root. `WithPromptFile` also
-resolves it relative to that file.
+`content_file` must be a relative path. It resolves from the directory that
+contains the prompt file and must remain within the configured prompt source
+root; parent components are allowed only when the resolved target remains
+inside that root. Absolute paths and paths that escape the root are rejected.
+Operating-system directory and single-file sources also reject symlink targets
+outside the root, while injected `fs.FS` sources apply containment in that
+filesystem's relative path namespace. For `WithPromptFile`, the source root is
+the directory containing the selected prompt file. Promptkit uses the parsed
+path text exactly after checking separately that it is not blank, so leading
+and trailing whitespace can name real filesystem entries.
 
 Request variables are the template data, so a variable named `audience` is
 referenced as `{{.audience}}`. The `{{input "note"}}` helper renders the body
@@ -91,7 +110,8 @@ of a named input. Missing variables and input references are errors.
 
 The optional `session_id` uses the same template data and input helper. Its
 rendered value is trimmed, omitted when empty, and limited to 256 Unicode code
-points.
+points. A nonblank direct request session ID bypasses this template completely;
+a blank direct value leaves the template behavior unchanged.
 
 ### Cache Control
 
@@ -112,7 +132,7 @@ outbound integration determines its wire representation.
 | `format` | yes | `text`, `markdown`, or `json`. |
 | `validation_mode` | yes | `none`, `basic`, `json`, or `json_schema`. |
 | `schema_path` | for `json_schema` | Path to a schema in the configured schema source. |
-| `repair_attempts` | no | Integer zero or greater; omitted means zero. |
+| `repair_attempts` | no | Integer from zero through three; omitted means zero. A positive value requires `basic`, `json`, or `json_schema` validation. |
 
 The validation modes behave as follows:
 
@@ -122,21 +142,38 @@ The validation modes behave as follows:
 - `json_schema` requires valid JSON that satisfies the selected schema.
 
 `format` controls output artifact metadata. JSON Schema mode also supplies the
-schema to compatible model clients as structured-output metadata. The public
-engine does not install an output repairer, so its validation is single-pass
-even when a positive `repair_attempts` value is present.
+schema to compatible model clients as structured-output metadata. Plain `json`
+validation accepts every valid JSON value and does not request a provider-native
+JSON-object constraint.
+
+`repair_attempts` counts additional generation calls after a failed validation.
+Zero is single-pass. With a positive eligible budget, Promptkit stops at the
+first valid candidate. If the budget is exhausted, it returns the final
+candidate and its complete failed validation result; generation and operational
+validation failures remain errors. `none` never permits repair.
 
 A request-level `OutputContract` replaces the complete prompt output contract.
 It does not merge individual fields. If its format is empty, Promptkit uses
 `text`.
 
+## Built-In Backends
+
+Every engine provides these reserved OpenAI-compatible backend IDs. Consumers
+must not register either ID with `WithBackend`; exact registration and
+reservation behavior belongs to the [`Backend` GoDoc](../backends.go).
+
+| ID | Base endpoint | API-key environment variable | Active generation limit | Default queue capacity |
+| --- | --- | --- | ---: | ---: |
+| `openrouter` | `https://openrouter.ai/api/v1` | `OPENROUTER_API_KEY` | 16 | 1024 |
+| `rakestrawhome` | `https://inference.ai.rakestrawhome.com/v1` | `RAKESTRAWHOME_INFERENCE_API_KEY` | 4 | 1024 |
+
 ## Profile Definitions
 
 A profile supplies model execution settings:
 
 ```yaml
 id: local-summary
-endpoint: http://localhost:8000/v1
+backend: openrouter
 model: example-model
 temperature: 0.2
 max_tokens: 500
@@ -144,15 +181,25 @@ top_p: 0.95
 timeout_seconds: 90
 service_tier: flex
 reasoning_effort: medium
-api_key_env: EXAMPLE_API_KEY
 extra_params:
   provider_option: enabled
 ```
 
+A derived profile can use a named base and override only the settings it owns:
+
+```yaml
+id: local-summary-fast
+base_profile: local-summary
+timeout_seconds: 30
+reasoning_effort: low
+```
+
 | Field | Required | Meaning |
 | --- | --- | --- |
-| `id` | yes | Non-empty profile identifier. IDs must be unique within one source. |
-| `endpoint` | yes | Non-empty OpenAI-compatible base URL, including an API version path when required. |
+| `id` | yes | Profile identifier, trimmed before selection and publication. It must be non-empty after trimming and unique within one source after normalization. |
+| `base_profile` | no | One optional parent profile ID. A derived profile may inherit target fields from it. |
+| `backend` | unless `endpoint` is present | Backend registry ID. It is trimmed and registry membership is checked when the profile is prepared or inspected. |
+| `endpoint` | unless `backend` is present | OpenAI-compatible base URL, including an API version path when required. A nonempty value is trimmed and must be absolute HTTP or HTTPS with a host and without user information, a query, or a fragment. When both connection fields are present, this overrides the backend endpoint without changing backend identity. |
 | `model` | yes | Non-empty provider model name. |
 | `temperature` | no | Number from 0 through 2. |
 | `max_tokens` | no | Integer zero or greater. |
@@ -160,93 +207,152 @@ extra_params:
 | `timeout_seconds` | no | Per-generation deadline in whole seconds; integer zero or greater. |
 | `service_tier` | no | Provider-specific request tier. |
 | `reasoning_effort` | no | Provider-specific reasoning setting. |
-| `api_key_env` | no | Name of an environment variable containing the API key. |
+| `api_key_env` | no | Optional environment-variable lookup source for an API key. |
 | `extra_params` | no | JSON-compatible provider-specific outbound fields. |
 
 Raw `api_key` is prohibited in profile YAML. Store only an environment
 variable name in `api_key_env`.
 
+A standalone profile must provide a model and at least one of `backend` or
+`endpoint`. A derived profile may omit those target fields because its selected
+base chain can provide them. Local parsing still validates a derived profile's
+own ID, supplied endpoint, execution-setting bounds, and `extra_params`.
+
+Promptkit does not infer a backend from a model or endpoint. Endpoint-only
+profiles remain supported and have no effective backend ID.
+The engine always provides the built-in `openrouter` and `rakestrawhome` IDs.
+Consumers can add engine-scoped IDs with
+[`WithBackend`](../backends.go); exact registration validation belongs to its
+GoDoc.
+
 `extra_params` accepts null, booleans, finite numbers, strings, arrays, and
 objects with string keys. Keys must be non-empty. With the built-in client,
 they also cannot collide with the standard fields listed in the
 [outbound request contract](integrations/openai-compatible-chat.md#request-body).
+Excessively deep or large JSON-shaped values are rejected for safety.
 
 ### Defaults And Overrides
 
 Execution settings resolve in this order:
 
-1. framework defaults;
-2. the selected profile; and
-3. request `ExecutionTargetOverride` values.
+1. the framework timeout baseline;
+2. the selected backend, when the profile names one;
+3. the selected profile; and
+4. request `ExecutionTargetOverride` values.
 
-The framework defaults are:
+The framework baseline is:
 
 | Setting | Default |
 | --- | --- |
-| `temperature` | `0` |
-| `max_tokens` | `0` |
-| `top_p` | `1` |
+| `temperature` | Unspecified and omitted from compatible provider requests unless a profile or runtime override selects it. |
+| `max_tokens` | Unspecified and omitted from compatible provider requests unless a profile or runtime override selects it. |
+| `top_p` | Unspecified and omitted from compatible provider requests unless a profile or runtime override selects it. |
 | `timeout_seconds` | `600` |
 
-Numeric zero in a file or in-memory profile means that the profile does not
-replace the framework default. Numeric request overrides use pointers, so an
-explicit zero is preserved. In particular, an explicit request
-`timeout_seconds` of zero disables the per-generation deadline while leaving
-the caller context and transport timeout intact.
+Numeric zero in a file or in-memory profile does not select a numeric value.
+For `temperature`, `max_tokens`, and `top_p`, it leaves the provider control
+unspecified. For `timeout_seconds`, it retains the framework deadline. Numeric
+request overrides use pointers, so an explicit zero is retained and sent to
+compatible providers. In particular, an explicit request `timeout_seconds` of
+zero disables the per-generation deadline while leaving the caller context and
+transport timeout intact.
 
-Non-empty request strings replace profile strings. A non-empty request
-`ExtraParams` map replaces the profile map rather than merging keys.
+Non-empty profile strings replace backend defaults, and non-empty request
+strings replace both. Request reasoning is the exception: a nil
+`ReasoningEffort` pointer inherits the profile, a pointer to a nonblank string
+trims and replaces it, and a pointer to a blank string clears it. Backend
+identity is retained when either layer overrides the endpoint, so the override
+also retains any engine-local capacity policy configured for that backend.
+Capacity configuration belongs to the Go
+[`Backend` API](../backends.go), not prompt or profile YAML. A non-empty
+`extra_params` map at each layer replaces the entire lower-precedence map
+rather than merging keys.
 The [outbound integration contract](integrations/openai-compatible-chat.md)
 defines how the effective settings are serialized.
 
 ### Source And Profile Precedence
 
 An explicit request profile ID takes precedence over the prompt's
-`default_profile`. If neither is present, preparation fails.
+`default_profile`. If neither is present, preparation fails. Exact profile
+inspection instead takes one explicit profile ID and does not use a prompt
+default.
 
 Profile sources resolve matching IDs in this order:
 
 1. in-memory profiles supplied with `WithProfiles`;
-2. a profile file, `fs.FS`, or configured profile directory; and
-3. embedded built-in profiles.
+2. the ordinary configured source selected by a profile file, `fs.FS`, or
+   configured profile directory;
+3. application fallback profiles supplied with `WithFallbackProfileFS`; and
+4. Promptkit-owned profiles; and
+5. maintained external catalog profiles.
 
-A higher-precedence source falls back only when the profile is absent. An
-invalid matching profile is an error and does not fall back. In-memory
-`Profile` values follow the same ranges as YAML profiles. They use
-`APIKeyRequired` for request-scoped credentials instead of `api_key_env`.
+A profile source supplies a complete definition; definitions and their fields
+are not merged across sources. A higher-precedence source falls back only when
+the requested profile ID is absent. An invalid matching profile is an error and
+does not fall back. In-memory `Profile` values follow the same ranges as YAML
+profiles. They use `APIKeyRequired` for request-scoped credentials instead of
+`api_key_env`. Preparation and exact profile inspection use this same source
+precedence.
+
+When a selected definition names `base_profile`, every profile ID in that
+chain is looked up through this same precedence order. A higher-precedence
+definition therefore shadows a lower-precedence definition of the same base
+ID, including a built-in. References are not source-qualified.
+
+### Profile Inheritance
+
+Promptkit resolves one linear base chain of at most 32 profiles, including the
+selected profile. It merges settings from the root base to the selected leaf.
+The leaf's `id` remains the selected profile identity. Nonblank string fields
+(`backend`, `endpoint`, `model`, `service_tier`, `reasoning_effort`, and
+`api_key_env`) and nonzero numeric fields replace inherited values. A nonempty
+`extra_params` map replaces the complete inherited map rather than merging
+keys, and `APIKeyRequired: true` remains true through the chain. Backend and
+endpoint are independent: replacing one does not clear the other.
+
+There is no profile-level clearing syntax. Blank strings, zero numbers, false,
+and empty maps remain unspecified and inherit from a base. Use existing
+presence-aware request overrides where an execution needs an explicit zero or
+empty reasoning setting.
+
+An absent directly selected profile reports the ordinary not-found error. Once
+the selected profile exists, a missing base, cycle, overlong chain, or
+incomplete resolved target is a profile-load failure. Ordinary operations
+resolve chains afresh; prepared execution retains the fully resolved target.
 
 ## Built-In Profile Catalog
 
-Built-ins use the OpenRouter-compatible endpoint and
-`OPENROUTER_API_KEY`. A custom or in-memory profile with the same ID takes
-precedence.
+Every built-in profile selects one maintained built-in backend and inherits
+that backend's connection and credential metadata. Profile files do not repeat
+those values. A configured, application fallback, or in-memory profile with
+the same profile ID takes precedence.
 
-| Provider | ID | Model |
-| --- | --- | --- |
-| aion-labs | `aion-2` | `aion-labs/aion-2.0` |
-| anthropic | `claude-fable-latest` | `~anthropic/claude-fable-latest` |
-| anthropic | `claude-haiku-latest` | `~anthropic/claude-haiku-latest` |
-| anthropic | `claude-opus-latest` | `~anthropic/claude-opus-latest` |
-| anthropic | `claude-sonnet-latest` | `~anthropic/claude-sonnet-latest` |
-| deepseek | `deepseek-3-2` | `deepseek/deepseek-v3.2` |
-| deepseek | `deepseek-4-flash` | `deepseek/deepseek-v4-flash` |
-| deepseek | `deepseek-4-pro` | `deepseek/deepseek-v4-pro` |
-| google | `gemini-2-flash` | `google/gemini-2.5-flash` |
-| google | `gemini-2-flash-lite` | `google/gemini-2.5-flash-lite` |
-| google | `gemini-2-pro` | `google/gemini-2.5-pro` |
-| google | `gemini-3-flash-lite` | `google/gemini-3.1-flash-lite` |
-| google | `gemini-flash-latest` | `~google/gemini-flash-latest` |
-| google | `gemini-pro-latest` | `~google/gemini-pro-latest` |
-| google | `gemma-4-31b` | `google/gemma-4-31b-it:exacto` |
-| minimax | `minimax-m2` | `minimax/minimax-m2.5` |
-| minimax | `minimax-m3` | `minimax/minimax-m3` |
-| mistral | `mistral-large-2512` | `mistralai/mistral-large-2512` |
-| mistral | `mistral-medium-3-5` | `mistralai/mistral-medium-3-5` |
-| mistral | `mistral-small-3` | `mistralai/mistral-small-3.2-24b-instruct` |
-| mistral | `mistral-small-4` | `mistralai/mistral-small-2603` |
-| nvidia | `nemotron-3-ultra` | `nvidia/nemotron-3-ultra-550b-a55b` |
-| openai | `gpt-5-mini` | `openai/gpt-5.4-mini` |
-| openai | `gpt-5-nano` | `openai/gpt-5.4-nano` |
+Promptkit owns two opt-in profiles. The following definitions are current
+selections, not automatic defaults:
+
+| ID | Current definition |
+| --- | --- |
+| `promptkit-openrouter-standard` | Inherits `gemini-flash-latest`. |
+| `promptkit-openrouter-auto` | Selects backend `openrouter` and model `openrouter/auto`. |
+
+Select either name through an existing request `profile_id` or prompt
+`default_profile`. Consumers can replace either definition or its inherited
+base through the ordinary profile-source precedence above. The
+[release policy](policy/release.md#catalog-profile-compatibility) defines the
+cross-version guarantee for these names.
+
+## External Profile Inventories
+
+The external profile inventory is defined by the selected catalog modules, not
+duplicated here. Browse the exact data selected by this Promptkit version:
+
+- [OpenRouter catalog v2.20260926.0 profiles](https://gitea.maximumdirect.net/eric/promptkit-backend-openrouter/src/tag/v2.20260926.0/catalog/profiles)
+- [Rakestrawhome catalog v2.20260926.0 profiles](https://gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/src/tag/v2.20260926.0/catalog/profiles)
+
+External profile entries are volatile across catalog releases. The
+[release policy](policy/release.md#catalog-profile-compatibility) owns the precise
+compatibility boundary; a selected module version identifies tested local data,
+not live provider availability.
 
 ## Schemas
 
@@ -265,12 +371,25 @@ schema produces a failed validation result.
 Credential values belong at the request or environment boundary, never in
 prompt, profile, schema, or example files:
 
-- a file profile names an environment variable with `api_key_env`;
-- an in-memory profile may set `APIKeyRequired`;
-- a request can provide a direct `APIKey` or override `APIKeyEnv`; and
+- a backend or file profile can name an optional environment lookup source
+  with `APIKeyEnv` or `api_key_env`;
+- an in-memory profile may set `APIKeyRequired` as an explicit local
+  requirement;
+- a request can provide a direct `APIKey` or override the optional `APIKeyEnv`
+  source; and
 - a direct request key takes precedence over environment lookup.
 
-Promptkit validates required credential availability during preparation.
+After a direct request key, the credential-source precedence is request
+`APIKeyEnv`, profile `api_key_env`, then the backend default. An in-memory
+profile with `APIKeyRequired` clears an inherited backend environment name and
+requires a direct key unless the request explicitly supplies `APIKeyEnv`.
+Named environment sources are optional: when the selected source is absent,
+empty, or whitespace-only, the built-in client omits the `Authorization`
+header and handles the provider response normally. `APIKeyRequired` is the
+only explicit local availability requirement. Promptkit validates required
+credential availability during preparation and rechecks it when a prepared
+execution runs. Injected clients receive resolved source metadata but define
+their own credential-resolution behavior.
 Direct keys are excluded from JSON results and redacted by public string
 formatters. Environment-variable names may appear in prepared metadata, but
 their values do not.

docs/integrations/openai-compatible-chat.md

@@ -13,18 +13,37 @@ that produce these outbound settings.
 ## Endpoint And Method
 
 Generation sends an HTTP `POST` with `Content-Type: application/json`.
-A non-empty endpoint from the execution target overrides the client's
-configured base URL. After trailing slashes are removed,
-`/chat/completions` is appended. Generation fails before sending when neither
-source supplies an endpoint.
+Before the client is called, the engine resolves framework, backend, profile,
+and request values into one execution target. Endpoint configuration is trimmed
+and must be an absolute HTTP or HTTPS URL with a host and without user
+information, a query, or a fragment. A non-empty endpoint from the target
+overrides the client's configured base URL. The final selected endpoint is
+validated again before transport.
+
+The completion URL is composed through parsed URL path operations. Nested base
+paths are retained, repeated trailing slashes are normalized, and the result
+has exactly one appended `/chat/completions` suffix. Generation fails before
+sending when neither source supplies a valid endpoint.
+
+The target's backend ID is routing metadata for prepared values, results, and
+injected clients. The built-in client does not derive the URL from that ID and
+does not serialize it in the provider request.
 
 ## Authentication
 
-A non-empty API key supplied directly on the execution target takes
-precedence. Otherwise, when an API-key environment-variable name is supplied,
-the client reads that variable and requires a non-empty value. The selected
-key is sent as `Authorization: Bearer <key>`. No authorization header is sent
-when neither mechanism is configured.
+A usable API key supplied directly on the execution target takes precedence.
+Otherwise, when an API-key environment-variable name is supplied, the client
+reads and trims that variable. A bearer header is sent only when the resolved
+direct or environment credential is non-empty. When neither source is usable,
+the client omits `Authorization` and handles the provider response normally.
+An explicitly required target with no usable source is rejected before
+transport.
+
+The target contains the already resolved environment-variable name: an
+explicit request override takes precedence over profile metadata, which takes
+precedence over the backend default. Only the name reaches prepared metadata;
+the environment value is read just before the provider call and is never added
+to the JSON body.
 
 ## Request Body
 
@@ -36,20 +55,32 @@ Each ordinary message contains its `role` and string `content`. A
 cache-controlled message instead uses a text content block containing `type`,
 `text`, and `cache_control`; an empty cache-control TTL is omitted.
 
-A non-empty session ID is trimmed, checked against the internal domain limit,
-and sent as top-level `session_id`. It is not sent as a session header.
+Promptkit sends only `developer`, `system`, `user`, and `assistant` roles and
+does so without provider-specific translation. Tool and deprecated function
+payloads are outside this text-message contract. A backend or model that
+rejects an otherwise supported role or context returns its ordinary provider
+error, which follows the normal generation-error path.
+
+The effective direct or prompt-rendered session ID is trimmed, limited to 256
+Unicode code points, and sent when nonempty as top-level `session_id`. It is
+never also sent as a session header.
 
 The client conditionally includes:
 
-- `temperature`, `max_tokens`, and `top_p` when non-zero or explicitly
-  present;
-- non-empty `service_tier` and `reasoning_effort`; and
+- `temperature`, `max_tokens`, and `top_p` only when selected by a profile or
+  runtime override, including an explicit runtime zero; they are absent when
+  unspecified;
+- non-empty `service_tier` and effective `reasoning_effort`; an explicitly
+  disabled reasoning setting is empty and therefore omitted; and
 - `response_format` for JSON Schema structured output, including its name,
-  strict flag, and schema document.
+  strict flag, and schema document. Plain JSON validation does not add an
+  object-only response constraint.
 
-Extra parameters are merged directly into the top-level body after JSON
-serialization is verified. Empty keys and collisions with these reserved
-fields are rejected before any provider call:
+The engine resolves backend, profile, and request extra-parameter maps by
+whole-map replacement rather than key merging. The resulting effective map is
+then merged directly into the top-level body after JSON serialization is
+verified. Empty keys and collisions with these reserved fields are rejected
+before any provider call:
 
 - `model`
 - `session_id`
@@ -61,15 +92,87 @@ fields are rejected before any provider call:
 - `reasoning_effort`
 - `response_format`
 
+`backend_id`, `api_key_env`, and resolved credential values are not provider
+request fields.
+
 ## Response Handling
 
-Any 2xx response is decoded as an OpenAI-compatible chat response. The client
-returns the first choice's non-empty message content and maps prompt,
-completion, total, cached, and cache-write token counts.
+Any 2xx response body is limited to 16 MiB (16,777,216 bytes). A larger
+declared `Content-Length` is rejected before the body is read, and streamed,
+chunked, or underreported bodies are read through the same bound with at most
+one additional byte used to detect overflow. A body exactly at the limit is
+allowed. The body is closed on every outcome and an oversized stream is not
+drained.
 
-Invalid JSON, absent choices, and empty first-choice content are malformed
-responses. For a non-2xx status, the error includes the status code but never
-the provider response body.
+The bounded body must contain exactly one OpenAI-compatible JSON response
+object followed only by JSON whitespace and EOF. The client returns the first
+choice's explicitly present string message content, including an empty or
+whitespace-only string, and maps prompt, completion, total, cached, and
+cache-write token counts. Invalid or truncated JSON, trailing non-whitespace
+data, a second JSON value, absent choices, missing content, `null` content,
+non-string content, and size overflow are malformed responses and return no
+partial result.
+
+Each of the five token fields retains whether the provider reported a
+non-null integer, including zero. Omitted and `null` fields are unknown for
+observations. A strictly decoded successful envelope can yield observed usage
+even when a later missing choice or content makes the attempt malformed.
+Invalid framing and non-2xx error bodies supply no observed usage; provider
+work may still have occurred. Reported counts are not inferred, reconciled,
+or proof of complete cost accounting.
+
+For a non-2xx status, Promptkit recognizes one JSON document with a top-level
+object-valued `error` member. Its optional `message` and `type` fields must be
+strings, and `code` may be a string or JSON number. Valid supported fields are
+handled independently, numeric codes retain their JSON number text, and
+unknown fields are ignored. Missing, invalid, malformed, or multiply framed
+envelopes contribute no provider detail.
+
+Non-success bodies have a 65,536-byte limit. A larger declared
+`Content-Length` is not read; otherwise the client reads at most one additional
+byte to detect streamed or underreported overflow. Empty, unreadable,
+oversized, malformed, and unrecognized bodies retain only the received status.
+The body is always closed and no oversized stream is drained beyond that probe.
+
+Extracted strings are made valid UTF-8, trimmed, and converted to one line by
+collapsing Unicode whitespace, control, and format-character runs. Blank
+values are omitted. Codes and types longer than 256 Unicode code points are
+omitted; messages longer than 4,096 code points are truncated at a code-point
+boundary with an ellipsis inside the limit. Promptkit never exposes raw bodies,
+headers, endpoints, credentials, request data, schemas, generated content, or
+unsupported provider metadata through this handling.
+
+An outbound `http.Client.Do` failure retains both Promptkit's request-failure
+identity and the exact transport error for `errors.Is` and `errors.As` checks.
+The rendered error does not include the selected endpoint, request headers,
+request content, credentials, or provider body.
+
+## Transient Status Retries
+
+The built-in path retries only HTTP 429, 500, 502, 503, and 504. It makes two
+additional attempts by default; engine configuration or an individual run can
+choose a different nonnegative count, including zero for single-attempt
+behavior. The same budget applies separately to initial generation and each
+structural repair generation. An injected `LLMClient` is dispatched once by
+Promptkit regardless of this setting. A custom `http.Client` on the built-in
+path remains subject to these retries.
+
+Each retry uses equal jitter between half and all of an exponential local
+delay, starting at 500 milliseconds and capped at 8 seconds. The first
+`Retry-After` header value sets a minimum not-before time measured from
+response receipt if it is valid unsigned decimal seconds or an HTTP date.
+Invalid values use local delay; past dates impose no extra delay. The provider
+minimum is not capped at 8 seconds. Retry waiting is cancellable and holds no
+active backend permit. A caller without a deadline can wait a long time for
+provider timing.
+
+The request body, selected URL, and resolved authorization are fixed across
+attempts of one generation. Each attempt creates a fresh HTTP request and
+receives its own configured generation and HTTP-client timeout after capacity
+admission. The caller context covers every attempt and wait without a reset.
+Transport failures, malformed responses, noneligible statuses, and invalid
+generated content are not transient retries. A positive budget ending in
+eligible statuses reports retry exhaustion with the final provider cause.
 
 ## Timeout And Cancellation
 
@@ -84,5 +187,7 @@ Timeouts are layered:
   timeout when the supplied value is not positive.
 
 The earliest applicable caller, generation, or transport deadline controls the
-request. Constructing the internal client does not mutate a supplied
-`http.Client`.
+request. Caller cancellation retains `context.Canceled`; caller, generation,
+and whole-request timeout failures retain `context.DeadlineExceeded`, together
+with the request-failure identity. Constructing the internal client does not
+mutate a supplied `http.Client`.

docs/internal/capacity.md

@@ -0,0 +1,130 @@
+# Internal Capacity Management
+
+## Purpose
+
+This document describes the implemented engine-local capacity coordination in
+`internal/capacity`. The [architecture policy](../policy/architecture.md) owns
+component boundaries, the [backend GoDoc](../../backends.go) owns exact public
+configuration semantics, and the
+[internal runner document](runner.md) owns orchestration around admission.
+
+Capacity scheduling is outside the provider wire contract. It does not add
+fields to execution targets, generated requests, prompt or profile YAML, or
+stable JSON values.
+
+## Construction And Pool Lifecycle
+
+Each internal engine construction obtains a normalized capacity-policy snapshot from
+its immutable backend registry and constructs a new `Manager`. The manager
+creates one pool for each limited backend ID. It has no package-global mutable
+state, background workers, shutdown protocol, or persistence, so engines with
+the same registrations still have independent capacity.
+
+Unlimited registered backends and endpoint-only profiles have no pool. Their
+admission and generation calls take the unrestricted fast path. An endpoint
+override does not change the selected backend ID and therefore does not change
+the pool.
+
+One pool owns immutable active and total limits plus mutex-protected admission
+count, active count, and ordered waiter list. Pool state exists only for the
+lifetime of its engine.
+
+## Bounded Execution Admission
+
+For ordinary `Run`, the runner asks the manager to admit after resolving the
+prompt, profile, selected backend, effective execution target, credentials, and
+output contract, but before schema loading, artifact loading, or rendering.
+`PrepareExecution` performs no admission. `RunPrepared` claims its handle,
+rechecks credential availability, and then asks the manager to admit the
+frozen backend before generation.
+
+Admission is immediate: a limited pool either reserves a slot or returns only
+the internal `ErrCapacityExceeded` identity. The runner attaches the selected
+backend identity at its use-case boundary, and the root facade translates that
+typed value without treating it as an invalid request or generation failure.
+
+The total admitted bound is the active-generation limit plus its configured
+waiting capacity. The returned release function is idempotent. The runner
+defers it as soon as admission succeeds. An ordinary run holds the lease across
+remaining preparation, initial generation, validation, every repair attempt,
+and all failure or cancellation exits. Prepared execution holds the normal
+lease across generation, validation, every internal repair attempt, and all
+execution exits. A repair is part of its original admission and does not
+reserve another bounded slot.
+
+## FIFO Generation Permits
+
+The engine supplies one [generation coordinator](generation.md) to initial
+generation and the default repairer. Their requests retain the same effective
+backend, credential, numeric-presence metadata, structured-output settings,
+and retry budget. Scheduling does not change provider omission semantics
+between calls.
+
+For each model attempt, the coordinator selects a pool from the request's
+effective backend ID. An unlimited call uses the unrestricted path. A limited
+call acquires an active permit and defers release around that attempt, so
+ordinary returns and panic unwinding both restore capacity.
+Preparation and validation never hold an active permit.
+
+The manager's `Acquire` operation owns that active-permit acquisition and
+returns an idempotent release function. The coordinator uses it around
+individual attempts. The earlier one-shot wrapper still delegates to the same
+operation for focused internal callers and tests, but engine assembly no
+longer uses it. There is one queue and one active limit per limited backend pool.
+
+When all active permits are occupied, calls join a mutex-protected FIFO waiter
+list. Releasing a permit transfers it directly to the oldest remaining waiter
+before making it generally available. Pools do not order work relative to
+other backend IDs.
+
+The coordinator does not retry injected clients; it normalizes a nil successful
+response as malformed generation. The built-in HTTP client remains responsible
+for provider transport behavior. The runner, rather than the
+capacity layer, sums all five usage fields from the initial response and every
+completed repair response into the successful run result.
+
+An invocation-local observer receives attempt events after active permit
+release, including canceled acquisition without dispatch. A retry wait holds
+the logical admission lease but no active permit. Observer callbacks must not
+block on work that requires the same run's admission slot.
+
+## Cancellation And Release
+
+Admission checks the caller context before reserving a slot. A call canceled
+while waiting for an active permit removes its waiter under the same pool lock
+used to grant permits. If cancellation removes the waiter first, no model
+attempt is dispatched. If a concurrent grant wins first, the call owns the
+permit; the coordinator checks the context before dispatch and releases the
+permit if cancellation has already occurred.
+
+This grant-or-cancel decision prevents lost and double-released permits.
+Admission leases and active permits are released after success, collaborator
+errors, validation failures, cancellation, and panic unwinding. Canceled
+waiters are unlinked so their contexts and requests are not retained by the
+pool.
+
+## Test Ownership
+
+The [manager tests](../../internal/capacity/manager_test.go) own policy
+validation, bounded admission, idempotent release, context handling, and
+unlimited admission. The
+[client tests](../../internal/capacity/client_test.go) own peak enforcement,
+FIFO transfer, canceled-waiter removal, grant/cancel races, independent pools,
+unlimited calls, passthrough behavior, and panic release.
+
+The [runner tests](../../internal/usecase/runner_test.go) own ordinary early
+admission, lease lifetime, failure release, and shared initial/repair
+scheduling. The
+[prepared-execution use-case tests](../../internal/usecase/prepared_execution_test.go)
+own deferred admission, credential ordering, and prepared-execution lease
+release. The
+[external package capacity tests](../../capacity_contract_test.go) own the
+assembled public-engine behavior for configured limits, capacity errors,
+endpoint identity, engine independence, and injected clients. The
+[reliable execution contract tests](../../reliable_execution_contract_test.go)
+cover shared and independent backend pools during retry and repair. The
+[prepared-execution contract tests](../../prepared_execution_contract_test.go)
+own the public prepared-capacity boundary. The
+[root error-boundary tests](../../errors_internal_test.go) own preservation of
+the public generation category and context identity when generation is
+canceled.

docs/internal/generation.md

@@ -0,0 +1,50 @@
+# Internal Generation Coordination
+
+`internal/generation` coordinates one model-generation request through the
+existing engine-local [capacity manager](capacity.md) and the
+[built-in HTTP client](llm.md). The engine supplies the same coordinator to
+initial generation and the default output repairer.
+
+The coordinator has explicit built-in and injected-client constructors. The
+built-in path prepares the provider request once, then acquires and releases an
+active backend permit around each actual HTTP attempt. Only HTTP 429, 500, 502,
+503, and 504 can lead to another attempt. The injected-client path acquires a
+permit and invokes its client once, regardless of the internal retry budget.
+The runner continues to own the logical execution's admission lease. A request
+can override the engine's retry budget; the runner freezes that choice for
+prepared execution and passes it to each repair generation.
+
+Retry waits hold no active permit. The local delay uses equal jitter between
+half and all of a capped exponential base, beginning at 500 milliseconds and
+capping at 8 seconds. A valid provider not-before time can extend that delay;
+the caller context interrupts it. The next attempt reacquires the ordinary
+FIFO permit. Preparation failures dispatch nothing. When a positive retry
+budget ends with eligible failures, the internal exhaustion error retains the
+final cause and actual dispatched-attempt count.
+
+When an invocation-local [observation recorder](observation.md) is present in
+the context, each acquisition emits an attempt event, including canceled
+capacity waits without dispatch. Each actual retry wait emits a delay event,
+including interrupted waits. Active permits are released before callbacks;
+generation duration ends before callback delivery. Built-in successful-envelope
+usage retains reported-field presence, while injected clients use explicit
+presence when supplied and otherwise treat zero fields as unknown.
+Malformed successful envelopes can retain strictly decoded usage; error
+response bodies are never mined for it. Arbitrary injected failures carry
+unknown usage. Transport, timeout, malformed, and noneligible status failures
+stop the sequence without retry exhaustion. Context is checked before each
+wait, acquisition, and dispatch.
+
+The public client adapter translates explicitly supplied public transport and
+malformed-response identities into internal categories while retaining the
+original error chain. This keeps injected attempt classifications consistent
+with terminal observations without parsing diagnostic text or retrying injected
+clients.
+
+Focused coordinator tests use controlled transport and wait functions. They
+cover eligibility, exhaustion, cancellation, backoff, request freezing, permit
+release, and the injected-client path. The capacity manager tests own permit
+acquisition and idempotent release. Public
+[integration tests](../../reliable_execution_contract_test.go) cover retry,
+repair, observation, frozen prepared execution, and shared-backend behavior
+through the assembled facade.

docs/internal/llm.md

@@ -10,7 +10,7 @@ owns the observable outbound HTTP contract. The
 [framework format reference](../formats.md) owns the profile and prompt
 settings consumed by the client.
 
-The concrete client remains under `internal/llm`. The root engine assembles it
+The concrete client remains under `internal/llm`. The internal engine assembles it
 as the default implementation behind Promptkit's public client boundary.
 
 ## Components And Flow
@@ -20,30 +20,110 @@ orchestration. `OpenAICompatibleClient` is the built-in implementation. It
 uses internal domain values for rendered prompts, execution targets,
 structured output, responses, and token usage.
 
-Construction validates the configured base URL and clones any supplied
-`http.Client` so Promptkit can apply its timeout default without mutating the
-caller's client. Generation then:
+The runner supplies a fully resolved target after applying backend, profile,
+and request precedence, plus canonical provider-bound text messages. The
+client uses its endpoint, credential metadata, generation fields, and extra
+parameters. `BackendID` remains routing metadata
+for the generation boundary and is not mapped into the provider payload.
 
-1. validates request-level timeout and endpoint requirements;
+Construction trims and validates a nonempty configured base URL and clones any
+supplied `http.Client` so Promptkit can apply its timeout default without
+mutating the caller's client. An empty configured base remains valid because a
+resolved request target may supply the endpoint. Generation preparation then:
+
+1. validates shared execution-setting invariants and the final selected base
+   endpoint;
 2. maps the internal request into the OpenAI-compatible chat payload;
 3. validates and merges extra parameters;
-4. resolves authentication;
-5. performs the outbound request under the applicable deadlines; and
-6. decodes the first response choice and token usage.
+4. composes `/chat/completions` through parsed URL path operations;
+5. resolves authentication and freezes the URL, body, and optional credential.
 
-The implementation has no retry loop, tool-call support, provider catalog,
-inbound HTTP behavior, or durable session store.
+Each execution of that prepared request creates a fresh HTTP request, body
+reader, and attempt timeout context. It closes the response body and returns
+the HTTP status, decoded response or error, reported token values and presence,
+and any valid provider `Retry-After` not-before time. A strictly decoded
+successful envelope can retain usage even if its first choice or content is
+missing. Invalid framing and non-success error bodies supply no usage. The
+ordinary `Generate` method prepares and executes once and returns no partial
+response on failure.
+
+`internal/llm` owns the set of reserved OpenAI-compatible request fields used
+when validating extra parameters. Backend registration consumes the same rule
+without making the model client depend on registry configuration.
+
+This client does not schedule retries; the [generation coordinator](generation.md)
+does so around its prepared attempts. The client has no tool-call support,
+provider catalog, inbound HTTP behavior, or durable session store.
+
+## Prepared Generation
+
+For [`RunPrepared`](../../engine.go), the runner supplies the model client with
+the target, rendered messages, and structured-output constraint retained by
+executable preparation. Execution does not reopen or rerender consumer
+sources.
+
+Before backend admission, the runner rechecks a frozen credential
+environment-variable name only when the target explicitly requires a
+credential. The handle does not retain the environment value; the model client
+resolves the value visible when generation begins. For optional sources with no
+usable value, the built-in client omits `Authorization` and continues to the
+provider. A direct request key remains in private execution state only until
+the claimed execution finishes or an unclaimed handle is discarded. Exact
+public ownership and redaction semantics belong to the
+[`PreparedExecution` GoDoc](../../prepared_execution.go).
 
 ## Failure Categories
 
 The package preserves distinct error identities for invalid client
 configuration, invalid generation requests, request execution failures,
 non-success provider statuses, and malformed successful responses. Provider
-response bodies are not included in non-success errors.
+response bodies are never exposed in raw form through non-success errors.
 
-Caller cancellation and deadline failures during the outbound request are
-reported as request execution failures. The runner classifies these identities
-without depending on HTTP status mapping.
+Invalid nonempty configured endpoints are configuration failures. A missing or
+invalid final selected endpoint is an invalid generation request and is
+rejected before transport.
+
+Authentication resolves a trimmed direct key before a trimmed configured
+environment value. Optional missing, empty, or whitespace-only sources do not
+block transport and produce no `Authorization` header. An explicitly required
+target with no usable source is rejected before transport with the existing
+invalid-request diagnostics.
+
+Successful response bodies have a fixed 16 MiB limit enforced by declared
+length and by reading at most one byte beyond the boundary. The decoder accepts
+exactly one JSON object plus trailing whitespace and EOF. Size overflow,
+truncation, malformed JSON, trailing data, and a second value are malformed
+responses with no partial result or provider content in the error. Every body
+is closed, and an unbounded oversized stream is not drained.
+
+After framing succeeds, the first choice must contain an explicitly present
+string `message.content`. The string is returned exactly, including empty or
+whitespace-only content. Missing choices, missing or `null` content, and
+non-string content are malformed responses. Output validation and correction
+eligibility remain outside this package.
+
+Successful-envelope usage is decoded with independent presence bits for each
+token field: omission and `null` are unknown, while a reported integer zero is
+known. Strictly decoded usage can still be observed if later choice/content
+checks fail; invalid framing or a non-success error body contributes none.
+Existing successful-result accounting remains value-based.
+
+For a non-success response, `ProviderHTTPError` retains the HTTP status and
+only normalized detail from the bounded recognized envelope. It retains
+`ErrUnexpectedStatus` through unwrapping. The client owns response closure;
+its bounded reader and parser never close or drain a body themselves. The root
+facade converts this concrete internal error into the public
+[`GenerationError`](../../generation_error.go), while arbitrary injected-client
+errors continue through the ordinary generation-error mapping unchanged.
+
+An `http.Client.Do` failure is represented by a redacting multi-cause error:
+the package request-failure sentinel and the exact returned transport error are
+both available through `errors.Is` and `errors.As`, while the rendered text
+does not expose the endpoint, headers, request content, credential, transport
+detail, or provider body. Caller cancellation retains `context.Canceled`;
+caller deadlines, generation deadlines, and whole-request client timeouts
+retain `context.DeadlineExceeded`. The runner adds its generation category
+without discarding those identities or depending on HTTP status mapping.
 
 ## Test Ownership
 
@@ -51,5 +131,15 @@ The
 [OpenAI-compatible client tests](../../internal/llm/openai_compatible_client_test.go)
 own configuration, client cloning, deterministic deadline precedence,
 authentication, request and response mapping, malformed data, error identity,
-cancellation, and response-body suppression. They use local test servers and
-test transports; the default suite makes no live or paid provider requests.
+cancellation, endpoint selection and composition, pre-transport rejection, and
+bounded single-document successful-response framing, closure, and
+response-body suppression. The focused
+[provider HTTP error tests](../../internal/llm/provider_http_error_test.go)
+own envelope parsing, normalization, and bounded-reader cases; their
+[transport tests](../../internal/llm/provider_http_error_transport_test.go)
+own non-success response closure and integration. Root transport contract tests
+own public `GenerationError` conversion, while also verifying that resolved
+backend settings reach this client without serializing backend identity and
+that ordinary-run cancellation retains its public generation and context
+identities. All use local test servers or controlled test transports; the
+default suite makes no live or paid provider requests.

docs/internal/observation.md

@@ -0,0 +1,48 @@
+# Internal Execution Observation
+
+`internal/observation` owns one invocation's run ID, presence-aware token
+aggregation, measured phase totals, and synchronous metadata event delivery.
+Its event values and callback type live in `internal/domain` so internal
+requests can carry them without depending on the recorder package. The
+recorder supplies run IDs to the runner and receives attempt and
+retry-delay measurements from the generation coordinator. Ordinary `Run`
+lifecycle instrumentation spans the facade and runner boundaries.
+Prepared execution starts only after its private payload is atomically claimed;
+the facade receives that invocation's recorder privately and emits the terminal
+event after public error mapping. Failed claims and preparation emit nothing.
+
+The facade masks inherited recorder and prepared-claim state when entering
+preparation or execution. Delegated calls from an injected collaborator retain
+the caller's cancellation, deadline, and unrelated context values, but do not
+reuse the enclosing invocation's accounting. Only the new request's observer
+(or the claimed handle's retained observer) enables its observation lifecycle.
+
+A recorder keeps only counters, resolved identity fields, and the selected
+callback. It has no global history, queue, goroutine, or mutex held across a
+callback. The caller supplies normalized failure metadata; the recorder never
+parses an error string or receives provider bodies, credentials, headers, or
+other content. Events are values with no mutable containers. Callback panics
+propagate to the caller.
+Per-operation callbacks are ordered and synchronous; different operations may
+invoke the same callback concurrently. The recorder marks each measured phase's
+end before delivery, so callback work does not inflate provider duration.
+Terminal phase durations sum measured phases, while wall duration may also
+include preparation, validation, and callbacks. Panics do not promise a
+terminal event.
+
+Attempt usage is known when its explicit presence bit is true. For legacy
+injected clients without presence metadata, nonzero counts are known and
+zeros are unknown. Aggregate values sum known contributions; `Known` means
+at least one reported value, while `Complete` means every dispatched attempt
+reported the field. Zero dispatched attempts produce known, complete zero
+totals. Non-dispatched acquisitions contribute capacity wait but no usage or
+generation duration. Terminal totals count dispatched attempts, transient
+attempts above the first in a generation, and repair generations with at least
+one dispatch. A terminal event is an aggregate and must not be added to its
+attempt events.
+
+The [recorder tests](../../internal/observation/recorder_test.go) own usage
+presence, phase sums, event ordering, empty-run accounting, identity snapshots,
+and callback panic behavior. The [generation coordinator](generation.md) owns
+attempt and retry-delay measurements and emits their completion events after
+releasing active permits.

docs/internal/overview.md

@@ -11,21 +11,29 @@ contributor workflow and validation.
 
 | Component | Implemented responsibility | References |
 | --- | --- | --- |
-| Root `promptkit` package | Provides the supported engine facade, source and injection options, public request and result values, built-in profile construction, extension interfaces, value conversion, redacted formatting, and public error mapping. | [Package GoDoc](../../doc.go), [engine assembly](../../engine.go) |
+| Root `promptkit` package | Provides the supported engine facade, source, backend-registration, and injection options, public request, result, prompt-inspection, profile-inspection, and ordinary-run observation values, opaque prepared-execution handles, profile construction, extension interfaces, value conversion, redacted formatting, and typed capacity and generation error mapping. | [Package GoDoc](../../doc.go), [observations](../../observations.go), [prepared execution](../../prepared_execution.go), [backend API](../../backends.go), [engine facade](../../engine.go) |
 | `examples/go-library/prepare` | Demonstrates an offline downstream consumer using a prompt file, in-memory profile, inline input, and `Prepare`. It is not a public library package. | [Example program](../../examples/go-library/prepare/main.go) |
-| `internal/domain` | Defines internal framework values for requests, artifacts, prompt definitions, profiles, execution targets, rendering, generation, and validation. | [Domain declarations](../../internal/domain/domain.go) |
+| `examples/go-library/run` | Demonstrates an offline downstream consumer using a prompt file, in-memory profile, inline input, an injected deterministic model client, and `Run`. It is not a public library package. | [Example program](../../examples/go-library/run/main.go) |
+| `examples/go-library/observe` | Demonstrates offline built-in HTTP retry and synchronous metadata observation across structured proposal and assessment runs using embedded sources, two profiles on one finite backend, and an application decision. It is not a public library package. | [Example program](../../examples/go-library/observe/main.go) |
+| `internal/backend` | Constructs each engine's immutable registry from maintained definitions and consumer additions, validates and defensively copies definitions through the shared JSON-value package, and consumes the LLM-owned OpenAI-compatible reserved request-field rule. | [Backend registry](../../internal/backend/registry.go) |
+| `internal/catalog` | Strictly validates imported immutable maintained backend and profile catalog assets before engine assembly uses them. | [Catalog adapter](../../internal/catalog/catalog.go), [internal sources](sources.md#profiles-and-built-ins) |
+| `internal/capacity` | Owns engine-local bounded execution admission and FIFO model-generation permits for limited backend IDs, including cancellation-safe waiter removal and client wrapping. | [Internal capacity management](capacity.md) |
+| `internal/domain` | Defines internal framework values for requests, artifacts, prompt definitions, profiles, execution targets, rendering, generation, and validation, and owns source-neutral invariants for shared execution settings, OpenAI-compatible base endpoints, session identifiers, and output contracts. Source parsing, required fields, other source-specific normalization, defaulting, and boundary-specific error classification remain with their callers. | [Domain declarations](../../internal/domain/domain.go), [endpoint invariant](../../internal/domain/endpoint.go) |
+| `internal/engine` | Assembles external catalogs, Promptkit-owned profiles, repositories, registry, capacity, collaborators, repairer, and the one use-case runner for each engine instance. | [Engine assembly](../../internal/engine/engine.go), [internal sources](sources.md#profiles-and-built-ins), [internal runner](runner.md) |
+| `internal/generation` | Coordinates frozen built-in HTTP attempts and one-shot injected calls through active backend permits, including bounded status retries, cancellable backoff, and attempt observations. | [Internal generation coordination](generation.md) |
 | `internal/defaults` | Defines application-neutral framework constants and constructs the default execution target. It contains no CLI, server, or inbound HTTP limits. | [Framework defaults](../../internal/defaults/defaults.go) |
 | `internal/filecatalog` | Provides deterministic YAML discovery and path helpers for operating-system filesystems and `fs.FS` sources. | [File catalog](../../internal/filecatalog/catalog.go) |
+| `internal/jsonvalue` | Validates and deeply copies bounded JSON-compatible extra-parameter and prepared-schema trees while preserving supported concrete value types and rejecting cycles or excessive depth and work. | [JSON values](../../internal/jsonvalue/jsonvalue.go) |
 | `internal/promptdef` | Loads strictly decoded, validated prompt definitions from filesystem and `fs.FS` sources, including version selection and contained file-backed message content. | [Framework formats](../formats.md), [prompt-definition repository](../../internal/promptdef/filesystem_repository.go) |
-| `internal/profile` | Loads strictly decoded, validated execution profiles from filesystem and `fs.FS` sources and composes repositories with error-preserving fallback. | [Framework formats](../formats.md), [profile repositories](../../internal/profile/filesystem_repository.go) |
-| `internal/profile/builtin` | Embeds the built-in execution profile catalog and combines it with an optional primary repository. | [Built-in catalog](../formats.md#built-in-profile-catalog), [repository](../../internal/profile/builtin/repository.go) |
+| `internal/profile` | Owns immutable in-memory and filesystem profile repositories, local profile validation, raw-source overlays with error-preserving fallback, and inherited-profile resolution. | [Framework formats](../formats.md), [profile repositories](../../internal/profile/filesystem_repository.go), [internal sources](sources.md#profiles-and-built-ins) |
 | `internal/prompt` | Renders prompt messages from Go templates with artifact, variable, session, and cache-control data. | [Go-template renderer](../../internal/prompt/go_renderer.go) |
 | `internal/artifact` | Resolves ordinary inline and unrestricted caller-selected file references into copied artifacts with metadata and hashes. | [Internal sources and validation](sources.md) |
-| `internal/validate` | Validates basic, JSON, and JSON Schema output using operating-system filesystem or `fs.FS` schema sources. | [Framework formats](../formats.md#schemas), [internal sources and validation](sources.md) |
-| `internal/llm` | Defines the internal generation boundary and implements outbound OpenAI-compatible chat requests, response decoding, authentication, and deadline handling. | [Internal model client](llm.md) |
-| `internal/usecase` | Coordinates preparation and execution across internal sources, rendering, artifact loading, generation, validation, and optional repair. | [Internal runner](runner.md) |
+| `internal/validate` | Validates basic, JSON, and JSON Schema output using operating-system filesystem or `fs.FS` schema sources and creates operation-local validation plans with canonical contained schema resources. | [Framework formats](../formats.md#schemas), [internal sources and validation](sources.md) |
+| `internal/llm` | Defines the internal generation boundary and implements outbound OpenAI-compatible chat requests from resolved execution targets, including bounded structured non-success response decoding, successful-response decoding, authentication, deadline handling, and ownership of the OpenAI-compatible reserved request-field policy. | [Internal model client](llm.md) |
+| `internal/observation` | Owns invocation-local run IDs, presence-aware usage and phase accounting, and synchronous metadata event delivery for ordinary and claimed prepared runs and generation attempts. | [Internal execution observation](observation.md) |
+| `internal/usecase` | Resolves prompt definitions and hashes, profiles, backends, and targets for exact inspection and request settings for preparation, and coordinates ordinary and single-claim prepared execution across internal sources, rendering, artifact loading, operation-local validation plans, generation, capacity, and bounded repair. | [Internal runner](runner.md), [prepared-execution implementation](../../internal/usecase/prepared_execution.go) |
 
-The root package assembles these internal components without exposing their
+The internal engine assembles these internal components without exposing their
 representations. Consumers depend only on the root facade.
 
 ## Maintenance

docs/internal/runner.md

@@ -9,59 +9,188 @@ artifact, rendering, and validation behavior, while the
 [model-client document](llm.md) owns generation behavior and failure
 categories.
 
-The runner remains under `internal/usecase` and is assembled by the root
-Promptkit engine. Its concrete type is not part of the public API.
+The runner remains under `internal/usecase` and is assembled by
+`internal/engine`. Its concrete type is not part of the public API.
 The [framework format reference](../formats.md) owns prompt, profile, schema,
 and override semantics consumed by the runner.
 
 ## Collaborators
 
 `Runner` coordinates narrow internal interfaces for prompt definitions,
-profiles, artifacts, rendering, model generation, and validation. Schema
-documents are loaded through the validator's optional schema-loader interface.
-An output repairer can be injected internally, but the ordinary runner
-constructor does not enable one.
+profiles, backend resolution, artifacts, rendering, model generation, and
+validation. The internal engine supplies one immutable registry containing the
+built-in backend and validated consumer additions, one engine-local run
+admitter, and a generation coordinator using the same capacity manager. Validation
+plans and provider-facing schema metadata come from the validator's preparation
+interface.
+The internal engine supplies one default output repairer through the explicit
+runner constructor, using the same coordinator as initial
+generation. The no-repair runner constructor remains available for focused
+internal callers and tests.
 
 Each invocation carries its state in request, prepared-run, and result values.
 The runner has no durable run or session store.
 
-## Preparation Flow
+## Shared Prompt Selection
 
-`Prepare` performs the reusable pre-generation workflow:
+The runner uses one prompt-selection and hashing boundary for ordinary
+preparation and exact prompt inspection. Preparation retains its early
+request-ID check before direct-session normalization; both operations then use
+the configured prompt repository to select one definition, load referenced
+message content, and calculate the same prompt hash.
 
-1. validate the prompt selection and load the prompt definition;
-2. hash the loaded definition;
+Inspection stops after that structural lookup. It does not parse templates or
+touch profile, artifact, schema, renderer, validator, admission, or model
+collaborators. The root [`Engine.InspectPrompt`](../../engine.go) GoDoc owns
+the public operation's exact contract.
+
+## Shared Profile Selection
+
+The runner uses one profile-selection and target-resolution boundary for
+ordinary preparation and exact profile inspection. Preparation first selects a
+request profile or a prompt default; inspection begins with its required
+explicit profile ID. Both then apply the ordinary source precedence, resolve a
+named backend, and construct the effective target from framework, backend, and
+profile values.
+
+Inspection stops after the resulting endpoint and model are structurally
+validated. It does not check credential availability or perform prompt,
+artifact, schema, rendering, admission, or model-client work. The root
+[`Engine.InspectProfile`](../../engine.go) GoDoc owns the public operation's
+exact contract.
+
+## Shared Preparation Pipeline
+
+`Prepare` and `Run` share one private preparation pipeline split at the point
+where a run can be assigned to its selected backend pool. The resolution phase
+performs only the work needed to validate routing and admission:
+
+1. validate the required prompt selection and normalize any direct session ID;
+2. load the prompt definition and hash the original definition;
 3. select the request profile or the prompt's default profile;
-4. resolve application-neutral defaults, profile values, and explicit request
-   overrides in that order;
-5. validate endpoint, model, numeric overrides, and credential requirements;
-6. resolve the output contract and load a structured-output schema when
-   required;
-7. load and hash input artifacts;
-8. render and hash the prompt; and
-9. return the effective settings, source identities, messages, hashes, and
-   preparation timing.
+4. resolve the profile's backend ID, when present;
+5. resolve application-neutral defaults, backend defaults, profile values,
+   and explicit request overrides in that order;
+6. validate endpoint, model, numeric overrides, and credential requirements;
+7. resolve and validate the effective output contract without loading its
+   schema; and
+8. retain the definition, source identities, effective settings, output
+   contract, and preparation start time in invocation-local state.
+
+The completion phase consumes that state without reloading the prompt,
+profile, or backend:
+
+1. create one operation-local validation plan and derive structured-output
+   schema metadata from it when required;
+2. load and hash input artifacts;
+3. render messages and the prompt-defined session;
+4. apply any direct session ID, then append already-normalized request messages
+   after the rendered definition messages;
+5. hash the effective rendered prompt; and
+6. construct the prepared value and preparation timing.
+
+`Prepare` runs both phases consecutively and never performs capacity admission.
+`Run` performs backend admission between the phases. This structure preserves
+one execution-precedence and error-ordering implementation while allowing a
+full backend pool to reject work before expensive schema, artifact, and
+rendering operations. `Prepare` discards the plan after returning its public
+metadata. `Run` retains the plan through initial and repaired-output validation
+and discards it when the operation ends. Prepared execution stores the same
+kind of plan only in its private payload.
 
 Pointer-based numeric overrides preserve an explicit zero. Invalid negative or
-out-of-range values fail as invalid requests. A direct API key takes
-precedence over environment lookup for execution; secret values remain
-excluded from serialized metadata.
+out-of-range values fail as invalid requests. Endpoint overrides do not change
+the selected backend identity. Non-empty extra-parameter maps replace whole
+lower-precedence maps. A direct API key takes precedence over environment
+lookup; otherwise request, profile, and backend environment-variable names
+apply in that order. A profile requiring a direct key clears an inherited
+backend environment name unless the request supplies its own name. Secret
+values remain excluded from serialized metadata.
+
+Reasoning overrides are tri-state: nil inherits the profile, a pointer to a
+nonblank string trims and replaces it, and a pointer to a blank string clears
+it. A nonblank direct session is normalized before source loading, bypasses
+the prompt session template, and is applied after ordinary message rendering.
+A blank direct value retains prompt-template behavior. The runner clears the
+template only on a value copy of the definition, so the definition hash always
+describes the original source while the rendered-prompt hash includes the
+effective direct or rendered session and the complete effective message
+sequence. The rendered-prompt hash uses a versioned, length-framed SHA-256
+encoding of that session, every role and content value, and cache-control
+presence and values; its hexadecimal value is opaque.
+
+The registry is read-only after engine construction. Concurrent `Prepare` and
+`Run` calls resolve independent defensive backend values and keep all
+invocation state local.
 
 ## Run Flow
 
-`Run` calls `Prepare` rather than maintaining a second preparation path. It
-performs one initial generation call, builds the named output artifact, and
-validates that artifact. Invalid generated content remains a validation result;
-an inability to perform validation is an operational error.
+`Run` records its start time, performs the shared resolution phase, and asks
+its `RunAdmitter` to reserve capacity for the effective backend ID. A nil
+admitter is an internal unlimited fallback. After successful admission, `Run`
+immediately defers the returned release function, performs the completion
+phase, makes one initial generation call, builds the named output artifact,
+and validates that artifact with the plan compiled during completion. Invalid
+generated content remains a validation result; an inability to generate or
+perform validation is an operational error.
 
-When an internal repairer is present, a JSON or JSON Schema content failure can
-trigger bounded repair attempts. Repair receives the effective execution
-target, validation errors, prior output, and structured-output specification.
-This capability remains internal and is not a public option.
+When the public facade installs an invocation-local observation recorder,
+ordinary `Run` reuses its run ID and carries it to the generation coordinator
+through context. Prompt and profile identities are enriched only after their
+respective resolutions succeed, before admission. The facade starts observation
+before request conversion and emits its terminal event after public error
+mapping and after the runner's deferred admission release. Preparation and
+prepared execution follows the same terminal mapping after a successful claim;
+invalid or discarded handles do not acquire an observer.
+
+Validation preparation and execution honor cancellation at every
+Promptkit-controlled boundary and do not publish a partial plan or result.
+Schema reads are bounded and context-checked between chunks; JSON decoding,
+schema compilation, and schema execution are checked immediately before and
+after their synchronous calls. Promptkit does not move arbitrary filesystem or
+JSON Schema work to background goroutines, so an already-blocked dependency
+method must return before cancellation can take precedence over its outcome.
+
+The admission lease covers completion-phase preparation, initial generation,
+validation, every repair, and every exit. It bounds accepted work without
+serializing preparation or validation behind the active-generation limit.
+The coordinator separately acquires a FIFO active permit only around each
+actual model attempt. It releases the permit before a transient retry wait.
+
+After a failed `basic`, JSON, or JSON Schema validation with a positive frozen
+budget, the installed repairer can make a bounded corrective call. Each request
+starts with a fresh copy of the complete effective message sequence (the
+configured prefix followed by the request suffix), includes only the latest
+nonempty candidate as an assistant message, and appends one corrective user
+message. Empty candidates omit that assistant message. The
+correction carries validation diagnostics as JSON data bounded to 64 KiB; the
+full diagnostics remain in the validation result.
+
+Repair receives the effective execution target, explicit numeric-presence bits,
+credential, backend identity, session ID, structured-output specification, and
+frozen transient retry budget.
+The same request constructor supplies those common fields to initial and repair
+generation. The default repairer uses the same coordinator as initial
+generation, so each repair reacquires the selected backend's active permit
+while remaining inside its original admission lease. Repair never performs a
+second bounded admission, and repaired outputs use the operation's existing
+validation plan. The runner stops at the first valid candidate, sums completed
+generation usage, reports calls actually started, and returns the final failed
+validation result on exhaustion. A repair generation failure follows the
+ordinary generation-error category rather than becoming a validation error.
 
 A successful result includes the output artifact and raw output, validation
-state, prompt and rendered-prompt hashes, selected profile, effective settings,
-input hashes, token usage, a generated run identifier, and UTC timing.
+state, effective session ID, prompt and rendered-prompt hashes, selected
+profile and backend, effective settings, input hashes, token usage, a generated
+run identifier, and UTC timing. The same effective session reaches initial
+generation and any repair attempt through the rendered prompt. The same
+effective target and presence metadata, including backend identity and direct
+credential during execution, reaches generation and every repair attempt.
+Result usage is the field-wise sum of all five usage values from the initial
+response and every completed repair response. Final raw output, artifact, and
+validation state still come from the last candidate. A repair error returns no
+partial run result or partial result usage, although the invocation-local
+observer retains completed-attempt usage and reports it in the terminal event.
 
 ## Failure Categories
 
@@ -69,17 +198,43 @@ Package errors distinguish invalid requests, required profile selection,
 credential failures, and prompt, profile, artifact, rendering, generation, and
 validation failures. Wrapping preserves the package identities mapped by the
 public facade and retains collaborator identities where they are part of the
-internal contract. Context cancellation propagates through the invoked
-collaborator and is classified by the owning operation.
+internal contract.
+
+Admission capacity exhaustion retains the internal capacity identity. At the
+use-case boundary, the runner attaches the selected backend ID in an internal
+typed error, and the root facade copies that value into the public
+[`CapacityError`](../../capacity_error.go) without parsing diagnostic text. It
+is not recategorized as an invalid request or generation failure, and no
+partial result is returned. A context already done at admission retains its
+context identity directly. Cancellation while waiting for an active generation
+permit prevents client invocation when it wins the grant race; the model-client
+boundary then preserves the context error through the generation-failure
+category. Deferred release restores the admission lease on preparation,
+generation, validation, repair, and cancellation failures.
+
+Other context cancellation propagates through the invoked collaborator and is
+classified by the owning operation. In particular, cancellation observed by
+validation retains the context identity through the validation error category.
+An overlong direct session is an invalid request before source loading, while
+an invalid or overlong prompt session template remains a prompt-render failure.
+An unknown selected backend, or a selected backend with no configured resolver,
+is classified as a profile-load failure.
 
 ## Test Ownership And Changes
 
 The [runner tests](../../internal/usecase/runner_test.go) own preparation order,
-selection and override precedence, schema-before-generation behavior, hashing,
-generation and validation outcomes, bounded repair, credentials and redaction,
-error categories, artifact metadata, usage, and timing.
+selection and override precedence, the two-phase boundary, early admission,
+lease lifetime and release, direct-session resolution, schema-before-generation
+behavior, hashing, generation and validation outcomes, backend propagation,
+bounded repair progression, initial/repair request parity, cumulative usage,
+shared initial/repair capacity, credentials and redaction, error categories,
+artifact metadata, and timing. The
+[capacity subsystem document](capacity.md) identifies the focused pool and
+waiter tests. The [generation document](generation.md) owns attempt and retry
+coordination tests.
 
 Changes to orchestration should continue to use the existing package
-interfaces, keep request state local to an invocation, and preserve `Run`'s use
-of `Prepare`. Source, renderer, validator, or model-client contract changes
-belong first in their owning package and document.
+interfaces, keep request state local to an invocation, and preserve the shared
+resolution and completion pipeline. Source, renderer, validator, or
+model-client contract changes belong first in their owning package and
+document.

docs/internal/sources.md

@@ -6,15 +6,38 @@ This document describes Promptkit's implemented internal source, artifact,
 rendering, and output-validation behavior. The
 [architecture policy](../policy/architecture.md) owns the library boundary and
 dependency rules. None of these internal packages is a supported consumer API,
-and the root engine assembles them behind its public source options and values.
+and the internal engine assembles them behind the public facade's source options and values.
 The [framework format reference](../formats.md) owns the exact file fields,
 validation modes, built-in catalog, and source precedence.
 
 ## Prompt Definitions
 
-`internal/promptdef` discovers YAML deterministically, decodes and validates
-definitions, selects an ID and optional version, and resolves file-backed
-message content within the selected operating-system or `fs.FS` source.
+`internal/promptdef` uses one source-neutral flow for prompt selection and
+normalization. That flow scans normalized YAML ID and version metadata,
+requires one strictly decoded document per file, classifies errors for the
+selected definition, detects duplicates, and normalizes the exact match.
+Small operating-system and `fs.FS` adapters own discovery, byte reads, display
+paths, content opening, and root containment. Each lookup remains a
+point-in-time scan: definitions and catalogs are not cached, and file-backed
+message content is opened only for the exact selected candidate.
+
+Message roles are normalized through the shared domain owner by trimming
+Unicode whitespace and lowercasing. Only `developer`, `system`, `user`, and
+`assistant` are published; invalid roles remain selected prompt-definition
+failures rather than becoming request errors. Cache-control metadata uses the
+same shared domain normalization and defensive-copy rule.
+
+Operating-system sources enforce containment against canonical roots and
+targets so symlinks cannot escape. Injected `fs.FS` sources enforce containment
+in their clean relative path namespace. A single-file source uses the selected
+prompt file's containing directory as its root. Every content path must be
+relative and is opened from its exact parsed text after a separate blank check;
+contained parent components and whitespace-bearing names remain valid.
+
+Exact prompt inspection performs one point-in-time lookup through that same
+repository and validates referenced message content before returning declared
+metadata. It does not parse templates or read profile, input, or schema
+sources, and it does not retain the definition for a later execution.
 
 Its package tests own prompt selection, strict decoding, definition validation,
 duplicate detection, and source containment:
@@ -22,23 +45,88 @@ duplicate detection, and source containment:
 
 ## Profiles And Built-Ins
 
-`internal/profile` loads and validates execution profiles from an
-operating-system filesystem or an `fs.FS`. It supports a primary repository
-with fallback only when the primary reports that a profile is absent.
+`internal/profile` owns immutable in-memory and filesystem repositories, local
+validation, overlays, and resolution for execution profiles. In-memory
+definitions are normalized and validated once at that repository boundary and
+are defensively copied on storage and lookup. A file contains
+exactly one YAML document and its trimmed YAML `id` is its only selection
+identity; filenames do not confer authority. Each point lookup reads discovered
+files once for their metadata and reuses the selected file's bytes for strict
+decoding; unrelated profiles are not fully decoded. Strict selected decoding
+recognizes `base_profile` and the optional `backend` field, trims their values,
+and permits inherited target fields only when a base is named. File-backed
+`extra_params` values are validated and defensively copied through the shared
+bounded JSON-value owner before a profile is published. OpenAI-compatible
+reserved-field policy remains with the model-client and backend-registry owners.
 
-`internal/profile/builtin` embeds the maintained built-in profile catalog and
-can place a caller-selected repository ahead of that catalog. Profile behavior
-is owned by the
-[profile repository tests](../../internal/profile/repository_test.go), while
-catalog completeness, duplicate IDs, and overlay behavior are owned by the
-[built-in repository tests](../../internal/profile/builtin/repository_test.go).
+`LoadFSRepository` is the eager immutable loading boundary for internal
+catalog consumers. It discovers and strictly validates every raw profile once,
+preserves safe source metadata including explicitly present YAML fields, and
+publishes independently copied values from memory. It does not resolve profile
+inheritance. Configured consumer sources continue to use the lazy point lookup
+repositories described above.
+
+`internal/catalog` validates the imported immutable OpenRouter and
+Rakestrawhome asset modules as one private adapter boundary. It enforces their
+manifest, layout, profile ownership, inheritance, and secret-safety rules
+before returning raw catalog sources. Internal engine assembly uses those validated
+catalogs as the lowest-precedence profile source.
+
+Normalized external catalog profile IDs with the exact `promptkit-` prefix are
+rejected at this adapter boundary. That reservation applies only to imported
+catalogs; configured consumer sources retain the ordinary profile-ID rules.
+
+The overlay repository consults the next repository only when the
+higher-precedence repository reports that a profile is absent. A reliably
+selected malformed profile stops fallback, while an unrelated malformed file
+does not become authoritative through its filename. Loading does not check
+backend registry membership because the available registry belongs to the
+assembled engine; the runner checks membership during preparation and exact
+profile inspection.
+
+The internal engine assembles one raw composite catalog in precedence order:
+in-memory profiles, one ordinary configured source, an application fallback
+source, Promptkit-owned profiles, then the maintained external catalog. It
+constructs the owned definitions through the in-memory repository and validates
+their maintained-only resolution and backend membership before consumer sources
+are overlaid. An explicit file or `fs.FS` profile source replaces
+`Config.ProfileDir` within the ordinary configured-source category. One outer
+resolving repository wraps that complete raw catalog, so each base lookup
+observes the same precedence and shadowing rules.
+
+The resolving repository traverses every selected chain afresh, retains no
+cache, detects cycles, limits a chain to 32 profiles, merges root-to-leaf into a
+new caller-owned value, and validates the final target before publishing it. It
+does not check backend registry membership. Exact `base_profile` syntax, merge
+rules, and consumer-visible failure behavior belong to the [framework format
+reference](../formats.md#profile-inheritance).
+
+Exact profile inspection performs one point-in-time resolved lookup through
+those profile sources and checks the final target without reading prompt, input,
+or schema sources. It does not retain that lookup for a later execution.
+Prepared execution instead freezes the fully resolved target; a later ordinary
+operation performs a fresh traversal.
+
+The imported external catalog provides external profiles and matching backend
+definitions. The internal engine owns the Promptkit profiles documented in the
+[framework format reference](../formats.md#built-in-profile-catalog). Profile
+loading and overlay behavior are owned by the [profile repository tests](../../internal/profile/repository_test.go), while
+catalog completeness, backend selection, and duplicate IDs are owned by the
+[catalog adapter tests](../../internal/catalog/catalog_test.go).
 
 ## Ordinary Artifacts
 
-`internal/artifact` resolves inline references and unrestricted,
-caller-selected file paths. It copies content into an artifact, records
-metadata and a content hash, applies a content-type fallback, and honors
-context cancellation.
+`internal/artifact` accepts explicitly typed inline references even when their
+body is empty. It also resolves unrestricted, caller-selected paths only when
+they identify regular operating-system files, checking that condition before
+and after opening the file. It copies content into an artifact, records
+metadata and an opaque content-equality value, and applies a content-type
+fallback.
+
+Regular files are read synchronously in bounded chunks. Cancellation is
+checked before opening, before and after every read, and before publishing the
+artifact, so a canceled read never publishes partial content. The ordinary
+reader does not detach file reads into background goroutines.
 
 This ordinary reader does not implement an inbound HTTP security boundary. In
 particular, it does not constrain files to an application root or impose an
@@ -50,7 +138,17 @@ implemented reader behavior and failures.
 ## Rendering
 
 `internal/prompt` renders definition messages as Go templates using named
-artifacts and variables. It carries message roles, session IDs, and cache
+artifacts and variables. Within one render, each referenced artifact body is
+converted to text lazily and cached by input name for reuse across the session
+and every message; the cache is not shared across renders. Conversion uses
+bounded chunks and preserves the artifact bytes exactly.
+
+Session and message parsing and execution remain synchronous. The renderer
+checks cancellation before and after each parse and execution boundary,
+between artifact conversion chunks, around each message, and before publishing
+the complete prompt. It cannot interrupt template work already in progress and
+never publishes a partial prompt after observing cancellation. It validates and
+canonicalizes message roles before carrying roles, session IDs, and cache
 control into the rendered prompt. The
 [renderer tests](../../internal/prompt/renderer_test.go) own rendering behavior.
 
@@ -61,6 +159,35 @@ filesystem or an `fs.FS`. Invalid generated content is returned as a validation
 result; inability to load, register, or compile a schema is an operational
 error.
 
+Every preparation operation creates one operation-local validation plan. None,
+basic, and JSON modes retain the effective output contract without source
+access. JSON Schema mode loads the root document once, resolves and compiles
+each transitive reference, and retains the compiled validator. Schema compiler
+resources use canonical escaped file or private-scheme URLs; loaders decode
+their paths once and enforce the configured source boundary. The
+provider-facing structured-output metadata uses the root document captured by
+the same plan.
+
+Schema preparation and execution remain synchronous. Promptkit checks
+cancellation before and after source resolution, JSON decoding, compilation,
+and validation, and between bounded schema-read chunks. Once cancellation is
+observed it returns the context error without publishing a partial plan or
+validation result, even when a compiler or validator has just returned a
+different error or a successful result. An `fs.FS` method or JSON Schema
+dependency call already in progress cannot be preempted; Promptkit waits for
+that call to return and then gives cancellation precedence. Validation does
+not detach dependency work into background goroutines.
+
+`Prepare` discards its validation plan after returning metadata. `Run` retains
+its plan for initial and repaired-output validation, then discards it with the
+operation. `PrepareExecution` retains the plan in its private frozen payload;
+`RunPrepared` uses that plan without reopening prompt, profile, input, or
+schema sources or rerendering the request. A later ordinary `Run` always
+performs fresh source resolution and preparation.
+
 The [validator tests](../../internal/validate/standard_validator_test.go) own
-basic, JSON, JSON Schema, source resolution, schema loading, compilation, and
-content-failure behavior.
+basic, JSON, JSON Schema, source resolution, schema loading, compilation,
+frozen-reference behavior, content-failure behavior, and the synchronous
+cancellation boundary. Prepared execution
+orchestration is owned by the
+[use-case tests](../../internal/usecase/prepared_execution_test.go).

docs/oss/attribution.md

@@ -0,0 +1,93 @@
+# Open Source Attribution Notices
+
+## Standard Repository Policies
+
+Material: policy documents under `docs/policy/` and the Policy Reading Guide in
+`docs/development.md`, adapted for this repository; root `AGENTS.md`, copied
+without modification from upstream `agents/AGENTS.md`.
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: CC-BY-SA-4.0
+
+License and notices: [CC BY-SA 4.0](licenses/CC-BY-SA-4.0.txt) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/LICENSE).
+
+[Source](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843).
+
+## Promptkit OpenRouter Catalog
+
+Selected module: `gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2`
+at `v2.20260926.0`.
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: MIT
+
+License and notices: [MIT](licenses/MIT.txt) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/promptkit-backend-openrouter/src/commit/4f731d217e0bc39151c010f50fb5912706e7b6b3/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/promptkit-backend-openrouter/src/commit/4f731d217e0bc39151c010f50fb5912706e7b6b3/LICENSE).
+
+[Source](https://gitea.maximumdirect.net/eric/promptkit-backend-openrouter/src/commit/4f731d217e0bc39151c010f50fb5912706e7b6b3).
+
+## Promptkit Rakestrawhome Catalog
+
+Selected module: `gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2`
+at `v2.20260926.0`.
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: MIT
+
+License and notices: [MIT](licenses/MIT.txt) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/src/commit/48918a3ad39fd99843cda94a86133b1b3881d596/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/src/commit/48918a3ad39fd99843cda94a86133b1b3881d596/LICENSE).
+
+[Source](https://gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/src/commit/48918a3ad39fd99843cda94a86133b1b3881d596).
+
+## jsonschema
+
+Selected module: `github.com/santhosh-tekuri/jsonschema/v6` at `v6.0.2`.
+
+SPDX-License-Identifier: Apache-2.0
+
+License and notices: [Apache 2.0](licenses/Apache-2.0.txt) |
+[LICENSE](https://github.com/santhosh-tekuri/jsonschema/blob/29cbed948d24a04700eb94436416b18a07953b71/LICENSE).
+
+[Source](https://github.com/santhosh-tekuri/jsonschema/tree/29cbed948d24a04700eb94436416b18a07953b71).
+
+## Go Text
+
+Selected module: `golang.org/x/text` at `v0.14.0` (transitive dependency).
+
+Copyright (c) 2009 The Go Authors. All rights reserved.
+
+SPDX-License-Identifier: BSD-3-Clause
+
+License and notices: [BSD 3-Clause](licenses/BSD-3-Clause.txt) |
+[LICENSE](https://github.com/golang/text/blob/6c97a165dd661335ff7bce6104a008558123c353/LICENSE) |
+[PATENTS](https://github.com/golang/text/blob/6c97a165dd661335ff7bce6104a008558123c353/PATENTS).
+
+[Source](https://github.com/golang/text/tree/6c97a165dd661335ff7bce6104a008558123c353).
+
+## Go YAML v3
+
+Selected module: `gopkg.in/yaml.v3` at `v3.0.1`.
+
+Copyright (c) 2006-2010 Kirill Simonov
+
+Copyright (c) 2006-2011 Kirill Simonov
+
+Copyright (c) 2011-2019 Canonical Ltd
+
+Copyright 2011-2016 Canonical Ltd.
+
+SPDX-License-Identifier: MIT AND Apache-2.0
+
+License and notices: [MIT](licenses/MIT.txt) |
+[Apache 2.0](licenses/Apache-2.0.txt) |
+[LICENSE](https://github.com/go-yaml/yaml/blob/f6f7691b1fdeb513f56608cd2c32c51f8194bf51/LICENSE) |
+[NOTICE](https://github.com/go-yaml/yaml/blob/f6f7691b1fdeb513f56608cd2c32c51f8194bf51/NOTICE).
+
+[Source](https://github.com/go-yaml/yaml/tree/f6f7691b1fdeb513f56608cd2c32c51f8194bf51).

docs/oss/licenses/Apache-2.0.txt

@@ -0,0 +1,202 @@
+
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+
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+
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+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
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+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
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+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
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+   2. Grant of Copyright License. Subject to the terms and conditions of
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+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
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+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
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+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
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+   4. Redistribution. You may reproduce and distribute copies of the
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+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
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+      (d) If the Work includes a "NOTICE" text file as part of its
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+          of the NOTICE file are for informational purposes only and
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docs/oss/licenses/BSD-3-Clause.txt

@@ -0,0 +1,11 @@
+Copyright (c) <year> <owner>.
+
+Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

docs/oss/licenses/CC-BY-SA-4.0.txt

@@ -0,0 +1,170 @@
+Creative Commons Attribution-ShareAlike 4.0 International
+
+ Creative Commons Corporation (“Creative Commons”) is not a law firm and does not provide legal services or legal advice. Distribution of Creative Commons public licenses does not create a lawyer-client or other relationship. Creative Commons makes its licenses and related information available on an “as-is” basis. Creative Commons gives no warranties regarding its licenses, any material licensed under their terms and conditions, or any related information. Creative Commons disclaims all liability for damages resulting from their use to the fullest extent possible.
+
+Using Creative Commons Public Licenses
+
+Creative Commons public licenses provide a standard set of terms and conditions that creators and other rights holders may use to share original works of authorship and other material subject to copyright and certain other rights specified in the public license below. The following considerations are for informational purposes only, are not exhaustive, and do not form part of our licenses.
+
+Considerations for licensors: Our public licenses are intended for use by those authorized to give the public permission to use material in ways otherwise restricted by copyright and certain other rights. Our licenses are irrevocable. Licensors should read and understand the terms and conditions of the license they choose before applying it. Licensors should also secure all rights necessary before applying our licenses so that the public can reuse the material as expected. Licensors should clearly mark any material not subject to the license. This includes other CC-licensed material, or material used under an exception or limitation to copyright. More considerations for licensors.
+
+Considerations for the public: By using one of our public licenses, a licensor grants the public permission to use the licensed material under specified terms and conditions. If the licensor’s permission is not necessary for any reason–for example, because of any applicable exception or limitation to copyright–then that use is not regulated by the license. Our licenses grant only permissions under copyright and certain other rights that a licensor has authority to grant. Use of the licensed material may still be restricted for other reasons, including because others have copyright or other rights in the material. A licensor may make special requests, such as asking that all changes be marked or described.
+
+Although not required by our licenses, you are encouraged to respect those requests where reasonable. More considerations for the public.
+
+Creative Commons Attribution-ShareAlike 4.0 International Public License
+
+By exercising the Licensed Rights (defined below), You accept and agree to be bound by the terms and conditions of this Creative Commons Attribution-ShareAlike 4.0 International Public License ("Public License"). To the extent this Public License may be interpreted as a contract, You are granted the Licensed Rights in consideration of Your acceptance of these terms and conditions, and the Licensor grants You such rights in consideration of benefits the Licensor receives from making the Licensed Material available under these terms and conditions.
+
+Section 1 – Definitions.
+
+     a.	Adapted Material means material subject to Copyright and Similar Rights that is derived from or based upon the Licensed Material and in which the Licensed Material is translated, altered, arranged, transformed, or otherwise modified in a manner requiring permission under the Copyright and Similar Rights held by the Licensor. For purposes of this Public License, where the Licensed Material is a musical work, performance, or sound recording, Adapted Material is always produced where the Licensed Material is synched in timed relation with a moving image.
+
+     b.	Adapter's License means the license You apply to Your Copyright and Similar Rights in Your contributions to Adapted Material in accordance with the terms and conditions of this Public License.
+
+     c.	BY-SA Compatible License means a license listed at creativecommons.org/compatiblelicenses, approved by Creative Commons as essentially the equivalent of this Public License.
+
+     d.	Copyright and Similar Rights means copyright and/or similar rights closely related to copyright including, without limitation, performance, broadcast, sound recording, and Sui Generis Database Rights, without regard to how the rights are labeled or categorized. For purposes of this Public License, the rights specified in Section 2(b)(1)-(2) are not Copyright and Similar Rights.
+
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+
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+
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+
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+
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+
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+
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+
+     a.	License grant.
+
+          1. Subject to the terms and conditions of this Public License, the Licensor hereby grants You a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to exercise the Licensed Rights in the Licensed Material to:
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+               B. produce, reproduce, and Share Adapted Material.
+
+          2. Exceptions and Limitations. For the avoidance of doubt, where Exceptions and Limitations apply to Your use, this Public License does not apply, and You do not need to comply with its terms and conditions.
+
+          3. Term. The term of this Public License is specified in Section 6(a).
+
+          4. Media and formats; technical modifications allowed. The Licensor authorizes You to exercise the Licensed Rights in all media and formats whether now known or hereafter created, and to make technical modifications necessary to do so. The Licensor waives and/or agrees not to assert any right or authority to forbid You from making technical modifications necessary to exercise the Licensed Rights, including technical modifications necessary to circumvent Effective Technological Measures. For purposes of this Public License, simply making modifications authorized by this Section 2(a)(4) never produces Adapted Material.
+
+          5. Downstream recipients.
+
+               A. Offer from the Licensor – Licensed Material. Every recipient of the Licensed Material automatically receives an offer from the Licensor to exercise the Licensed Rights under the terms and conditions of this Public License.
+
+               B. Additional offer from the Licensor – Adapted Material. Every recipient of Adapted Material from You automatically receives an offer from the Licensor to exercise the Licensed Rights in the Adapted Material under the conditions of the Adapter’s License You apply.
+
+               C. No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.
+
+          6. No endorsement. Nothing in this Public License constitutes or may be construed as permission to assert or imply that You are, or that Your use of the Licensed Material is, connected with, or sponsored, endorsed, or granted official status by, the Licensor or others designated to receive attribution as provided in Section 3(a)(1)(A)(i).
+
+     b.	Other rights.
+
+          1. Moral rights, such as the right of integrity, are not licensed under this Public License, nor are publicity, privacy, and/or other similar personality rights; however, to the extent possible, the Licensor waives and/or agrees not to assert any such rights held by the Licensor to the limited extent necessary to allow You to exercise the Licensed Rights, but not otherwise.
+
+          2. Patent and trademark rights are not licensed under this Public License.
+
+          3. To the extent possible, the Licensor waives any right to collect royalties from You for the exercise of the Licensed Rights, whether directly or through a collecting society under any voluntary or waivable statutory or compulsory licensing scheme. In all other cases the Licensor expressly reserves any right to collect such royalties.
+
+Section 3 – License Conditions.
+
+Your exercise of the Licensed Rights is expressly made subject to the following conditions.
+
+     a.	Attribution.
+
+          1. If You Share the Licensed Material (including in modified form), You must:
+
+               A. retain the following if it is supplied by the Licensor with the Licensed Material:
+
+                    i.	identification of the creator(s) of the Licensed Material and any others designated to receive attribution, in any reasonable manner requested by the Licensor (including by pseudonym if designated);
+
+                    ii.	a copyright notice;
+
+                    iii. a notice that refers to this Public License;
+
+                    iv.	a notice that refers to the disclaimer of warranties;
+
+                    v.	a URI or hyperlink to the Licensed Material to the extent reasonably practicable;
+
+               B. indicate if You modified the Licensed Material and retain an indication of any previous modifications; and
+
+               C. indicate the Licensed Material is licensed under this Public License, and include the text of, or the URI or hyperlink to, this Public License.
+
+          2. You may satisfy the conditions in Section 3(a)(1) in any reasonable manner based on the medium, means, and context in which You Share the Licensed Material. For example, it may be reasonable to satisfy the conditions by providing a URI or hyperlink to a resource that includes the required information.
+
+          3. If requested by the Licensor, You must remove any of the information required by Section 3(a)(1)(A) to the extent reasonably practicable.
+
+     b.	ShareAlike.In addition to the conditions in Section 3(a), if You Share Adapted Material You produce, the following conditions also apply.
+
+          1. The Adapter’s License You apply must be a Creative Commons license with the same License Elements, this version or later, or a BY-SA Compatible License.
+
+          2. You must include the text of, or the URI or hyperlink to, the Adapter's License You apply. You may satisfy this condition in any reasonable manner based on the medium, means, and context in which You Share Adapted Material.
+
+          3. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, Adapted Material that restrict exercise of the rights granted under the Adapter's License You apply.
+
+Section 4 – Sui Generis Database Rights.
+
+Where the Licensed Rights include Sui Generis Database Rights that apply to Your use of the Licensed Material:
+
+     a.	for the avoidance of doubt, Section 2(a)(1) grants You the right to extract, reuse, reproduce, and Share all or a substantial portion of the contents of the database;
+
+     b.	if You include all or a substantial portion of the database contents in a database in which You have Sui Generis Database Rights, then the database in which You have Sui Generis Database Rights (but not its individual contents) is Adapted Material, including for purposes of Section 3(b); and
+
+     c.	You must comply with the conditions in Section 3(a) if You Share all or a substantial portion of the contents of the database.
+For the avoidance of doubt, this Section 4 supplements and does not replace Your obligations under this Public License where the Licensed Rights include other Copyright and Similar Rights.
+
+Section 5 – Disclaimer of Warranties and Limitation of Liability.
+
+     a.	Unless otherwise separately undertaken by the Licensor, to the extent possible, the Licensor offers the Licensed Material as-is and as-available, and makes no representations or warranties of any kind concerning the Licensed Material, whether express, implied, statutory, or other. This includes, without limitation, warranties of title, merchantability, fitness for a particular purpose, non-infringement, absence of latent or other defects, accuracy, or the presence or absence of errors, whether or not known or discoverable. Where disclaimers of warranties are not allowed in full or in part, this disclaimer may not apply to You.
+
+     b.	To the extent possible, in no event will the Licensor be liable to You on any legal theory (including, without limitation, negligence) or otherwise for any direct, special, indirect, incidental, consequential, punitive, exemplary, or other losses, costs, expenses, or damages arising out of this Public License or use of the Licensed Material, even if the Licensor has been advised of the possibility of such losses, costs, expenses, or damages. Where a limitation of liability is not allowed in full or in part, this limitation may not apply to You.
+
+     c.	The disclaimer of warranties and limitation of liability provided above shall be interpreted in a manner that, to the extent possible, most closely approximates an absolute disclaimer and waiver of all liability.
+
+Section 6 – Term and Termination.
+
+     a.	This Public License applies for the term of the Copyright and Similar Rights licensed here. However, if You fail to comply with this Public License, then Your rights under this Public License terminate automatically.
+
+     b.	Where Your right to use the Licensed Material has terminated under Section 6(a), it reinstates:
+
+          1. automatically as of the date the violation is cured, provided it is cured within 30 days of Your discovery of the violation; or
+
+          2. upon express reinstatement by the Licensor.
+
+     c.	For the avoidance of doubt, this Section 6(b) does not affect any right the Licensor may have to seek remedies for Your violations of this Public License.
+
+     d.	For the avoidance of doubt, the Licensor may also offer the Licensed Material under separate terms or conditions or stop distributing the Licensed Material at any time; however, doing so will not terminate this Public License.
+
+     e.	Sections 1, 5, 6, 7, and 8 survive termination of this Public License.
+
+Section 7 – Other Terms and Conditions.
+
+     a.	The Licensor shall not be bound by any additional or different terms or conditions communicated by You unless expressly agreed.
+
+     b.	Any arrangements, understandings, or agreements regarding the Licensed Material not stated herein are separate from and independent of the terms and conditions of this Public License.
+
+Section 8 – Interpretation.
+
+     a.	For the avoidance of doubt, this Public License does not, and shall not be interpreted to, reduce, limit, restrict, or impose conditions on any use of the Licensed Material that could lawfully be made without permission under this Public License.
+
+     b.	To the extent possible, if any provision of this Public License is deemed unenforceable, it shall be automatically reformed to the minimum extent necessary to make it enforceable. If the provision cannot be reformed, it shall be severed from this Public License without affecting the enforceability of the remaining terms and conditions.
+
+     c.	No term or condition of this Public License will be waived and no failure to comply consented to unless expressly agreed to by the Licensor.
+
+     d.	Nothing in this Public License constitutes or may be interpreted as a limitation upon, or waiver of, any privileges and immunities that apply to the Licensor or You, including from the legal processes of any jurisdiction or authority.
+
+Creative Commons is not a party to its public licenses. Notwithstanding, Creative Commons may elect to apply one of its public licenses to material it publishes and in those instances will be considered the “Licensor.” Except for the limited purpose of indicating that material is shared under a Creative Commons public license or as otherwise permitted by the Creative Commons policies published at creativecommons.org/policies, Creative Commons does not authorize the use of the trademark “Creative Commons” or any other trademark or logo of Creative Commons without its prior written consent including, without limitation, in connection with any unauthorized modifications to any of its public licenses or any other arrangements, understandings, or agreements concerning use of licensed material. For the avoidance of doubt, this paragraph does not form part of the public licenses.
+
+Creative Commons may be contacted at creativecommons.org.

docs/oss/licenses/MIT.txt

@@ -0,0 +1,18 @@
+MIT License
+
+Copyright (c) <year> <copyright holders>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+associated documentation files (the "Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
+following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial
+portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
+LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
+EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+USE OR OTHER DEALINGS IN THE SOFTWARE.

docs/policy/agents.md

@@ -0,0 +1,96 @@
+# Agent Policy
+
+**Base Policy Version:** 1.3
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [agents.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/agents.md)
+
+## Purpose
+
+Agents must read and follow these rules.
+
+## Implementation Discipline
+
+**KEY PRINCIPLES:** Write the simplest idiomatic code that satisfies the user's
+request. Do not implicitly strengthen requirements, restrictions, or guarantees
+beyond what the user actually requested.
+
+**Keep implementation machinery proportionate.** Use straightforward,
+idiomatic code and introduce only the machinery needed to support the requested
+behavior and flexibility. Optimize for conceptual simplicity and
+maintainability, not for the fewest lines, fewest options, or narrowest product
+surface.
+
+**Do not invent restrictions.** Do not reject, prohibit, constrain, cap,
+harden, or otherwise narrow behavior unless required by the user, an explicit
+repository contract, or an unavoidable correctness constraint. Preserve
+operator and caller choice where policy has not been established. If an
+additional restriction appears advisable, present it as a decision rather than
+silently implementing it.
+
+**Do not invent guarantees.** Do not strengthen public contracts, guarantees,
+or invariants beyond those expressly requested by the user.
+
+**Use the standard library.** For example: in almost every case, the best
+approach to copying files is to use the standard library. Writing custom code to
+implement power-loss protection at the application level, or to guard against
+bad actors with privileged and concurrent access to the host's filesystem,
+is wasteful, unnecessary, and not idiomatic. Stick to the simple, standard, and
+idiomatic approach unless another path is expressly requested by the user.
+
+**An implementation detail is not repository policy.** Tests and documentation
+must not elevate incidental behavior into a durable guarantee or restriction
+unless that behavior was expressly selected as part of the contract.
+
+## Promptkit Contract Authority
+
+The following clarification preserves Promptkit's established distinction
+between implementation choices and authorized contracts.
+
+A correctness constraint must follow from the requested behavior or an
+established invariant, not from the convenience of the chosen implementation.
+Explain the specific failure it prevents and why a less restrictive
+implementation cannot satisfy the contract.
+
+Existing explicit contracts remain authoritative; changing or weakening one
+requires a deliberate decision. Agent-authored plans, tests, documentation,
+and prior implementations are not evidence that an additional restriction was
+deliberately approved. Identify the authorizing requirement or decision; when
+that authority is unclear, surface the ambiguity rather than treating repetition
+as approval.
+
+## Git Commit Policy
+
+By default, commit each completed, nonempty unit of work using a
+concise, plain-English message describing what changed. This policy is standing
+authorization to create those local commits; a separate user request is not
+required. An explicit user instruction to leave work uncommitted takes precedence.
+
+A unit of work is a focused, reviewable outcome, including its relevant tests and
+documentation.
+Complete the appropriate validation before committing. If work is incomplete or
+validation is blocked, report that state accurately.
+
+Before committing:
+
+1. Run `git status --short` and review the relevant diff, including any staged
+   changes. Identify changes that predate the current unit of work.
+2. Exclude secrets, local environment files, generated junk, and unrelated changes.
+3. Stage only the files or hunks belonging to the completed unit. Use `git add .`
+   only when every included change belongs to that unit. Preserve unrelated
+   staged and unstaged work.
+4. Review `git diff --staged` and run appropriate checks for the change. Reuse
+   successful checks for unchanged content.
+5. Review `git log --oneline -n 10` and use
+   `git commit -m "<concise plain-English commit message>"`.
+6. Report the commit identifier and any remaining uncommitted work.
+
+If the unit cannot be safely separated from pre-existing work, leave it uncommitted
+and explain the overlap rather than silently including that work. If a commit
+fails, preserve the changes and report the failure; do not bypass hooks.
+
+Default commit authorization does not authorize pushing, publishing, amending,
+resetting, reverting, or rewriting history. Those actions require a separate user
+instruction. Do not use `git commit -a` or `git commit --no-verify` to bypass the
+staging and validation discipline above.

docs/policy/architecture.md

@@ -1,11 +1,41 @@
 # Architecture Policy
 
-## Purpose
+**Base Policy Version:** 1.3
 
-This document defines Promptkit's current high-level architecture and the
-durable boundaries that implementation changes must preserve. The
-[internal component overview](../internal/overview.md) inventories concrete
-implemented packages without redefining these rules.
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [architecture.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/architecture.md)
+
+## Purpose And Ownership
+
+The adopted policy defines Promptkit's purpose and the architectural
+constraints contributors must follow. It owns system boundaries, responsibility
+and dependency rules, established invariants, and explicit non-goals.
+
+Describe the concrete package inventory and implementation mechanics in internal
+documentation. Link to canonical public contracts for their exact behavior and
+to ADRs for decision rationale.
+
+## Architectural Approach
+
+Hexagonal architecture is strongly recommended, including encapsulating external
+integrations and APIs within internal adapters. Keep domain and application
+logic independent of external integration details, and make dependency direction
+clear in the adopted policy.
+
+Implement that separation with proportionate, idiomatic code. Choose interfaces
+and package layout to serve the application's actual boundaries. Use adapters
+for collaborators with external integration responsibilities.
+
+## Adopted Constraints And Implemented Structure
+
+Architectural constraints govern current and future development. Record
+implemented structure accurately, proposals and implementation status in the
+roadmap, and significant decisions and rationale in ADRs. Describe a target
+structure as implemented when its changes land.
+
+Constraints must reflect deliberately selected requirements and decisions.
+Do not promote incidental implementation choices into architectural invariants.
 
 ## System Shape
 
@@ -17,45 +47,27 @@ The module root contains package `promptkit`, which is the public facade. It
 provides the supported engine, configuration and source options, requests,
 results, public values, extension interfaces, profiles, and error sentinels.
 
-The implemented internal components consist of:
+The [internal component overview](../internal/overview.md) owns the inventory
+of implemented packages and their concrete responsibilities. This policy owns
+the boundaries and dependency rules those components must preserve.
 
-- `internal/domain`, which owns framework data values shared by later internal
-  components;
-- `internal/defaults`, which owns application-neutral framework defaults and
-  constructs the default execution target;
-- `internal/filecatalog`, which discovers YAML files and provides source-path
-  helpers for filesystem and `fs.FS` consumers;
-- `internal/promptdef`, which loads and validates prompt definitions from
-  filesystem and `fs.FS` sources;
-- `internal/profile`, which loads, validates, and overlays execution profiles
-  from filesystem and `fs.FS` sources;
-- `internal/profile/builtin`, which embeds the built-in execution profile
-  catalog;
-- `internal/prompt`, which renders prompt messages from Go templates;
-- `internal/artifact`, which resolves ordinary inline and unrestricted
-  caller-selected file references;
-- `internal/validate`, which validates basic, JSON, and JSON Schema output
-  using filesystem and `fs.FS` schema sources;
-- `internal/llm`, which defines the provider-neutral generation boundary and
-  implements outbound OpenAI-compatible chat requests; and
-- `internal/usecase`, which coordinates preparation and execution across the
-  internal framework components.
-
-The `examples/go-library/prepare` package is a maintained downstream consumer
-of the root facade. It does not expose a library package or participate in
-internal assembly.
-
-The root facade assembles the internal repositories, renderer, validator,
-outbound client, and use-case runner while translating public values and
-errors at the library boundary. The defaults and renderer depend on the domain
-model. Prompt-definition and profile repositories use the domain model, file
-catalog, and YAML decoder. The built-in profile repository supplies an
-embedded `fs.FS` to the profile package. Artifact reading uses the domain model
-and application-neutral defaults. Validation uses the domain model, file
-catalog, and JSON Schema implementation. The model client uses the domain
-model, application-neutral defaults, and an injected or standard-library HTTP
+The internal engine assembles one immutable backend registry, one capacity manager,
+the internal repositories, renderer, validator, outbound client, and use-case
+runner. The registry contains validated maintained definitions plus engine-scoped
+consumer additions. The root facade translates public values and errors at the
+library boundary.
+The internal engine constructs the capacity manager from the registry's immutable
+policy snapshot, wraps the selected built-in or injected model client, and
+supplies bounded admission to the runner. The defaults and renderer depend on
+the domain model. Prompt-definition and profile repositories use the domain
+model, file catalog, and YAML decoder. The catalog adapter validates imported
+immutable maintained data, including its reserved namespace, before internal
+engine assembly supplies it to the profile package. Artifact reading uses the
+domain model and application-neutral defaults. Validation uses the domain model,
+file catalog, and JSON Schema implementation. The model client uses the domain
+model and application-neutral defaults, and an injected or standard-library HTTP
 client. The use-case runner depends on the narrow interfaces owned by each
-internal component.
+internal component, including backend lookup and run admission.
 
 The current implementation follows this dependency direction:
 
@@ -72,9 +84,22 @@ downstream consumers, including Scriptorium
         narrow injected abstractions
 ```
 
-The facade coordinates internal components and adapts the supported public
-extension interfaces to narrow internal abstractions. Internal components must
-not depend on consumers or on Scriptorium.
+The backend registry depends on the domain model and shared JSON-value
+validation, has no mutation API after construction, and consumes the
+OpenAI-compatible reserved request-field rule owned by the model client. The
+capacity component depends on the domain model and the narrow internal
+model-client boundary, not on provider transport implementation. The model
+client does not depend on registry or capacity configuration. The facade
+coordinates internal components and adapts the supported public extension
+interfaces to narrow internal abstractions. Internal components must not depend
+on consumers or on Scriptorium.
+
+`internal/domain` owns source-neutral invariants for values shared across
+multiple input and execution boundaries, including execution-setting bounds,
+OpenAI-compatible base endpoints, session identifiers, and output-contract
+legality. Callers retain source parsing, required-field rules, other
+source-specific normalization, defaulting, error classification, and policy
+specific to their own boundary.
 
 ## Repository And Consumer Boundary
 
@@ -102,8 +127,10 @@ consumer contract requires a public package.
 Each package must have one cohesive responsibility and a clear dependency
 direction. Internal packages must not expose their types merely to simplify
 wiring, and the public facade must not leak internal representations through
-exported signatures. New public packages require a durable consumer need that
-cannot be served cleanly by the root facade.
+exported signatures. Production packages under `internal/` must not import the
+module root; the root facade may depend on internal implementation packages.
+New public packages require a durable consumer need that cannot be served
+cleanly by the root facade.
 
 The [internal component overview](../internal/overview.md) must be updated as
 packages are implemented or their responsibilities change.
@@ -154,3 +181,21 @@ state.
 Do not list planned packages as implemented components. When implementation
 introduces a package, update the internal inventory and the owning contract or
 subsystem document in the same change.
+
+## Trust Boundaries And Threat Scope
+
+Where useful, state the trust boundaries and threat scenarios relevant to the
+application's adopted requirements, along with scenarios it explicitly excludes.
+For example, distinguish handling untrusted application input from defending
+against a privileged actor concurrently modifying the host filesystem.
+
+Threat exclusions define the scope of the adopted requirements. Base defenses
+and guarantees on those requirements and raise unsettled scope for a deliberate
+decision under the [agent policy](agents.md).
+
+Keep this discussion proportionate to the application. A separate threat
+assessment or security document is optional when adopting this template.
+For this library, the framework format and integration documents own credential
+supply and external contracts; internal documents own implementation mechanisms.
+Consumer-specific filesystem and security policy remains outside Promptkit's
+boundary as described above.

docs/policy/documentation.md

@@ -1,120 +1,139 @@
 # Documentation Policy
 
+**Base Policy Version:** 1.11
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [documentation.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/documentation.md)
+
 ## Purpose
 
-This policy assigns each Promptkit documentation topic to one canonical owner.
-Its goal is to keep documentation for this reusable Go library accurate,
-concise, discoverable, and resistant to drift for consumers, contributors,
-maintainers, integrators, and coding agents.
+This policy assigns each documentation topic to one canonical owner. Its goal is
+to keep this library's documentation accurate, concise, discoverable, and resistant
+to drift for users, operators, developers, integrators, and LLM coding agents.
 
 ## Core Rules
 
 ### One Canonical Owner
 
-Each authoritative fact belongs in one document or source form. A non-owning
-document may give a short, stable summary for orientation, but it must link to
-the canonical owner instead of repeating exact contracts.
+Each authoritative fact belongs in one document. A non-owning document may give
+a short, stable summary for orientation, but it must link to the canonical owner
+for volatile details.
 
-Volatile details include exported declarations, accepted inputs, defaults,
-schemas, file names, paths, error identities, retry behavior, and runtime
-guarantees. If readers could reasonably treat a statement as a contract,
-maintain its exact definition only in the owning source.
+Volatile details include commands, flags, configuration fields and defaults,
+module keys, schemas, file names, paths, status codes, retry behavior, and
+runtime guarantees. If readers could reasonably treat a statement as a
+contract, maintain it only in the owning document.
 
-### Current State, Decisions, And Future Work
+### Current And Future Behavior
 
 Outside `docs/roadmap/`, documentation describes implemented behavior only.
 Partial features may be described only to their implemented boundary.
 
-An accepted architecture decision may describe an approved direction before it
-is implemented, but acceptance is not evidence that the behavior exists.
-Current-state documents change when the implementation lands. Temporary
-roadmaps own future work, sequencing, and implementation status; they do not
-replace durable policies or current contracts.
+Architectural constraints may govern future changes. Describe current structure
+from implemented behavior.
+
+ADRs may record an accepted architectural decision before implementation. The
+roadmap owns implementation status and sequencing until the decision is
+implemented. Current architecture, user, operator, integration, and internal
+documentation are updated when the behavior lands.
 
 ### Audience And Detail
 
 Write for the document's stated audience and include only the detail needed for
-its owned topic. Consumer guidance should not expose incidental implementation
-detail. Contributor documentation should link to public contracts and durable
-policies instead of restating them.
+its owned topic. Keep user and operator docs focused on using and operating the
+application. Developer docs should link to user-facing and external contracts
+for their definitions.
 
-### Links
+### Examples
 
-Use descriptive link text and repository-relative links for repository
-documents. Link to the canonical owner rather than to a duplicate summary.
-Check every added or changed link and repair or remove links when their target
-moves or is retired.
+Complete copyable files belong in `examples/`. Documentation may use the
+smallest illustrative snippet needed to explain its owned topic, but should link
+to maintained examples for complete copyable files.
 
-### Examples And Code Fences
-
-Complete copyable files belong in `examples/` when maintained examples exist.
-Documentation may use the smallest illustrative snippet needed for its owned
-topic, but should link to a maintained example instead of embedding a second
-complete copy.
-
-Examples must be valid, secret-free, and tested where practical. Commands,
-imports, and Go snippets must match the implemented library. Use a language tag
-on fenced code blocks and make clear when a fragment is illustrative rather
-than directly runnable.
+Examples must be valid, secret-free, and tested where practical. Commands and
+configuration used in documentation should match the application.
 
 ### Security And Privacy
 
 Documentation and examples must not contain real credentials, private keys,
-private environment dumps, sensitive source material, or private
-infrastructure details unless intentionally public. Document secret-handling
-mechanisms, not secret values.
+private environment dumps, sensitive source material, or private infrastructure
+details unless intentionally public. Document secret-handling mechanisms, not
+secret values.
 
 ## Canonical Ownership
 
 | Topic | Canonical owner | Owned content | Content owned elsewhere |
 | --- | --- | --- | --- |
-| Project orientation | `README.md` | What Promptkit is, its current usability, module identity, license summary, and links onward. | Exact API contracts, contributor procedures, architecture detail, and release steps. |
-| Contributor workflow | `docs/development.md` | Task-oriented reading guide, local workflow, validation commands, and repository hygiene. | Architecture rules, API semantics, subsystem behavior, and release procedure. |
-| Current architecture | `docs/policy/architecture.md` | System shape, normative ownership, dependency direction, package boundaries, invariants, and non-goals. | Concrete component inventory, implementation mechanics, contributor procedures, decision history, and future work. |
-| Documentation organization | `docs/policy/documentation.md` | Documentation ownership, audience boundaries, maintenance rules, and document lifecycle. | Library architecture or runtime behavior. |
-| Testing policy | `docs/policy/testing.md` | Test philosophy, risk-based sufficiency, test boundaries, doubles, coverage guidance, regression policy, and test maintenance. | Subsystem behavior, exact public contracts, subsystem-specific test inventories, and implementation plans. |
-| Release procedure | `docs/release.md`, when present | Required release validation, version and tag procedure, release ordering, and post-publication checks. | General contributor workflow, public API semantics, and decision history. |
+| Product orientation and minimal end-to-end quickstart | `README.md` | Purpose, value, shortest successful invocation, and navigation, including licensing and attribution. | Complete command reference, configuration reference, operational procedures, implementation detail. |
+| Contributor entry point | `docs/development.md` | Task-oriented reading guide, contributor orientation, baseline validation commands, and canonical links. | Package inventory, architecture rules, subsystem behavior, detailed change recipes. |
+| Application architecture policy | `docs/policy/architecture.md` | System shape, normative ownership, dependency direction, boundaries, invariants, safety properties, and non-goals. | Concrete package inventory, implementation mechanics, contributor procedures, decision history, future work. |
+| Policy-set provenance and upstream navigation | `docs/policy/meta.md` | Policy-set origin, local authority, adoption baselines, and upstream adoption and update links. | Task-specific reading triggers, detailed adoption procedures, and formal attribution notices. |
+| Agent policy | `docs/policy/agents.md` | Proportionate, idiomatic implementation; rules against inventing requirements, restrictions, guarantees, or policy. | Application contracts, architecture, testing policy, and contributor procedures. |
+| Documentation policy | `docs/policy/documentation.md` | Documentation ownership, audience boundaries, maintenance rules, and ADR/document lifecycle. | Application architecture or product behavior. |
+| Testing policy | `docs/policy/testing.md` | Test philosophy, risk sufficiency, boundaries, doubles, coverage, regressions, and test maintenance. | Subsystem behavior, application contracts, subsystem-specific test inventories, and implementation plans. |
+| Release policy | `docs/policy/release.md` | Versioning, compatibility, release integrity and immutability, release documentation, proportionate gates, publication controls, completion, and required versus optional checks. | Repository-specific commands, product installation guidance, CLI version semantics, historical release summaries, and CI implementation detail. |
+| Open source licensing and attribution policy | `docs/policy/oss.md` | License defaults and author choices, COPYRIGHT and attribution formats, license/notice links, discoverability, maintenance, and concrete exceptions. | Component entries, license texts, release commands, and dependency security review. |
+| Project copyright and license grant | `COPYRIGHT` | Project identity, copyright holders and years, SPDX expression, grant, warranty disclaimer, and third-party statement. | Complete license texts and upstream component attribution. |
+| Project license texts | `LICENSE` | Complete project and incorporated companion license texts, with required project-specific fields. | General licensing policy and upstream component attribution. |
+| Upstream component attribution | `docs/oss/attribution.md` | House Format component entries: identity, material scope and modifications where applicable, copyright, license, required notices, and license, notice, and source links. | General attribution policy, exception reasoning, research narratives, compliance commentary, and complete standard license texts. |
+| Standard dependency license texts | `docs/oss/licenses/` | Complete, verbatim standard license texts shared by applicable entries. | Project-specific upstream notices, attribution prose, and policy interpretation. |
+| Repository-specific release procedure | `docs/release.md` | Maintainer prerequisites, candidate preparation, validation and publication commands and automated guards, asynchronous deliverables, delivery status, optional consumer verification, and recovery. | General release requirements, product installation guidance, historical release summaries, and current compatibility contracts. |
+| Consumer guidance for the public Go API (if applicable) | `docs/consumers/` | Task-oriented public Go API usage, minimal examples, and consumer responsibilities. | HTTP wire semantics, external protocol contracts, internal implementation detail. |
+| Integration contracts for external components (if applicable) | `docs/integrations/` | External formats and protocols, upstream and downstream contracts, logical output paths and schemas, media types, and compatibility. | Physical runtime placement and lifecycle, internal transformations, CLI syntax, configuration defaults. |
+| Inventory of implemented internal packages | `docs/internal/overview.md` | Implemented packages and components, responsibilities, and links to focused internal docs. | Normative architecture, contributor reading policy, external contracts. |
+| Behavior and architecture of internal packages | Other files under `docs/internal/` | Implementation flow, collaborators, state transitions, package-local guarantees and failures, and relevant tests. | Global architecture invariants, configuration definitions and defaults, external schemas, operator procedures. |
+| Architectural decision records | `docs/adr/` | Significant decisions, context, alternatives, rationale, consequences, and supersession history. | Current behavior reference, implementation status, task sequencing. |
+| Future work and implementation status | `docs/roadmap/` | Proposed, accepted, deferred, or rejected work; implementation status, sequencing, and task breakdowns. | Implemented behavior reference and architectural decision rationale. |
+| Release-note history | `docs/releases/` | One checked-in summary per source release under the procedure; the note at its immutable tag is the release record. | Current commands, behavior, contracts, and compatibility definitions. |
+| Complete copyable artifacts | `examples/` | Maintained configuration, inputs, and other copyable or runnable files. | Field-by-field reference, command reference, prose explanation. |
 | Exact exported Go API | Go declarations and GoDoc, as APIs are implemented | Exported names, signatures, types, values, errors, and exact behavioral contracts. | Task-oriented consumer walkthroughs, implementation details, and future API proposals. |
 | Framework file formats | `docs/formats.md` | Prompt-definition and profile YAML fields, schema references, defaults, validation modes, built-in profiles, credentials, and file-to-request precedence. | Exported Go declarations, outbound wire behavior, internal parsing mechanics, and application configuration. |
-| Consumer guidance | `docs/consumers/`, when consumer workflows require dedicated guidance | Task-oriented use of implemented public APIs, minimal examples, and consumer responsibilities. | Exact exported declarations and internal mechanics. |
-| Durable integration contracts | `docs/integrations/`, when integrations exist | External formats and protocols, compatibility behavior, and upstream or downstream responsibilities. | Internal transformations and public Go declarations. |
-| Implemented component inventory | `docs/internal/overview.md` | Current packages and components, their implemented responsibilities, and links to focused internal documents. | Normative architecture, contributor workflow, external contracts, and proposed components. |
-| Internal subsystem behavior | Other files under `docs/internal/`, when a subsystem needs durable detail | Implementation flow, internal collaborators and state transitions, package-local guarantees and failures, and relevant tests. | Global architecture invariants, public API definitions, and future package plans. |
-| Architectural decision history | `docs/adr/`, when repository-local decisions require records | Significant decisions, context, alternatives, rationale, consequences, and supersession history. | Current behavior reference, implementation status, and task sequencing. |
-| Temporary feature roadmaps | `docs/roadmap/`, while planned work needs coordination | Proposed or accepted scope, sequencing, gates, and implementation status. | Implemented behavior reference and durable decision rationale. |
-| Complete copyable artifacts | `examples/` | Valid inputs, Go programs, and other files intended to be copied or run. | Field-by-field reference, exact API declarations, and prose explanation. |
 
-Conditional owners do not require placeholder files or directories. Create a
-consumer, integration, subsystem, ADR, roadmap, or example document only when
-the corresponding implemented interface, decision, planned effort, or
-maintained artifact exists.
+Create supporting documents for existing interfaces and responsibilities when
+substantive content is available.
 
 ## Boundary Rules
 
 ### Orientation
 
-The README owns project orientation. The development guide routes
-contributors. Architecture owns normative structure. The internal overview
-owns the current concrete component map. These documents may link to one
-another but must not maintain parallel package or behavior descriptions.
+Link among orientation, architecture, and internal documents; maintain each
+package or behavior description in its canonical owner.
 
 ### Public Contracts And Implementation
 
-Go declarations and GoDoc own exact exported API contracts once those APIs
-exist. Consumer and integration documents explain how to use those contracts
-for a task. Internal documents explain how Promptkit implements them. Internal
-documentation may identify a public type or external format as a dependency,
-but must link to its canonical definition rather than restate it.
+Go declarations and GoDoc own exact exported Go API contracts. The
+[framework format reference](../formats.md) owns prompt, profile, and schema
+formats; integration documents own external wire behavior. Consumer and
+internal documents link to those owners for exact definitions.
 
-The [framework format reference](../formats.md) owns exact prompt, profile, and
-schema-file contracts. Integration documents own external wire formats.
+### Releases
+
+The release policy defines requirements and invariants that every release must
+satisfy. The repository-specific release procedure defines the commands and
+workflow maintainers use to satisfy that policy. Release notes record history
+at immutable tags. Maintain current behavior in its canonical documentation,
+update it with the corresponding behavior changes, and keep release procedures
+consistent with adopted policy.
+
+### Project Licensing And Upstream Attribution
+
+README and release documents link to the canonical licensing and attribution
+materials under the [OSS policy](oss.md). The release procedure owns URL
+construction and publication mechanics.
+
+### Contracts And Implementation
+
+Integration and API documents define externally observable shapes and
+semantics. Internal documents explain how this application implements or consumes those
+contracts. Internal docs may name a field, file, or protocol to identify a
+dependency, but must link to its canonical contract for the definition.
 
 ### Security Topics
 
 This policy owns what documentation and examples may contain. Architecture owns
-library security boundaries and invariants. Public declarations and integration
-documents own consumer-visible security contracts. Internal documents own
-implementation mechanisms only.
+library security boundaries. Public declarations and integration documents own
+consumer-visible contracts; internal documents own implementation mechanisms.
 
 ## Architecture Decision Records
 
@@ -129,44 +148,47 @@ Use sequentially numbered ADR filenames such as
 6. alternatives considered;
 7. consequences.
 
-Use one of these statuses:
+Treat the decision content of an accepted ADR as immutable. When a decision
+changes, create a new ADR and update the earlier ADR's status to superseded.
+Rejected architectural alternatives belong in the ADR; rejected product ideas
+belong in the roadmap.
 
-- **Proposed:** the decision is under consideration and may change;
-- **Accepted:** the decision is approved, whether or not implementation is
-  complete;
-- **Rejected:** the proposed decision was considered and not adopted;
-- **Superseded:** a later accepted ADR replaces the accepted decision.
+## Maintenance
 
-A proposed ADR transitions to Accepted or Rejected. An Accepted ADR transitions
-to Superseded only when a later Accepted ADR replaces it. An ADR may be created
-as Accepted when the decision has already been made.
+When behavior changes, update its canonical owner in the same change. If
+ownership moves, remove the old definition and replace it with a link where
+navigation remains useful.
 
-Treat the decision content of an Accepted ADR as immutable. A changed decision
-requires a later ADR rather than a rewrite of the accepted record. A Superseded
-ADR must link to its replacement, and the replacement must link back. Rejected
-architectural alternatives belong in the ADR; rejected feature ideas belong in
-a roadmap when they need to be retained.
+Before completing documentation work:
+
+- verify affected behavior and examples;
+- check commands, flags, fields, defaults, schemas, and paths against their
+  implementation;
+- keep unimplemented behavior in the roadmap, subject to the ADR exception;
+- remove stale references and validate links;
+- confirm that non-owning documents summarize and link rather than redefine;
+- confirm that no secrets or sensitive private data were added.
+
+## Promptkit Documentation Scope
+
+Promptkit is a Go library, so exported GoDoc and framework formats replace
+application CLI, configuration, operations, and HTTP-service owners. Reading
+triggers belong in the development guide, not this topic map.
 
 ## Document Lifecycle
 
-Create durable current-state documentation with the implementation it
-describes. Update its canonical owner in the same change when behavior changes.
-If ownership moves, remove the old definition and leave a link where navigation
-remains useful.
-
 Roadmaps are temporary coordination documents. When their work is complete,
 record completion, move any still-useful decisions or contracts to their
 durable owners, update incoming links, and archive or remove the roadmap
 according to repository practice. Do not preserve completed roadmaps as a
 second current-state reference.
 
-Before completing documentation work:
+Retain release notes as historical records under the release policy. Do not
+apply temporary-roadmap retirement rules to published release notes.
 
-- verify affected behavior and examples;
-- check commands, imports, declarations, defaults, schemas, and paths against
-  their implementation;
-- keep unimplemented behavior in a roadmap, subject to the ADR exception;
-- validate links and fenced examples;
-- confirm non-owning documents summarize and link rather than redefine;
-- remove stale or unsupported claims; and
-- confirm that no secrets or sensitive private data were added.
+For Promptkit ADRs, retain the existing Proposed, Accepted, Rejected, and
+Superseded statuses. Proposed records may become Accepted or Rejected;
+Accepted records may become Superseded, with links between the earlier record
+and its replacement. Records may be created as Accepted when the decision has
+already been made. These lifecycle rules preserve existing local document
+semantics.

docs/policy/meta.md

@@ -0,0 +1,27 @@
+# Policy Set Provenance
+
+**Base Policy Version:** 1.0
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [meta.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/meta.md)
+
+## Origin And Local Authority
+
+This repository's policy set is adapted from
+[Standard Repository Policies](https://gitea.maximumdirect.net/eric/policy).
+The adopted local policies govern work in this repository. Upstream revisions
+become local policy through deliberate adoption, preserving local decisions.
+Each policy's `Upstream Source` identifies its adopted baseline.
+
+## Adoption And Updates
+
+For policy adoption, upstream revision reviews, and updates, consult the
+[upstream adoption and update guide](https://gitea.maximumdirect.net/eric/policy/src/branch/main/docs/adoption.md).
+That guide and the reference example collection are maintained upstream and
+accessed through links. Keep discovery links pointed at the current upstream
+project and guide; keep adopted-source and example links pinned to commits.
+
+The local [developer guide](../development.md) routes tasks to applicable
+policies. Formal credit and licensing notices for the copied policy material
+belong in the local [attribution document](../oss/attribution.md).

docs/policy/oss.md

@@ -0,0 +1,227 @@
+# Open Source Licensing And Attribution Policy
+
+**Base Policy Version:** 1.8
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [oss.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/oss.md)
+
+## Purpose And Scope
+
+This policy defines project licensing conventions and a repeatable House Format
+for upstream attribution and license notices. It covers the project's own code
+and upstream components incorporated into or distributed with the application
+or library, including relevant transitive dependencies and copied code,
+documentation, or assets.
+Determine treatment from the component's terms and actual use.
+
+Consulting development guidance or using tooling alone does not require an
+attribution entry. Copying or adapting documentation for inclusion in the
+repository is different: preserve its applicable attribution and license terms.
+A material's role as development guidance does not exempt copied documents.
+Apply any express permissions for attribution-free reuse of example formatting.
+
+The baseline is a publicly available source repository with releases published
+alongside it. The format is independent of language, forge, and build system.
+It does not require attribution for every development tool, establish license
+compatibility, or resolve every obligation arising from use or distribution.
+
+## Canonical Locations
+
+The [documentation policy](documentation.md) assigns ownership:
+
+- `COPYRIGHT`: project name, copyright statements, SPDX expression, grant,
+  warranty disclaimer, and third-party statement.
+- `LICENSE` contains the complete, unmodified project license text, including
+  incorporated companion text. Dependency attribution does not relicense the project.
+- `docs/oss/attribution.md`: canonical component entries.
+- `docs/oss/licenses/`: complete, verbatim standard and applicable companion texts.
+
+Use recognizable license filenames, such as `Apache-2.0.txt` or `LGPL-3.0.txt`.
+A shared standard text may serve multiple entries. Keep explanations outside
+license texts and preserve distinct versions and exceptions.
+
+## Upstream Reference Examples
+
+Use the commit-pinned upstream examples to create actual project notices.
+Retain their links and keep the example collection upstream; keep applicable
+license texts locally as specified above.
+
+## Project Licensing
+
+Unless the author specifies otherwise, use **GPL version 3 or later**
+(`GPL-3.0-or-later`) for applications and **LGPL version 3 or later**
+(`LGPL-3.0-or-later`) for libraries. An author's explicit choice takes precedence:
+for example, a one-off script may use MIT. Such a choice requires no exception
+rationale, additional approval, or compensating controls under this policy.
+
+These defaults guide new license selection. Adopting this policy does not
+relicense existing code or override third-party terms. Preserve an existing
+license unless the author deliberately changes it. For mixed-purpose projects,
+follow the author's selected scope rather than inferring different licenses for
+individual packages.
+
+Use the upstream [application COPYRIGHT example](https://gitea.maximumdirect.net/eric/policy/src/commit/a469273adda336625f96b9d769ea27b33999f146/examples/licensing/application/COPYRIGHT)
+or [library COPYRIGHT example](https://gitea.maximumdirect.net/eric/policy/src/commit/a469273adda336625f96b9d769ea27b33999f146/examples/licensing/library/COPYRIGHT)
+to create the project’s root `COPYRIGHT` file.
+Use verified project names, contribution years, and copyright holders.
+For another selected license, adapt the grant, SPDX expression, disclaimer, and
+text references together to reflect the author's selected grant.
+
+For GPLv3 projects, copy the complete GPLv3 text into `LICENSE`. For LGPLv3
+projects, place the complete LGPLv3 text followed by the complete GPLv3 text in
+`LICENSE`; the LGPL incorporates the GPL terms. Keep the texts unmodified and
+place project-specific statements in `COPYRIGHT`. For the default grants, the
+grant and SPDX expression in `COPYRIGHT` must expressly identify `or-later`;
+follow the author’s choice if a different grant is selected.
+
+For other licenses, provide their complete text and any required project-specific
+fields; the standard reference collection remains unchanged. Keep `COPYRIGHT`,
+`LICENSE`, SPDX expressions, and README descriptions consistent with the actual
+grant. This convention introduces no blanket requirement for per-file headers;
+preserve notices or add them where the applicable terms require them.
+
+Identify separately licensed documentation or assets in the project grant, with
+links to their attribution and license information. An application's default
+code license does not override the terms of incorporated documentation.
+
+## Upstream Attribution House Format
+
+Begin `docs/oss/attribution.md` with `# Open Source Attribution Notices`,
+followed directly by component entries. These comprise the complete document.
+
+Each entry presents these five fields in order, with blank lines between them:
+
+1. **Project name** as a level-two heading. An optional identification paragraph
+   may follow, such as `Selected module: MODULE at VERSION.` with the module and
+   version in backticks. For copied documentation, a concise `Material:` sentence
+   may identify the affected files and whether they were adapted or copied
+   without modification. A factual qualifier such as `(transitive dependency)`
+   is permitted. Limit optional identification prose to factual component and
+   material scope.
+2. **Upstream copyright statement or statements**, preserving their wording.
+   Put multiple statements in separate paragraphs. Include this field when the
+   selected upstream source supplies an applicable statement; otherwise, omit it.
+3. **SPDX license identifier or expression**, when applicable, using
+   `SPDX-License-Identifier: EXPRESSION`.
+4. **License and notice links**, beginning `License and notices:`, separated
+   by ` | `, and ending with a period. Label local standard texts by license
+   name, such as `MIT` or `Apache 2.0`. Label upstream files by their actual
+   filenames, such as `COPYRIGHT`, `LICENSE`, `NOTICE`, or `PATENTS`.
+5. **Source repository link**, rendered exactly as:
+
+   ```markdown
+   [Source](COMMIT_URL).
+   ```
+
+Use the upstream [attribution example](https://gitea.maximumdirect.net/eric/policy/src/commit/a469273adda336625f96b9d769ea27b33999f146/examples/licensing/attribution.md)
+to create the project’s `docs/oss/attribution.md`.
+The example illustrates omitted fields and multiple copyrights and licenses.
+Replace the uppercase placeholders and illustrative URLs with actual component
+information. Local license links are relative to the destination
+`docs/oss/attribution.md`; copy the applicable texts into its `licenses/`
+directory. Do not copy example entries for components the project does not use.
+
+These are five fields, not a line limit. Omit the SPDX field when no applicable
+identifier exists; identify nonstandard terms through the linked text. Preserve
+licensing alternatives and exceptions, and record a selected option when
+relevant through the factual license identification. Do not invent an identifier
+or silently resolve an unsettled licensing choice.
+
+Keep entries factual. Do not add agent-authored explanations of license
+expressions, file-level license scope, research performed, retained source
+notices, or compliance conclusions. Avoid filler such as "none is invented
+here" and embellished link labels such as "upstream LICENSE", "additional
+patent grant", or "at the imported commit". Preserve actual required upstream
+content; this rule excludes editorial additions, not required notices. Policy
+interpretation and exception reasoning belong in the adopted OSS policy or an
+appropriate decision record, not the attribution document.
+
+## License Texts And Upstream Links
+
+Link standard license texts to their local copies. Link project-specific
+notices to their upstream copies. Every upstream repository or notice link must
+identify the exact commit corresponding to the
+imported version, including the selected source revision for copied material.
+
+Classify material according to its contents. An upstream `LICENSE`,
+`COPYING`, or similar file may contain project-specific notices or exceptions
+in addition to standard wording. Link both the local standard text and the
+commit-specific upstream file when needed. Make companion license texts directly
+reachable from the entry.
+
+For project-specific license and attribution material, this policy accepts
+direct links to the applicable upstream texts as satisfying reproduction,
+inclusion, or copy requirements. This is the adopted house interpretation.
+Agents must apply it without adding local-copy requirements or seeking repeated
+approval solely because a license uses those terms.
+
+This interpretation concerns notice reproduction. Concrete obligations such as
+marking modified files or supplying corresponding source receive their own
+applicable treatment. Preserve required notices already present in incorporated
+source files; the central attribution entry does not authorize stripping them.
+
+## Discoverability
+
+End the project's README with two friendly statements linking to its actual
+grant in `COPYRIGHT` and the attribution document. For example, for a project
+with the stated license:
+
+```markdown
+PROJECT_NAME is licensed under the [LGPL v3.0 or later](COPYRIGHT).
+
+[Open Source attribution notices](docs/oss/attribution.md) are available.
+```
+
+Each new checked-in release document and its hosted download page must end
+with links whose visible text is `COPYRIGHT | LICENSE | ATTRIBUTION`. Use absolute
+URLs to those files at the release's immutable tag or corresponding immutable source
+revision so the links work in both locations. This release navigation is distinct
+from upstream component links, which must use the imported commit.
+
+Reuse the checked-in release document as the hosted release body where supported.
+The release procedure owns concrete URLs and publication mechanics for delivering
+the links through the selected channel. Do not maintain duplicate notice lists.
+These conventions do not by themselves require separate downloadable license
+assets, source bundles, or a different binary package format.
+
+## Maintenance And Exceptions
+
+Update project licensing statements together when the author changes the grant
+or its scope. Update upstream notices in the change that adds, removes, upgrades,
+copies, or changes the distribution of a relevant component. Check the selected source's license
+and notices rather than assuming they are unchanged. Update affected entries,
+commit links, and texts; retain historical versions through Git.
+
+Check affected statements, faithful standard-text copies, and link destinations
+as part of ordinary change review. For a future release tag, check intended file
+paths against the candidate source; the tag need not resolve remotely before
+publication. Do not add publication-time network checks, CI polling, recurring
+legal sign-offs, mandatory scanners, or a full software bill of materials merely
+to implement this policy.
+
+Use the House Format routinely. Raise an exception only for a concrete obligation
+or unresolved rights question it does not address, including any arising from a
+particular distribution channel. Record the issue and selected treatment in the
+adopted OSS policy or an appropriate decision record. Attribution entries
+contain the resulting factual identification and required material, without
+repeating that reasoning. Resolve the issue before the affected use or
+distribution without reopening settled choices.
+Common ownership of projects is neither required nor a blanket exception.
+
+Apply the formatting convention prospectively. Do not rewrite published tags,
+notes, binaries, or checksums to retrofit it. Address actual omissions deliberately
+under the applicable terms and the [release correction policy](release.md#immutability-and-failure-recovery).
+Ordinary attribution maintenance and release links are preparation work, not new
+release approval gates.
+
+## Promptkit Adoption
+
+Promptkit retains its LGPL-3.0-or-later library grant in
+[COPYRIGHT](../../COPYRIGHT). Adapted policy documentation has the separate
+scope identified there and in [attribution](../oss/attribution.md).
+
+Promptkit publishes source-only Go module tags on Gitea, with no binaries or
+separate hosted download page. The [release procedure](../release.md) owns
+publication and concrete footer URLs. The hosted-page guidance applies if such
+a channel is deliberately introduced; it does not require creating one.

docs/policy/release.md

@@ -0,0 +1,252 @@
+# Release Policy
+
+**Base Policy Version:** 1.4
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [release.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/release.md)
+
+## Purpose
+
+This policy defines a proportionate workflow for validating and publishing an
+intended source revision under a fresh version. Releases should require little
+routine intervention, avoid repeated work, and preserve published contents.
+
+The repository-specific commands belong in `docs/release.md`. Historical release
+summaries belong in `docs/releases/`. The procedure must agree with the adopted
+policy and link to it rather than introduce additional release requirements.
+
+## Release Model And Completion
+
+A source release identifies one exact committed source revision through an
+immutable version tag and a version-matched, checked-in release note. The
+primary release branch is `main` unless the adopted policy specifies otherwise.
+The procedure must name the authoritative publication remote.
+
+A successful push of the intended tag, with its source commit available on the
+authoritative primary branch, completes the release. The source commit may be
+pushed before the tag or published together with it through an atomic push.
+The procedure must choose and document the supported approach.
+
+Release commands must finish at successful publication. They must not wait for
+or poll CI, require successful CI status, inspect downloadable artifacts, or
+check consumer installation or Go module availability as completion gates.
+A failed or ambiguous push requires resolving the authoritative remote state
+before declaring success or retrying; successful pushes do not require a
+separate remote read-back gate.
+
+Repositories may publish source only. Additional binaries, images, packages,
+checksums, or other declared deliverables may be published asynchronously from
+the tagged source. The procedure must identify those deliverables and the
+responsibility of their automation. Published deliverables must be traceable
+to that source and identify the same version.
+
+Track source-release completion and artifact delivery separately. Report delivery
+failures and optional investigations under artifact-delivery status.
+
+## Versioning And Compatibility
+
+Stable releases use Semantic Versioning in the form `vMAJOR.MINOR.PATCH`, with
+no leading zeroes. Prereleases require an explicit adopted policy defining
+their format and use.
+
+The selected version must be unused locally and on the authoritative remote.
+Do not require queries to every configured remote or publication service.
+A version known to have already been published must not be reused, even if the
+normal guards do not inspect that channel. Adding a distribution channel
+requires a deliberate update to the policy and procedure where needed.
+
+For releases at or after `v1.0.0`:
+
+- a major release may make intentional incompatible changes;
+- a minor release may add backward-compatible behavior; and
+- a patch release may make backward-compatible fixes.
+
+Before `v1.0.0`, a minor release may change a documented public, operational,
+configuration, data, integration, or compatibility contract when the release
+note explains the impact and required consumer action. A patch release must
+not intentionally break those contracts within its minor line.
+
+Additional compatibility promises and deliberate exceptions belong in the
+adopted policy or canonical contract documentation. Release notes explain
+changes; they do not redefine current compatibility contracts.
+
+## Release Documentation
+
+Every new release must include `docs/releases/<version>.md` in the tagged
+source tree. Use the complete version tag as the filename and begin with a
+title containing the product name and that exact version.
+
+Include a short summary and any relevant compatibility impact or upgrade
+instructions. Use the Promptkit section structure below and keep the note
+proportionate to the change.
+
+Keep exact current contracts in their canonical documents and update affected
+documentation with the behavior change. Link to those documents from the note
+where useful. If annotated tags are used, derive their summary from the
+checked-in note.
+
+Include the release footer defined by the [OSS policy](oss.md#discoverability)
+in each new release document and preserve it on the hosted download page. The
+release procedure defines the concrete URLs and publication mechanics. Prepare
+these links with the release note; they do not add a network check or approval
+gate.
+
+Handle version selection, release-note content, and retirement of completed
+roadmaps during preparation. Preserve planned and deferred work and repair
+affected links when retiring roadmaps. Reuse ordinary change review for
+unintended files, credentials, and private data. Scope release-content review
+to the tagged source.
+
+## Candidate Validation
+
+Provide one publication command that validates the final committed candidate,
+checks publication state, and publishes the intended refs. A validation-only
+mode or command may be provided for diagnosis, but must not be a required step
+before publication repeats the same checks.
+
+Run the complete deterministic, offline default test suite once for the final
+candidate, following the [testing policy](testing.md). For repositories that
+publish builds, verify the required build targets. Select those targets for
+the application's actual support commitments; native testing on each platform
+and access to particular hardware are not default release prerequisites.
+
+Additional gates must address a concrete risk that the existing checks do not
+adequately cover. Do not automatically require linting, race testing, module
+hygiene audits, documentation audits, credential scans, example validation, or
+expanded platform matrices solely because they are possible. Retain such
+checks when their distinct protection justifies their cost. A one-time migration
+check must not silently become a permanent release requirement.
+
+Release tests must not require real credentials, mutable application services,
+paid APIs, provider probes, or inference calls. The procedure may describe dependency
+preparation separately from offline validation.
+
+Avoid duplicate validation across release phases. Successful checks for the
+same final candidate need not be repeated solely to satisfy another phase;
+any reuse must clearly apply to that exact candidate. Persistent validation
+caches are not required. If the candidate changes, validate the new candidate.
+Cheap publication-state checks may be repeated immediately before pushing
+because local or remote state may have changed during validation.
+
+Automate mechanical guards. Human review gates are strongly disfavored: add one
+only through an explicit project-specific policy decision explaining the
+concrete risk and why ordinary change review or automation is insufficient.
+Do not add routine confirmations for checks the command can perform itself.
+
+## Publication Guards
+
+Automate the checks needed to publish the intended source under a fresh version:
+
+- the version has the adopted format and is unused locally and on the
+  authoritative remote;
+- the worktree and index are clean on the primary release branch;
+- the source being published is the exact candidate that passed validation,
+  including its matching release note;
+- the remote primary branch already identifies that candidate, or an atomic
+  source/tag push will advance it to that candidate without discarding remote
+  history; and
+- the tag identifies the validated candidate and only the intended refs are
+  published.
+
+Fetch the authoritative branch and tag state as needed for these checks.
+Do not force branch or tag updates to bypass a failed guard. Publish explicit
+refs rather than all local tags. Do not require CI success, publication-service
+availability checks, or a separate manual confirmation for each guard.
+
+## Immutability And Failure Recovery
+
+Published version tags and published contents are immutable. Do not move,
+overwrite, recreate, or delete a published tag, or replace a published artifact,
+checksum, signature, provenance statement, or release note under that version.
+The checked-in note at the immutable tag is that release's historical record.
+
+If validation fails before publication, correct and commit the candidate and
+rerun the publication command. If a push fails or its outcome is ambiguous,
+inspect the authoritative remote before retrying. Remove an unpublished local
+tag only after confirming it was never published or used by a release channel.
+An unavailable remote leaves publication status unknown; do not overwrite a tag
+to resolve uncertainty.
+
+Transient network, authentication, CI, or consumer-availability failures do not
+by themselves require a new version. Asynchronous delivery may be retried from
+the same immutable tag. Missing artifacts may be published later, provided
+existing published contents are not replaced and the additions remain consistent
+with the tagged source and any already-published checksum manifest. If that
+cannot be achieved, publish a new version.
+
+A defect requiring changes to published source or contents requires a corrected
+commit, a new semantically appropriate version, a matching release note, and
+the release procedure again. Leave the original release intact. A channel's
+yank, deprecation, or advisory mechanism may warn consumers away from a defective
+release without replacing its contents or reusing its version.
+
+## Repository Release Procedure
+
+Maintain `docs/release.md` as a short, executable maintainer runbook. It must
+identify:
+
+1. prerequisites, primary branch, and authoritative remote;
+2. version and release-note preparation;
+3. one publication command with its selected local checks and automated guards;
+4. declared deliverables, required build targets, and automation responsibilities;
+5. the successful-push completion point and separately reported delivery status;
+   and
+6. failure handling, ambiguous-push recovery, and asynchronous delivery retries.
+
+Use copyable commands where practical. Keep optional diagnostics and consumer
+verification clearly optional. The procedure must not turn preparation work,
+ordinary change review, or post-publication investigation into additional
+release gates.
+
+## Promptkit Release Configuration
+
+The release-note requirements were adopted on 2026-09-23 and licensing
+navigation on 2026-09-26. Apply them prospectively; previously published notes
+and tags retain their original records.
+
+Promptkit publishes source-only Go modules from main to origin on Gitea, using
+annotated stable SemVer tags. It has no binaries, hosted download pages, or
+asynchronous deliverables. The source commit is pushed through main before the
+tag. The [release procedure](../release.md) owns commands and recovery.
+
+The existing publication script requires Summary, Compatibility, Upgrade, and
+Changes headings beneath a title of `# Promptkit vMAJOR.MINOR.PATCH`. State
+“No action required” or “None” where appropriate. This retained local structure
+matches the automated release-note guard; changing it is separate work.
+
+The [publication script](../../scripts/release.sh) runs the
+[local checks](../../scripts/release-check.sh) once for the final committed
+candidate: race-enabled tests, vet, three offline consumer examples, tracked
+Go formatting, Markdown links, module/workspace hygiene, whitespace, and a
+credential-pattern scan. These protect concurrency, assembled library use,
+source distribution, and documentation integrity. A separate ordinary test run
+or standalone build is not an additional release gate. Candidate, tag, and
+synchronized-main checks remain automated. No CI or module-availability wait
+is required. Licensing footer URLs are preparation work, not a network gate.
+
+## Catalog Profile Compatibility
+
+External catalog profile data may be added, removed, renamed, or modified
+without deprecation or advance notice. This exception is limited to profile
+data imported from the maintained catalog modules. It does not weaken ordinary
+compatibility for Promptkit's public Go API, configuration and format semantics,
+runtime behavior, catalog-module APIs, manifest schema, backend definitions, or
+consumer-owned definitions.
+
+Within the catalog versions selected and tested by a Promptkit release, and
+unless a consumer overrides the name or its base, Promptkit keeps the literal
+profile IDs `promptkit-openrouter-standard` and
+`promptkit-openrouter-auto` available. The names do not promise a permanent
+model, backend, routing behavior, settings, cost, output, or upstream
+availability. The [framework format reference](../formats.md#built-in-profile-catalog)
+owns their current definitions.
+
+`v0.10.0` is the initial minor release for this compatibility transition.
+Afterward, catalog-only updates and adjustments to the current selections may
+ship in a patch release when all other compatibility obligations remain intact.
+External profile removals can require consumer action; they are not automatic
+migrations.
+
+Catalog adoption and release validation remain local and offline. They do not
+probe provider endpoints, request model lists, or make inference calls.

docs/policy/testing.md

@@ -1,39 +1,32 @@
 # Testing Policy
 
+**Base Policy Version:** 1.3
+
+**Last Updated**: 2026-09-27
+
+**Upstream Source:** [testing.md](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843/docs/policy/testing.md)
+
 ## Purpose
 
 Our tests exist to make **incorrect changes expensive and correct changes cheap**.
 
-We do not optimize for test count, line coverage, exhaustive isolation, or the fewest possible tests. We optimize for sufficient confidence in important behavior while imposing as little unnecessary friction as possible on future development.
+We optimize for sufficient confidence in important behavior while minimizing friction on future development.
 
 ## Every test has a cost
 
-Testing is not an unqualified good. Every test imposes both an immediate cost and a continuing lifetime cost.
-
-A test must be:
-
-- written and reviewed;
-- understood by future maintainers and coding agents;
-- executed in maintainer-run validation;
-- diagnosed when it fails;
-- updated when legitimate behavior changes;
-- maintained as fixtures, APIs, and dependencies evolve; and
-- removed or rewritten when it becomes redundant, brittle, misleading, or obsolete.
-
-Tests also create cognitive and architectural friction. They can constrain refactoring, duplicate policy, slow feedback loops, add noise to failures, and cause harmless implementation changes to require unrelated edits across the suite.
+Every test has an immediate and continuing cost: writing, review, execution,
+diagnosis, fixture maintenance, and updates when legitimate behavior changes.
+Tests can also constrain refactoring, duplicate policy, and add failure noise.
 
 A test is warranted only when the confidence it provides justifies these costs.
-
-Apply this cost-benefit analysis at two levels:
+Evaluate that tradeoff at two levels:
 
 1. **Per test:** What realistic defect does this test detect, how consequential would that defect be, and is that protection worth the test's lifetime cost?
 2. **Across the suite:** Does this collection provide materially more confidence than a smaller, simpler suite would?
 
-The preferred test suite is a **lean suite that provides sufficient confidence in the risks that matter, without redundant or low-value tests**. We seek sufficient confidence with the least unnecessary testing friction, not the fewest possible tests.
+Some friction is intentional. Tests should make dangerous changes—such as breaking compatibility, corrupting data, violating security boundaries, or reintroducing subtle bugs—require deliberate review. Keep ordinary internal changes inexpensive.
 
-Some friction is intentional. Tests should make dangerous changes—such as breaking compatibility, corrupting data, violating security boundaries, or reintroducing subtle bugs—require deliberate review. They should not make ordinary internal changes needlessly expensive.
-
-The cost of a test is not a reason to omit testing by default. Do not cite maintenance cost abstractly. When omitting a plausible test, be able to state why the protected failure is low-risk, already covered, obvious, reversible, or cheaper to detect elsewhere. For consequential, subtle, or difficult-to-observe behavior, the presumption should favor testing.
+Evaluate maintenance cost against the specific failure being protected. When omitting a plausible test, be able to state why the protected failure is low-risk, already covered, obvious, reversible, or cheaper to detect elsewhere. For consequential, subtle, or difficult-to-observe behavior, the presumption should favor testing.
 
 ## Default testing style
 
@@ -47,22 +40,34 @@ Use a **classical/Detroit-style** approach:
 
 Examples of appropriate seams include clocks, randomness, subprocesses, remote APIs, object storage, email, and paid LLM calls.
 
+## Promptkit Test Boundaries
+
+Promptkit is a library without a CLI or hosted CI. The execution requirements,
+facade test ownership, public error guidance, and offline consumer examples
+below tailor the standard to that boundary.
+
 ## Test execution requirements
 
 Promptkit currently uses maintainer-run validation rather than hosted CI.
-Maintainers run the repository-documented test, vet, build, formatting,
-documentation-link, and repository-hygiene checks before accepting changes.
+Ordinary work requires validation proportionate to its scope and risk. Do not
+repeat successful checks for unchanged content merely to create a commit.
+Release candidates require the complete local workflow in the
+[development guide](../development.md#maintainer-validation). That guide routes
+contributors to the executable checks for formatting, documentation links,
+and repository hygiene.
 Introducing hosted CI later would supplement, not silently redefine, this
 documented validation model.
 
-The complete test sequence includes ordinary and race-enabled package tests.
-The maintained offline consumer workflow is also run from the repository root:
-
-```sh
-go test ./...
-go test -race ./...
-go run ./examples/go-library/prepare
-```
+Full release-candidate validation includes race-enabled package tests, explicit
+static analysis, and execution with automated semantic checks of the three maintained
+offline consumer examples. The test run builds the packages; the examples
+also exercise ordinary compilation. Separate ordinary tests and a standalone
+build are not additional release gates. Ordinary tests remain useful during
+development. The preparation example protects assembled preparation and
+inspection behavior. The execution example separately protects assembled
+`Run`, injected-client, validation, usage, and result behavior. The observation
+example protects assembled built-in retries, structured proposal and assessment
+runs, and application-owned interpretation of metadata.
 
 Tests in the default suite must be deterministic, offline, and independent of
 real credentials. They must not invoke paid APIs, use live network
@@ -88,8 +93,9 @@ Use each test type where it protects a distinct risk:
   interaction, while replacing live or nondeterministic external boundaries.
 - External-package root tests exercise the public facade as a Go consumer,
   while internal package tests own focused implementation behavior.
-- The maintained offline preparation example protects one representative
-  assembled consumer workflow without contacting a model provider.
+- The maintained offline preparation, execution, and observation examples protect distinct
+  representative assembled consumer workflows without contacting a model
+  provider.
 - Fixtures should be minimal, synthetic, versioned with the behavior they
   exercise, and free of credentials or private data.
 - Golden files are appropriate only when the complete output is intentionally
@@ -99,7 +105,7 @@ Use each test type where it protects a distinct risk:
 
 ## What deserves tests
 
-Prioritize tests for:
+To the extent the following features are present in the application, prioritize tests for:
 
 1. Public and package-level contracts.
 2. Domain rules and important invariants.
@@ -107,17 +113,29 @@ Prioritize tests for:
 4. Failure handling, cancellation, retries, recovery, and partial success.
 5. Serialization, schemas, compatibility, and round trips.
 6. Previously observed or plausible regressions.
-7. Representative integration and consumer workflows.
+7. Representative integration and end-to-end workflows.
 
-A package-level contract is behavior relied upon by another package or major collaborator, not every observable detail of a package implementation.
+A package-level contract comprises behavior relied upon by another package or major collaborator.
 
-For behavior involving **data integrity, destructive operations, compatibility, security, concurrency, idempotency, or recovery**, presume that durable tests are required unless the behavior is already credibly protected at another layer.
+Choose tests for requested behavior and established contracts. Tests must not
+introduce new restrictions, guarantees, or threat scenarios merely because they
+could be asserted. Follow the [agent policy](agents.md) when deciding whether a
+behavior belongs to the contract; current implementation behavior alone is not
+sufficient authority.
+
+For established behavior involving **data integrity, destructive operations,
+compatibility, security, concurrency, idempotency, or recovery**, favor durable
+tests for realistic failures whose consequences warrant protection. Identify
+the failure and the existing contract it would violate. These categories call
+for attention, not an automatic test inventory or permission to strengthen the
+application's guarantees. Account for protection already provided at other layers.
 
 Do not add tests merely because a function, branch, or line exists. Do not add a test when the same meaningful risk is already adequately protected elsewhere.
 
 ## Choose the right test boundary
 
-Test through the narrowest stable boundary that expresses the behavior clearly.
+Choose the narrowest stable boundary that expresses the behavior clearly and
+provides durable confidence with minimal incidental coupling.
 
 This is often the package API, but it may instead be:
 
@@ -125,30 +143,15 @@ This is often the package API, but it may instead be:
 - a package-level operation when several internal collaborators jointly produce the behavior; or
 - a larger integration boundary when correctness emerges from interaction with a real dependency.
 
-Do not force all behavior through oversized consumer-workflow tests. Do not
-test every private helper merely because it exists. Choose the boundary that
-gives durable confidence with the least incidental coupling.
-
 ## Test behavior, not implementation
 
-A test should protect a decision, contract, or invariant—not memorialize the current implementation.
+A test should protect a selected decision, contract, or invariant.
 
-Before adding or retaining a test, ask:
+A test is suspect when it primarily detects changes to private constants or
+helpers, equivalent operation ordering, incidental formatting, equivalent
+algorithms, or internal structure that preserves behavior.
 
-> What realistic defect would this test catch?
-
-A test is suspect when its main purpose is to detect that someone:
-
-- changed an internal constant;
-- renamed or split a private helper;
-- reordered equivalent internal operations;
-- changed incidental formatting;
-- replaced one correct algorithm with another; or
-- refactored internal object structure without changing behavior.
-
-Refactoring should normally require no test edits unless the refactored structure is itself part of the contract.
-
-A test can be factually correct and still have negative value. Accurately describing current behavior is not enough; the protected behavior must be important enough to justify the future friction.
+Behavioral tests should normally remain stable through internal refactoring that preserves the contract.
 
 ## Expected effects of different changes
 
@@ -165,13 +168,13 @@ A test failing is not the same as a test needing to be edited. Many tests may co
 
 ## Separate mechanism from policy
 
-Configurable thresholds and defaults must not be duplicated throughout the test suite.
+Derive expectations from test-controlled configuration and relationships.
 
-The following fragments are illustrative rather than standalone Go programs.
-Do not encode an internal concurrency limit indirectly:
+For this example, assume the selected contract rejects a request to start more
+processes than a configured limit. Do not encode its production default indirectly:
 
 ```go
-// Production policy:
+// Production default:
 const maxConcurrency = 4
 
 // Brittle test:
@@ -189,37 +192,40 @@ require.NoError(t, runner.Start(limit))
 require.ErrorIs(t, runner.Start(limit+1), ErrTooMuchConcurrency)
 ```
 
-The test should prove:
+For this selected contract, the test should prove:
 
 - the configured limit is accepted; and
 - one beyond the configured limit is rejected.
 
+Rejection is not a general requirement for concurrency control. If the selected
+contract queues excess work or limits active workers while accepting larger
+batches, test that behavior instead. Do not add rejection or a configurable
+limit solely to reproduce this example.
+
 The production default should be tested exactly only when its literal value is itself a public, operational, safety, protocol, or compatibility requirement.
 
-Apply the same rule to limits, timeouts, capacities, retry counts, and ranges: test relationships and behavior, not duplicated literals.
+Apply the same rule to limits, timeouts, capacities, retry counts, and ranges: test relationships and behavior.
 
-For concurrency limits, test both kinds of behavior when relevant:
+For established concurrency limits, distinguish these behaviors where the contract requires them:
 
-1. **Configuration enforcement:** invalid or excessive requested values are handled correctly.
+1. **Configuration handling:** values are accepted or rejected according to the selected contract.
 2. **Runtime enforcement:** observed peak concurrency never exceeds the configured limit.
 
-Use a test-controlled limit and measure the behavior relative to that limit. Do not merely assert today's default value.
+Use a test-controlled limit and measure the behavior relative to that limit.
 
-## Avoid semantic duplication across layers
+## Assign each behavior a test owner
 
-Each behavior should have a clear test owner.
+Where these layers exist, assign ownership as follows:
 
 - Parser tests own parsing cases.
 - Validator tests own validation rules.
 - Domain tests own transformations and invariants.
-- Boundary tests own external integration behavior.
+- Adapter tests own external integration behavior.
 - Orchestrator tests own coordination and failure propagation.
-- Consumer-workflow tests prove that representative assembled library use
-  works.
+- External-package root tests own the public Go facade contract.
+- Consumer-workflow tests prove that representative assembled library use works.
 
-Higher-level tests should not repeat every lower-level case. A single intentional policy change should not require unrelated edits across many test files.
-
-Tests that are individually reasonable may still be collectively redundant. Evaluate the marginal value of each additional test in light of the protection already provided by the rest of the suite.
+Give each layer its distinct responsibility and keep expectation updates localized to the contract being changed.
 
 ## Use test doubles deliberately
 
@@ -240,111 +246,78 @@ Mocks are appropriate when the contract includes facts such as:
 - an expensive API is called no more than once; or
 - a security audit event is emitted.
 
-Do not use mocks merely to isolate every object or reproduce the implementation's call graph.
-
 ## Go-specific guidance
 
-Use:
+Select techniques by behavior and risk:
 
 - table-driven tests for meaningful behavioral categories and boundaries;
 - `t.TempDir()` for real filesystem behavior;
 - `httptest.Server` for realistic HTTP interactions;
-- fuzz tests for parsers, normalization, path handling, and broad input spaces;
+- fuzz tests when exploring broad input spaces, such as parsers or path handling, adds useful protection beyond representative cases;
 - golden files only when the complete output is intentionally stable;
 - integration tests where correctness depends on component interaction; and
-- a small number of representative consumer-workflow tests.
+- a small number of representative end-to-end tests when assembled workflows expose meaningful risks not adequately covered at narrower boundaries.
 
-Avoid exact error-string assertions unless the wording is itself contractual. Prefer `errors.Is`, `errors.As`, typed errors, or structured error fields.
+Prefer `errors.Is`, `errors.As`, typed errors, or structured error fields. Use exact error-wording assertions only when the wording is contractual.
 
 At public API boundaries, prefer stable error identity, structured values, and
-the smallest semantic fragment needed to identify the failure. Do not snapshot
-complete diagnostic wording unless it is contractual.
+the smallest semantic fragment needed to identify the failure. Use complete
+diagnostic snapshots only when the wording is contractual.
 
-Golden-file updates must require an explicit local flag. Ordinary validation
-runs must never update golden files automatically, and maintainers must inspect
-the semantic diff before accepting an update.
+Golden-file updates must require an explicit local flag. Ordinary validation runs must never update golden files automatically, and reviewers must inspect the semantic diff before accepting an update.
 
-Keep tests readable and direct. Test helpers and fixture frameworks must earn their own maintenance cost; do not build elaborate test infrastructure for small or isolated needs.
+Keep tests readable and direct. Size test helpers and fixture frameworks to the maintenance benefit they provide.
 
 ## Coverage
 
-Coverage is a diagnostic, not a target.
+Use coverage to locate untested critical branches and unexpectedly weak packages. Evaluate test quality through meaningful behavioral protection and choose coverage according to risk.
 
-Use it to find untested critical branches and unexpectedly weak packages. Do not write low-value tests solely to increase a percentage, and do not infer test quality from coverage alone.
-
-Pure domain logic will often warrant higher coverage than facade wiring or
-external adapters. Uneven coverage is acceptable when it reflects risk.
-
-Increasing coverage is valuable only when the newly covered behavior protects a meaningful risk at an acceptable cost.
+Pure domain logic will often warrant higher coverage than facade wiring or external adapters. Uneven coverage is acceptable when it reflects risk.
 
 ## Regression tests
 
 A bug fix should normally include a regression test that fails before the fix and passes afterward.
 
-Retain the test when the defect could realistically recur and its consequences justify the ongoing cost. Prefer the narrowest durable test of the violated contract or invariant; do not preserve accidental implementation details from the original bug.
+Retain the test when the defect could realistically recur and its consequences justify the ongoing cost. Prefer the narrowest durable test of the violated contract or invariant.
 
-Not every historical bug requires a permanent test. If the underlying design has made recurrence impossible, the test has become redundant, or a stronger invariant test now subsumes it, remove or consolidate it.
+Remove or consolidate a test when the underlying design has made recurrence impossible, its protection is redundant, or a stronger invariant test subsumes it.
 
 ## Deleting or rewriting tests
 
-Tests are maintained code, not permanent historical artifacts.
-
-Delete or rewrite a test when its maintenance cost exceeds the confidence it provides.
+Delete or rewrite tests when maintenance cost exceeds their continuing
+protective value.
 
 Strong candidates include tests that:
 
 - require updates after harmless internal changes;
-- directly assert private constants without protecting a real contract;
-- duplicate the same policy across several layers;
+- assert incidental private constants or snapshot large amounts of incidental output;
 - verify mock choreography rather than outcomes;
-- snapshot large amounts of incidental output;
-- test trivial private helpers already exercised through stable package behavior;
-- protect risks already covered more effectively elsewhere;
+- duplicate policy across layers, retest trivial helpers covered by package
+  behavior, or protect risks covered more effectively elsewhere;
 - are flaky, misleading, obsolete, or disproportionately expensive to diagnose; or
 - no longer correspond to a plausible failure mode.
 
-Several brittle tests may encode one genuine requirement. Replace them with one durable behavior-level or invariant test rather than preserving all of them.
-
-Deleting a low-value test can improve the quality of the suite by reducing noise, maintenance burden, and friction around legitimate change.
+Several brittle tests may encode one genuine requirement. Consolidate them into one durable behavior-level or invariant test.
 
 ## Reviewing a proposed test
 
-Use the following questions when the value, boundary, or durability of a proposed test is not self-evident. Significant test additions should be reviewable against them, but written answers are not required for every routine test.
+Use the following questions when a proposed test needs closer evaluation. Significant test additions should be reviewable against them; written answers are optional for routine tests.
 
-1. What realistic defect would it catch?
-2. How likely is that defect?
-3. How consequential would it be?
-4. Is the behavior already protected elsewhere?
-5. At which layer should this behavior be owned?
-6. Does the test assert a durable contract or an incidental implementation detail?
-7. Could the implementation be refactored without changing the behavior and without editing this test?
-8. What should cause this test to fail?
-9. What legitimate changes should not cause this test to fail?
-10. What ongoing maintenance, execution, and diagnostic cost will the test impose?
-11. Is there a smaller or more direct test that protects the same risk?
-
-Do not add the test when its expected lifetime cost exceeds its expected protective value.
-
-When deciding not to test plausible behavior, record or be able to explain why the risk is low, already protected, obvious, reversible, or cheaper to detect elsewhere.
+1. Which requested behavior or established contract does it protect, and what realistic defect would violate it?
+2. How likely and consequential is that defect, and is it already protected elsewhere?
+3. What is the narrowest stable boundary that can test it clearly?
+4. Would a correct internal refactor or a change to an incidental default require test edits?
+5. Does its confidence justify its maintenance, execution, and diagnostic cost, or would a smaller test suffice?
 
 ## Definition of sufficient
 
 A test suite is sufficient when:
 
-- important contracts and invariants are protected;
-- meaningful boundaries and failure modes are exercised;
-- realistic and consequential regressions are credibly protected against silent recurrence;
-- behavior involving data integrity, destructive operations, compatibility, security, concurrency, idempotency, and recovery is credibly protected;
-- important external boundaries have realistic integration coverage;
-- representative complete workflows are tested;
-- failures provide useful signal rather than redundant noise;
-- legitimate internal changes usually do not require test edits; and
+- important requested behavior and established contracts are protected against realistic, consequential failures;
+- boundaries and component interactions have coverage where they introduce meaningful risks not protected elsewhere;
+- failures provide useful, distinct signals;
+- tests usually remain stable through legitimate internal changes; and
 - additional tests would mostly repeat existing protection or preserve inconsequential implementation details.
 
-Sufficiency is a risk judgment, not a coverage percentage or test count.
-Reassess it as the library, its consumers, and the consequences of failure
-evolve.
-
-The governing rule is:
-
-> Test heavily where failure is consequential, subtle, or difficult to detect after the fact. Test lightly where failure is obvious, reversible, and inexpensive—and retain no test whose lifetime cost exceeds the confidence it provides.
+Reassess sufficiency as the application, its users, and the consequences of
+failure evolve.

docs/release.md

@@ -1,140 +1,97 @@
 # Release Procedure
 
-## Release Model
+This runbook implements the [release policy](policy/release.md). A successful
+push of the selected annotated tag to origin completes the release. Never wait
+for CI to finish or succeed.
 
-Promptkit publishes a Go library through source commits and semantic Go module
-tags. It does not publish runnable binaries or binary packages and does not
-currently use hosted CI. The release maintainer performs and records the
-required validation.
+## Prepare The Candidate
 
-The first planned release is `v0.1.0`. Do not create that tag until the
-framework has been extracted and the resulting public library has passed this
-procedure. Later tags use the `vMAJOR.MINOR.PATCH` form. While Promptkit remains
-pre-`v1`, release notes must identify intentional public API changes and any
-consumer migration required by them.
+Required tools are Git, Go with race-detector support, POSIX shell, and Python
+3. Publication requires push access to origin. Work from the repository root.
 
-## Prepare The Release
+Select an unused version and create `docs/releases/<version>.md` using the
+[required structure](policy/release.md#release-documentation). Describe
+compatibility impact and consumer actions and update affected canonical docs.
+For catalog updates, record selected catalog versions and any consumer action,
+linking to the catalog policy rather than repeating its contracts.
 
-Work from a clean checkout of the intended release commit, outside any Go
-workspace and without a local module replacement. Confirm the source commit is
-already published through the normal branch workflow.
+Follow the [OSS policy](policy/oss.md) when preparing licensing and attribution
+changes. Each new note must end with the following navigation, replacing
+`vMAJOR.MINOR.PATCH` with the selected release tag:
 
-From the Promptkit repository root, verify the checkout:
+```markdown
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/promptkit/src/tag/vMAJOR.MINOR.PATCH/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/promptkit/src/tag/vMAJOR.MINOR.PATCH/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/promptkit/src/tag/vMAJOR.MINOR.PATCH/docs/oss/attribution.md)
+```
+
+Check these file paths against the candidate; a future tag need not resolve
+remotely during preparation. The annotated tag derives from this same note,
+including its footer. Promptkit publishes no separate hosted release body or
+download page. If such a channel is deliberately introduced, reuse the note
+and preserve its footer. No extra network checks, artifacts, or approval gates
+are introduced, and published notes are not retrofitted.
+
+Retire completed roadmaps, preserving planned or deferred work and repairing
+links. This is housekeeping, not a separate approval gate. Review changes
+through the ordinary development workflow, commit them, and push main to
+origin. No repeated release-specific diff review is required.
+
+## Validate And Publish
+
+Run the following with the chosen unused version (replace the placeholder):
 
 ```sh
-gowork=$(go env GOWORK)
-test -z "$gowork" || test "$gowork" = off
-test -z "$(git status --short)"
-git fetch --tags origin
+./scripts/release.sh vMAJOR.MINOR.PATCH
 ```
 
-Confirm the module and root package metadata:
+The [publication script](../scripts/release.sh) checks a clean, synchronized
+main candidate, the version and unused tag, and the release note's title and
+required headings. It runs the [local checks](../scripts/release-check.sh)
+once, rechecks candidate identity and publication state, generates the
+annotation from the committed note plus the validated commit, and pushes only
+the selected annotated tag.
+
+There is no separate tag-message authoring, example-output inspection,
+metadata inspection, or human sign-off. Compatibility and release-note content
+remain ordinary editorial responsibilities. Development validation is useful
+but does not require a second full run before invoking the publication script.
+
+The script stops successfully after the tag push. CI completion, CI success,
+remote read-back, and Go module availability are not release completion gates.
+Do not wait or poll for them. Provider probes and inference calls are never
+part of release validation.
+
+## Catalog Profile Compatibility
+
+The [release policy](policy/release.md#catalog-profile-compatibility) owns the
+catalog compatibility boundary. This heading preserves older incoming links.
+
+## Failure Recovery
+
+If local checks fail, fix the candidate, commit and push changes, then rerun
+the publication command. It never automatically removes a tag.
+
+If a push fails or its result is ambiguous, set `RELEASE_VERSION` to the
+attempted version and inspect origin before retrying:
 
 ```sh
-go list -m -f '{{.Path}} {{.GoVersion}}'
-go list -f '{{.Name}} {{.ImportPath}}' .
+git ls-remote --tags origin "refs/tags/$RELEASE_VERSION" "refs/tags/$RELEASE_VERSION^{}"
+git rev-parse "refs/tags/$RELEASE_VERSION" "refs/tags/$RELEASE_VERSION^{}"
 ```
 
-The output must be:
+Matching remote tag and peeled commit values confirm publication, even if the
+push command reported an error. If the remote query fails, publication status
+is still unknown. Do not delete or recreate the local tag until absence on
+origin is confirmed. Once confirmed unpublished, an unsuccessful attempt's
+local tag can be removed and the publication command rerun. Never overwrite
+a published tag.
 
-```text
-gitea.maximumdirect.net/eric/promptkit 1.25.5
-promptkit gitea.maximumdirect.net/eric/promptkit
-```
-
-Run the same default Go validation required by the
-[development guide](development.md):
-
-```sh
-go test ./...
-go test -race ./...
-go vet ./...
-go build ./...
-go run ./examples/go-library/prepare
-```
-
-Check every tracked Go file and repository whitespace:
-
-```sh
-gofmt -l $(git ls-files '*.go')
-git diff --check
-```
-
-The formatting command must produce no paths. Follow every maintained Markdown
-link and confirm its target exists. Review the repository for generated
-binaries, test or coverage output, credentials, template residue, and other
-files that do not belong in source control.
-
-Confirm that no workspace override is tracked and that `go.mod` contains no
-`replace` directive:
-
-```sh
-git ls-files go.work go.work.sum
-rg -n '^replace\b' go.mod
-```
-
-Both commands must produce no output. Re-run `git status --short` and require a
-clean result after every validation and review check.
-
-## Create And Publish The Tag
-
-Choose the semantic version from the intended compatibility change. Record the
-release commit before tagging:
-
-```sh
-release_version=v0.1.0
-release_commit=$(git rev-parse HEAD)
-```
-
-Replace the example version for later releases and keep both values in the same
-shell for the remaining commands. Confirm the tag does not already exist
-locally or remotely:
-
-```sh
-test -z "$(git tag --list "$release_version")"
-test -z "$(git ls-remote --tags origin "refs/tags/$release_version")"
-```
-
-Create an annotated tag whose message identifies the release and records that
-the documented validation passed for the tagged commit:
-
-```sh
-git tag --annotate "$release_version" \
-  --message "Promptkit $release_version; documented validation passed for $release_commit"
-```
-
-Inspect the tag before publication:
-
-```sh
-git show --no-patch --decorate "$release_version"
-test "$(git rev-list -n 1 "$release_version")" = "$release_commit"
-```
-
-Publish the tag without relying on a hosting-provider-specific release
-interface:
-
-```sh
-git push origin "refs/tags/$release_version"
-```
-
-## Verify Publication
-
-Confirm that the remote tag object matches the local annotated tag and still
-resolves to the intended source commit:
-
-```sh
-remote_tag=$(git ls-remote --tags origin "refs/tags/$release_version" | awk '{print $1}')
-test "$remote_tag" = "$(git rev-parse "refs/tags/$release_version")"
-test "$(git rev-list -n 1 "refs/tags/$release_version")" = "$release_commit"
-```
-
-Promptkit must publish the required tag before Scriptorium or another consumer
-publishes a release that depends on that version. Released consumer modules
-must not use a local replacement or unpublished Promptkit revision.
+CI or module-resolution problems may be investigated separately; temporary
+service, network, or authentication failures do not require another release.
+Only an actual defect requiring changes to published contents warrants a new
+appropriate version. See the [recovery policy](policy/release.md#immutability-and-failure-recovery).
 
 ## Policy Changes
 
-Document and approve a durable policy change before introducing hosted
-automation, binary artifacts, or different release governance. Update this
-procedure in the same change so maintainers do not rely on hidden release
-requirements.
+Update the policy and this procedure together when changing release governance.
+Consumers own their dependency-availability and release checks; their readiness
+does not delay completion of a Promptkit release.

docs/releases/v0.10.0.md

@@ -0,0 +1,44 @@
+# Promptkit v0.10.0
+
+This supplemental guide summarizes the `v0.10.0` changes and migration needs.
+The annotated tag remains the authoritative release record.
+
+## Transition Summary
+
+`v0.10.0` adopts independently versioned OpenRouter and Rakestrawhome catalog
+modules whose external profile data can change between catalog releases. It
+also introduces the maintained literal names
+`promptkit-openrouter-standard` and `promptkit-openrouter-auto`.
+
+The public package now delegates assembly to an internal engine while retaining
+the existing Go API. This refactor requires no consumer code changes.
+
+This release selects OpenRouter `v2.20260922.1` and Rakestrawhome
+`v2.20260922.0`; their exact inventories are linked from the
+[format reference](../formats.md#external-profile-inventories).
+
+The maintained names provide continuity only within the catalog versions
+selected and tested by a Promptkit release and when consumers do not override
+the name or its base. Their current selections may change. External catalog
+profile IDs can be removed, renamed, or modified, so an application that
+selects one directly may need to update its configuration when upgrading.
+
+## Consumer Migration
+
+Before upgrading, review every profile ID used by prompts, requests, and
+application-owned inheritance. Choose a maintained name, accept an external
+catalog profile's volatility, or define a complete application-owned profile
+when the application must control its target and settings. An alias that
+inherits from an external base is not a frozen copy.
+
+In particular, the selected OpenRouter catalog removes `deepseek-3-2`,
+`deepseek-4-flash`, and `deepseek-4-pro`. Consumers using those IDs must choose
+an available profile or supply their own complete definition; the new
+`deepseek-flash-latest` and `deepseek-pro-latest` profiles are not automatic
+aliases and need not preserve the previous settings.
+
+See the [release policy](../release.md#catalog-profile-compatibility) for the
+compatibility boundary, the [format reference](../formats.md#built-in-profile-catalog)
+for current Promptkit-owned definitions and selected external inventories, and
+the [consumer guide](../consumers/pkg-promptkit.md#choose-a-profile-ownership-model)
+for configuration choices.

docs/releases/v0.11.0.md

@@ -0,0 +1,76 @@
+# Promptkit v0.11.0
+
+This release adds reliable, observable model execution and changes Promptkit's
+license to LGPL-3.0-or-later.
+
+## Summary
+
+- Built-in model calls can recover from selected transient HTTP failures.
+- Optional execution observations report attempts, timing, outcomes, and known
+  token usage, including work completed before a run fails.
+- Public errors distinguish transport failures, malformed responses, and retry
+  exhaustion without parsing diagnostic text.
+
+## Compatibility
+
+The built-in client now defaults to two additional transient attempts. This can
+increase latency, request counts, and cost; retries do not guarantee exactly-once
+generation. Injected `LLMClient` implementations retain their own retry policy
+and are not automatically replayed. Existing generation timeouts apply per
+attempt, while the caller context governs the complete operation. See the
+[provider integration contract](../integrations/openai-compatible-chat.md).
+
+Public retry and observation controls are additive. Existing successful-result
+usage semantics remain unchanged, and operational failures still return no
+partial `RunResult`. Observations distinguish unknown usage from reported zero;
+they are not a complete billing ledger. See the
+[consumer guide](../consumers/pkg-promptkit.md) and
+[observation GoDoc](../../observations.go).
+
+Promptkit is now licensed under LGPL-3.0-or-later. Review the
+[license summary](../../README.md#license), [LGPL text](../../LICENSE), and
+[accompanying GPL text](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.0/COPYING) before adoption or distribution.
+Previously published releases and dependency licenses are unchanged.
+
+## Upgrade
+
+Update the dependency:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.11.0
+```
+
+To retain single-attempt behavior for built-in generation, set
+`Config.TransientRetries` to a pointer to zero. `RunRequest.TransientRetries`
+can override the engine choice per request. Review any existing application or
+HTTP-transport retry loops to avoid unintentionally multiplying attempts.
+Transient retries and structural repairs have separate budgets; provide a
+caller deadline when a total execution time limit is needed.
+
+Observation is opt-in through `RunRequest.Observer`, including for prepared
+execution. Callbacks are synchronous; shared observers must support concurrent
+runs. Injected clients can supply `GenerateResponse.UsagePresence` to explicitly
+report known zero counts. No observer or usage-presence changes are required
+for existing consumers. See the [consumer guide](../consumers/pkg-promptkit.md)
+for adoption and the [offline example](../../examples/go-library/observe/main.go)
+for a structured proposal-and-assessment workflow.
+
+## Changes
+
+- Centralized built-in retry coordination with cancellable backoff and provider
+  retry timing. Retries and structural repair share existing backend capacity;
+  backoff releases active permits without releasing logical run admission.
+- Added `ErrTransport`, `ErrMalformedResponse`, `ErrRetriesExhausted`, and
+  `RetryExhaustedError`, retaining applicable underlying error identities.
+- Added request-scoped lifecycle observations and presence-aware token accounting
+  for ordinary and prepared execution, without recording prompt/response bodies.
+- Isolated delegated operations' observation state and made injected-client
+  attempt classifications consistent with terminal classifications.
+- Added an offline observation example and regression coverage for retry,
+  repair, capacity, error, and observation interactions.
+- Adopted LGPL-3.0-or-later and streamlined the documented local release process.
+
+Backend catalog selections are unchanged from v0.10.0: OpenRouter
+`v2.20260922.1` and Rakestrawhome `v2.20260922.0`. See the
+[catalog compatibility policy](../policy/release.md#catalog-profile-compatibility)
+and [profile inventories](../formats.md#external-profile-inventories).

docs/releases/v0.11.1.md

@@ -0,0 +1,43 @@
+# Promptkit v0.11.1
+
+This patch updates the maintained catalogs to MIT-licensed releases and
+improves licensing documentation.
+
+## Summary
+
+Both OpenRouter and Rakestrawhome catalogs now use `v2.20260926.0`. These
+catalog releases change licensing and documentation only; their profiles,
+backend definitions, and Go code are unchanged.
+
+## Compatibility
+
+No public API, runtime behavior, or profile changes are introduced.
+Promptkit remains LGPL-3.0-or-later; the catalogs are now MIT-licensed.
+See the [project grant](../../COPYRIGHT),
+[component attribution](../oss/attribution.md), and
+[catalog compatibility policy](../policy/release.md#catalog-profile-compatibility).
+
+## Upgrade
+
+Update the module dependency:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.11.1
+```
+
+No code or configuration migration is required from v0.11.0.
+Consumers upgrading from earlier versions should also read the
+[v0.11.0 migration guide](v0.11.0.md).
+
+## Changes
+
+- Adopt the MIT-licensed catalog releases and update inventory links.
+- Add centralized attribution and dependency license texts.
+- Separate the project grant into COPYRIGHT and consolidate the LGPLv3 and
+  incorporated GPLv3 texts in LICENSE, replacing the separate COPYING file.
+- Align documentation ownership and future release navigation with the
+  [OSS policy](../policy/oss.md), without adding release gates.
+- Repair the historical v0.11.0 GPL-text link and retire the completed
+  licensing roadmap.
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.1/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.1/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.1/docs/oss/attribution.md)

docs/releases/v0.11.2.md

@@ -0,0 +1,38 @@
+# Promptkit v0.11.2
+
+This patch aligns repository policies with the current standard and clarifies
+licensing and attribution for the copied policy documents.
+
+## Summary
+
+The update adds policy provenance, selective contributor reading guidance, and
+consistent upstream policy language while preserving Promptkit-specific rules.
+
+## Compatibility
+
+No public API, runtime behavior, dependency, or catalog changes are introduced.
+Promptkit remains LGPL-3.0-or-later. The [project grant](../../COPYRIGHT)
+identifies the separate CC-BY-SA-4.0 scope for copied or adapted policy material;
+the [attribution notices](../oss/attribution.md) identify the affected documents.
+The existing release checks and successful-tag-push completion point are unchanged.
+
+## Upgrade
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.11.2
+```
+
+No code or configuration migration is required from v0.11.1.
+
+## Changes
+
+- Align adopted policies with Standard Repository Policies while retaining
+  library-specific requirements and deliberate local decisions.
+- Add per-document upstream source links and the
+  [policy-set provenance document](../policy/meta.md).
+- Add selective policy reading to the [contributor guide](../development.md)
+  and update agent orientation.
+- Standardize factual attribution entries and identify copied-policy licensing.
+- Retire the completed policy-alignment roadmap.
+
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.2/COPYRIGHT) | [LICENSE](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.2/LICENSE) | [ATTRIBUTION](https://gitea.maximumdirect.net/eric/promptkit/src/tag/v0.11.2/docs/oss/attribution.md)

docs/releases/v0.2.0.md

@@ -0,0 +1,243 @@
+# Promptkit v0.2.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.1.0` to `v0.2.0`. The annotated `v0.2.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.2.0` adds three major capabilities:
+
+- an engine-scoped registry for reusable OpenAI-compatible backend
+  definitions;
+- bounded, backend-specific run admission and model-generation concurrency;
+  and
+- direct per-run session IDs and tri-state reasoning-effort overrides.
+
+Existing endpoint-only profiles remain supported. Consumers can adopt backend
+registration and runtime overrides incrementally rather than rewriting all
+profiles during the upgrade.
+
+## Compatibility At A Glance
+
+Promptkit remains pre-`v1`, and this minor release includes source-level and
+behavioral changes that deserve review.
+
+| Area | `v0.1.0` consumer impact |
+| --- | --- |
+| Endpoint-only profiles | Continue to work without migration. |
+| Built-in profiles | Continue to use OpenRouter and `OPENROUTER_API_KEY`; they now select the built-in `openrouter` backend. |
+| Custom backends | Registration is optional. Existing profiles may keep their endpoint and credential configuration. |
+| Reasoning overrides | String assignments must migrate to the new pointer field. |
+| `RunRequest.Metadata` | Removed; delete assignments to this field. |
+| OpenRouter concurrency | Now limited to 16 active generations with waiting capacity of 1024 per engine. |
+| Public JSON | `v0.2.0` formalizes supported JSON representations; consumers relying on `v0.1.0` encodings should review the notes below. |
+| Unkeyed public struct literals | May require updates because fields were added. Keyed literals are recommended. |
+
+## Upgrade
+
+After the `v0.2.0` tag is published, update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.2.0
+go mod tidy
+```
+
+Run the consuming project's ordinary tests and race-enabled tests after the
+upgrade, especially if it calls one engine concurrently or persists Promptkit
+JSON values.
+
+## Backend Registry
+
+Consumers may now register reusable OpenAI-compatible backend definitions with
+`WithBackend`, then select them by ID from file-backed or in-memory profiles.
+A backend can supply its endpoint, API-key environment-variable name,
+request-wide extra parameters, and optional capacity policy.
+
+Registrations are immutable and belong to one engine. Consumer registrations
+can add new IDs but cannot replace Promptkit's reserved `openrouter` backend.
+Profiles that select a backend may still override its endpoint without losing
+the backend's routing or capacity identity.
+
+An existing endpoint-only in-memory profile remains valid:
+
+```go
+promptkit.Profile{
+	ID:       "local",
+	Endpoint: "http://localhost:8000/v1",
+	Model:    "example-model",
+}
+```
+
+Adopting the registry is optional and can be done when several profiles should
+share connection or capacity settings:
+
+```go
+engine, err := promptkit.NewEngine(
+	promptkit.Config{PromptDir: "prompts"},
+	promptkit.WithBackend(promptkit.Backend{
+		ID:        "local",
+		Endpoint:  "http://localhost:8000/v1",
+		APIKeyEnv: "LOCAL_LLM_API_KEY",
+	}),
+	promptkit.WithProfiles(promptkit.Profile{
+		ID:        "local-summary",
+		BackendID: "local",
+		Model:     "example-model",
+	}),
+)
+```
+
+See the
+[local-endpoint consumer guide](../consumers/pkg-promptkit.md#configure-a-local-openai-compatible-endpoint)
+for task-oriented usage. The
+[`Backend` and `WithBackend` GoDoc](../../backends.go) owns exact registration,
+validation, copying, defaulting, and uniqueness semantics. The
+[framework format reference](../formats.md) owns the profile `backend` field
+and execution precedence.
+
+## Backend-Specific Concurrency
+
+Each registered backend may now define:
+
+- an active model-generation limit; and
+- a bounded number of additional admitted `Run` calls.
+
+Promptkit owns scheduling for both its built-in model client and an injected
+`LLMClient`. `Run` remains synchronous: an admitted caller waits for its
+ordinary result, while a call beyond the bounded admission capacity returns
+`ErrCapacityExceeded`. Capacity is engine-local and keyed by backend ID.
+Endpoint-only profiles and custom backends without a configured limit remain
+unlimited.
+
+The built-in OpenRouter backend now permits 16 active generations and 1024
+additional admitted calls per engine. Applications that can exceed this bound
+should handle capacity exhaustion separately from provider and request
+failures:
+
+```go
+result, err := engine.Run(ctx, request)
+if errors.Is(err, promptkit.ErrCapacityExceeded) {
+	// Apply application-specific overload or retry policy.
+}
+```
+
+Promptkit does not prescribe retries or map this error to an HTTP status. See
+the
+[concurrency consumer guidance](../consumers/pkg-promptkit.md#limit-backend-concurrency)
+and the [`Backend` GoDoc](../../backends.go) for the canonical configuration
+contract. Runtime behavior and public error identities belong to the
+[`Engine.Run` GoDoc](../../engine.go).
+
+## Per-Run Session IDs
+
+`RunRequest.SessionID` can now supply a consumer-managed correlation ID for one
+`Prepare` or `Run` invocation. A nonblank direct value overrides the prompt's
+session template and is exposed in prepared values, results, injected-client
+requests, and provider observability. Session IDs should therefore be stable,
+non-secret values.
+
+```go
+result, err := engine.Run(ctx, promptkit.RunRequest{
+	PromptID: "meeting.summary",
+	SessionID: "conversation-42",
+})
+```
+
+The built-in OpenAI-compatible client sends a nonempty effective session as the
+top-level `session_id` request-body field, not as an `x-session-id` header. See
+the
+[session and reasoning consumer guide](../consumers/pkg-promptkit.md#set-a-per-run-session-and-reasoning),
+the [`RunRequest` GoDoc](../../types.go), and the
+[OpenAI-compatible request contract](../integrations/openai-compatible-chat.md#request-body)
+for exact normalization, length, exposure, and wire behavior.
+
+## Per-Run Reasoning Effort
+
+`ExecutionTargetOverride.ReasoningEffort` changed from `string` to `*string` so
+one request can distinguish inheritance, replacement, and explicit clearing.
+
+Update a `v0.1.0` override like this:
+
+```go
+// v0.1.0
+Execution: &promptkit.ExecutionTargetOverride{
+	ReasoningEffort: "high",
+}
+```
+
+to:
+
+```go
+// v0.2.0
+reasoning := "high"
+Execution: &promptkit.ExecutionTargetOverride{
+	ReasoningEffort: &reasoning,
+}
+```
+
+The three states are:
+
+- `nil` inherits the selected profile's value;
+- a pointer to a nonblank string replaces it for that invocation; and
+- a pointer to an empty or whitespace-only string clears it for that
+  invocation.
+
+This allows consumers to consolidate profiles that differed only by reasoning
+effort. The [`ExecutionTargetOverride` GoDoc](../../types.go) owns the exact
+override contract.
+
+## Other Migration Notes
+
+### Remove `RunRequest.Metadata`
+
+`RunRequest.Metadata` is no longer part of the public request. Remove any
+assignment to that field. Use application-owned state keyed by `RunResult.RunID`
+or a direct `SessionID` when correlation is needed; these identifiers have
+different purposes, so choose according to the application's lifecycle.
+
+### Review Persisted JSON
+
+`v0.2.0` defines stable JSON representations for the public result, artifact,
+execution, validation, and model-client values listed in the
+[package documentation](../../doc.go). Consumers that treated `v0.1.0`
+reflection-derived encodings as stable should update fixtures and stored-data
+adapters.
+
+In particular:
+
+- `RunResult` encodes elapsed time as integer milliseconds in `duration_ms`
+  instead of encoding `time.Duration` under `duration`;
+- result JSON can include the new `session_id` and `selected_backend_id`
+  fields;
+- execution-target JSON can include `backend_id`; and
+- artifact and target-presence fields now use their documented lower-case
+  names.
+
+The `v0.2.0` `RunResult` decoder reads `duration_ms`; it does not translate a
+persisted `v0.1.0` `duration` field. Transform old payloads before decoding
+when preserving their elapsed duration matters.
+
+### Prefer Keyed Struct Literals
+
+New fields were added to several public structs. Replace positional composite
+literals with keyed literals so future additive fields do not cause another
+source migration.
+
+## Migration Checklist
+
+- Update the module dependency and run the consumer's tests.
+- Change reasoning overrides from strings to pointers.
+- Remove uses of `RunRequest.Metadata`.
+- Review unkeyed Promptkit struct literals.
+- Decide whether shared endpoints should move into registered backends.
+- If using built-in OpenRouter profiles at high concurrency, handle
+  `ErrCapacityExceeded` and review the new engine-local bound.
+- Review stored JSON, fixtures, and downstream decoders.
+- Optionally replace profile-specific session or reasoning variants with
+  per-run overrides.
+
+For complete consumer workflows, use the
+[package consumer guide](../consumers/pkg-promptkit.md) and maintained
+[offline execution example](../../examples/go-library/run/main.go).

docs/releases/v0.3.0.md

@@ -0,0 +1,74 @@
+# Promptkit v0.3.0
+
+This supplemental changelog summarizes the consumer-facing changes from
+`v0.2.0` to `v0.3.0`. The annotated `v0.3.0` tag is the authoritative release
+record. Exact current contracts belong to the linked GoDoc and durable
+documentation.
+
+## Summary
+
+`v0.3.0` adds a concise way to register the common local OpenAI-compatible
+backend configuration:
+
+- `BackendLocal` provides the conventional, non-reserved backend ID `"local"`;
+  and
+- `LocalBackend` constructs an ordinary `Backend` from an endpoint and
+  concurrency limit.
+
+The helper is explicit and additive. It does not pre-register a backend, read
+environment variables, select a model, or replace the complete `Backend`
+configuration interface.
+
+## Compatibility
+
+Existing `v0.2.0` consumers require no migration. Endpoint-only profiles,
+complete custom `Backend` values, the built-in OpenRouter backend, and existing
+registrations using the literal ID `"local"` continue to work unchanged.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.3.0
+go mod tidy
+```
+
+Run the consuming project's ordinary tests and race-enabled tests after the
+upgrade.
+
+## Configure A Local Backend
+
+Register the convenience value through the existing `WithBackend` option and
+select it from one or more profiles:
+
+```go
+engine, err := promptkit.NewEngine(
+	promptkit.Config{PromptDir: "prompts"},
+	promptkit.WithBackend(
+		promptkit.LocalBackend("http://localhost:8000/v1", 2),
+	),
+	promptkit.WithProfiles(promptkit.Profile{
+		ID:        "local-summary",
+		BackendID: promptkit.BackendLocal,
+		Model:     "example-model",
+	}),
+)
+```
+
+Use an endpoint-only profile when shared backend identity and capacity policy
+are unnecessary. Continue to use a complete keyed `Backend` value for custom
+IDs, authentication, extra request parameters, explicit queue capacity, or
+multiple local endpoints.
+
+See the
+[local-endpoint consumer guide](../consumers/pkg-promptkit.md#configure-a-local-openai-compatible-endpoint)
+for task-oriented configuration choices. The
+[`BackendLocal`, `LocalBackend`, and `WithBackend` GoDoc](../../backends.go)
+owns their exact construction, registration, validation, and concurrency
+semantics.
+
+## Consumer Action
+
+None. Adopt the convenience constructor when it simplifies local endpoint
+configuration.

docs/releases/v0.4.0.md

@@ -0,0 +1,189 @@
+# Promptkit v0.4.0
+
+This supplemental changelog and adoption guide summarizes the consumer-facing
+changes from `v0.3.0` to `v0.4.0`. The annotated `v0.4.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.4.0` adds four complementary capabilities:
+
+- opaque prepared-execution handles for preparing once, inspecting safe
+  details, and executing the same frozen snapshot;
+- exact prompt-definition inspection without profile resolution or execution;
+- exact profile inspection without selecting a prompt or checking credential
+  availability; and
+- structured backend identity on engine admission-capacity rejection.
+
+These APIs let consumers perform more precise preflight work and retain useful
+operational context without reproducing Promptkit's internal resolution logic.
+
+## Compatibility
+
+The release is additive for `v0.3.0` consumers. Existing uses of `Prepare`,
+`Run`, backend registration, endpoint-only profiles, local-backend helpers,
+runtime overrides, public JSON values, and error sentinels continue to work
+without migration.
+
+Capacity rejection now returns a structured error while continuing to match
+`ErrCapacityExceeded` through `errors.Is`. Error-string wording and direct
+sentinel equality were not public contracts.
+
+The new inspection values, capacity error, and prepared-execution handle do not
+have stable JSON representations. `PreparedExecution.Details` returns the
+existing stable `PreparedRun` value.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.4.0
+go mod tidy
+```
+
+Run the consuming project's ordinary and race-enabled tests after upgrading.
+No source migration is required.
+
+## Prepare Once And Execute The Same Snapshot
+
+Consumers that need to persist preparation details before generation can now
+prepare an opaque, engine-bound execution:
+
+```go
+prepared, err := engine.PrepareExecution(ctx, request)
+if err != nil {
+	// Handle preparation failure.
+}
+defer prepared.Discard()
+
+details := prepared.Details()
+// Persist a consumer-selected, appropriately protected preparation record.
+
+result, err := engine.RunPrepared(ctx, prepared)
+```
+
+Preparation freezes the selected sources, rendered messages, effective
+settings, input content, structured-output metadata, and validation resources
+needed by execution. `Details` returns a fresh, caller-owned,
+credential-redacted `PreparedRun`.
+
+A handle belongs to its creating engine and permits one execution attempt.
+`RunPrepared` consumes that attempt on success and on operational failure.
+`Discard` is idempotent and releases an unclaimed handle's execution-only
+state. Consumers should discard handles they will not execute, particularly
+when a direct request API key may be retained privately until claim or
+discard.
+
+Prepared execution does not reserve backend admission during preparation.
+Credential availability and backend admission are checked when execution
+begins. The execution context is independent of the preparation context.
+
+See the
+[prepared-execution consumer guide](../consumers/pkg-promptkit.md#prepare-now-and-execute-the-same-snapshot-later),
+the [`PreparedExecution` GoDoc](../../prepared_execution.go), and the
+[`Engine.PrepareExecution` and `Engine.RunPrepared` GoDoc](../../engine.go)
+for the exact lifecycle, ownership, cancellation, capacity, timing, and
+failure contracts.
+
+## Inspect A Prompt
+
+`Engine.InspectPrompt` resolves one prompt ID and optional version through the
+engine's configured prompt source:
+
+```go
+inspection, err := engine.InspectPrompt(ctx, "report.summary", "")
+```
+
+The result includes prompt identity, the opaque prompt hash, declared default
+profile ID, declared input metadata, and normalized output contract. It
+structurally loads the selected definition and referenced message content but
+does not resolve a profile, load schemas or artifacts, render templates,
+reserve capacity, or contact a model.
+
+Use inspection for exact configuration checks and metadata discovery. Use
+`PrepareExecution` rather than relying on a prior inspection when later
+execution must freeze one exact source state, because filesystem-backed
+inspection is only a point-in-time lookup.
+
+See the
+[prompt-inspection consumer guide](../consumers/pkg-promptkit.md#inspect-a-prompt-before-preparation)
+and [`Engine.InspectPrompt` GoDoc](../../engine.go) for exact selection,
+ownership, and error behavior.
+
+## Inspect A Profile
+
+`Engine.InspectProfile` resolves one explicit profile independently of a
+prompt:
+
+```go
+inspection, err := engine.InspectProfile(ctx, "report-production")
+```
+
+The result includes the resolved effective execution target and whether a
+later request must provide a direct credential. Environment-variable names may
+be reported, but inspection does not read credential values or require the
+named variable to be populated.
+
+Inspection applies the engine's profile source precedence and resolves any
+selected backend. It does not load a prompt, render content, reserve capacity,
+or contact a model.
+
+See the
+[profile-inspection consumer guide](../consumers/pkg-promptkit.md#inspect-a-profile-before-prompt-work)
+and [`Engine.InspectProfile` GoDoc](../../engine.go) for the exact resolution,
+credential, ownership, and error contracts.
+
+## Identify Capacity-Rejected Backends
+
+Calls rejected at Promptkit's bounded engine admission boundary continue to
+match `ErrCapacityExceeded`. Consumers can additionally obtain the selected
+registered backend ID without parsing diagnostic text:
+
+```go
+result, err := engine.Run(ctx, request)
+if errors.Is(err, promptkit.ErrCapacityExceeded) {
+	var capacityErr *promptkit.CapacityError
+	if errors.As(err, &capacityErr) {
+		// Record capacityErr.BackendID using application-owned diagnostics.
+	}
+
+	// Apply application-owned overload or retry policy.
+}
+```
+
+The structured error applies to `Run` and `RunPrepared` admission rejection.
+It does not represent provider throttling, quota exhaustion, cancellation
+while waiting for generation capacity, or another model-client failure.
+Promptkit does not prescribe retry timing or transport status mapping.
+
+See the
+[error-handling consumer guide](../consumers/pkg-promptkit.md#handle-errors),
+the [`CapacityError` GoDoc](../../capacity_error.go), and the
+[`ErrCapacityExceeded` GoDoc](../../engine.go) for the canonical contracts.
+
+## Public API Additions
+
+The release adds:
+
+- `Engine.PrepareExecution`;
+- `Engine.RunPrepared`;
+- `PreparedExecution`, including `Details`, `Discard`, `String`, and
+  `GoString`;
+- `Engine.InspectPrompt`;
+- `PromptInspection`;
+- `PromptInputDefinition`;
+- `Engine.InspectProfile`;
+- `ProfileInspection`; and
+- `CapacityError`.
+
+No public API was removed.
+
+## Consumer Action
+
+None. Existing `v0.3.0` workflows may upgrade without adopting the new APIs.
+
+Consumers that adopt prepared execution should discard unused handles.
+Consumers that need backend-specific capacity diagnostics may add an
+`errors.As` check while retaining their existing `errors.Is` classification.

docs/releases/v0.5.0.md

@@ -0,0 +1,125 @@
+# Promptkit v0.5.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.4.0` to `v0.5.0`. The annotated `v0.5.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.5.0` makes provider requests less prescriptive and adds an application
+fallback layer for profile definitions:
+
+- unset optional provider controls are omitted from OpenAI-compatible request
+  bodies instead of being populated with framework values; and
+- `WithFallbackProfileFS` lets an application package profile defaults that
+  operators can override through the existing ordinary profile sources.
+
+These changes let compatible providers apply their own model defaults while
+giving applications stable embedded profile IDs without weakening operator
+configuration precedence.
+
+## Compatibility
+
+The release adds one public function and removes no public declaration.
+Existing source code should continue to compile.
+
+There is one intentional behavior change: when no profile or runtime override
+selects `top_p`, Promptkit no longer sends the former framework value of `1`.
+It omits `top_p` and lets the provider choose its behavior. Unset
+`temperature` and `max_tokens` are likewise omitted. Explicit nonzero profile
+values and runtime values—including explicit runtime zero values—retain their
+precedence and wire effect.
+
+Consumers that relied on Promptkit always sending `top_p: 1` should add that
+value to the relevant profile or runtime override before upgrading. Consumers
+that did not rely on the implicit sampling value require no migration.
+
+Application fallback profiles are opt-in. Engines that do not call
+`WithFallbackProfileFS` retain the previous profile-source behavior.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.5.0
+go mod tidy
+```
+
+Run the consuming project's ordinary and race-enabled tests after upgrading.
+If request payloads or model behavior are asserted in fixtures, review them for
+the optional-parameter omission described below.
+
+## Omitted Optional Provider Controls
+
+The built-in OpenAI-compatible client now includes `temperature`,
+`max_tokens`, and `top_p` only when a profile or runtime override selects the
+value. An explicit runtime zero remains present because runtime override
+pointers distinguish zero from an unspecified value.
+
+Promptkit's positive generation deadline remains a framework concern and is
+not a provider request-body default. Required request fields, session IDs,
+structured output, reasoning selection, credentials, and explicit extra
+parameters retain their existing behavior.
+
+See the [framework default and precedence reference](../formats.md#defaults-and-overrides),
+the [`ExecutionTargetOverride` GoDoc](../../types.go), and the
+[OpenAI-compatible request-body contract](../integrations/openai-compatible-chat.md#request-body)
+for current details.
+
+## Embedded Application Fallback Profiles
+
+Applications can package ordinary profile YAML in an `fs.FS` and register it
+as a fallback source:
+
+```go
+//go:embed profiles/*.yaml
+var applicationProfiles embed.FS
+
+engine, err := promptkit.NewEngine(promptkit.Config{
+	PromptDir:  "prompts",
+	ProfileDir: operatorProfileDir,
+},
+	promptkit.WithFallbackProfileFS(applicationProfiles, "profiles"),
+)
+```
+
+Leave `operatorProfileDir` empty when no operator source is configured. A
+configured ordinary source is authoritative: a matching definition overrides
+the application fallback, while a read or validation failure remains an error
+instead of silently reaching a lower layer.
+
+Profile definitions resolve in this order:
+
+1. in-memory profiles supplied with `WithProfiles`;
+2. the ordinary configured source selected by `WithProfileFile`,
+   `WithProfileFS`, or `Config.ProfileDir`;
+3. the application source supplied with `WithFallbackProfileFS`; and
+4. Promptkit's embedded built-in profiles.
+
+Only an absent profile ID falls through. Sources provide complete profiles and
+do not merge fields. Loading remains lazy, and the new source uses the existing
+strict profile YAML and credential rules.
+
+See the
+[embedded-default consumer guidance](../consumers/pkg-promptkit.md#supply-embedded-application-defaults),
+the [`WithFallbackProfileFS` GoDoc](../../engine.go), and the
+[profile source reference](../formats.md#source-and-profile-precedence) for
+current details.
+
+## Public API Changes
+
+The release adds:
+
+- `WithFallbackProfileFS`.
+
+No public declaration was removed or changed.
+
+## Consumer Action
+
+- Review any workflow that depended on Promptkit's implicit `top_p: 1` and
+  configure the value explicitly when required.
+- Optionally adopt `WithFallbackProfileFS` when an application should package
+  overridable profile defaults.
+- Run consumer tests after updating the module dependency.

docs/releases/v0.6.0.md

@@ -0,0 +1,131 @@
+# Promptkit v0.6.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.5.0` to `v0.6.0`. The annotated `v0.6.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.6.0` is a broad correctness, safety, efficiency, and maintainability
+release. It does not add or remove public declarations. The release:
+
+- centralizes shared execution-setting, output-contract, endpoint, and
+  JSON-compatible-value rules;
+- unifies prompt repository behavior and avoids unnecessary prompt and profile
+  decoding;
+- bounds consumer-controlled JSON trees and successful provider responses;
+- hardens prompt content paths, artifact files, provider URLs, JSON framing,
+  and error propagation;
+- reuses compiled schema plans and rendered artifact text within an operation;
+  and
+- improves cancellation behavior, prepared-value ownership, deterministic
+  transport testing, and maintainer validation.
+
+## Compatibility
+
+No public declaration was added, removed, or changed. Ordinary valid `v0.5.0`
+configurations and requests should continue to compile and behave as before.
+
+The release intentionally rejects or reports several inputs that were
+previously accepted, altered, or misclassified:
+
+- execution settings must be finite, within their documented ranges, and safe
+  to convert to Go durations;
+- output formats, validation modes, repair counts, and JSON Schema dependencies
+  are validated consistently;
+- file-backed prompt and profile identity comes from normalized YAML metadata,
+  not filenames;
+- prompt `content_file` values must be exact relative paths contained by their
+  configured source root;
+- built-in file artifacts must resolve to regular files;
+- selected provider endpoints must be absolute HTTP or HTTPS URLs without user
+  information, query strings, or fragments;
+- JSON documents and successful provider responses must contain exactly one
+  value, and successful provider bodies are limited to 16 MiB; and
+- excessively deep or expansive JSON-compatible values fail with ordinary
+  validation errors.
+
+These are compatibility corrections and safety boundaries rather than new
+consumer configuration requirements. Consumers relying on an invalid or
+ambiguous input should correct that input before upgrading.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.6.0
+go mod tidy
+```
+
+Run the consuming project's ordinary and race-enabled tests after upgrading.
+Applications with custom prompt/profile sources, local provider endpoints,
+unusual artifact paths, or assertions over provider error identities should
+pay particular attention to the compatibility notes below.
+
+## Source Loading And Identity
+
+Prompt definitions now share one source-neutral selection and normalization
+flow across operating-system and `fs.FS` sources. YAML `id` and `version`
+metadata are authoritative; filenames do not create a second identity system.
+Only selected content bodies are loaded, malformed unrelated definitions do
+not shadow valid exact matches, and per-file read failures are reported as
+prompt-load failures rather than false absence.
+
+File-backed profiles likewise use normalized YAML IDs, reuse their metadata
+read for selected strict decoding, and avoid fully decoding unrelated files.
+Selected malformed definitions remain authoritative and do not silently fall
+through to a lower-precedence source.
+
+Prompt `content_file` paths are opened exactly as declared after a separate
+blank check. They must remain relative to and contained by the configured
+prompt source root, including across operating-system symlinks.
+
+See the [framework source and identity reference](../formats.md) and
+[internal source overview](../internal/sources.md) for the current contracts.
+
+## Validation, Cancellation, And Efficiency
+
+JSON Schema documents preserve exact JSON-number representations. Schema
+resource URLs safely escape legal filesystem names, and each operation loads
+and compiles its schema graph once. `Run` and prepared execution reuse that
+operation-local plan; Promptkit does not introduce a cross-operation cache.
+
+Artifact reading, rendering, schema loading, compilation, and validation now
+check cancellation at the synchronous boundaries Promptkit controls. Rendering
+memoizes each artifact's text within one render operation, while plain JSON
+validation avoids materializing an unnecessary generic tree.
+
+The shared JSON-compatible-value owner now limits nesting and produced work so
+unsafe consumer-controlled structures return errors instead of risking
+unbounded recursion or allocation. See the
+[architecture policy](../policy/architecture.md) for invariant ownership and
+the [format reference](../formats.md) for validation behavior.
+
+## Provider Transport Hardening
+
+OpenAI-compatible endpoints are parsed and composed structurally, including
+nested base paths. Underlying transport cancellation and deadline errors remain
+discoverable with `errors.Is` through Promptkit's generation error category.
+
+Successful provider bodies are read with a fixed 16 MiB bound and must contain
+exactly one JSON response object followed only by whitespace. Oversized,
+truncated, malformed, or multiply framed responses fail without returning a
+partial result. See the
+[OpenAI-compatible integration contract](../integrations/openai-compatible-chat.md)
+for the canonical request, endpoint, error, and response behavior.
+
+## Public API Changes
+
+None.
+
+## Consumer Action
+
+- Correct any configuration or request that depends on the formerly permissive
+  cases described under Compatibility.
+- Confirm custom local provider endpoints are absolute HTTP or HTTPS base URLs
+  without credentials, queries, or fragments.
+- Confirm prompt content paths remain within their configured source root and
+  file artifacts resolve to regular files.
+- Run ordinary and race-enabled consumer tests after updating the dependency.

docs/releases/v0.7.0.md

@@ -0,0 +1,155 @@
+# Promptkit v0.7.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.6.0` to `v0.7.0`. The annotated `v0.7.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.7.0` expands provider integration and profile composition while making
+credential and generation-failure handling more flexible:
+
+- Promptkit now includes the `rakestrawhome` backend and its Gemma profile;
+- built-in generation failures expose bounded structured provider details;
+- an unavailable optional API-key environment source no longer prevents a
+  request from reaching an upstream that permits unauthenticated access; and
+- profiles can inherit from and selectively refine another profile.
+
+## Compatibility
+
+This release adds public declarations and fields but removes none. Existing
+keyed configuration literals and ordinary `errors.Is` handling continue to
+work.
+
+Adding `BaseProfileID` to `Profile` and `OpenAICompatibleProfileConfig` changes
+their struct shape. Consumers using positional composite literals for either
+type must convert them to keyed literals. Existing keyed literals require no
+change.
+
+The `rakestrawhome` backend ID is now built in and reserved. A consumer that
+previously registered that exact ID with `WithBackend` must remove its manual
+registration before upgrading. Other custom backend registrations are
+unchanged.
+
+When an optional backend, profile, or request `APIKeyEnv` is unset, empty, or
+whitespace-only, the built-in client now omits `Authorization` and sends the
+request. Previously this condition could fail before transport. Set
+`Profile.APIKeyRequired` when missing credentials must remain a local
+preflight error.
+
+Provider non-success responses continue to match `ErrLLMGenerate`. Their
+rendered wording is not a compatibility contract; consumers can now use
+`errors.As` with `*GenerationError` when structured status information is
+needed.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.7.0
+go mod tidy
+```
+
+Remove any manual `rakestrawhome` backend registration, convert positional
+profile literals to keyed literals, and run the consuming project's ordinary
+and race-enabled tests.
+
+## Rakestrawhome Built-In Backend And Profile
+
+Every engine now includes the reserved `rakestrawhome` backend, identified by
+`BackendRakestrawHome`. The built-in `rakestrawhome-gemma-4-31b` profile
+selects that backend. Consumers can use the maintained endpoint, credential,
+capacity, and model defaults without registering either definition themselves.
+
+See the [built-in backend and profile catalogs](../formats.md#built-in-backends)
+and the [consumer adoption example](../consumers/pkg-promptkit.md#use-the-rakestrawhome-built-in-profile)
+for the current contracts.
+
+## Structured Generation Errors
+
+Non-2xx responses from the built-in OpenAI-compatible client now return an
+immutable `*GenerationError`. Consumers can inspect the HTTP status and any
+safely extracted provider code, type, or message while retaining the ordinary
+generation-error category:
+
+```go
+var generationErr *promptkit.GenerationError
+if errors.As(err, &generationErr) {
+	status := generationErr.StatusCode()
+	_ = status
+}
+```
+
+Provider fields are bounded and normalized but remain untrusted and may
+contain sensitive request or schema details. Default and Go-syntax formatting
+omit those fields. Applications must apply their own disclosure policy before
+logging or presenting accessor values.
+
+See the [`GenerationError` GoDoc](../../generation_error.go), the
+[consumer error-handling guide](../consumers/pkg-promptkit.md#handle-errors),
+and the [OpenAI-compatible response contract](../integrations/openai-compatible-chat.md#response-handling).
+
+## Optional Credential Sources
+
+`APIKeyEnv` names an optional environment lookup source unless the selected
+profile explicitly sets `APIKeyRequired`. When neither a direct request key nor
+a usable environment value exists, the built-in client omits the bearer header
+and handles the upstream response normally. This supports local and other
+OpenAI-compatible providers that permit unauthenticated requests without
+hiding an authentication error returned by a provider that requires one.
+
+The [credential format reference](../formats.md#credentials), the
+[`Backend` GoDoc](../../backends.go), the
+[`ExecutionTargetOverride` GoDoc](../../types.go), and the
+[authentication integration contract](../integrations/openai-compatible-chat.md#authentication)
+define the current precedence and availability rules.
+
+## Profile Inheritance
+
+YAML profiles can name one parent with `base_profile`; in-memory profiles use
+`Profile.BaseProfileID`, and `OpenAICompatibleProfileConfig` forwards the same
+field. A profile can act as an application-owned alias of a built-in or refine
+selected inherited settings:
+
+```go
+promptkit.WithProfiles(promptkit.Profile{
+	ID:              "weather-light",
+	BaseProfileID:   "deepseek-4-flash",
+	ReasoningEffort: "high",
+})
+```
+
+Base lookup observes the existing source precedence. Chains are linear,
+cycle-safe, and resolved afresh for ordinary operations. Prepared execution
+freezes the fully resolved target. The selected leaf ID remains public while
+effective execution settings reflect the resolved chain.
+
+See the [profile inheritance format reference](../formats.md#profile-inheritance),
+the [consumer alias example](../consumers/pkg-promptkit.md#alias-a-built-in-profile),
+and the [`Profile` GoDoc](../../types.go) for exact merge and validation
+behavior.
+
+## Public API Changes
+
+The release adds:
+
+- `BackendRakestrawHome`;
+- `GenerationError`, including `StatusCode`, `ProviderCode`, `ProviderType`,
+  `ProviderMessage`, `Error`, `GoString`, and `Unwrap`;
+- `Profile.BaseProfileID`; and
+- `OpenAICompatibleProfileConfig.BaseProfileID`.
+
+No public declaration was removed.
+
+## Consumer Action
+
+- Remove a manual backend registration whose ID is exactly `rakestrawhome`.
+- Convert positional `Profile` or `OpenAICompatibleProfileConfig` literals to
+  keyed literals.
+- Set `Profile.APIKeyRequired` where a missing credential must fail locally
+  instead of reaching the provider unauthenticated.
+- Treat `GenerationError` provider fields as untrusted and potentially
+  sensitive when adopting the new accessors.
+- Run consumer ordinary and race-enabled tests after updating the module.

docs/releases/v0.8.0.md

@@ -0,0 +1,109 @@
+# Promptkit v0.8.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.7.0` to `v0.8.0`. The annotated `v0.8.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.8.0` activates Promptkit's bounded output-repair workflow:
+
+- failed nonempty-text, JSON, and JSON Schema validation can make a limited
+  number of corrective model calls;
+- corrective calls preserve the original rendered conversation, effective
+  target, session, structured-output contract, and backend capacity policy;
+- results report cumulative usage and the number of corrective calls actually
+  made; and
+- explicitly empty OpenAI-compatible response content now reaches output
+  validation instead of being classified as a malformed provider envelope.
+
+## Compatibility
+
+This release adds no public declarations or fields and removes none. Existing
+source code remains source-compatible.
+
+The behavior of the existing `OutputContract.RepairAttempts` field and prompt
+YAML `repair_attempts` field has changed. A positive value now authorizes real
+additional model calls after eligible validation failures; earlier releases
+accepted the field but the public engine remained single-pass. Consumers that
+set a positive value should expect additional latency, token usage, and
+provider cost when repair is needed.
+
+Repair budgets must now be between zero and three. A positive budget requires
+`basic`, `json`, or `json_schema` validation. Values above three and a positive
+budget paired with `none` are invalid contracts rather than ignored settings.
+
+An explicitly present empty or whitespace-only string returned by the built-in
+OpenAI-compatible client is now a completed generation candidate. `none`
+validation permits it, while `basic`, `json`, and `json_schema` classify it
+under their ordinary validation rules and may repair it when configured.
+Missing, `null`, or non-string content remains a malformed provider response.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.8.0
+go mod tidy
+```
+
+Review every prompt definition and request override that sets a positive repair
+budget. Use zero or omit the field to retain single-pass execution. Ensure each
+positive budget is no greater than three and uses an eligible validation mode,
+then run the consuming project's ordinary and race-enabled tests.
+
+## Bounded Output Repair
+
+`repair_attempts` counts corrective calls in addition to the initial model
+call. Promptkit validates each completed candidate, stops at the first valid
+one, and never exceeds the configured bound. If every candidate remains
+invalid, the run completes successfully with the final candidate and its
+failed validation result rather than returning an operational error.
+
+Each correction starts from the original rendered messages and includes only
+the latest invalid candidate and latest validation diagnostics. JSON Schema
+mode retains the provider-native structured-output request as its first line of
+defense. Promptkit performs only deterministic structural validation; a valid
+response is not necessarily factual or correct for an application's domain.
+
+Usage in the final result is cumulative across the initial response and every
+completed corrective response. `ValidationResult.RepairAttempts` reports the
+number of corrective calls actually made. Corrective generation failures use
+the same public generation-error categories and structured provider details as
+an initial generation failure.
+
+See the [output-contract format reference](../formats.md#output-contract), the
+[consumer repair example](../consumers/pkg-promptkit.md#repair-a-structured-result),
+and the [`OutputContract` and `ValidationResult` GoDoc](../../types.go) for the
+current contracts.
+
+## Explicit Empty Content
+
+The built-in OpenAI-compatible client now distinguishes an explicitly present
+empty string from a missing or malformed `content` field. This aligns built-in
+and injected clients by letting the selected output contract decide whether an
+empty candidate is acceptable, invalid, or eligible for repair.
+
+See the
+[OpenAI-compatible response contract](../integrations/openai-compatible-chat.md#response-handling)
+for the exact envelope behavior.
+
+## Public API Changes
+
+None. This release activates and tightens the documented behavior of existing
+fields.
+
+## Consumer Action
+
+- Remove or set `repair_attempts` to zero where execution must remain
+  single-pass.
+- Keep every positive repair budget at three or fewer and pair it with
+  `basic`, `json`, or `json_schema` validation.
+- Account for additional latency, usage, and provider cost when enabling
+  repair.
+- Continue checking the returned validation status because bounded repair can
+  exhaust without producing a valid candidate.
+- Review workflows that previously treated explicit empty provider content as
+  a generation error.

docs/releases/v0.9.0.md

@@ -0,0 +1,125 @@
+# Promptkit v0.9.0
+
+This supplemental changelog and migration guide summarizes the consumer-facing
+changes from `v0.8.0` to `v0.9.0`. The annotated `v0.9.0` tag is the
+authoritative release record. Exact current contracts belong to the linked
+GoDoc and durable documentation.
+
+## Summary
+
+`v0.9.0` adds stateless request-message composition and separates maintained
+provider data from Promptkit's core implementation:
+
+- callers can append already-rendered messages to a configured prompt for
+  application-owned conversations and semantic correction workflows;
+- the public package now publishes constants for the four supported text-chat
+  roles, and prompt definitions use the same normalized role vocabulary; and
+- the OpenRouter and Rakestrawhome backend/profile catalogs now come from two
+  independently versioned Go module dependencies.
+
+## Compatibility
+
+This release adds one field and four constants to the public API and removes no
+public declarations. Existing keyed `RunRequest` literals that omit
+`AppendedMessages` retain their behavior. Adding the field changes the struct
+shape, so consumers using positional `RunRequest` literals must convert them
+to keyed literals.
+
+Message roles in prompt definitions are now trimmed, lowercased, and required
+to be `developer`, `system`, `user`, or `assistant`. Definitions using another
+role that earlier releases accepted as an arbitrary nonblank string now fail
+prompt loading. In particular, the text-only message contract does not support
+`tool` or the deprecated `function` role. Otherwise valid roles with different
+case or surrounding whitespace are normalized rather than rejected.
+
+The catalog extraction preserves Promptkit's public API, built-in backend and
+profile IDs, configuration, precedence, credential handling, and capacity
+behavior. Consumers do not import or register either catalog themselves, and
+no configuration migration is required. Promptkit now selects two
+independently versioned data dependencies and guarantees only the catalog
+versions selected and tested by this Promptkit release.
+
+## Upgrade
+
+Update the module dependency with:
+
+```sh
+go get gitea.maximumdirect.net/eric/promptkit@v0.9.0
+go mod tidy
+```
+
+Convert any positional `RunRequest` literals to keyed literals. Review prompt
+definitions for unsupported roles, then run the consuming project's ordinary
+and race-enabled tests.
+
+## Appended Request Messages
+
+`RunRequest.AppendedMessages` accepts caller-owned `RenderedMessage` values
+that Promptkit validates, copies, and appends after every rendered
+prompt-definition message in caller order. Promptkit does not template this
+content, retain conversation state between calls, impose a retry policy, or
+apply a message-count, byte-size, token, or context-window limit. Upstream
+rejections continue through the ordinary generation-error boundary.
+
+This primitive supports application-owned conversation continuations and
+domain-aware correction loops while preserving Promptkit's existing
+preparation, hashing, prepared-execution, structural repair, backend-capacity,
+credential, and cancellation behavior. Appended content can include sensitive
+model output or application feedback; prepared values expose the complete
+effective messages by design, while default request formatting reports only
+the appended-message count.
+
+See the
+[consumer appended-message example](../consumers/pkg-promptkit.md#append-already-rendered-messages),
+the [`RunRequest`, `RenderedMessage`, and `CacheControl` GoDoc](../../types.go),
+and the [OpenAI-compatible request contract](../integrations/openai-compatible-chat.md#request-body)
+for current behavior.
+
+## Supported Message Roles
+
+The new `RoleDeveloper`, `RoleSystem`, `RoleUser`, and `RoleAssistant`
+constants identify the complete role vocabulary accepted by Promptkit's
+text-chat message model. The same validation and normalization now apply to
+prompt-definition messages and request-supplied appended messages. Promptkit
+does not translate between roles; provider- or model-specific rejection of an
+otherwise supported role remains an upstream generation error.
+
+See the [message format reference](../formats.md#messages-and-templates) for
+the canonical prompt-definition contract.
+
+## Independently Versioned Backend Catalogs
+
+Promptkit imports immutable catalog data for its maintained OpenRouter and
+Rakestrawhome backends and profiles. Engine construction validates and
+assembles both catalogs behind the existing built-in registry and profile
+precedence rules. Promptkit no longer keeps duplicate embedded profile assets
+or hard-coded definitions for those maintained backends.
+
+The module versions in Promptkit's `go.mod` identify the catalog releases
+tested with this release. The [built-in backend and profile format
+reference](../formats.md#built-in-backends) remains the canonical consumer
+contract, while the [internal source documentation](../internal/sources.md#profiles-and-built-ins)
+describes the dependency boundary.
+
+## Public API Changes
+
+The release adds:
+
+- `RunRequest.AppendedMessages`;
+- `RoleDeveloper`;
+- `RoleSystem`;
+- `RoleUser`; and
+- `RoleAssistant`.
+
+No public declaration was removed.
+
+## Consumer Action
+
+- Convert positional `RunRequest` literals to keyed literals.
+- Replace unsupported prompt-definition roles with an appropriate supported
+  role, or keep richer tool-call protocols in an application-owned client.
+- Treat appended messages and prepared effective messages according to the
+  application's sensitive-data policy.
+- Do not add direct catalog imports or registration calls; existing Promptkit
+  construction and configuration remain correct.
+- Run consumer ordinary and race-enabled tests after updating the module.

docs/roadmap/deferred.md

@@ -0,0 +1,61 @@
+# Deferred Feature Ideas
+
+## Purpose
+
+This document catalogs feature ideas that remain potentially useful but have
+been deliberately postponed. These ideas are not awaiting ordinary selection
+from the [future feature catalog](future.md); each has a stated reason to wait
+and should be reconsidered only when its trigger becomes relevant.
+
+Deferred entries are not commitments, schedules, active implementation plans,
+or descriptions of current behavior. When an entry is reactivated, move it to
+`future.md` for evaluation or directly into a focused roadmap after its open
+design dependencies have been resolved.
+
+## Deferred Ideas
+
+### Semantic Execution-Target Fingerprints
+
+**Reason for deferral:** A stable digest requires a deliberate semantic-
+equality and versioning design. Notarius can safely use conservative source
+hashes and a Promptkit release marker today, while Weatherreporter does not
+currently reuse LLM-dependent checkpoints.
+
+Promptkit could expose an opaque equality value for a resolved profile and its
+effective generation target. This would let checkpointing consumers detect
+generation-affecting configuration changes without hashing YAML presentation
+or depending on Promptkit's built-in catalog layout.
+
+The digest should change with semantically relevant state such as the resolved
+model, endpoint, backend routing identity, request defaults, extra parameters,
+profile generation settings, and selected built-in profile semantics. It
+should exclude credential values, concurrency and queue policy, source paths,
+comments, formatting, and other representation-only changes. Whether a
+credential environment-variable name affects equality must be decided
+explicitly. The encoding should remain opaque and internally versioned so
+Promptkit can deliberately invalidate earlier digests when its resolution
+semantics change.
+
+Reconsider this idea when a downstream consumer needs Promptkit-owned
+checkpoint equality or when a broader semantic identity design is selected.
+
+### Eager Source Validation
+
+**Reason for deferral:** Exact prompt and profile inspection may already
+provide a sufficiently small validation surface. Experience from downstream
+adoption should establish whether an engine-wide operation would add enough
+value to justify its broader contract.
+
+Promptkit could provide an explicit offline operation that discovers and
+structurally validates configured prompt, profile, and schema sources without
+model generation. The normal `NewEngine` path would remain lazy.
+
+An eager operation would need coherent handling for duplicate prompt IDs and
+versions, strict YAML decoding, referenced content files, profile/backend
+membership, schema syntax and transitive references, context cancellation,
+and source-specific public errors. Credential declarations must remain
+separate from credential values; checking current environment availability,
+if supported at all, should be an explicit option and must not expose secrets.
+
+Reconsider this idea after downstream use of `InspectPrompt`,
+`InspectProfile`, and fixture-based preparation demonstrates a concrete gap.

docs/roadmap/future.md

@@ -0,0 +1,57 @@
+# Future Feature Ideas
+
+## Purpose
+
+This document catalogs reasonably specific ideas that may be useful in future
+Promptkit development. It is an idea pool, not a commitment, schedule, or
+description of current behavior.
+
+Ideas belong here while they are worth retaining but have not been selected
+for active development. Keep each entry at the level of intended capability,
+consumer value, and important scope boundaries. Defer API design,
+implementation details, sequencing, and acceptance criteria until an idea is
+selected.
+
+Ideas that have been deliberately postponed rather than left available for
+ordinary selection belong in the [deferred catalog](deferred.md).
+
+## Using This Catalog
+
+- Add an idea when its purpose and likely value can be stated clearly.
+- Keep entries independent enough that maintainers can evaluate and select
+  them individually.
+- Note significant dependencies or boundary concerns, but do not turn entries
+  into implementation plans.
+- Treat inclusion as an invitation to evaluate, not as approval or priority.
+- When an idea is selected, move its active planning to a focused roadmap or,
+  when it requires a durable architectural decision, an ADR. Update
+  current-state documentation only when implementation lands.
+- Move an idea to `deferred.md` when maintainers decide to retain it but wait
+  for a stated design dependency, demand signal, or reconsideration trigger.
+- Remove ideas that are no longer relevant. Retain a rejected idea only when
+  its rationale is likely to prevent repeated reconsideration.
+
+Future capabilities must continue to respect the
+[architecture policy](../policy/architecture.md), particularly Promptkit's
+role as an application-neutral library and its boundary with downstream
+consumers.
+
+## Ideas
+
+No ideas are currently awaiting selection. Active feature work belongs in its
+focused roadmap rather than this catalog.
+
+## Entry Format
+
+Use a short heading followed by a concise summary. Add focused bullets when
+they help preserve important scope boundaries without becoming an
+implementation plan:
+
+```markdown
+### Idea name
+
+Describe the intended capability, who benefits, and the most important scope
+boundary or dependency.
+
+- Optionally record an important behavior or boundary.
+```

engine.go

@@ -6,58 +6,134 @@ import (
 	"fmt"
 	"io/fs"
 	"net/http"
-	"os"
-	"path/filepath"
-	"strings"
 	"time"
 
-	artifactadapter "gitea.maximumdirect.net/eric/promptkit/internal/artifact"
-	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
-	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
-	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
-	"gitea.maximumdirect.net/eric/promptkit/internal/profile/builtin"
-	"gitea.maximumdirect.net/eric/promptkit/internal/prompt"
-	"gitea.maximumdirect.net/eric/promptkit/internal/promptdef"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	internalengine "gitea.maximumdirect.net/eric/promptkit/internal/engine"
+	"gitea.maximumdirect.net/eric/promptkit/internal/observation"
 	"gitea.maximumdirect.net/eric/promptkit/internal/usecase"
-	"gitea.maximumdirect.net/eric/promptkit/internal/validate"
 )
 
-// ErrInvalidConfig indicates invalid public engine configuration.
+// ErrInvalidConfig identifies invalid engine construction, including missing
+// required configuration, invalid options or backend registrations, and a nil
+// Engine receiver.
 var ErrInvalidConfig = errors.New("invalid engine configuration")
 
 var (
-	ErrInvalidRequest   = errors.New("invalid run request")
-	ErrPromptNotFound   = errors.New("prompt not found")
-	ErrProfileNotFound  = errors.New("profile not found")
-	ErrProfileRequired  = errors.New("profile selection is required")
-	ErrPromptLoad       = errors.New("failed to load prompt definition")
-	ErrProfileLoad      = errors.New("failed to load execution profile")
+	// ErrInvalidRequest identifies a request whose required values, overrides,
+	// credentials, or effective settings are invalid.
+	ErrInvalidRequest = errors.New("invalid run request")
+	// ErrPromptNotFound identifies a requested prompt ID or version that is not
+	// present in the selected prompt source. It does not also match
+	// ErrPromptLoad.
+	ErrPromptNotFound = errors.New("prompt not found")
+	// ErrProfileNotFound identifies a selected profile ID that is absent from
+	// every configured profile source. It does not also match ErrProfileLoad.
+	ErrProfileNotFound = errors.New("profile not found")
+	// ErrProfileRequired identifies a request for which neither RunRequest.ProfileID
+	// nor the selected prompt's default profile is present. Such an error also
+	// matches ErrInvalidRequest.
+	ErrProfileRequired = errors.New("profile selection is required")
+	// ErrPromptLoad identifies a failure to read, decode, validate, select, or
+	// hash a prompt definition, except for the not-found case represented by
+	// ErrPromptNotFound.
+	ErrPromptLoad = errors.New("failed to load prompt definition")
+	// ErrProfileLoad identifies a failure to read, decode, validate, or select
+	// an execution profile or resolve its backend, except for the profile
+	// not-found case represented by ErrProfileNotFound.
+	ErrProfileLoad = errors.New("failed to load execution profile")
+	// ErrAPIKeyEnvMissing identifies an explicitly required APIKeyEnv whose
+	// environment variable is unset or empty after direct RunRequest.APIKey
+	// precedence is applied. Such an error also matches ErrInvalidRequest.
 	ErrAPIKeyEnvMissing = errors.New("api_key_env points to an unset environment variable")
-	ErrArtifactLoad     = errors.New("failed to load artifact")
-	ErrPromptRender     = errors.New("failed to render prompt")
-	ErrLLMGenerate      = errors.New("failed to generate output")
-	ErrValidation       = errors.New("failed to validate output")
+	// ErrArtifactLoad identifies a failure to resolve an input artifact. Errors
+	// returned by an injected ArtifactReader remain available through errors.Is.
+	ErrArtifactLoad = errors.New("failed to load artifact")
+	// ErrPromptRender identifies a failure to render prompt messages or the
+	// session ID from the resolved inputs and variables.
+	ErrPromptRender = errors.New("failed to render prompt")
+	// ErrCapacityExceeded identifies a Run or RunPrepared rejected because the
+	// selected backend already admitted ConcurrencyLimit + QueueCapacity calls.
+	// A [CapacityError] reports the selected backend ID. It is not an invalid
+	// request, an LLM or provider rate-limit response, or ErrLLMGenerate.
+	ErrCapacityExceeded = errors.New("backend capacity exceeded")
+	// ErrLLMGenerate identifies a model-client failure or a nil successful
+	// response. A built-in OpenAI-compatible non-2xx response is available as a
+	// [GenerationError]. Errors returned by an injected LLMClient remain
+	// available through errors.Is.
+	ErrLLMGenerate = errors.New("failed to generate output")
+	// ErrTransport identifies a failed HTTP request by the built-in model
+	// client. Generation errors in this category also match ErrLLMGenerate and
+	// retain the transport cause for errors.Is and errors.As. It does not imply
+	// that the provider received no work.
+	ErrTransport = errors.New("model transport failed")
+	// ErrMalformedResponse identifies an invalid successful model response or
+	// a nil successful response from an injected client. Generation errors in
+	// this category also match ErrLLMGenerate.
+	ErrMalformedResponse = errors.New("malformed model response")
+	// ErrRetriesExhausted identifies a built-in generation sequence whose
+	// positive transient retry budget ended with another eligible HTTP status.
+	// RetryExhaustedError retains the final cause and actual attempt count.
+	ErrRetriesExhausted = errors.New("transient model retries exhausted")
+	// ErrValidation identifies an operational failure to load or compile a
+	// schema or validate output. A completed validation whose Status is
+	// ValidationFailed is returned in RunResult without this error.
+	ErrValidation = errors.New("failed to validate output")
 )
 
-// Engine prepares and runs Promptkit prompt requests.
+// Engine inspects prompts and profiles and prepares and runs Promptkit prompt
+// requests.
+//
+// An Engine is safe for concurrent calls to [Engine.InspectPrompt],
+// [Engine.InspectProfile], [Engine.Prepare], [Engine.PrepareExecution],
+// [Engine.Run], and [Engine.RunPrepared]. Each Engine owns independent
+// backend-capacity pools that coordinate Run and RunPrepared admission and
+// model generation. Injected collaborators may still be invoked concurrently
+// across different backend pools or for unlimited backends.
 type Engine struct {
-	runner *usecase.Runner
+	internal *internalengine.Engine
 }
 
-// Config configures a public Promptkit engine.
+// Config selects the directory-backed sources and built-in model-client
+// transport used by [NewEngine]. Config has no stable JSON representation.
 type Config struct {
-	PromptDir  string
+	// PromptDir is the directory searched recursively for prompt definitions.
+	// It is required unless a WithPromptFS or WithPromptFile option supplies the
+	// prompt source.
+	PromptDir string
+	// ProfileDir is an optional ordinary configured source whose profiles take
+	// precedence over application fallback and maintained catalog profiles. An
+	// empty value selects the lower-precedence sources unless a profile-source
+	// option supplies the ordinary source.
 	ProfileDir string
-	SchemaDir  string
+	// SchemaDir is the root for JSON Schema files. An empty value uses the
+	// current directory. WithSchemaFS or WithSchemaFile replaces this source.
+	SchemaDir string
 	// Timeout is the transport-wide safety cap for the built-in LLM client
-	// when HTTPClient is absent or has a non-positive timeout.
+	// when HTTPClient is absent or has a non-positive timeout. A zero or negative
+	// value selects the 10-minute default.
 	Timeout time.Duration
 	// HTTPClient is cloned for the built-in LLM client. Its positive Timeout
-	// takes precedence over Config.Timeout as the transport-wide safety cap.
+	// takes precedence over Timeout. A zero or negative client Timeout inherits
+	// Timeout or the 10-minute default. The supplied client is not mutated. This
+	// field is ignored when WithLLMClient is used.
 	HTTPClient *http.Client
+	// TransientRetries selects additional built-in HTTP attempts after eligible
+	// provider statuses. Nil defaults to two; zero disables retries. Negative
+	// values are invalid. Injected LLMClient implementations are never retried
+	// automatically.
+	TransientRetries *int
 }
 
 // Option customizes engine construction.
+//
+// NewEngine applies options in argument order and ignores nil options. Within
+// each prompt-source, ordinary-profile-source, fallback-profile-source,
+// in-memory-profile, schema-source, model-client, and artifact-reader
+// category, the last non-nil valid option replaces earlier options in that
+// category. WithBackend is the additive exception: unique registrations
+// accumulate, and a repeated backend ID is an error rather than a replacement.
+// An invalid option fails construction even if a later option would replace it.
 type Option interface {
 	apply(*engineOptions) error
 }
@@ -69,38 +145,38 @@ func (f optionFunc) apply(options *engineOptions) error {
 }
 
 type engineOptions struct {
-	llmClient       llm.Client
-	artifactReader  artifactadapter.Reader
-	promptDefs      promptdef.Repository
-	profiles        profile.Repository
-	memoryProfiles  profile.Repository
-	validator       validate.Validator
-	promptSource    bool
-	profileSource   bool
-	memorySource    bool
-	validatorSource bool
-	artifactSource  bool
+	internal internalengine.Options
 }
 
-// WithLLMClient injects a custom LLM client for execution.
+// WithLLMClient replaces the built-in model client used by [Engine.Run] and
+// [Engine.RunPrepared].
+//
+// A nil client makes NewEngine fail with ErrInvalidConfig. The Engine schedules
+// Generate calls according to the selected backend's capacity policy, but the
+// client may still be called concurrently across different backend pools or for
+// unlimited backends. The client is not used by [Engine.Prepare] or
+// [Engine.PrepareExecution].
 func WithLLMClient(client LLMClient) Option {
 	return optionFunc(func(options *engineOptions) error {
 		if client == nil {
 			return ErrInvalidConfig
 		}
-		options.llmClient = publicLLMClientAdapter{client: client}
+		options.internal.SetLLMClient(publicLLMClientAdapter{client: client})
 		return nil
 	})
 }
 
-// WithArtifactReader injects a reader for every input artifact reference.
+// WithArtifactReader replaces the default reader for every input artifact
+// reference, regardless of its ArtifactRef.Type.
+//
+// A nil reader makes NewEngine fail with ErrInvalidConfig. The reader may be
+// called concurrently.
 func WithArtifactReader(reader ArtifactReader) Option {
 	return optionFunc(func(options *engineOptions) error {
 		if reader == nil {
 			return ErrInvalidConfig
 		}
-		options.artifactReader = publicArtifactReaderAdapter{reader: reader}
-		options.artifactSource = true
+		options.internal.SetArtifactReader(publicArtifactReaderAdapter{reader: reader})
 		return nil
 	})
 }
@@ -109,117 +185,134 @@ func WithArtifactReader(reader ArtifactReader) Option {
 //
 // The source uses the same strict prompt YAML rules as configured prompt
 // directories, and prompt content_file paths resolve within this source.
+// fsys must be non-nil and root must be non-empty; otherwise NewEngine fails
+// with ErrInvalidConfig. This option replaces Config.PromptDir and earlier
+// prompt-source options.
 func WithPromptFS(fsys fs.FS, root string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		if fsys == nil {
-			return ErrInvalidConfig
-		}
-		if strings.TrimSpace(root) == "" {
-			return ErrInvalidConfig
-		}
-		options.promptDefs = promptdef.NewFSRepository(fsys, root)
-		options.promptSource = true
-		return nil
+		return options.internal.SetPromptFS(fsys, root)
 	})
 }
 
 // WithPromptFile loads prompt definitions from the single prompt file at path.
 //
-// Relative prompt content_file paths resolve from the file's directory.
+// Relative prompt content_file paths resolve from the file's directory. path
+// must name an existing non-directory file when NewEngine applies the option.
+// This option replaces Config.PromptDir and earlier prompt-source options.
 func WithPromptFile(path string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		fsys, root, err := fileSource(path)
-		if err != nil {
-			return err
-		}
-		options.promptDefs = promptdef.NewFSRepository(fsys, root)
-		options.promptSource = true
-		return nil
+		return options.internal.SetPromptFile(path)
 	})
 }
 
 // WithProfileFS loads execution profiles from fsys under root.
 //
-// Profiles from this source overlay built-in profiles. Profile YAML must use
-// api_key_env for environment-based credentials; raw API keys are rejected.
+// Profiles from this ordinary configured source take precedence over
+// application fallback and built-in profiles. Profile YAML must use api_key_env
+// for environment-based credentials; raw API keys are rejected. fsys must be
+// non-nil and root must be non-empty; otherwise NewEngine fails with
+// ErrInvalidConfig. This option replaces Config.ProfileDir and earlier file or
+// FS profile-source options, but remains below WithProfiles in precedence.
 func WithProfileFS(fsys fs.FS, root string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		if fsys == nil {
-			return ErrInvalidConfig
-		}
-		if strings.TrimSpace(root) == "" {
-			return ErrInvalidConfig
-		}
-		options.profiles = profile.NewFSRepository(fsys, root)
-		options.profileSource = true
-		return nil
+		return options.internal.SetProfileFS(fsys, root)
 	})
 }
 
 // WithProfileFile loads execution profiles from the single profile file at path.
 //
-// The profile overlays built-in profiles. Profile YAML must use api_key_env for
-// environment-based credentials; raw API keys are rejected.
+// The profile takes precedence over application fallback and built-in profiles.
+// Profile YAML must use api_key_env for environment-based credentials; raw API
+// keys are rejected. path must name an existing non-directory file when
+// NewEngine applies the option. This option replaces Config.ProfileDir and
+// earlier file or FS profile-source options, but remains below WithProfiles in
+// precedence.
 func WithProfileFile(path string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		fsys, root, err := fileSource(path)
-		if err != nil {
-			return err
-		}
-		options.profiles = profile.NewFSRepository(fsys, root)
-		options.profileSource = true
-		return nil
+		return options.internal.SetProfileFile(path)
+	})
+}
+
+// WithFallbackProfileFS supplies application-owned fallback profile
+// definitions from fsys under root.
+//
+// Profile lookup checks, in order, profiles supplied by WithProfiles; the
+// ordinary configured source selected by WithProfileFile, WithProfileFS, or
+// Config.ProfileDir; this fallback source; and Promptkit's maintained catalog
+// profiles. Each source supplies a complete profile definition; profile fields
+// are not merged between sources. Only an absent profile ID proceeds to the
+// next source. A matching read, parse, duplicate, validation, or credential
+// format failure stops resolution.
+//
+// Files use the ordinary strict profile YAML and api_key_env credential rules.
+// Loading and validation are lazy: NewEngine validates this option's arguments
+// but does not read profile files. fsys must be non-nil and root must be
+// nonblank; otherwise NewEngine returns an error matching ErrInvalidConfig.
+// Repeating this option replaces the earlier valid fallback source.
+//
+// This option controls profile-definition lookup, not provider or generation
+// failover.
+func WithFallbackProfileFS(fsys fs.FS, root string) Option {
+	return optionFunc(func(options *engineOptions) error {
+		return options.internal.SetFallbackProfileFS(fsys, root)
 	})
 }
 
 // WithProfiles configures in-memory profiles that take precedence over
-// configured profile files and built-in profiles.
+// ordinary configured, application fallback, and built-in profiles.
+//
+// NewEngine locally validates and copies every profile. IDs must be unique
+// within one call. An invalid local definition, duplicate ID, or unsupported
+// ExtraParams value makes construction fail with ErrInvalidConfig. A derived
+// profile's base reference and resolved target completeness are checked when it
+// is selected or inspected. Repeating WithProfiles replaces the complete
+// earlier in-memory set rather than merging it.
 func WithProfiles(profiles ...Profile) Option {
 	return optionFunc(func(options *engineOptions) error {
-		repo, err := newMemoryProfileRepository(profiles)
-		if err != nil {
-			return err
+		definitions := make([]domain.ExecutionProfile, len(profiles))
+		for index, publicProfile := range profiles {
+			definitions[index] = toDomainProfile(publicProfile)
 		}
-		options.memoryProfiles = repo
-		options.memorySource = true
-		return nil
+		return options.internal.SetMemoryProfiles(definitions)
 	})
 }
 
 // WithSchemaFS loads JSON Schema documents from fsys under root.
 //
 // Prompt schema_path values resolve within this source when schema validation
-// or structured output is requested.
+// or structured output is requested. fsys must be non-nil and root must be
+// non-empty; otherwise NewEngine fails with ErrInvalidConfig. This option
+// replaces Config.SchemaDir and earlier schema-source options.
 func WithSchemaFS(fsys fs.FS, root string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		if fsys == nil {
-			return ErrInvalidConfig
-		}
-		if strings.TrimSpace(root) == "" {
-			return ErrInvalidConfig
-		}
-		options.validator = validate.NewFSValidator(fsys, root)
-		options.validatorSource = true
-		return nil
+		return options.internal.SetSchemaFS(fsys, root)
 	})
 }
 
 // WithSchemaFile loads JSON Schema documents from the single schema file at path.
 //
-// Prompt schema_path values refer to the file's base name.
+// Prompt schema_path values refer to the file's base name. path must name an
+// existing non-directory file when NewEngine applies the option. This option
+// replaces Config.SchemaDir and earlier schema-source options.
 func WithSchemaFile(path string) Option {
 	return optionFunc(func(options *engineOptions) error {
-		fsys, root, err := fileSource(path)
-		if err != nil {
-			return err
-		}
-		options.validator = validate.NewFSValidator(fsys, root)
-		options.validatorSource = true
-		return nil
+		return options.internal.SetSchemaFile(path)
 	})
 }
 
 // NewEngine constructs an Engine from configuration and options.
+//
+// Options are applied in order according to [Option]. PromptDir is required
+// unless a prompt-source option is present. Construction validates option
+// arguments, in-memory profiles, and backend registrations but defers reading
+// and validating prompt, file-backed profile, and schema contents until Prepare
+// or Run needs them.
+//
+// NewEngine returns an error matching ErrInvalidConfig for invalid
+// configuration, options, or backend-capacity policies. Each constructed
+// Engine has independent backend-capacity pools. Construction does not perform
+// model requests or require credentials. A negative Config.TransientRetries
+// is invalid.
 func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 	var options engineOptions
 	for _, opt := range opts {
@@ -231,83 +324,125 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 		}
 	}
 
-	promptDefs := options.promptDefs
-	if !options.promptSource {
-		if strings.TrimSpace(cfg.PromptDir) == "" {
-			return nil, fmt.Errorf("%w: prompt directory is required", ErrInvalidConfig)
-		}
-		promptDefs = promptdef.NewFilesystemRepository(cfg.PromptDir)
-	}
-
-	profiles := builtin.NewRepositoryWithDirectory(cfg.ProfileDir)
-	if options.profileSource {
-		profiles = builtin.NewRepositoryWithPrimary(options.profiles)
-	}
-	if options.memorySource {
-		profiles = profile.NewOverlayRepository(options.memoryProfiles, profiles)
-	}
-
-	validator := options.validator
-	if !options.validatorSource {
-		schemaDir := cfg.SchemaDir
-		if strings.TrimSpace(schemaDir) == "" {
-			schemaDir = defaults.SchemaDirDefault
-		}
-		validator = validate.NewStandardValidator(schemaDir)
-	}
-
-	llmClient := options.llmClient
-	if llmClient == nil {
-		var err error
-		llmClient, err = llm.NewOpenAICompatibleClient(llm.OpenAICompatibleConfig{
-			Timeout:    cfg.Timeout,
-			HTTPClient: cfg.HTTPClient,
-		})
-		if err != nil {
-			return nil, fmt.Errorf("%w: %v", ErrInvalidConfig, err)
-		}
-	}
-
-	artifacts := options.artifactReader
-	if !options.artifactSource {
-		artifacts = artifactadapter.NewCompositeReader()
-	}
-
-	return &Engine{
-		runner: usecase.NewRunner(
-			promptDefs,
-			profiles,
-			artifacts,
-			prompt.NewGoRenderer(),
-			llmClient,
-			validator,
-		),
-	}, nil
-}
-
-func fileSource(name string) (fs.FS, string, error) {
-	cleanName := strings.TrimSpace(name)
-	if cleanName == "" {
-		return nil, "", ErrInvalidConfig
-	}
-	dir := filepath.Dir(cleanName)
-	base := filepath.Base(cleanName)
-	if base == "." || base == string(filepath.Separator) || strings.TrimSpace(base) == "" {
-		return nil, "", ErrInvalidConfig
-	}
-	info, err := os.Stat(cleanName)
+	assembled, err := internalengine.New(
+		internalengine.Config{PromptDir: cfg.PromptDir, ProfileDir: cfg.ProfileDir, SchemaDir: cfg.SchemaDir, Timeout: cfg.Timeout, HTTPClient: cfg.HTTPClient, TransientRetries: copyIntPtr(cfg.TransientRetries)},
+		options.internal,
+	)
 	if err != nil {
-		return nil, "", fmt.Errorf("%w: failed to access source file %q: %v", ErrInvalidConfig, cleanName, err)
+		return nil, fmt.Errorf("%w: %v", ErrInvalidConfig, err)
 	}
-	if info.IsDir() {
-		return nil, "", fmt.Errorf("%w: source path %q must be a file", ErrInvalidConfig, cleanName)
-	}
-	return os.DirFS(dir), filepath.ToSlash(base), nil
+	return &Engine{internal: assembled}, nil
 }
 
-// Prepare resolves a prompt request without calling an LLM.
+// InspectPrompt resolves one explicit prompt definition without selecting a
+// profile or starting execution work.
+//
+// InspectPrompt requires a nonblank promptID. It passes nonblank promptID and
+// promptVersion values unchanged to the engine's ordinary, case-sensitive
+// prompt selection. An empty version succeeds only when that source has one
+// selected ID; a nonempty version selects one exact ID/version pair. The
+// configured prompt source is used without merging, fallback, or enumeration.
+//
+// A successful result proves that the selected definition and any referenced
+// message content files were structurally loaded. Inputs are returned in
+// definition order. DefaultProfileID is declared metadata only and is not
+// resolved. OutputContract is the normalized declared contract, with a JSON
+// Schema path when declared but without loading or compiling that schema.
+// PromptHash is the same opaque equality value as PreparedRun.PromptHash for
+// the selected definition and observed source state; its spelling, length,
+// encoding, algorithm, and security properties are not contracts.
+//
+// This method does not return prompt bodies, templates, source paths, schemas,
+// rendered messages, or execution settings. It does not resolve a profile or
+// credential, read artifacts or schemas, render, validate, admit capacity,
+// contact a provider, or generate model output. The returned PromptInspection
+// and its input slice are caller-owned. Filesystem-backed inspection is a
+// point-in-time lookup and does not freeze a definition for later execution.
+//
+// A nil Engine returns an error matching ErrInvalidConfig. A blank prompt ID
+// matches ErrInvalidRequest. An absent exact ID or version matches
+// ErrPromptNotFound and not ErrPromptLoad. Malformed, unreadable, duplicate,
+// ambiguous, referenced-content, or hashing failures match ErrPromptLoad.
+// Cancellation during lookup matches ErrPromptLoad while preserving the
+// context error. InspectPrompt returns no partial result on error.
+func (e *Engine) InspectPrompt(
+	ctx context.Context,
+	promptID string,
+	promptVersion string,
+) (*PromptInspection, error) {
+	if e == nil || e.internal == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	inspection, err := e.internal.InspectPrompt(ctx, promptID, promptVersion)
+	if err != nil {
+		return nil, mapPublicError(err)
+	}
+	return fromDomainPromptInspection(inspection), nil
+}
+
+// InspectProfile resolves one explicit profile without selecting a prompt or
+// starting execution work.
+//
+// InspectProfile trims surrounding whitespace from profileID and looks up the
+// resulting nonblank ID exactly and case-sensitively through the engine's
+// in-memory, ordinary configured-source, application fallback, and built-in
+// profile precedence. It applies the framework timeout baseline, selected
+// backend, and then selected profile to EffectiveModelParams without a request
+// override. BackendID is empty for an endpoint-only profile.
+//
+// APIKeyEnv in the returned target is an environment-variable name, never its
+// value. APIKeyRequired instead reports a direct credential requirement and is
+// mutually exclusive with a nonblank APIKeyEnv. InspectProfile neither derives
+// an ID from a prompt default_profile nor checks credential availability, so an
+// absent or blank named environment variable is not an error.
+//
+// The returned ProfileInspection and all nested mutable values are
+// caller-owned. Filesystem-backed inspection is a point-in-time lookup and
+// does not freeze the profile for a later execution. This method does not load
+// a prompt, render, read artifacts or schemas, admit backend capacity, contact
+// a provider, or generate model output.
+//
+// A nil Engine returns an error matching ErrInvalidConfig. A blank profile ID
+// matches ErrInvalidRequest. An absent exact ID matches ErrProfileNotFound and
+// not ErrProfileLoad. Malformed or unreadable profile data, an unknown backend,
+// or an invalid resolved target matches ErrProfileLoad. Cancellation during
+// profile loading matches ErrProfileLoad while preserving the context error.
+// InspectProfile returns no partial result on error.
+func (e *Engine) InspectProfile(ctx context.Context, profileID string) (*ProfileInspection, error) {
+	if e == nil || e.internal == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	inspection, err := e.internal.InspectProfile(ctx, profileID)
+	if err != nil {
+		return nil, mapPublicError(err)
+	}
+	return fromDomainProfileInspection(inspection), nil
+}
+
+// Prepare resolves and renders a prompt request without calling an LLM.
+// It appends any validated RunRequest.AppendedMessages after rendered
+// definition messages in the returned caller-owned snapshot.
+//
+// Prepare selects the prompt and profile, resolves any selected backend and
+// effective execution settings, resolves the output contract, loads and hashes
+// inputs, loads structured-output schema metadata when required, and renders
+// the session ID and messages. The returned PreparedRun is owned by the caller
+// and never contains a resolved API-key value, model output, or validation
+// result.
+//
+// A nil Engine returns an error matching ErrInvalidConfig. Request and
+// preparation failures may match ErrInvalidRequest, ErrPromptNotFound,
+// ErrPromptLoad, ErrProfileNotFound, ErrProfileLoad, ErrProfileRequired,
+// ErrAPIKeyEnvMissing, ErrArtifactLoad, ErrPromptRender, or ErrValidation as
+// applicable. Cancellation is passed to the active collaborator and is
+// reported in the applicable operation category; no general errors.Is
+// relationship to ctx.Err is promised. Prepare returns no partial result on
+// error. It validates RunRequest.TransientRetries but makes no model attempts.
 func (e *Engine) Prepare(ctx context.Context, req RunRequest) (*PreparedRun, error) {
-	if e == nil || e.runner == nil {
+	ctx = observation.WithoutExecutionState(ctx)
+	if e == nil || e.internal == nil {
 		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
 	}
 
@@ -316,16 +451,34 @@ func (e *Engine) Prepare(ctx context.Context, req RunRequest) (*PreparedRun, err
 		return nil, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
 	}
 
-	prepared, err := e.runner.Prepare(ctx, domainReq)
+	prepared, err := e.internal.Prepare(ctx, domainReq)
 	if err != nil {
 		return nil, mapPublicError(err)
 	}
 	return fromDomainPreparedRun(prepared), nil
 }
 
-// Run executes a prompt request and returns the generated artifact and metadata.
-func (e *Engine) Run(ctx context.Context, req RunRequest) (*RunResult, error) {
-	if e == nil || e.runner == nil {
+// PrepareExecution completely prepares a prompt request without calling the
+// configured LLMClient or reserving backend admission capacity. Validated
+// RunRequest.AppendedMessages are included in the frozen effective messages.
+//
+// The returned opaque handle is bound to this Engine and permits one
+// [Engine.RunPrepared] invocation. Preparation freezes the selected sources,
+// rendered messages, effective settings, inputs, provider structured-output
+// metadata, and validation resources needed by that invocation. The handle
+// retains a direct RunRequest.APIKey only in private execution state;
+// [PreparedExecution.Details] is credential-redacted.
+//
+// The context governs preparation only. Cancellation after this method
+// returns does not invalidate the handle or propagate to RunPrepared.
+// PrepareExecution returns the same error categories as [Engine.Prepare] and
+// returns no handle on error. A nil Engine returns an error matching
+// ErrInvalidConfig. The effective transient retry budget is frozen privately
+// for RunPrepared and is absent from Details. A supplied Observer is retained
+// privately for RunPrepared; preparation itself emits no events.
+func (e *Engine) PrepareExecution(ctx context.Context, req RunRequest) (*PreparedExecution, error) {
+	ctx = observation.WithoutExecutionState(ctx)
+	if e == nil || e.internal == nil {
 		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
 	}
 
@@ -334,9 +487,149 @@ func (e *Engine) Run(ctx context.Context, req RunRequest) (*RunResult, error) {
 		return nil, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
 	}
 
-	result, err := e.runner.Run(ctx, domainReq)
+	prepared, err := e.internal.PrepareExecution(ctx, domainReq)
+	if err != nil {
+		return nil, mapPublicError(err)
+	}
+	return &PreparedExecution{internal: prepared}, nil
+}
+
+// Run prepares a request, invokes the configured LLMClient, and validates the
+// generated output. Each call resolves current sources and composes a fresh,
+// stateless effective prompt with any validated RunRequest.AppendedMessages.
+//
+// A content-validation failure is a successful run whose
+// RunResult.Validation has Status ValidationFailed. When its output contract
+// has a positive repair budget, a failed eligible validation can make bounded
+// additional model calls and stops at the first valid candidate. Exhaustion
+// returns the final failed validation result with cumulative usage and actual
+// repair attempts. An inability to generate or validate returns an error and
+// no partial result.
+//
+// The built-in client retries eligible provider statuses using the effective
+// Config or request budget. With R additional transient attempts and P repair
+// generations, one run can dispatch at most (R+1)×(P+1) Promptkit-controlled
+// model attempts. Each dispatched attempt receives its own generation and
+// HTTP-client timeout; the caller context governs the full operation.
+// Injected LLMClient implementations are not retried automatically.
+// With Observer, Run emits started before facade request conversion or a nil
+// engine check, and finished on every normal return after public error mapping
+// and resource release. The event RunID matches a successful result. Without
+// Observer, result timing retains its existing convention; observed wall
+// duration can be slightly longer because it spans the facade boundary.
+//
+// Run can return every error category documented by [Engine.Prepare], plus
+// ErrCapacityExceeded and ErrLLMGenerate. Built-in HTTP execution failures
+// additionally match ErrTransport; malformed successful responses and nil
+// successful injected responses additionally match ErrMalformedResponse.
+// An engine admission rejection is
+// discoverable as [CapacityError] and still matches ErrCapacityExceeded. It
+// occurs before artifacts, schemas, rendering, or model generation because the
+// selected backend's admission capacity is full; it does not match
+// ErrInvalidRequest or ErrLLMGenerate. A built-in OpenAI-compatible non-2xx
+// response is discoverable as [GenerationError]. Eligible-status exhaustion
+// with a positive budget is discoverable as [RetryExhaustedError]. Injected
+// errors remain available through errors.Is. Cancellation while waiting for
+// model-generation capacity matches both ErrLLMGenerate and the context error.
+// Cancellation otherwise follows the active collaborator's documented
+// behavior. A nil Engine returns ErrInvalidConfig. Run returns no partial
+// result on error.
+func (e *Engine) Run(ctx context.Context, req RunRequest) (*RunResult, error) {
+	ctx = observation.WithoutExecutionState(ctx)
+	if req.Observer == nil {
+		return e.run(ctx, req)
+	}
+	recorder, idErr := observation.New(func(event domain.ExecutionEvent) { req.Observer(fromDomainExecutionEvent(event)) })
+	recorder.Start()
+	if idErr != nil {
+		err := fmt.Errorf("failed to create run id: %w", idErr)
+		terminal := observedFinish(nil, err)
+		recorder.Finish(observation.FinishData{Outcome: terminal.Outcome, Failure: terminal.Failure})
+		return nil, err
+	}
+	result, err := e.run(observation.WithRecorder(ctx, recorder), req)
+	terminal := observedFinish(result, err)
+	recorder.Finish(observation.FinishData{Outcome: terminal.Outcome, Failure: terminal.Failure,
+		StatusCode: terminal.StatusCode, RetriesExhausted: terminal.RetriesExhausted})
+	return result, err
+}
+
+func (e *Engine) run(ctx context.Context, req RunRequest) (*RunResult, error) {
+	if e == nil || e.internal == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	domainReq, err := toDomainRunRequest(req)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
+	}
+
+	result, err := e.internal.Run(ctx, domainReq)
 	if err != nil {
 		return nil, mapPublicError(err)
 	}
 	return fromDomainRunResult(result), nil
 }
+
+// RunPrepared atomically claims and executes a handle created by
+// [Engine.PrepareExecution].
+//
+// A valid owning-Engine invocation consumes the handle's one attempt before
+// credential revalidation, backend admission, generation, or validation.
+// Cancellation, capacity rejection, generation failure, operational
+// validation failure, and success all leave the handle unusable. A nil,
+// zero-value, foreign-Engine, discarded, claimed, or used handle returns an
+// error matching ErrInvalidRequest; a nil Engine returns ErrInvalidConfig and
+// does not claim the handle.
+//
+// The supplied context governs this execution attempt independently of the
+// preparation context. It covers credential revalidation, admission,
+// generation, validation, and any bounded output repair. Result timing begins
+// after the claim and excludes preparation and consumer-held delay.
+//
+// RunPrepared can return ErrInvalidRequest, ErrAPIKeyEnvMissing,
+// ErrCapacityExceeded, ErrLLMGenerate, or ErrValidation as applicable while
+// preserving documented collaborator and context identities. An engine
+// admission rejection is discoverable as [CapacityError] and still matches
+// ErrCapacityExceeded. A built-in OpenAI-compatible non-2xx response is
+// discoverable as [GenerationError]. Built-in HTTP execution failures match
+// ErrTransport; malformed successful responses and nil successful injected
+// responses match ErrMalformedResponse. Positive-budget eligible-status
+// exhaustion is discoverable as [RetryExhaustedError]. A completed
+// content-validation rejection, including repair exhaustion, is returned in
+// RunResult, not as an operational
+// error. RunPrepared uses the retry choice frozen during PrepareExecution. An
+// operational error returns no partial RunResult. A retained Observer begins
+// only after a successful atomic claim, with identities from the frozen
+// snapshot, and receives a terminal event on normal return after public error
+// mapping. Invalid, foreign, discarded, or reused handles emit no events.
+// Callbacks run outside the handle and capacity locks; panics propagate and
+// do not promise a terminal event.
+func (e *Engine) RunPrepared(ctx context.Context, prepared *PreparedExecution) (*RunResult, error) {
+	ctx = observation.WithoutExecutionState(ctx)
+	if e == nil || e.internal == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	var internal *usecase.PreparedExecution
+	if prepared != nil {
+		internal = prepared.internal
+	}
+	var recorder *observation.Recorder
+	result, err := e.internal.RunPrepared(observation.WithClaimSink(ctx, &recorder), internal)
+	if err != nil {
+		mapped := mapPublicError(err)
+		if recorder != nil {
+			terminal := observedFinish(nil, mapped)
+			recorder.Finish(observation.FinishData{Outcome: terminal.Outcome, Failure: terminal.Failure,
+				StatusCode: terminal.StatusCode, RetriesExhausted: terminal.RetriesExhausted})
+		}
+		return nil, mapped
+	}
+	publicResult := fromDomainRunResult(result)
+	if recorder != nil {
+		terminal := observedFinish(publicResult, nil)
+		recorder.Finish(observation.FinishData{Outcome: terminal.Outcome})
+	}
+	return publicResult, nil
+}

errors.go

@@ -3,7 +3,11 @@ package promptkit
 import (
 	"errors"
 	"fmt"
+	"strings"
 
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+	"gitea.maximumdirect.net/eric/promptkit/internal/generation"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
 	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
 	"gitea.maximumdirect.net/eric/promptkit/internal/promptdef"
 	"gitea.maximumdirect.net/eric/promptkit/internal/usecase"
@@ -13,11 +17,47 @@ func mapPublicError(err error) error {
 	if err == nil {
 		return nil
 	}
+	var internalCapacityError *usecase.CapacityError
+	if errors.As(err, &internalCapacityError) && internalCapacityError != nil &&
+		strings.TrimSpace(internalCapacityError.BackendID) != "" {
+		return &CapacityError{BackendID: internalCapacityError.BackendID}
+	}
+	var internalExhausted *generation.ExhaustedError
+	if errors.As(err, &internalExhausted) && internalExhausted != nil {
+		mapped := newRetryExhaustedError(internalExhausted.Attempts(), mapPublicError(internalExhausted.Unwrap()))
+		if errors.Is(err, usecase.ErrValidation) && !errors.Is(mapped, ErrValidation) {
+			return fmt.Errorf("%w: %w", ErrValidation, mapped)
+		}
+		if publicErr := publicErrorFor(err); publicErr != nil && !errors.Is(mapped, publicErr) {
+			return fmt.Errorf("%w: %w", publicErr, mapped)
+		}
+		return mapped
+	}
 	publicErr := publicErrorFor(err)
+	var providerHTTPError *llm.ProviderHTTPError
+	if errors.As(err, &providerHTTPError) && providerHTTPError != nil {
+		generationErr := newGenerationError(
+			providerHTTPError.StatusCode(),
+			providerHTTPError.ProviderCode(),
+			providerHTTPError.ProviderType(),
+			providerHTTPError.ProviderMessage(),
+		)
+		if publicErr != nil && !errors.Is(publicErr, ErrLLMGenerate) {
+			return fmt.Errorf("%w: %w", publicErr, generationErr)
+		}
+		return generationErr
+	}
 	if publicErr == nil {
 		return err
 	}
-	return fmt.Errorf("%w: %w", publicErr, err)
+	switch {
+	case errors.Is(err, llm.ErrTransport):
+		return fmt.Errorf("%w: %w: %w", publicErr, ErrTransport, err)
+	case errors.Is(err, llm.ErrMalformedResponse):
+		return fmt.Errorf("%w: %w: %w", publicErr, ErrMalformedResponse, err)
+	default:
+		return fmt.Errorf("%w: %w", publicErr, err)
+	}
 }
 
 func publicErrorFor(err error) error {
@@ -38,6 +78,8 @@ func publicErrorFor(err error) error {
 		return ErrProfileLoad
 	case errors.Is(err, usecase.ErrAPIKeyEnvMissing):
 		return errors.Join(ErrInvalidRequest, ErrAPIKeyEnvMissing)
+	case errors.Is(err, capacity.ErrCapacityExceeded):
+		return ErrCapacityExceeded
 	case errors.Is(err, usecase.ErrArtifactLoad):
 		return ErrArtifactLoad
 	case errors.Is(err, usecase.ErrPromptRender):

errors_internal_test.go

@@ -0,0 +1,82 @@
+package promptkit
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+	"gitea.maximumdirect.net/eric/promptkit/internal/usecase"
+)
+
+func TestMapPublicErrorPreservesGenerationCancellation(t *testing.T) {
+	internalErr := fmt.Errorf("%w: %w", usecase.ErrLLMGenerate, context.Canceled)
+
+	err := mapPublicError(internalErr)
+	if !errors.Is(err, ErrLLMGenerate) {
+		t.Fatalf("mapped error=%v, want ErrLLMGenerate", err)
+	}
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("mapped error=%v, want context.Canceled", err)
+	}
+}
+
+func TestMapPublicErrorTranslatesCapacityError(t *testing.T) {
+	internalErr := &usecase.CapacityError{BackendID: "limited"}
+
+	err := mapPublicError(internalErr)
+	var publicErr *CapacityError
+	if !errors.As(err, &publicErr) || publicErr == nil {
+		t.Fatalf("mapped error=%v, want public CapacityError", err)
+	}
+	if publicErr.BackendID != "limited" {
+		t.Fatalf("mapped backend ID=%q, want limited", publicErr.BackendID)
+	}
+	if !errors.Is(err, ErrCapacityExceeded) {
+		t.Fatalf("mapped error=%v, want ErrCapacityExceeded", err)
+	}
+	if errors.Is(err, ErrInvalidRequest) || errors.Is(err, ErrLLMGenerate) {
+		t.Fatalf("mapped capacity error has an unrelated category: %v", err)
+	}
+	var leakedInternalErr *usecase.CapacityError
+	if errors.As(err, &leakedInternalErr) {
+		t.Fatalf("mapped error exposes internal CapacityError: %v", err)
+	}
+
+	internalErr.BackendID = "changed"
+	if publicErr.BackendID != "limited" {
+		t.Fatalf("mapped backend ID changed with source error: %q", publicErr.BackendID)
+	}
+}
+
+func TestMapPublicErrorPreservesValidationAroundGenerationError(t *testing.T) {
+	internalErr := fmt.Errorf(
+		"%w: %w",
+		usecase.ErrValidation,
+		&llm.ProviderHTTPError{},
+	)
+
+	err := mapPublicError(internalErr)
+	if !errors.Is(err, ErrValidation) {
+		t.Fatalf("mapped error=%v, want ErrValidation", err)
+	}
+	if !errors.Is(err, ErrLLMGenerate) {
+		t.Fatalf("mapped error=%v, want ErrLLMGenerate", err)
+	}
+	var generationErr *GenerationError
+	if !errors.As(err, &generationErr) || generationErr == nil {
+		t.Fatalf("mapped error=%v, want GenerationError", err)
+	}
+	var leakedInternalErr *llm.ProviderHTTPError
+	if errors.As(err, &leakedInternalErr) {
+		t.Fatalf("mapped error exposes internal ProviderHTTPError: %v", err)
+	}
+}
+
+func TestMapPublicErrorDoesNotTreatRequestEncodingAsTransport(t *testing.T) {
+	err := mapPublicError(fmt.Errorf("%w: %w", usecase.ErrLLMGenerate, llm.ErrRequestFailed))
+	if !errors.Is(err, ErrLLMGenerate) || errors.Is(err, ErrTransport) {
+		t.Fatalf("request encoding category = %v", err)
+	}
+}

examples/go-library/observe/main.go

@@ -0,0 +1,157 @@
+package main
+
+import (
+	"context"
+	"embed"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+//go:embed prompts/*.yaml schemas/*.json
+var assets embed.FS
+
+type scriptedTransport struct {
+	proposalCalls int
+}
+
+func (t *scriptedTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if err := req.Context().Err(); err != nil {
+		return nil, err
+	}
+	var request struct {
+		Model string `json:"model"`
+	}
+	if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+		return nil, err
+	}
+	switch request.Model {
+	case "proposal-model":
+		t.proposalCalls++
+		if t.proposalCalls == 1 {
+			return httpResponse(http.StatusServiceUnavailable, `{"error":{}}`), nil
+		}
+		return modelResponse(`{"title":"Queue cleanup","risk":"low"}`, 10, 8), nil
+	case "assessment-model":
+		return modelResponse(`{"recommendation":"accept","confidence":0.9}`, 7, 5), nil
+	default:
+		return nil, fmt.Errorf("unexpected model in offline transport")
+	}
+}
+
+func modelResponse(content string, promptTokens, completionTokens int) *http.Response {
+	body, _ := json.Marshal(map[string]any{
+		"choices": []any{map[string]any{"message": map[string]string{"content": content}}},
+		"usage":   map[string]int{"prompt_tokens": promptTokens, "completion_tokens": completionTokens},
+	})
+	return httpResponse(http.StatusOK, string(body))
+}
+
+func httpResponse(status int, body string) *http.Response {
+	return &http.Response{StatusCode: status, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(body))}
+}
+
+type eventLog struct{ events []promptkit.ExecutionEvent }
+
+func (l *eventLog) record(event promptkit.ExecutionEvent) { l.events = append(l.events, event) }
+
+func (l *eventLog) terminal() (promptkit.ExecutionEvent, error) {
+	if len(l.events) == 0 || l.events[len(l.events)-1].Kind != promptkit.ExecutionFinished {
+		return promptkit.ExecutionEvent{}, fmt.Errorf("execution did not finish")
+	}
+	return l.events[len(l.events)-1], nil
+}
+
+type summary struct {
+	ProposalAttempts           uint64 `json:"proposal_attempts"`
+	ProposalTransientRetries   uint64 `json:"proposal_transient_retries"`
+	ProposalUsageComplete      bool   `json:"proposal_usage_complete"`
+	AssessmentAttempts         uint64 `json:"assessment_attempts"`
+	AssessmentTransientRetries uint64 `json:"assessment_transient_retries"`
+	AssessmentOutcome          string `json:"assessment_outcome"`
+}
+
+func run() (summary, error) {
+	transport := &scriptedTransport{}
+	engine, err := promptkit.NewEngine(promptkit.Config{HTTPClient: &http.Client{Transport: transport}},
+		promptkit.WithPromptFS(assets, "prompts"),
+		promptkit.WithSchemaFS(assets, "schemas"),
+		promptkit.WithBackend(promptkit.Backend{ID: "offline-backend", Endpoint: "https://example.invalid/v1", ConcurrencyLimit: 1}),
+		promptkit.WithProfiles(
+			promptkit.Profile{ID: "proposal-profile", BackendID: "offline-backend", Model: "proposal-model"},
+			promptkit.Profile{ID: "assessment-profile", BackendID: "offline-backend", Model: "assessment-model"},
+		))
+	if err != nil {
+		return summary{}, err
+	}
+
+	var proposalLog eventLog
+	proposal, err := engine.Run(context.Background(), promptkit.RunRequest{
+		PromptID: "example.proposal", Inputs: map[string]promptkit.ArtifactRef{"idea": promptkit.Inline("Reduce queue cleanup toil.")}, Observer: proposalLog.record,
+	})
+	if err != nil {
+		return summary{}, err
+	}
+	if !proposal.Validation.IsValid {
+		return summary{}, fmt.Errorf("proposal failed structural validation")
+	}
+	proposalTerminal, err := proposalLog.terminal()
+	if err != nil {
+		return summary{}, err
+	}
+	var assessmentLog eventLog
+	assessment, err := engine.Run(context.Background(), promptkit.RunRequest{
+		PromptID: "example.assessment", Inputs: map[string]promptkit.ArtifactRef{"proposal": promptkit.Inline(proposal.RawOutput)}, Observer: assessmentLog.record,
+	})
+	if err != nil {
+		return summary{}, err
+	}
+	if !assessment.Validation.IsValid {
+		return summary{}, fmt.Errorf("assessment failed structural validation")
+	}
+	assessmentTerminal, err := assessmentLog.terminal()
+	if err != nil {
+		return summary{}, err
+	}
+	var proposalValue struct {
+		Risk string `json:"risk"`
+	}
+	var assessmentValue struct {
+		Recommendation string `json:"recommendation"`
+	}
+	if err := json.Unmarshal([]byte(proposal.RawOutput), &proposalValue); err != nil {
+		return summary{}, err
+	}
+	if err := json.Unmarshal([]byte(assessment.RawOutput), &assessmentValue); err != nil {
+		return summary{}, err
+	}
+	decision := "rejected"
+	if proposalValue.Risk == "low" && assessmentValue.Recommendation == "accept" {
+		decision = "accepted"
+	}
+	return summary{
+		ProposalAttempts:           proposalTerminal.Attempts,
+		ProposalTransientRetries:   proposalTerminal.TransientRetries,
+		ProposalUsageComplete:      proposalTerminal.Usage.PromptTokens.Complete,
+		AssessmentAttempts:         assessmentTerminal.Attempts,
+		AssessmentTransientRetries: assessmentTerminal.TransientRetries,
+		AssessmentOutcome:          decision,
+	}, nil
+}
+
+func main() {
+	value, err := run()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if err := json.NewEncoder(os.Stdout).Encode(value); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}

examples/go-library/observe/prompts/assessment.yaml

@@ -0,0 +1,17 @@
+id: example.assessment
+version: "1.0.0"
+default_profile: assessment-profile
+description: Assess a structured proposal independently of schema validity.
+inputs:
+  - name: proposal
+    required: true
+    content_type: application/json
+messages:
+  - role: system
+    content: Return a concise assessment as JSON.
+  - role: user
+    content: '{{input "proposal"}}'
+output:
+  format: json
+  validation_mode: json_schema
+  schema_path: assessment.schema.json

examples/go-library/observe/prompts/proposal.yaml

@@ -0,0 +1,17 @@
+id: example.proposal
+version: "1.0.0"
+default_profile: proposal-profile
+description: Propose a bounded improvement from a synthetic idea.
+inputs:
+  - name: idea
+    required: true
+    content_type: text/plain
+messages:
+  - role: system
+    content: Return a concise proposal as JSON.
+  - role: user
+    content: '{{input "idea"}}'
+output:
+  format: json
+  validation_mode: json_schema
+  schema_path: proposal.schema.json

examples/go-library/observe/schemas/assessment.schema.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "object",
+  "required": ["recommendation", "confidence"],
+  "properties": {
+    "recommendation": {"type": "string"},
+    "confidence": {"type": "number"}
+  },
+  "additionalProperties": false
+}

examples/go-library/observe/schemas/proposal.schema.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "object",
+  "required": ["title", "risk"],
+  "properties": {
+    "title": {"type": "string"},
+    "risk": {"type": "string"}
+  },
+  "additionalProperties": false
+}

examples/go-library/run/main.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+type deterministicClient struct{}
+
+func (deterministicClient) Generate(
+	ctx context.Context,
+	_ promptkit.GenerateRequest,
+) (*promptkit.GenerateResponse, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	return &promptkit.GenerateResponse{
+		Content: "Ada finished the migration review.",
+		Usage: promptkit.TokenUsage{
+			PromptTokens:     12,
+			CompletionTokens: 6,
+			TotalTokens:      18,
+		},
+	}, nil
+}
+
+type summary struct {
+	Output           string                     `json:"output"`
+	ValidationStatus promptkit.ValidationStatus `json:"validation_status"`
+	IsValid          bool                       `json:"is_valid"`
+	Model            string                     `json:"model"`
+	TotalTokens      int                        `json:"total_tokens"`
+}
+
+func main() {
+	engine, err := promptkit.NewEngine(
+		promptkit.Config{},
+		promptkit.WithPromptFile("examples/go-library/run/prompt.yaml"),
+		promptkit.WithProfiles(promptkit.Profile{
+			ID:       "offline-example",
+			Endpoint: "https://example.invalid/v1",
+			Model:    "offline-model",
+		}),
+		promptkit.WithLLMClient(deterministicClient{}),
+	)
+	if err != nil {
+		exit(err)
+	}
+
+	result, err := engine.Run(context.Background(), promptkit.RunRequest{
+		PromptID: "example.run",
+		Inputs: map[string]promptkit.ArtifactRef{
+			"note": promptkit.Inline("Ada finished the migration review."),
+		},
+	})
+	if err != nil {
+		exit(err)
+	}
+
+	encoder := json.NewEncoder(os.Stdout)
+	encoder.SetIndent("", "  ")
+	if err := encoder.Encode(summary{
+		Output:           result.RawOutput,
+		ValidationStatus: result.Validation.Status,
+		IsValid:          result.Validation.IsValid,
+		Model:            result.ModelName,
+		TotalTokens:      result.Usage.TotalTokens,
+	}); err != nil {
+		exit(err)
+	}
+}
+
+func exit(err error) {
+	fmt.Fprintln(os.Stderr, err)
+	os.Exit(1)
+}

examples/go-library/run/prompt.yaml

@@ -0,0 +1,16 @@
+id: example.run
+version: "1.0.0"
+default_profile: offline-example
+description: Run a prompt with a deterministic injected model client.
+inputs:
+  - name: note
+    required: true
+    content_type: text/plain
+messages:
+  - role: system
+    content: Summarize the note in one sentence.
+  - role: user
+    content: '{{input "note"}}'
+output:
+  format: text
+  validation_mode: basic

formatting.go

@@ -2,19 +2,23 @@ package promptkit
 
 import "fmt"
 
-// String returns a concise request summary without exposing direct API keys.
+// String returns a concise request summary without exposing the direct API key
+// or input and variable contents. Reflection-based formatting does not carry
+// this guarantee.
 func (r RunRequest) String() string {
 	return r.redactedString()
 }
 
-// GoString returns a concise request summary without exposing direct API keys.
+// GoString returns a concise request summary without exposing the direct API
+// key or input and variable contents. Reflection-based formatting does not
+// carry this guarantee.
 func (r RunRequest) GoString() string {
 	return r.redactedString()
 }
 
 func (r RunRequest) redactedString() string {
 	return fmt.Sprintf(
-		"promptkit.RunRequest{PromptID:%q PromptVersion:%q ProfileID:%q APIKeySet:%t Inputs:%d Vars:%d ExecutionSet:%t ValidationSet:%t Metadata:%d}",
+		"promptkit.RunRequest{PromptID:%q PromptVersion:%q ProfileID:%q APIKeySet:%t Inputs:%d Vars:%d ExecutionSet:%t ValidationSet:%t AppendedMessages:%d}",
 		r.PromptID,
 		r.PromptVersion,
 		r.ProfileID,
@@ -23,18 +27,20 @@ func (r RunRequest) redactedString() string {
 		len(r.Vars),
 		r.Execution != nil,
 		r.Validation != nil,
-		len(r.Metadata),
+		len(r.AppendedMessages),
 	)
 }
 
 // String returns a concise request summary without exposing direct API keys or
-// rendered prompt content.
+// rendered prompt content. Reflection-based formatting does not carry this
+// guarantee.
 func (r GenerateRequest) String() string {
 	return r.redactedString()
 }
 
 // GoString returns a concise request summary without exposing direct API keys or
-// rendered prompt content.
+// rendered prompt content. Reflection-based formatting does not carry this
+// guarantee.
 func (r GenerateRequest) GoString() string {
 	return r.redactedString()
 }

generation_error.go

@@ -0,0 +1,87 @@
+package promptkit
+
+import "fmt"
+
+// GenerationError reports a non-2xx response from Promptkit's built-in
+// OpenAI-compatible client during [Engine.Run] or [Engine.RunPrepared].
+//
+// Engine-produced values are immutable, caller-owned values. Use errors.Is to
+// match [ErrLLMGenerate] and errors.As with a *GenerationError target to obtain
+// this type. The four provider accessors expose untrusted provider-controlled
+// values that can contain sensitive request or schema fragments. Applications
+// must apply their own disclosure policy before logging, displaying, or
+// returning them to another caller.
+//
+// Accessors, Error, GoString, and Unwrap are safe on a nil receiver and a zero
+// value. Default and Go-syntax formatting deliberately redact provider details.
+// GenerationError has no stable JSON representation.
+type GenerationError struct {
+	statusCode      int
+	providerCode    string
+	providerType    string
+	providerMessage string
+}
+
+func newGenerationError(statusCode int, providerCode, providerType, providerMessage string) *GenerationError {
+	return &GenerationError{
+		statusCode:      statusCode,
+		providerCode:    providerCode,
+		providerType:    providerType,
+		providerMessage: providerMessage,
+	}
+}
+
+// StatusCode returns the received provider HTTP status code, or zero for a nil
+// receiver or zero value.
+func (e *GenerationError) StatusCode() int {
+	if e == nil {
+		return 0
+	}
+	return e.statusCode
+}
+
+// ProviderCode returns the normalized provider error code, if present. Its
+// value is untrusted and may contain sensitive data.
+func (e *GenerationError) ProviderCode() string {
+	if e == nil {
+		return ""
+	}
+	return e.providerCode
+}
+
+// ProviderType returns the normalized provider error type, if present. Its
+// value is untrusted and may contain sensitive data.
+func (e *GenerationError) ProviderType() string {
+	if e == nil {
+		return ""
+	}
+	return e.providerType
+}
+
+// ProviderMessage returns the bounded normalized provider diagnostic, if
+// present. Its value is untrusted and may contain sensitive data.
+func (e *GenerationError) ProviderMessage() string {
+	if e == nil {
+		return ""
+	}
+	return e.providerMessage
+}
+
+// Error returns a redacted diagnostic that is not a parsing contract.
+func (e *GenerationError) Error() string {
+	if e == nil || e.statusCode == 0 {
+		return ErrLLMGenerate.Error()
+	}
+	return fmt.Sprintf("%s: provider returned HTTP status %d", ErrLLMGenerate, e.statusCode)
+}
+
+// GoString returns the same redacted diagnostic as Error.
+func (e *GenerationError) GoString() string {
+	return e.Error()
+}
+
+// Unwrap returns ErrLLMGenerate. It is safe to call on a nil receiver or zero
+// value.
+func (e *GenerationError) Unwrap() error {
+	return ErrLLMGenerate
+}

generation_error_contract_test.go

@@ -0,0 +1,235 @@
+package promptkit_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+func TestBuiltInGenerationError(t *testing.T) {
+	const (
+		codeMarker    = "provider-code-marker"
+		typeMarker    = "provider-type-marker"
+		messageMarker = "provider-message-marker"
+	)
+	engine := newBuiltInGenerationErrorEngine(t, http.StatusUnprocessableEntity,
+		`{"error":{"code":"`+codeMarker+`","type":"`+typeMarker+`","message":"`+messageMarker+`"}}`)
+
+	result, err := engine.Run(context.Background(), generationErrorRunRequest())
+	if result != nil {
+		t.Fatalf("Run result = %#v, want nil", result)
+	}
+	assertGenerationError(t, err, http.StatusUnprocessableEntity, codeMarker, typeMarker, messageMarker)
+
+	preparedEngine := newBuiltInGenerationErrorEngine(t, http.StatusServiceUnavailable, `{"error":{}}`)
+	prepared, err := preparedEngine.PrepareExecution(context.Background(), generationErrorRunRequest())
+	if err != nil {
+		t.Fatalf("PrepareExecution: %v", err)
+	}
+	result, err = preparedEngine.RunPrepared(context.Background(), prepared)
+	if result != nil {
+		t.Fatalf("RunPrepared result = %#v, want nil", result)
+	}
+	assertGenerationError(t, err, http.StatusServiceUnavailable, "", "", "")
+}
+
+func TestBuiltInGenerationErrorWithAppendedMessages(t *testing.T) {
+	const messageMarker = "combined-request-provider-marker"
+	engine := newBuiltInGenerationErrorEngine(t, http.StatusUnprocessableEntity,
+		`{"error":{"message":"`+messageMarker+`"}}`)
+	request := generationErrorRunRequest()
+	request.AppendedMessages = []promptkit.RenderedMessage{
+		{Role: promptkit.RoleAssistant, Content: "previous response"},
+		{Role: promptkit.RoleUser, Content: "consumer correction"},
+	}
+
+	result, err := engine.Run(context.Background(), request)
+	if result != nil {
+		t.Fatalf("Run result = %#v, want nil", result)
+	}
+	assertGenerationError(t, err, http.StatusUnprocessableEntity, "", "", messageMarker)
+}
+
+func TestBuiltInRepairGenerationError(t *testing.T) {
+	const (
+		codeMarker    = "repair-code-marker"
+		typeMarker    = "repair-type-marker"
+		messageMarker = "repair-message-marker"
+	)
+	calls := 0
+	config := contractConfig(frameworkSchemaDir)
+	config.HTTPClient = &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+		calls++
+		if calls == 1 {
+			body := `{"choices":[{"message":{"content":"not-json"}}]}`
+			return &http.Response{StatusCode: http.StatusOK, ContentLength: int64(len(body)), Body: io.NopCloser(strings.NewReader(body))}, nil
+		}
+		body := `{"error":{"code":"` + codeMarker + `","type":"` + typeMarker + `","message":"` + messageMarker + `"}}`
+		return &http.Response{StatusCode: http.StatusUnprocessableEntity, ContentLength: int64(len(body)), Body: io.NopCloser(strings.NewReader(body))}, nil
+	})}
+	engine, err := promptkit.NewEngine(config)
+	if err != nil {
+		t.Fatalf("NewEngine: %v", err)
+	}
+	req := generationErrorRunRequest()
+	req.Validation = &promptkit.OutputContract{
+		Format:         promptkit.FormatJSON,
+		ValidationMode: promptkit.ValidationJSON,
+		RepairAttempts: 1,
+	}
+
+	result, err := engine.Run(context.Background(), req)
+	if result != nil {
+		t.Fatalf("Run result = %#v, want nil", result)
+	}
+	if calls != 2 {
+		t.Fatalf("provider calls = %d, want 2", calls)
+	}
+	assertGenerationError(t, err, http.StatusUnprocessableEntity, codeMarker, typeMarker, messageMarker)
+}
+
+func TestBuiltInGenerationFailureCategories(t *testing.T) {
+	transportCause := errors.New("private transport diagnostic")
+	config := contractConfig(frameworkSchemaDir)
+	config.HTTPClient = &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+		return nil, transportCause
+	})}
+	engine, err := promptkit.NewEngine(config)
+	if err != nil {
+		t.Fatal(err)
+	}
+	result, err := engine.Run(context.Background(), generationErrorRunRequest())
+	if result != nil || !errors.Is(err, promptkit.ErrLLMGenerate) || !errors.Is(err, promptkit.ErrTransport) || !errors.Is(err, transportCause) {
+		t.Fatalf("transport result=%#v, error=%v", result, err)
+	}
+	if errors.Is(err, promptkit.ErrMalformedResponse) || strings.Contains(fmt.Sprintf("%#v", err), transportCause.Error()) {
+		t.Fatalf("transport category or formatting = %v", err)
+	}
+
+	for _, tc := range []struct {
+		name string
+		body string
+	}{
+		{name: "invalid framing", body: `{"choices":[]}{}`},
+		{name: "missing choices", body: `{"choices":[]}`},
+		{name: "missing content", body: `{"choices":[{"message":{}}]}`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			engine := newBuiltInGenerationErrorEngine(t, http.StatusOK, tc.body)
+			result, err := engine.Run(context.Background(), generationErrorRunRequest())
+			if result != nil || !errors.Is(err, promptkit.ErrLLMGenerate) || !errors.Is(err, promptkit.ErrMalformedResponse) || errors.Is(err, promptkit.ErrTransport) {
+				t.Fatalf("malformed result=%#v, error=%v", result, err)
+			}
+		})
+	}
+}
+
+func TestBuiltInGenerationPreservesContextIdentity(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		cause error
+	}{
+		{name: "canceled", cause: context.Canceled},
+		{name: "deadline", cause: context.DeadlineExceeded},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			config := contractConfig(frameworkSchemaDir)
+			config.HTTPClient = &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+				return nil, tc.cause
+			})}
+			engine, err := promptkit.NewEngine(config)
+			if err != nil {
+				t.Fatal(err)
+			}
+			result, err := engine.Run(context.Background(), generationErrorRunRequest())
+			if result != nil || !errors.Is(err, tc.cause) || !errors.Is(err, promptkit.ErrLLMGenerate) || !errors.Is(err, promptkit.ErrTransport) {
+				t.Fatalf("context result=%#v, error=%v", result, err)
+			}
+		})
+	}
+}
+
+func TestInjectedGenerationFailureCategories(t *testing.T) {
+	for _, tc := range []struct {
+		name      string
+		client    *fakeLLMClient
+		malformed bool
+	}{
+		{name: "nil response", client: &fakeLLMClient{}, malformed: true},
+		{name: "arbitrary error", client: &fakeLLMClient{err: errors.New("injected failure")}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			engine := newContractEngineWithOptions(t, frameworkSchemaDir, promptkit.WithLLMClient(tc.client))
+			result, err := engine.Run(context.Background(), generationErrorRunRequest())
+			if result != nil || !errors.Is(err, promptkit.ErrLLMGenerate) || errors.Is(err, promptkit.ErrTransport) || errors.Is(err, promptkit.ErrMalformedResponse) != tc.malformed {
+				t.Fatalf("injected result=%#v, error=%v", result, err)
+			}
+			if tc.client.err != nil && !errors.Is(err, tc.client.err) {
+				t.Fatalf("injected cause lost: %v", err)
+			}
+		})
+	}
+}
+
+func assertGenerationError(t *testing.T, err error, statusCode int, code, providerType, message string) {
+	t.Helper()
+
+	if !errors.Is(err, promptkit.ErrLLMGenerate) {
+		t.Fatalf("errors.Is(%v, ErrLLMGenerate) = false", err)
+	}
+	var generationErr *promptkit.GenerationError
+	if !errors.As(err, &generationErr) || generationErr == nil {
+		t.Fatalf("error = %T, want *GenerationError", err)
+	}
+	if generationErr.StatusCode() != statusCode || generationErr.ProviderCode() != code || generationErr.ProviderType() != providerType || generationErr.ProviderMessage() != message {
+		t.Fatalf("GenerationError = %#v", generationErr)
+	}
+
+	wantFormatted := fmt.Sprintf("failed to generate output: provider returned HTTP status %d", statusCode)
+	for _, rendered := range []string{fmt.Sprintf("%v", generationErr), fmt.Sprintf("%+v", generationErr), fmt.Sprintf("%#v", generationErr)} {
+		if rendered != wantFormatted {
+			t.Fatalf("formatted error = %q, want %q", rendered, wantFormatted)
+		}
+		for _, marker := range []string{code, providerType, message} {
+			if marker != "" && strings.Contains(rendered, marker) {
+				t.Fatalf("formatted error exposed provider marker %q: %q", marker, rendered)
+			}
+		}
+	}
+}
+
+func newBuiltInGenerationErrorEngine(t *testing.T, statusCode int, body string) *promptkit.Engine {
+	t.Helper()
+
+	config := contractConfig(frameworkSchemaDir)
+	noRetries := 0
+	config.TransientRetries = &noRetries
+	config.HTTPClient = &http.Client{Transport: roundTripFunc(func(*http.Request) (*http.Response, error) {
+		return &http.Response{
+			StatusCode:    statusCode,
+			ContentLength: int64(len(body)),
+			Body:          io.NopCloser(strings.NewReader(body)),
+		}, nil
+	})}
+	engine, err := promptkit.NewEngine(config)
+	if err != nil {
+		t.Fatalf("NewEngine: %v", err)
+	}
+	return engine
+}
+
+func generationErrorRunRequest() promptkit.RunRequest {
+	return promptkit.RunRequest{
+		PromptID: frameworkMarkdownSummaryPromptID,
+		Inputs: map[string]promptkit.ArtifactRef{
+			"transcript": promptkit.Inline("Rin opens the gate."),
+			"glossary":   promptkit.Inline("gate: A guarded passage."),
+		},
+	}
+}

generation_error_internal_test.go

@@ -0,0 +1,32 @@
+package promptkit
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestGenerationErrorNilAndZeroValue(t *testing.T) {
+	var nilError *GenerationError
+	zeroError := &GenerationError{}
+
+	for name, err := range map[string]*GenerationError{
+		"nil":  nilError,
+		"zero": zeroError,
+	} {
+		t.Run(name, func(t *testing.T) {
+			if err.StatusCode() != 0 || err.ProviderCode() != "" || err.ProviderType() != "" || err.ProviderMessage() != "" {
+				t.Fatalf("accessors returned provider details: %#v", err)
+			}
+			if err.Error() != "failed to generate output" || err.GoString() != "failed to generate output" {
+				t.Fatalf("redacted formatting = (%q, %q)", err.Error(), err.GoString())
+			}
+			if fmt.Sprintf("%v", err) != "failed to generate output" || fmt.Sprintf("%#v", err) != "failed to generate output" {
+				t.Fatalf("formatted error = (%q, %q)", fmt.Sprintf("%v", err), fmt.Sprintf("%#v", err))
+			}
+			if !errors.Is(err, ErrLLMGenerate) {
+				t.Fatalf("errors.Is(%v, ErrLLMGenerate) = false", err)
+			}
+		})
+	}
+}

go.mod

@@ -3,6 +3,8 @@ module gitea.maximumdirect.net/eric/promptkit
 go 1.25.5
 
 require (
+	gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0
+	gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2 v2.20260926.0
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.2
 	gopkg.in/yaml.v3 v3.0.1
 )

go.sum

@@ -1,3 +1,7 @@
+gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0 h1:wdab+R+lgMZxzYwhbAuCrW7zdSQ1cW9ovBR6UzLmZR4=
+gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0/go.mod h1:a3VBbh9oaGXD6ruxhtwHj+AWW6DY/SSyby1QtMmYSUo=
+gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2 v2.20260926.0 h1:baCCIB6Ee5t0S4Zc++NTBIPcJEv5UPS6DlSrpZfykwg=
+gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2 v2.20260926.0/go.mod h1:mtgD1E0SGm0e/I8Ffhz+AYX7GN7RKUWJXehNFIKHs4Y=
 github.com/dlclark/regexp2 v1.11.0 h1:G/nrcoOa7ZXlpoa/91N3X7mM3r8eIlMBBJZvsz/mxKI=
 github.com/dlclark/regexp2 v1.11.0/go.mod h1:DHkYz0B9wPfa6wondMfaivmHpzrQ3v9q8cnmRbL6yW8=
 github.com/santhosh-tekuri/jsonschema/v6 v6.0.2 h1:KRzFb2m7YtdldCEkzs6KqmJw4nqEVZGK7IN2kJkjTuQ=

internal/artifact/reader.go

@@ -16,10 +16,12 @@ import (
 
 var (
 	ErrUnsupportedRefType = errors.New("unsupported artifact reference type")
-	ErrMissingInlineBody  = errors.New("missing body for inline artifact")
 	ErrMissingFilePath    = errors.New("missing file path for file artifact")
+	ErrUnsupportedFile    = errors.New("file artifact path is not a regular file")
 )
 
+const fileReadChunkSize = 64 * 1024
+
 // Reader resolves artifact references into actual artifacts.
 type Reader interface {
 	Read(ctx context.Context, ref domain.ArtifactRef) (*domain.Artifact, error)
@@ -34,7 +36,7 @@ type CompositeReader struct {
 func NewCompositeReader() Reader {
 	return &CompositeReader{
 		inlineReader: &inlineReader{},
-		fileReader:   &fileReader{},
+		fileReader:   &fileReader{open: openArtifactFile},
 	}
 }
 
@@ -64,10 +66,6 @@ func (r *inlineReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domai
 	default:
 	}
 
-	if ref.Body == "" {
-		return nil, ErrMissingInlineBody
-	}
-
 	body := []byte(ref.Body)
 	return &domain.Artifact{
 		ContentType: defaults.ContentTypeTextPlain,
@@ -78,7 +76,15 @@ func (r *inlineReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domai
 	}, nil
 }
 
-type fileReader struct{}
+type artifactFile interface {
+	Read([]byte) (int, error)
+	Stat() (os.FileInfo, error)
+	Close() error
+}
+
+type fileReader struct {
+	open func(string) (artifactFile, error)
+}
 
 func (r *fileReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domain.Artifact, error) {
 	select {
@@ -91,25 +97,71 @@ func (r *fileReader) Read(ctx context.Context, ref domain.ArtifactRef) (*domain.
 		return nil, ErrMissingFilePath
 	}
 
-	return readFileArtifact(ref.URI)
+	return readFileArtifact(ctx, ref.URI, r.open)
 }
 
-func readFileArtifact(path string) (*domain.Artifact, error) {
-	file, err := os.Open(path)
+func openArtifactFile(path string) (artifactFile, error) {
+	return os.Open(path)
+}
+
+func readFileArtifact(ctx context.Context, path string, open func(string) (artifactFile, error)) (*domain.Artifact, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	info, err := os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read file %s: %w", path, err)
+	}
+	if !info.Mode().IsRegular() {
+		return nil, fmt.Errorf("%w: %s", ErrUnsupportedFile, path)
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+
+	file, err := open(path)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read file %s: %w", path, err)
 	}
 	defer file.Close()
 
-	data, err := io.ReadAll(file)
+	openedInfo, err := file.Stat()
 	if err != nil {
-		return nil, fmt.Errorf("failed to read file %s: %w", path, err)
+		return nil, fmt.Errorf("failed to inspect opened file %s: %w", path, err)
+	}
+	if !openedInfo.Mode().IsRegular() {
+		return nil, fmt.Errorf("%w: %s", ErrUnsupportedFile, path)
+	}
+
+	data := make([]byte, 0)
+	chunk := make([]byte, fileReadChunkSize)
+	for {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		n, readErr := file.Read(chunk)
+		if n > 0 {
+			data = append(data, chunk[:n]...)
+		}
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		if errors.Is(readErr, io.EOF) {
+			break
+		}
+		if readErr != nil {
+			return nil, fmt.Errorf("failed to read file %s: %w", path, readErr)
+		}
 	}
 
 	contentType := mime.TypeByExtension(filepath.Ext(path))
 	if contentType == "" {
 		contentType = defaults.ContentTypeTextPlain
 	}
+	hash := fmt.Sprintf("%x", sha256.Sum256(data))
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
 
 	return &domain.Artifact{
 		Name:        filepath.Base(path),
@@ -117,6 +169,6 @@ func readFileArtifact(path string) (*domain.Artifact, error) {
 		Body:        data,
 		URI:         path,
 		Size:        int64(len(data)),
-		Hash:        fmt.Sprintf("%x", sha256.Sum256(data)),
+		Hash:        hash,
 	}, nil
 }

internal/artifact/reader_fifo_linux_test.go

@@ -0,0 +1,43 @@
+//go:build linux
+
+package artifact
+
+import (
+	"context"
+	"errors"
+	"path/filepath"
+	"syscall"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+func TestFileReaderRejectsFIFOBeforeOpen(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "artifact.fifo")
+	if err := syscall.Mkfifo(path, 0o600); err != nil {
+		t.Fatalf("create fifo: %v", err)
+	}
+
+	type result struct {
+		artifact *domain.Artifact
+		err      error
+	}
+	done := make(chan result, 1)
+	go func() {
+		artifact, err := NewCompositeReader().Read(context.Background(), domain.ArtifactRef{
+			Type: domain.ArtifactRefFile,
+			URI:  path,
+		})
+		done <- result{artifact: artifact, err: err}
+	}()
+
+	select {
+	case got := <-done:
+		if got.artifact != nil || !errors.Is(got.err, ErrUnsupportedFile) {
+			t.Fatalf("artifact=%#v err=%v, want nil/ErrUnsupportedFile", got.artifact, got.err)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("FIFO read blocked instead of rejecting the non-regular file")
+	}
+}

internal/artifact/reader_test.go

@@ -1,6 +1,7 @@
 package artifact
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"os"
@@ -11,54 +12,97 @@ import (
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
 )
 
-func TestCompositeReader_Read(t *testing.T) {
+func TestCompositeReaderRejectsUnsupportedReferences(t *testing.T) {
+	_, err := NewCompositeReader().Read(context.Background(), domain.ArtifactRef{
+		Type: domain.ArtifactRefType("unsupported"),
+		URI:  "unsupported://bucket/key",
+	})
+	if !errors.Is(err, ErrUnsupportedRefType) {
+		t.Fatalf("expected ErrUnsupportedRefType, got %v", err)
+	}
+}
+
+func TestCompositeReaderSourceParityAndOpaqueHashes(t *testing.T) {
 	reader := NewCompositeReader()
-	ctx := context.Background()
+	hashes := make(map[string]string)
+	tests := []struct {
+		name    string
+		content string
+	}{
+		{name: "empty", content: ""},
+		{name: "ordinary", content: "same content"},
+		{name: "changed", content: "changed content"},
+	}
 
-	t.Run("inline artifact", func(t *testing.T) {
-		ref := domain.ArtifactRef{
-			Type: domain.ArtifactRefInline,
-			Body: "hello world",
-		}
-		art, err := reader.Read(ctx, ref)
-		if err != nil {
-			t.Fatalf("unexpected error: %v", err)
-		}
-		if string(art.Body) != "hello world" {
-			t.Errorf("expected 'hello world', got %s", string(art.Body))
-		}
-		if art.ContentType != "text/plain" {
-			t.Errorf("expected text/plain content type, got %q", art.ContentType)
-		}
-		if art.Hash != "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9" {
-			t.Errorf("unexpected hash: %s", art.Hash)
-		}
-		if art.Size != int64(len(ref.Body)) {
-			t.Errorf("expected size %d, got %d", len(ref.Body), art.Size)
-		}
-	})
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			filePath := filepath.Join(t.TempDir(), "artifact.txt")
+			if err := os.WriteFile(filePath, []byte(tc.content), 0o600); err != nil {
+				t.Fatal(err)
+			}
 
-	t.Run("inline artifact missing body", func(t *testing.T) {
-		ref := domain.ArtifactRef{
-			Type: domain.ArtifactRefInline,
-			Body: "",
-		}
-		_, err := reader.Read(ctx, ref)
-		if !errors.Is(err, ErrMissingInlineBody) {
-			t.Errorf("expected ErrMissingInlineBody, got %v", err)
-		}
-	})
+			sources := []struct {
+				name    string
+				ref     domain.ArtifactRef
+				wantURI string
+			}{
+				{
+					name: "inline",
+					ref:  domain.ArtifactRef{Type: domain.ArtifactRefInline, Body: tc.content},
+				},
+				{
+					name:    "inline with uri",
+					ref:     domain.ArtifactRef{Type: domain.ArtifactRefInline, URI: "memory://input", Body: tc.content},
+					wantURI: "memory://input",
+				},
+				{
+					name:    "file",
+					ref:     domain.ArtifactRef{Type: domain.ArtifactRefFile, URI: filePath},
+					wantURI: filePath,
+				},
+			}
 
-	t.Run("unsupported ref type", func(t *testing.T) {
-		ref := domain.ArtifactRef{
-			Type: domain.ArtifactRefType("unsupported"),
-			URI:  "unsupported://bucket/key",
-		}
-		_, err := reader.Read(ctx, ref)
-		if !errors.Is(err, ErrUnsupportedRefType) {
-			t.Error("expected error for unsupported type")
-		}
-	})
+			var sourceHash string
+			for _, source := range sources {
+				t.Run(source.name, func(t *testing.T) {
+					first, err := reader.Read(context.Background(), source.ref)
+					if err != nil {
+						t.Fatalf("first read: %v", err)
+					}
+					second, err := reader.Read(context.Background(), source.ref)
+					if err != nil {
+						t.Fatalf("second read: %v", err)
+					}
+					if string(first.Body) != tc.content || first.Size != int64(len(tc.content)) {
+						t.Fatalf("body=%q size=%d, want %q/%d", first.Body, first.Size, tc.content, len(tc.content))
+					}
+					if first.URI != source.wantURI {
+						t.Fatalf("URI = %q, want %q", first.URI, source.wantURI)
+					}
+					if first.Hash == "" || first.Hash != second.Hash {
+						t.Fatalf("hashes are not non-empty and stable: %q/%q", first.Hash, second.Hash)
+					}
+					if sourceHash == "" {
+						sourceHash = first.Hash
+					} else if first.Hash != sourceHash {
+						t.Fatalf("equal content hashes differ: %q/%q", sourceHash, first.Hash)
+					}
+					if source.ref.Type == domain.ArtifactRefFile {
+						if first.Name != filepath.Base(filePath) || !strings.HasPrefix(first.ContentType, "text/plain") {
+							t.Fatalf("unexpected file metadata: %+v", first)
+						}
+					} else if first.ContentType != "text/plain" {
+						t.Fatalf("inline content type = %q", first.ContentType)
+					}
+				})
+			}
+			hashes[tc.name] = sourceHash
+		})
+	}
+
+	if hashes["empty"] == hashes["ordinary"] || hashes["ordinary"] == hashes["changed"] {
+		t.Fatalf("changed content did not change opaque hash: %#v", hashes)
+	}
 }
 
 func TestCompositeReaderCopiesInlineData(t *testing.T) {
@@ -87,94 +131,154 @@ func TestCompositeReaderCopiesInlineData(t *testing.T) {
 	}
 }
 
-func TestCompositeReaderHonorsCancellation(t *testing.T) {
-	ctx, cancel := context.WithCancel(context.Background())
-	cancel()
+func TestCompositeReaderHonorsPreCancellation(t *testing.T) {
+	filePath := filepath.Join(t.TempDir(), "artifact.txt")
+	if err := os.WriteFile(filePath, []byte("ignored"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	tests := []struct {
+		name string
+		ref  domain.ArtifactRef
+	}{
+		{name: "inline", ref: domain.ArtifactRef{Type: domain.ArtifactRefInline, Body: "ignored"}},
+		{name: "file", ref: domain.ArtifactRef{Type: domain.ArtifactRefFile, URI: filePath}},
+	}
 
-	_, err := NewCompositeReader().Read(ctx, domain.ArtifactRef{
-		Type: domain.ArtifactRefInline,
-		Body: "ignored",
-	})
-	if !errors.Is(err, context.Canceled) {
-		t.Fatalf("expected context cancellation, got %v", err)
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx, cancel := context.WithCancel(context.Background())
+			cancel()
+
+			artifact, err := NewCompositeReader().Read(ctx, tc.ref)
+			if artifact != nil || !errors.Is(err, context.Canceled) {
+				t.Fatalf("artifact=%#v err=%v, want nil/context.Canceled", artifact, err)
+			}
+		})
 	}
 }
 
-func TestFileReader_Read(t *testing.T) {
-	content := []byte("test file content")
-	filePath := filepath.Join(t.TempDir(), "artifact.txt")
-	if err := os.WriteFile(filePath, content, 0o600); err != nil {
-		t.Fatal(err)
-	}
-
+func TestFileReaderFailuresAndMetadata(t *testing.T) {
 	reader := NewCompositeReader()
-	ctx := context.Background()
-
-	t.Run("file artifact loading", func(t *testing.T) {
-		ref := domain.ArtifactRef{
-			Type: domain.ArtifactRefFile,
-			URI:  filePath,
-		}
-		art, err := reader.Read(ctx, ref)
-		if err != nil {
-			t.Fatalf("unexpected error: %v", err)
-		}
-		if string(art.Body) != string(content) {
-			t.Errorf("expected %s, got %s", string(content), string(art.Body))
-		}
-		if art.Name != filepath.Base(filePath) {
-			t.Errorf("expected name %q, got %q", filepath.Base(filePath), art.Name)
-		}
-		if !strings.HasPrefix(art.ContentType, "text/plain") {
-			t.Errorf("expected text content type, got %q", art.ContentType)
-		}
-		if art.URI != filePath {
-			t.Errorf("expected URI %q, got %q", filePath, art.URI)
-		}
-		if art.Size != int64(len(content)) {
-			t.Errorf("expected size %d, got %d", len(content), art.Size)
-		}
-		if art.Hash != "60f5237ed4049f0382661ef009d2bc42e48c3ceb3edb6600f7024e7ab3b838f3" {
-			t.Errorf("unexpected hash: %s", art.Hash)
-		}
-	})
 
 	t.Run("missing file path", func(t *testing.T) {
-		ref := domain.ArtifactRef{
-			Type: domain.ArtifactRefFile,
-			URI:  "",
-		}
-		_, err := reader.Read(ctx, ref)
+		_, err := reader.Read(context.Background(), domain.ArtifactRef{Type: domain.ArtifactRefFile})
 		if !errors.Is(err, ErrMissingFilePath) {
-			t.Errorf("expected ErrMissingFilePath, got %v", err)
+			t.Fatalf("expected ErrMissingFilePath, got %v", err)
 		}
 	})
 
 	t.Run("missing file", func(t *testing.T) {
-		ref := domain.ArtifactRef{
+		_, err := reader.Read(context.Background(), domain.ArtifactRef{
 			Type: domain.ArtifactRefFile,
 			URI:  filepath.Join(t.TempDir(), "missing.txt"),
-		}
-		if _, err := reader.Read(ctx, ref); err == nil {
+		})
+		if err == nil {
 			t.Fatal("expected missing file error")
 		}
 	})
 
+	t.Run("directory rejected before open", func(t *testing.T) {
+		artifact, err := reader.Read(context.Background(), domain.ArtifactRef{
+			Type: domain.ArtifactRefFile,
+			URI:  t.TempDir(),
+		})
+		if artifact != nil || !errors.Is(err, ErrUnsupportedFile) {
+			t.Fatalf("artifact=%#v err=%v, want nil/ErrUnsupportedFile", artifact, err)
+		}
+	})
+
+	t.Run("non-regular opened target rejected", func(t *testing.T) {
+		filePath := filepath.Join(t.TempDir(), "artifact.txt")
+		if err := os.WriteFile(filePath, []byte("content"), 0o600); err != nil {
+			t.Fatal(err)
+		}
+		directoryInfo, err := os.Stat(t.TempDir())
+		if err != nil {
+			t.Fatal(err)
+		}
+		fileReader := &fileReader{open: func(path string) (artifactFile, error) {
+			file, err := os.Open(path)
+			if err != nil {
+				return nil, err
+			}
+			return &reportedInfoFile{artifactFile: file, info: directoryInfo}, nil
+		}}
+
+		artifact, err := fileReader.Read(context.Background(), domain.ArtifactRef{
+			Type: domain.ArtifactRefFile,
+			URI:  filePath,
+		})
+		if artifact != nil || !errors.Is(err, ErrUnsupportedFile) {
+			t.Fatalf("artifact=%#v err=%v, want nil/ErrUnsupportedFile", artifact, err)
+		}
+	})
+
 	t.Run("unknown extension uses text fallback", func(t *testing.T) {
-		path := filepath.Join(t.TempDir(), "artifact.unknownextension")
-		if err := os.WriteFile(path, content, 0o600); err != nil {
+		filePath := filepath.Join(t.TempDir(), "artifact.unknownextension")
+		if err := os.WriteFile(filePath, []byte("content"), 0o600); err != nil {
 			t.Fatal(err)
 		}
 
-		art, err := reader.Read(ctx, domain.ArtifactRef{
+		artifact, err := reader.Read(context.Background(), domain.ArtifactRef{
 			Type: domain.ArtifactRefFile,
-			URI:  path,
+			URI:  filePath,
 		})
 		if err != nil {
-			t.Fatalf("unexpected error: %v", err)
+			t.Fatalf("read artifact: %v", err)
 		}
-		if art.ContentType != "text/plain" {
-			t.Errorf("expected text/plain fallback, got %q", art.ContentType)
+		if artifact.ContentType != "text/plain" {
+			t.Fatalf("content type = %q", artifact.ContentType)
 		}
 	})
 }
+
+func TestFileReaderCancelsAfterReadProgress(t *testing.T) {
+	filePath := filepath.Join(t.TempDir(), "artifact.bin")
+	content := bytes.Repeat([]byte("x"), fileReadChunkSize*2)
+	if err := os.WriteFile(filePath, content, 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	var opened *cancelAfterProgressFile
+	reader := &fileReader{open: func(path string) (artifactFile, error) {
+		file, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		opened = &cancelAfterProgressFile{artifactFile: file, cancel: cancel}
+		return opened, nil
+	}}
+
+	artifact, err := reader.Read(ctx, domain.ArtifactRef{Type: domain.ArtifactRefFile, URI: filePath})
+	if artifact != nil || !errors.Is(err, context.Canceled) {
+		t.Fatalf("artifact=%#v err=%v, want nil/context.Canceled", artifact, err)
+	}
+	if opened == nil || opened.reads != 1 {
+		t.Fatalf("read count = %v, want one progressing read", opened)
+	}
+}
+
+type reportedInfoFile struct {
+	artifactFile
+	info os.FileInfo
+}
+
+func (f *reportedInfoFile) Stat() (os.FileInfo, error) {
+	return f.info, nil
+}
+
+type cancelAfterProgressFile struct {
+	artifactFile
+	cancel context.CancelFunc
+	reads  int
+}
+
+func (f *cancelAfterProgressFile) Read(buffer []byte) (int, error) {
+	n, err := f.artifactFile.Read(buffer)
+	if n > 0 {
+		f.reads++
+		f.cancel()
+	}
+	return n, err
+}

internal/backend/registry.go

@@ -0,0 +1,179 @@
+// Package backend owns validated, immutable OpenAI-compatible backend
+// definitions.
+package backend
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+	"sort"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+)
+
+const (
+	// OpenRouterID is the reserved ID of Promptkit's built-in OpenRouter
+	// backend.
+	OpenRouterID = "openrouter"
+	// RakestrawHomeID is the reserved ID of Promptkit's built-in Rakestrawhome
+	// backend.
+	RakestrawHomeID = "rakestrawhome"
+
+	defaultQueueCapacity = 1024
+)
+
+// ErrBackendNotFound identifies a registry lookup for an unknown backend ID.
+var ErrBackendNotFound = errors.New("backend not found")
+
+var environmentVariableName = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)
+
+// Registry is an immutable collection of validated backend definitions.
+type Registry struct {
+	backends map[string]domain.Backend
+}
+
+// NewRegistry constructs a registry containing maintained definitions followed
+// by consumer additions. Every ID must be unique across both groups.
+func NewRegistry(maintained, additions []domain.Backend) (*Registry, error) {
+	registry := &Registry{
+		backends: make(map[string]domain.Backend, len(maintained)+len(additions)),
+	}
+
+	definitions := make([]domain.Backend, 0, len(maintained)+len(additions))
+	definitions = append(definitions, maintained...)
+	definitions = append(definitions, additions...)
+
+	for _, definition := range definitions {
+		definition.ID = strings.TrimSpace(definition.ID)
+		if definition.ID == "" {
+			return nil, errors.New("backend ID must not be blank")
+		}
+		if _, exists := registry.backends[definition.ID]; exists {
+			return nil, fmt.Errorf("backend ID %q is already registered", definition.ID)
+		}
+
+		normalized, err := NormalizeDefinition(definition)
+		if err != nil {
+			return nil, err
+		}
+		registry.backends[normalized.ID] = normalized
+	}
+
+	return registry, nil
+}
+
+// GetBackend returns a defensive copy of the backend registered with id.
+func (r *Registry) GetBackend(id string) (domain.Backend, error) {
+	if r == nil {
+		return domain.Backend{}, fmt.Errorf("%w: %q", ErrBackendNotFound, id)
+	}
+	definition, ok := r.backends[id]
+	if !ok {
+		return domain.Backend{}, fmt.Errorf("%w: %q", ErrBackendNotFound, id)
+	}
+	extraParams, err := jsonvalue.CopyMap(definition.ExtraParams)
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("copy backend %q: %w", id, err)
+	}
+	definition.ExtraParams = extraParams
+	return definition, nil
+}
+
+// CapacityPolicies returns a copy of the normalized policies for limited
+// backends.
+func (r *Registry) CapacityPolicies() map[string]domain.BackendCapacityPolicy {
+	policies := make(map[string]domain.BackendCapacityPolicy)
+	if r == nil {
+		return policies
+	}
+	for id, definition := range r.backends {
+		if definition.ConcurrencyLimit == 0 {
+			continue
+		}
+		policies[id] = domain.BackendCapacityPolicy{
+			ConcurrencyLimit: definition.ConcurrencyLimit,
+			QueueCapacity:    definition.QueueCapacity,
+		}
+	}
+	return policies
+}
+
+// NormalizeDefinition validates and defensively copies one backend definition.
+func NormalizeDefinition(definition domain.Backend) (domain.Backend, error) {
+	endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(definition.Endpoint)
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("backend %q endpoint: %w", definition.ID, err)
+	}
+	definition.Endpoint = endpoint
+
+	definition.APIKeyEnv = strings.TrimSpace(definition.APIKeyEnv)
+	if definition.APIKeyEnv != "" && !environmentVariableName.MatchString(definition.APIKeyEnv) {
+		return domain.Backend{}, fmt.Errorf(
+			"backend %q api key environment variable %q is invalid",
+			definition.ID,
+			definition.APIKeyEnv,
+		)
+	}
+
+	if definition.ConcurrencyLimit < 0 {
+		return domain.Backend{}, fmt.Errorf(
+			"backend %q concurrency limit must not be negative",
+			definition.ID,
+		)
+	}
+	if definition.QueueCapacity < 0 {
+		return domain.Backend{}, fmt.Errorf(
+			"backend %q queue capacity must not be negative",
+			definition.ID,
+		)
+	}
+	if definition.ConcurrencyLimit == 0 {
+		if definition.QueueCapacitySet {
+			return domain.Backend{}, fmt.Errorf(
+				"backend %q queue capacity requires a positive concurrency limit",
+				definition.ID,
+			)
+		}
+		definition.QueueCapacity = 0
+	} else {
+		if !definition.QueueCapacitySet {
+			definition.QueueCapacity = defaultQueueCapacity
+			definition.QueueCapacitySet = true
+		}
+		maxInt := int(^uint(0) >> 1)
+		if definition.QueueCapacity > maxInt-definition.ConcurrencyLimit {
+			return domain.Backend{}, fmt.Errorf(
+				"backend %q total capacity overflows int",
+				definition.ID,
+			)
+		}
+	}
+
+	keys := make([]string, 0, len(definition.ExtraParams))
+	for key := range definition.ExtraParams {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		if key == "" {
+			return domain.Backend{}, fmt.Errorf("backend %q extra parameter key must not be empty", definition.ID)
+		}
+		if llm.IsReservedOpenAIChatRequestField(key) {
+			return domain.Backend{}, fmt.Errorf(
+				"backend %q extra parameter %q collides with a reserved request field",
+				definition.ID,
+				key,
+			)
+		}
+	}
+
+	extraParams, err := jsonvalue.CopyMap(definition.ExtraParams)
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("backend %q extra parameters: %w", definition.ID, err)
+	}
+	definition.ExtraParams = extraParams
+	return definition, nil
+}

internal/backend/registry_test.go

@@ -0,0 +1,376 @@
+package backend_test
+
+import (
+	"errors"
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+const validEndpoint = "https://backend.example/v1"
+
+func TestRegistryIncludesMaintainedDefinitions(t *testing.T) {
+	maintained := []domain.Backend{
+		{ID: backend.OpenRouterID, Endpoint: validEndpoint, ConcurrencyLimit: 2, QueueCapacity: 3, QueueCapacitySet: true},
+		{ID: backend.RakestrawHomeID, Endpoint: "https://second.example/v1", ConcurrencyLimit: 4, QueueCapacity: 5, QueueCapacitySet: true},
+	}
+	registry, err := backend.NewRegistry(maintained, nil)
+	if err != nil {
+		t.Fatalf("construct registry: %v", err)
+	}
+
+	for _, expected := range maintained {
+		t.Run(expected.ID, func(t *testing.T) {
+			definition, err := registry.GetBackend(expected.ID)
+			if err != nil {
+				t.Fatalf("look up maintained definition: %v", err)
+			}
+			if !reflect.DeepEqual(definition, expected) {
+				t.Fatalf("unexpected maintained definition: %#v", definition)
+			}
+		})
+	}
+
+	policies := registry.CapacityPolicies()
+	if len(policies) != 2 ||
+		policies[backend.OpenRouterID] != (domain.BackendCapacityPolicy{
+			ConcurrencyLimit: 2,
+			QueueCapacity:    3,
+		}) ||
+		policies[backend.RakestrawHomeID] != (domain.BackendCapacityPolicy{
+			ConcurrencyLimit: 4,
+			QueueCapacity:    5,
+		}) {
+		t.Fatalf("unexpected built-in capacity policies: %#v", policies)
+	}
+}
+
+func TestRegistryNormalizesUniqueAdditionsAndIsolatesMutations(t *testing.T) {
+	nested := map[string]int{"limit": 2}
+	extraParams := map[string]any{
+		"count":  int64(7),
+		"nested": nested,
+	}
+	registry, err := backend.NewRegistry(nil, []domain.Backend{
+		{
+			ID:               " custom ",
+			Endpoint:         " https://custom.example/openai/v1 ",
+			APIKeyEnv:        " CUSTOM_API_KEY ",
+			ExtraParams:      extraParams,
+			ConcurrencyLimit: 3,
+			QueueCapacity:    2,
+			QueueCapacitySet: true,
+		},
+		{
+			ID:       "Custom",
+			Endpoint: validEndpoint,
+		},
+	})
+	if err != nil {
+		t.Fatalf("construct registry: %v", err)
+	}
+
+	nested["limit"] = 99
+	extraParams["added"] = true
+
+	got, err := registry.GetBackend("custom")
+	if err != nil {
+		t.Fatalf("look up custom backend: %v", err)
+	}
+	if got.ID != "custom" ||
+		got.Endpoint != "https://custom.example/openai/v1" ||
+		got.APIKeyEnv != "CUSTOM_API_KEY" ||
+		got.ConcurrencyLimit != 3 ||
+		got.QueueCapacity != 2 ||
+		!got.QueueCapacitySet {
+		t.Fatalf("unexpected normalized definition: %#v", got)
+	}
+	if count, ok := got.ExtraParams["count"].(int64); !ok || count != 7 {
+		t.Fatalf("integer type or value changed: %#v", got.ExtraParams["count"])
+	}
+	gotNested, ok := got.ExtraParams["nested"].(map[string]int)
+	if !ok || gotNested["limit"] != 2 {
+		t.Fatalf("container type or value changed: %#v", got.ExtraParams["nested"])
+	}
+	if _, exists := got.ExtraParams["added"]; exists {
+		t.Fatalf("registry retained caller map: %#v", got.ExtraParams)
+	}
+
+	gotNested["limit"] = 100
+	got.ExtraParams["added"] = true
+	again, err := registry.GetBackend("custom")
+	if err != nil {
+		t.Fatalf("look up custom backend again: %v", err)
+	}
+	if again.ExtraParams["nested"].(map[string]int)["limit"] != 2 {
+		t.Fatalf("lookup exposed registry nested map: %#v", again.ExtraParams)
+	}
+	if _, exists := again.ExtraParams["added"]; exists {
+		t.Fatalf("lookup exposed registry map: %#v", again.ExtraParams)
+	}
+
+	if _, err := registry.GetBackend("Custom"); err != nil {
+		t.Fatalf("backend IDs should be case-sensitive: %v", err)
+	}
+
+	policies := registry.CapacityPolicies()
+	if len(policies) != 1 {
+		t.Fatalf("unexpected capacity policy count: %#v", policies)
+	}
+	policies["custom"] = domain.BackendCapacityPolicy{}
+	delete(policies, "custom")
+	againPolicies := registry.CapacityPolicies()
+	if againPolicies["custom"] != (domain.BackendCapacityPolicy{
+		ConcurrencyLimit: 3,
+		QueueCapacity:    2,
+	}) {
+		t.Fatalf("capacity policy map mutated registry state: %#v", againPolicies)
+	}
+}
+
+func TestNewRegistryNormalizesCapacityPolicy(t *testing.T) {
+	maxInt := int(^uint(0) >> 1)
+	tests := []struct {
+		name       string
+		definition domain.Backend
+		want       domain.BackendCapacityPolicy
+		wantSet    bool
+		wantError  bool
+	}{
+		{
+			name:       "unlimited when omitted",
+			definition: domain.Backend{},
+		},
+		{
+			name: "default queue",
+			definition: domain.Backend{
+				ConcurrencyLimit: 2,
+			},
+			want: domain.BackendCapacityPolicy{
+				ConcurrencyLimit: 2,
+				QueueCapacity:    1024,
+			},
+			wantSet: true,
+		},
+		{
+			name: "explicit zero queue",
+			definition: domain.Backend{
+				ConcurrencyLimit: 2,
+				QueueCapacitySet: true,
+			},
+			want: domain.BackendCapacityPolicy{
+				ConcurrencyLimit: 2,
+			},
+			wantSet: true,
+		},
+		{
+			name: "negative concurrency limit",
+			definition: domain.Backend{
+				ConcurrencyLimit: -1,
+			},
+			wantError: true,
+		},
+		{
+			name: "negative queue capacity",
+			definition: domain.Backend{
+				ConcurrencyLimit: 1,
+				QueueCapacity:    -1,
+				QueueCapacitySet: true,
+			},
+			wantError: true,
+		},
+		{
+			name: "queue without limit",
+			definition: domain.Backend{
+				QueueCapacitySet: true,
+			},
+			wantError: true,
+		},
+		{
+			name: "total overflow",
+			definition: domain.Backend{
+				ConcurrencyLimit: maxInt,
+				QueueCapacity:    1,
+				QueueCapacitySet: true,
+			},
+			wantError: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			tc.definition.ID = "custom"
+			tc.definition.Endpoint = validEndpoint
+			registry, err := backend.NewRegistry(nil, []domain.Backend{tc.definition})
+			if tc.wantError {
+				if err == nil {
+					t.Fatal("expected invalid capacity policy error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("construct registry: %v", err)
+			}
+
+			definition, err := registry.GetBackend("custom")
+			if err != nil {
+				t.Fatalf("look up custom backend: %v", err)
+			}
+			if definition.ConcurrencyLimit != tc.want.ConcurrencyLimit ||
+				definition.QueueCapacity != tc.want.QueueCapacity ||
+				definition.QueueCapacitySet != tc.wantSet {
+				t.Fatalf("normalized capacity=(%d, %d, %t), want (%d, %d, %t)",
+					definition.ConcurrencyLimit,
+					definition.QueueCapacity,
+					definition.QueueCapacitySet,
+					tc.want.ConcurrencyLimit,
+					tc.want.QueueCapacity,
+					tc.wantSet,
+				)
+			}
+			policies := registry.CapacityPolicies()
+			got, ok := policies["custom"]
+			if ok != tc.wantSet || got != tc.want {
+				t.Fatalf("capacity policy=(%#v, %t), want (%#v, %t)", got, ok, tc.want, tc.wantSet)
+			}
+		})
+	}
+}
+
+func TestNewRegistryRejectsDuplicateIDs(t *testing.T) {
+	tests := []struct {
+		name      string
+		additions []domain.Backend
+		wantID    string
+	}{
+		{
+			name:      "OpenRouter collision after normalization",
+			additions: []domain.Backend{{ID: " openrouter "}},
+			wantID:    backend.OpenRouterID,
+		},
+		{
+			name:      "Rakestrawhome collision after normalization",
+			additions: []domain.Backend{{ID: " rakestrawhome "}},
+			wantID:    backend.RakestrawHomeID,
+		},
+		{
+			name: "consumer collision after normalization",
+			additions: []domain.Backend{
+				{ID: "custom", Endpoint: validEndpoint},
+				{ID: " custom ", Endpoint: "https://other.example/v1"},
+			},
+			wantID: "custom",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := backend.NewRegistry(nil, tc.additions)
+			if err == nil {
+				t.Fatal("expected duplicate ID error")
+			}
+			if !strings.Contains(err.Error(), tc.wantID) {
+				t.Fatalf("expected error to identify %q, got %v", tc.wantID, err)
+			}
+		})
+	}
+}
+
+func TestNewRegistryValidatesIDs(t *testing.T) {
+	for _, id := range []string{"", " \t\n "} {
+		t.Run(id, func(t *testing.T) {
+			_, err := backend.NewRegistry(nil, []domain.Backend{{
+				ID:       id,
+				Endpoint: validEndpoint,
+			}})
+			if err == nil {
+				t.Fatal("expected blank ID error")
+			}
+		})
+	}
+}
+
+func TestNewRegistryValidatesEndpoints(t *testing.T) {
+	tests := []struct {
+		name     string
+		endpoint string
+	}{
+		{name: "blank", endpoint: ""},
+		{name: "relative", endpoint: "/v1"},
+		{name: "missing host", endpoint: "https:///v1"},
+		{name: "unsupported scheme", endpoint: "ftp://backend.example/v1"},
+		{name: "user information", endpoint: "https://user@backend.example/v1"},
+		{name: "query", endpoint: "https://backend.example/v1?mode=chat"},
+		{name: "empty query", endpoint: "https://backend.example/v1?"},
+		{name: "fragment", endpoint: "https://backend.example/v1#chat"},
+		{name: "empty fragment", endpoint: "https://backend.example/v1#"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := backend.NewRegistry(nil, []domain.Backend{{
+				ID:       "custom",
+				Endpoint: tc.endpoint,
+			}})
+			if err == nil {
+				t.Fatal("expected invalid endpoint error")
+			}
+		})
+	}
+}
+
+func TestNewRegistryValidatesEnvironmentVariableNames(t *testing.T) {
+	for _, name := range []string{"1API_KEY", "API-KEY", "API KEY", "ÅPI_KEY"} {
+		t.Run(name, func(t *testing.T) {
+			_, err := backend.NewRegistry(nil, []domain.Backend{{
+				ID:        "custom",
+				Endpoint:  validEndpoint,
+				APIKeyEnv: name,
+			}})
+			if err == nil {
+				t.Fatal("expected invalid environment-variable name error")
+			}
+		})
+	}
+}
+
+func TestNewRegistryRejectsInvalidAndReservedExtraParameters(t *testing.T) {
+	tests := []struct {
+		name        string
+		extraParams map[string]any
+	}{
+		{name: "unsupported value", extraParams: map[string]any{"value": make(chan int)}},
+		{name: "reserved key", extraParams: map[string]any{"model": "override"}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := backend.NewRegistry(nil, []domain.Backend{{
+				ID:          "custom",
+				Endpoint:    validEndpoint,
+				ExtraParams: tc.extraParams,
+			}})
+			if err == nil {
+				t.Fatal("expected invalid extra parameters error")
+			}
+		})
+	}
+}
+
+func TestRegistryLookupReportsNotFound(t *testing.T) {
+	registry, err := backend.NewRegistry(nil, nil)
+	if err != nil {
+		t.Fatalf("construct registry: %v", err)
+	}
+
+	_, err = registry.GetBackend("missing")
+	if !errors.Is(err, backend.ErrBackendNotFound) {
+		t.Fatalf("expected ErrBackendNotFound, got %v", err)
+	}
+	if !strings.Contains(err.Error(), "missing") {
+		t.Fatalf("expected error to identify backend, got %v", err)
+	}
+}

internal/capacity/client.go

@@ -0,0 +1,40 @@
+package capacity
+
+import (
+	"context"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+)
+
+type client struct {
+	manager *Manager
+	next    llm.Client
+}
+
+// NewClient wraps next with configured active-generation limits. A nil manager
+// leaves next unchanged.
+func NewClient(manager *Manager, next llm.Client) llm.Client {
+	if manager == nil {
+		return next
+	}
+	return &client{
+		manager: manager,
+		next:    next,
+	}
+}
+
+func (c *client) Generate(
+	ctx context.Context,
+	req domain.GenerateRequest,
+) (*domain.GenerateResponse, error) {
+	if c.manager.getPool(req.Target.BackendID) == nil {
+		return c.next.Generate(ctx, req)
+	}
+	release, err := c.manager.Acquire(ctx, req.Target.BackendID)
+	if err != nil {
+		return nil, err
+	}
+	defer release()
+	return c.next.Generate(ctx, req)
+}

internal/capacity/client_test.go

@@ -0,0 +1,517 @@
+package capacity
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+)
+
+type generateResult struct {
+	response *domain.GenerateResponse
+	err      error
+}
+
+type clientFunc func(
+	context.Context,
+	domain.GenerateRequest,
+) (*domain.GenerateResponse, error)
+
+func (f clientFunc) Generate(
+	ctx context.Context,
+	req domain.GenerateRequest,
+) (*domain.GenerateResponse, error) {
+	return f(ctx, req)
+}
+
+type blockingClient struct {
+	mu       sync.Mutex
+	active   int
+	peak     int
+	calls    map[string]int
+	started  chan string
+	releases map[string]chan struct{}
+}
+
+func newBlockingClient(releases map[string]chan struct{}) *blockingClient {
+	return &blockingClient{
+		calls:    make(map[string]int),
+		started:  make(chan string, 64),
+		releases: releases,
+	}
+}
+
+func (c *blockingClient) Generate(
+	ctx context.Context,
+	req domain.GenerateRequest,
+) (*domain.GenerateResponse, error) {
+	id := req.Prompt.SessionID
+	c.mu.Lock()
+	c.active++
+	if c.active > c.peak {
+		c.peak = c.active
+	}
+	c.calls[id]++
+	c.mu.Unlock()
+	defer func() {
+		c.mu.Lock()
+		c.active--
+		c.mu.Unlock()
+	}()
+
+	c.started <- id
+	if release := c.releases[id]; release != nil {
+		select {
+		case <-release:
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+	return &domain.GenerateResponse{Content: id}, nil
+}
+
+func (c *blockingClient) callCount(id string) int {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.calls[id]
+}
+
+func (c *blockingClient) peakConcurrency() int {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.peak
+}
+
+func generateAsync(
+	client llm.Client,
+	ctx context.Context,
+	backendID string,
+	id string,
+) <-chan generateResult {
+	result := make(chan generateResult, 1)
+	go func() {
+		response, err := client.Generate(ctx, domain.GenerateRequest{
+			Prompt: domain.RenderedPrompt{SessionID: id},
+			Target: domain.ExecutionTarget{BackendID: backendID},
+		})
+		result <- generateResult{response: response, err: err}
+	}()
+	return result
+}
+
+func waitForWaiterCount(t *testing.T, manager *Manager, backendID string, want int) {
+	t.Helper()
+	pool := manager.pools[backendID]
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		pool.mu.Lock()
+		got := pool.waiters.Len()
+		pool.mu.Unlock()
+		if got == want {
+			return
+		}
+		if time.Now().After(deadline) {
+			t.Fatalf("waiter count=%d, want %d", got, want)
+		}
+		runtime.Gosched()
+	}
+}
+
+func receiveStarted(t *testing.T, started <-chan string) string {
+	t.Helper()
+	select {
+	case id := <-started:
+		return id
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for wrapped client invocation")
+		return ""
+	}
+}
+
+func receiveResult(t *testing.T, result <-chan generateResult) generateResult {
+	t.Helper()
+	select {
+	case got := <-result:
+		return got
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for generation result")
+		return generateResult{}
+	}
+}
+
+func newTestManager(t *testing.T, policies map[string]domain.BackendCapacityPolicy) *Manager {
+	t.Helper()
+	manager, err := NewManager(policies)
+	if err != nil {
+		t.Fatalf("construct manager: %v", err)
+	}
+	return manager
+}
+
+func TestClientLimitsPeakConcurrencyAndServesWaitersFIFO(t *testing.T) {
+	manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1},
+	})
+	firstRelease := make(chan struct{})
+	secondRelease := make(chan struct{})
+	thirdRelease := make(chan struct{})
+	next := newBlockingClient(map[string]chan struct{}{
+		"first":  firstRelease,
+		"second": secondRelease,
+		"third":  thirdRelease,
+	})
+	client := NewClient(manager, next)
+
+	first := generateAsync(client, context.Background(), "limited", "first")
+	if got := receiveStarted(t, next.started); got != "first" {
+		t.Fatalf("first invocation=%q, want first", got)
+	}
+	second := generateAsync(client, context.Background(), "limited", "second")
+	waitForWaiterCount(t, manager, "limited", 1)
+	third := generateAsync(client, context.Background(), "limited", "third")
+	waitForWaiterCount(t, manager, "limited", 2)
+
+	close(firstRelease)
+	if got := receiveResult(t, first); got.err != nil {
+		t.Fatalf("first generation: %v", got.err)
+	}
+	if got := receiveStarted(t, next.started); got != "second" {
+		t.Fatalf("second invocation=%q, want second", got)
+	}
+	close(secondRelease)
+	if got := receiveResult(t, second); got.err != nil {
+		t.Fatalf("second generation: %v", got.err)
+	}
+	if got := receiveStarted(t, next.started); got != "third" {
+		t.Fatalf("third invocation=%q, want third", got)
+	}
+	close(thirdRelease)
+	if got := receiveResult(t, third); got.err != nil {
+		t.Fatalf("third generation: %v", got.err)
+	}
+	if peak := next.peakConcurrency(); peak != 1 {
+		t.Fatalf("peak concurrency=%d, want 1", peak)
+	}
+}
+
+func TestClientPeakConcurrencyDoesNotExceedConfiguredLimit(t *testing.T) {
+	const limit = 2
+	manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: limit},
+	})
+	gate := make(chan struct{})
+	releases := make(map[string]chan struct{})
+	for i := range 5 {
+		releases[string(rune('a'+i))] = gate
+	}
+	next := newBlockingClient(releases)
+	client := NewClient(manager, next)
+
+	results := make([]<-chan generateResult, 0, len(releases))
+	for id := range releases {
+		results = append(results, generateAsync(client, context.Background(), "limited", id))
+	}
+	for range limit {
+		receiveStarted(t, next.started)
+	}
+	waitForWaiterCount(t, manager, "limited", len(releases)-limit)
+
+	close(gate)
+	for _, result := range results {
+		if got := receiveResult(t, result); got.err != nil {
+			t.Fatalf("generation: %v", got.err)
+		}
+	}
+	if peak := next.peakConcurrency(); peak != limit {
+		t.Fatalf("peak concurrency=%d, want %d", peak, limit)
+	}
+}
+
+func TestClientRemovesCanceledWaiters(t *testing.T) {
+	tests := []struct {
+		name      string
+		cancelID  string
+		wantOrder []string
+	}{
+		{name: "first waiter", cancelID: "one", wantOrder: []string{"two", "three"}},
+		{name: "middle waiter", cancelID: "two", wantOrder: []string{"one", "three"}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+				"limited": {ConcurrencyLimit: 1},
+			})
+			holderRelease := make(chan struct{})
+			releases := map[string]chan struct{}{
+				"holder": holderRelease,
+				"one":    make(chan struct{}),
+				"two":    make(chan struct{}),
+				"three":  make(chan struct{}),
+			}
+			next := newBlockingClient(releases)
+			client := NewClient(manager, next)
+
+			holder := generateAsync(client, context.Background(), "limited", "holder")
+			if got := receiveStarted(t, next.started); got != "holder" {
+				t.Fatalf("initial invocation=%q, want holder", got)
+			}
+
+			contexts := make(map[string]context.Context)
+			cancels := make(map[string]context.CancelFunc)
+			results := make(map[string]<-chan generateResult)
+			for _, id := range []string{"one", "two", "three"} {
+				contexts[id], cancels[id] = context.WithCancel(context.Background())
+				results[id] = generateAsync(client, contexts[id], "limited", id)
+				waitForWaiterCount(t, manager, "limited", len(results))
+			}
+
+			cancels[tc.cancelID]()
+			if got := receiveResult(t, results[tc.cancelID]); !errors.Is(got.err, context.Canceled) {
+				t.Fatalf("canceled waiter error=%v, want context.Canceled", got.err)
+			}
+			waitForWaiterCount(t, manager, "limited", 2)
+
+			close(holderRelease)
+			if got := receiveResult(t, holder); got.err != nil {
+				t.Fatalf("holder generation: %v", got.err)
+			}
+			for _, id := range tc.wantOrder {
+				if got := receiveStarted(t, next.started); got != id {
+					t.Fatalf("next invocation=%q, want %q", got, id)
+				}
+				close(releases[id])
+				if got := receiveResult(t, results[id]); got.err != nil {
+					t.Fatalf("%s generation: %v", id, got.err)
+				}
+			}
+			if calls := next.callCount(tc.cancelID); calls != 0 {
+				t.Fatalf("canceled waiter invoked wrapped client %d times", calls)
+			}
+			for _, cancel := range cancels {
+				cancel()
+			}
+		})
+	}
+}
+
+func TestClientGrantCancellationRaceDoesNotLeakPermit(t *testing.T) {
+	const iterations = 200
+	for i := range iterations {
+		manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+			"limited": {ConcurrencyLimit: 1},
+		})
+		holderRelease := make(chan struct{})
+		var waiterCalls atomic.Int64
+		next := clientFunc(func(
+			_ context.Context,
+			req domain.GenerateRequest,
+		) (*domain.GenerateResponse, error) {
+			if req.Prompt.SessionID == "holder" {
+				<-holderRelease
+			} else if req.Prompt.SessionID == "waiter" {
+				waiterCalls.Add(1)
+			}
+			return &domain.GenerateResponse{Content: req.Prompt.SessionID}, nil
+		})
+		client := NewClient(manager, next)
+
+		holder := generateAsync(client, context.Background(), "limited", "holder")
+		waitForActiveCount(t, manager, "limited", 1)
+		ctx, cancel := context.WithCancel(context.Background())
+		waiterResult := generateAsync(client, ctx, "limited", "waiter")
+		waitForWaiterCount(t, manager, "limited", 1)
+
+		start := make(chan struct{})
+		var race sync.WaitGroup
+		race.Add(2)
+		go func() {
+			defer race.Done()
+			<-start
+			cancel()
+		}()
+		go func() {
+			defer race.Done()
+			<-start
+			close(holderRelease)
+		}()
+		close(start)
+		race.Wait()
+
+		if got := receiveResult(t, holder); got.err != nil {
+			t.Fatalf("iteration %d holder generation: %v", i, got.err)
+		}
+		got := receiveResult(t, waiterResult)
+		switch calls := waiterCalls.Load(); {
+		case calls == 0 && errors.Is(got.err, context.Canceled):
+		case calls == 1 && got.err == nil:
+		default:
+			t.Fatalf("iteration %d waiter calls=%d error=%v", i, calls, got.err)
+		}
+
+		probe := generateAsync(client, context.Background(), "limited", "probe")
+		if got := receiveResult(t, probe); got.err != nil {
+			t.Fatalf("iteration %d probe generation: %v", i, got.err)
+		}
+		waitForActiveCount(t, manager, "limited", 0)
+		waitForWaiterCount(t, manager, "limited", 0)
+	}
+}
+
+func waitForActiveCount(t *testing.T, manager *Manager, backendID string, want int) {
+	t.Helper()
+	pool := manager.pools[backendID]
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		pool.mu.Lock()
+		got := pool.active
+		pool.mu.Unlock()
+		if got == want {
+			return
+		}
+		if time.Now().After(deadline) {
+			t.Fatalf("active count=%d, want %d", got, want)
+		}
+		runtime.Gosched()
+	}
+}
+
+func TestClientUsesIndependentPoolsAndUnlimitedFastPaths(t *testing.T) {
+	manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+		"alpha": {ConcurrencyLimit: 1},
+		"beta":  {ConcurrencyLimit: 1},
+	})
+	alphaRelease := make(chan struct{})
+	betaRelease := make(chan struct{})
+	next := newBlockingClient(map[string]chan struct{}{
+		"alpha": alphaRelease,
+		"beta":  betaRelease,
+	})
+	client := NewClient(manager, next)
+
+	alpha := generateAsync(client, context.Background(), "alpha", "alpha")
+	beta := generateAsync(client, context.Background(), "beta", "beta")
+	started := map[string]bool{
+		receiveStarted(t, next.started): true,
+		receiveStarted(t, next.started): true,
+	}
+	if !started["alpha"] || !started["beta"] {
+		t.Fatalf("independent pools did not both start: %#v", started)
+	}
+	close(alphaRelease)
+	close(betaRelease)
+	if got := receiveResult(t, alpha); got.err != nil {
+		t.Fatalf("alpha generation: %v", got.err)
+	}
+	if got := receiveResult(t, beta); got.err != nil {
+		t.Fatalf("beta generation: %v", got.err)
+	}
+
+	for _, backendID := range []string{"", "unknown"} {
+		response, err := client.Generate(context.Background(), domain.GenerateRequest{
+			Prompt: domain.RenderedPrompt{SessionID: backendID},
+			Target: domain.ExecutionTarget{BackendID: backendID},
+		})
+		if err != nil || response == nil {
+			t.Fatalf("unlimited backend %q response=(%#v, %v)", backendID, response, err)
+		}
+	}
+	if got := NewClient(nil, next); got != next {
+		t.Fatal("nil manager did not return the wrapped client unchanged")
+	}
+}
+
+func TestClientPreservesRequestsResponsesAndErrors(t *testing.T) {
+	manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1},
+	})
+	request := domain.GenerateRequest{
+		Prompt: domain.RenderedPrompt{
+			SessionID: "session",
+			Messages: []domain.RenderedMessage{
+				{Role: "user", Content: "content"},
+			},
+		},
+		Target: domain.ExecutionTarget{
+			BackendID:   "limited",
+			Model:       "model",
+			ExtraParams: map[string]any{"key": "value"},
+		},
+	}
+	response := &domain.GenerateResponse{
+		Content: "output",
+		Usage:   domain.TokenUsage{TotalTokens: 7},
+	}
+	collaboratorErr := errors.New("collaborator failure")
+	tests := []struct {
+		name     string
+		response *domain.GenerateResponse
+		err      error
+	}{
+		{name: "successful response", response: response},
+		{name: "nil response"},
+		{name: "collaborator error", response: response, err: collaboratorErr},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var captured domain.GenerateRequest
+			next := clientFunc(func(
+				_ context.Context,
+				req domain.GenerateRequest,
+			) (*domain.GenerateResponse, error) {
+				captured = req
+				return tc.response, tc.err
+			})
+			gotResponse, gotErr := NewClient(manager, next).Generate(context.Background(), request)
+			if !reflect.DeepEqual(captured, request) {
+				t.Fatalf("request changed: %#v", captured)
+			}
+			if gotResponse != tc.response || gotErr != tc.err {
+				t.Fatalf("response=(%p, %v), want (%p, %v)",
+					gotResponse, gotErr, tc.response, tc.err)
+			}
+		})
+	}
+}
+
+func TestClientReleasesPermitDuringPanicUnwinding(t *testing.T) {
+	manager := newTestManager(t, map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1},
+	})
+	var calls atomic.Int64
+	next := clientFunc(func(
+		_ context.Context,
+		_ domain.GenerateRequest,
+	) (*domain.GenerateResponse, error) {
+		if calls.Add(1) == 1 {
+			panic("test panic")
+		}
+		return &domain.GenerateResponse{Content: "recovered"}, nil
+	})
+	client := NewClient(manager, next)
+	request := domain.GenerateRequest{
+		Target: domain.ExecutionTarget{BackendID: "limited"},
+	}
+
+	func() {
+		defer func() {
+			if recover() == nil {
+				t.Fatal("expected wrapped client panic")
+			}
+		}()
+		_, _ = client.Generate(context.Background(), request)
+	}()
+
+	response, err := client.Generate(context.Background(), request)
+	if err != nil || response == nil || response.Content != "recovered" {
+		t.Fatalf("generation after panic=(%#v, %v)", response, err)
+	}
+}

internal/capacity/manager.go

@@ -0,0 +1,180 @@
+// Package capacity coordinates engine-local run admission and model-generation
+// concurrency for configured backends.
+package capacity
+
+import (
+	"container/list"
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+// ErrCapacityExceeded identifies an admission rejected because a backend's
+// configured run capacity is full.
+var ErrCapacityExceeded = errors.New("backend capacity exceeded")
+
+// Manager owns independent backend capacity pools with immutable limits.
+type Manager struct {
+	pools map[string]*pool
+}
+
+type pool struct {
+	mu               sync.Mutex
+	concurrencyLimit int
+	totalCapacity    int
+	admitted         int
+	active           int
+	waiters          list.List
+}
+
+type waiter struct {
+	ready   chan struct{}
+	element *list.Element
+	granted bool
+}
+
+// NewManager constructs independent pools from normalized backend policies.
+func NewManager(policies map[string]domain.BackendCapacityPolicy) (*Manager, error) {
+	manager := &Manager{
+		pools: make(map[string]*pool, len(policies)),
+	}
+	maxInt := int(^uint(0) >> 1)
+	for id, policy := range policies {
+		if strings.TrimSpace(id) == "" {
+			return nil, errors.New("backend capacity policy ID must not be blank")
+		}
+		if policy.ConcurrencyLimit <= 0 {
+			return nil, fmt.Errorf(
+				"backend %q concurrency limit must be positive",
+				id,
+			)
+		}
+		if policy.QueueCapacity < 0 {
+			return nil, fmt.Errorf(
+				"backend %q queue capacity must not be negative",
+				id,
+			)
+		}
+		if policy.QueueCapacity > maxInt-policy.ConcurrencyLimit {
+			return nil, fmt.Errorf("backend %q total capacity overflows int", id)
+		}
+		manager.pools[id] = &pool{
+			concurrencyLimit: policy.ConcurrencyLimit,
+			totalCapacity:    policy.ConcurrencyLimit + policy.QueueCapacity,
+		}
+	}
+	return manager, nil
+}
+
+// Admit immediately reserves one configured backend run slot. Backends without
+// a configured pool are unlimited.
+func (m *Manager) Admit(ctx context.Context, backendID string) (func(), error) {
+	pool := m.getPool(backendID)
+	if pool == nil {
+		return releaseNothing, nil
+	}
+
+	pool.mu.Lock()
+	defer pool.mu.Unlock()
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if pool.admitted >= pool.totalCapacity {
+		return nil, ErrCapacityExceeded
+	}
+	pool.admitted++
+
+	var once sync.Once
+	return func() {
+		once.Do(func() {
+			pool.mu.Lock()
+			pool.admitted--
+			pool.mu.Unlock()
+		})
+	}, nil
+}
+
+func releaseNothing() {}
+
+func (m *Manager) getPool(backendID string) *pool {
+	if m == nil || backendID == "" {
+		return nil
+	}
+	return m.pools[backendID]
+}
+
+// Limited reports whether a backend uses an active-generation pool.
+func (m *Manager) Limited(backendID string) bool { return m.getPool(backendID) != nil }
+
+// Acquire obtains one active-generation permit for a backend. Its release
+// function is idempotent. Backends without a configured pool are unlimited.
+func (m *Manager) Acquire(ctx context.Context, backendID string) (func(), error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	pool := m.getPool(backendID)
+	if pool == nil {
+		return releaseNothing, nil
+	}
+	if err := pool.acquire(ctx); err != nil {
+		return nil, err
+	}
+	var once sync.Once
+	return func() { once.Do(pool.releaseActive) }, nil
+}
+
+func (p *pool) acquire(ctx context.Context) error {
+	p.mu.Lock()
+	if err := ctx.Err(); err != nil {
+		p.mu.Unlock()
+		return err
+	}
+	if p.active < p.concurrencyLimit && p.waiters.Len() == 0 {
+		p.active++
+		p.mu.Unlock()
+		return nil
+	}
+
+	waiter := &waiter{ready: make(chan struct{})}
+	waiter.element = p.waiters.PushBack(waiter)
+	p.mu.Unlock()
+
+	select {
+	case <-waiter.ready:
+		return nil
+	case <-ctx.Done():
+		p.mu.Lock()
+		if !waiter.granted {
+			p.waiters.Remove(waiter.element)
+			waiter.element = nil
+			p.mu.Unlock()
+			return ctx.Err()
+		}
+		p.mu.Unlock()
+		return nil
+	}
+}
+
+func (p *pool) releaseActive() {
+	var ready chan struct{}
+
+	p.mu.Lock()
+	if element := p.waiters.Front(); element != nil {
+		waiter := element.Value.(*waiter)
+		p.waiters.Remove(element)
+		waiter.element = nil
+		waiter.granted = true
+		ready = waiter.ready
+	} else {
+		p.active--
+	}
+	p.mu.Unlock()
+
+	if ready != nil {
+		close(ready)
+	}
+}

internal/capacity/manager_test.go

@@ -0,0 +1,183 @@
+package capacity
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+func TestNewManagerRejectsInvalidPolicies(t *testing.T) {
+	maxInt := int(^uint(0) >> 1)
+	tests := []struct {
+		name   string
+		id     string
+		policy domain.BackendCapacityPolicy
+	}{
+		{
+			name:   "blank ID",
+			id:     " \t ",
+			policy: domain.BackendCapacityPolicy{ConcurrencyLimit: 1},
+		},
+		{
+			name:   "zero concurrency",
+			id:     "backend",
+			policy: domain.BackendCapacityPolicy{},
+		},
+		{
+			name:   "negative concurrency",
+			id:     "backend",
+			policy: domain.BackendCapacityPolicy{ConcurrencyLimit: -1},
+		},
+		{
+			name: "negative queue",
+			id:   "backend",
+			policy: domain.BackendCapacityPolicy{
+				ConcurrencyLimit: 1,
+				QueueCapacity:    -1,
+			},
+		},
+		{
+			name: "total overflow",
+			id:   "backend",
+			policy: domain.BackendCapacityPolicy{
+				ConcurrencyLimit: maxInt,
+				QueueCapacity:    1,
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := NewManager(map[string]domain.BackendCapacityPolicy{
+				tc.id: tc.policy,
+			})
+			if err == nil {
+				t.Fatal("expected invalid policy error")
+			}
+		})
+	}
+}
+
+func TestManagerAcquireReleaseIsIdempotent(t *testing.T) {
+	manager, err := NewManager(map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	release, err := manager.Acquire(context.Background(), "limited")
+	if err != nil {
+		t.Fatal(err)
+	}
+	release()
+	release()
+	other, err := manager.Acquire(context.Background(), "limited")
+	if err != nil {
+		t.Fatal(err)
+	}
+	other()
+}
+
+func TestManagerAdmissionIsBoundedAndReleaseIsIdempotent(t *testing.T) {
+	policies := map[string]domain.BackendCapacityPolicy{
+		"limited": {
+			ConcurrencyLimit: 2,
+			QueueCapacity:    1,
+		},
+		"independent": {
+			ConcurrencyLimit: 1,
+		},
+	}
+	manager, err := NewManager(policies)
+	if err != nil {
+		t.Fatalf("construct manager: %v", err)
+	}
+	policies["limited"] = domain.BackendCapacityPolicy{
+		ConcurrencyLimit: 100,
+		QueueCapacity:    100,
+	}
+
+	releases := make([]func(), 0, 3)
+	for range 3 {
+		release, err := manager.Admit(context.Background(), "limited")
+		if err != nil {
+			t.Fatalf("admit within configured capacity: %v", err)
+		}
+		releases = append(releases, release)
+	}
+	if release, err := manager.Admit(context.Background(), "limited"); release != nil ||
+		!errors.Is(err, ErrCapacityExceeded) {
+		t.Fatalf("admission beyond capacity=(release=%t, err=%v), want ErrCapacityExceeded",
+			release != nil, err)
+	}
+	independentRelease, err := manager.Admit(context.Background(), "independent")
+	if err != nil {
+		t.Fatalf("admit independent backend while first is full: %v", err)
+	}
+	independentRelease()
+
+	releases[0]()
+	releases[0]()
+	replacement, err := manager.Admit(context.Background(), "limited")
+	if err != nil {
+		t.Fatalf("admit after release: %v", err)
+	}
+	replacement()
+	releases[1]()
+	releases[2]()
+
+	pool := manager.pools["limited"]
+	pool.mu.Lock()
+	admitted := pool.admitted
+	pool.mu.Unlock()
+	if admitted != 0 {
+		t.Fatalf("admitted runs after releases=%d, want 0", admitted)
+	}
+}
+
+func TestManagerAdmissionHonorsContextAndUnlimitedBackends(t *testing.T) {
+	manager, err := NewManager(map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1},
+	})
+	if err != nil {
+		t.Fatalf("construct manager: %v", err)
+	}
+	release, err := manager.Admit(context.Background(), "limited")
+	if err != nil {
+		t.Fatalf("fill limited pool: %v", err)
+	}
+	defer release()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if release, err := manager.Admit(ctx, "limited"); release != nil ||
+		!errors.Is(err, context.Canceled) {
+		t.Fatalf("canceled limited admission=(release=%t, err=%v), want context cancellation",
+			release != nil, err)
+	}
+
+	var nilManager *Manager
+	for _, tc := range []struct {
+		name      string
+		manager   *Manager
+		backendID string
+	}{
+		{name: "nil manager", manager: nilManager, backendID: "limited"},
+		{name: "blank ID", manager: manager},
+		{name: "unknown ID", manager: manager, backendID: "unknown"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			release, err := tc.manager.Admit(ctx, tc.backendID)
+			if err != nil {
+				t.Fatalf("unlimited admission: %v", err)
+			}
+			if release == nil {
+				t.Fatal("unlimited admission returned nil release")
+			}
+			release()
+			release()
+		})
+	}
+}

internal/catalog/catalog.go

@@ -0,0 +1,249 @@
+// Package catalog validates immutable maintained backend catalog assets.
+package catalog
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"path"
+	"sort"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
+)
+
+// Source identifies one immutable backend catalog asset tree.
+type Source struct {
+	Name              string
+	ExpectedBackendID string
+	FS                fs.FS
+	Root              string
+}
+
+// Set is the validated maintained backend and raw profile catalog.
+type Set struct {
+	Backends   []domain.Backend
+	Profiles   profile.Repository
+	profileIDs []string
+}
+
+// Load validates and combines immutable catalog sources in source order.
+func Load(sources ...Source) (Set, error) {
+	if len(sources) == 0 {
+		return Set{}, errors.New("at least one catalog source is required")
+	}
+	loaded := Set{Backends: make([]domain.Backend, 0, len(sources))}
+	names := map[string]bool{}
+	backendIDs := map[string]bool{}
+	profileIDs := map[string]bool{}
+	for _, source := range sources {
+		if err := validateSource(source, names); err != nil {
+			return Set{}, err
+		}
+		names[source.Name] = true
+		definition, err := loadBackend(source)
+		if err != nil {
+			return Set{}, err
+		}
+		if backendIDs[definition.ID] {
+			return Set{}, fmt.Errorf("catalog %s: backend ID duplicates an earlier catalog", source.Name)
+		}
+		backendIDs[definition.ID] = true
+		repository, metadata, err := profile.LoadFSRepository(context.Background(), source.FS, path.Join(source.Root, "profiles"))
+		if err != nil {
+			return Set{}, fmt.Errorf("catalog %s: %w", source.Name, err)
+		}
+		if len(metadata) == 0 {
+			return Set{}, fmt.Errorf("catalog %s: profiles must not be empty", source.Name)
+		}
+		resolvingRepository := profile.NewResolvingRepository(repository)
+		for _, entry := range metadata {
+			if strings.HasPrefix(entry.ID, "promptkit-") {
+				return Set{}, fmt.Errorf("catalog %s: %s uses the reserved promptkit- profile ID prefix", source.Name, entry.Path)
+			}
+			if profileIDs[entry.ID] {
+				return Set{}, fmt.Errorf("catalog %s: %s duplicates an earlier profile ID", source.Name, entry.Path)
+			}
+			if containsField(entry.ExplicitFields, "endpoint") || containsField(entry.ExplicitFields, "api_key_env") {
+				return Set{}, fmt.Errorf("catalog %s: %s contains connection metadata", source.Name, entry.Path)
+			}
+			value, err := repository.GetProfile(context.Background(), entry.ID)
+			if err != nil {
+				return Set{}, fmt.Errorf("catalog %s: %s: %w", source.Name, entry.Path, err)
+			}
+			if err := rejectSecretKeys(value.ExtraParams); err != nil {
+				return Set{}, fmt.Errorf("catalog %s: %s: prohibited extra parameter key", source.Name, entry.Path)
+			}
+			resolved, err := resolvingRepository.GetProfile(context.Background(), entry.ID)
+			if err != nil {
+				return Set{}, fmt.Errorf("catalog %s: %s has invalid profile inheritance", source.Name, entry.Path)
+			}
+			if resolved.BackendID != definition.ID {
+				return Set{}, fmt.Errorf("catalog %s: %s selects a different backend", source.Name, entry.Path)
+			}
+			profileIDs[entry.ID] = true
+			loaded.profileIDs = append(loaded.profileIDs, entry.ID)
+		}
+		if loaded.Profiles == nil {
+			loaded.Profiles = repository
+		} else {
+			loaded.Profiles = profile.NewOverlayRepository(loaded.Profiles, repository)
+		}
+		loaded.Backends = append(loaded.Backends, definition)
+	}
+	sort.Strings(loaded.profileIDs)
+	return loaded, nil
+}
+
+func validateSource(source Source, names map[string]bool) error {
+	if strings.TrimSpace(source.Name) == "" || source.Name != strings.TrimSpace(source.Name) {
+		return errors.New("catalog source name must not be blank")
+	}
+	if names[source.Name] {
+		return fmt.Errorf("duplicate catalog source name %q", source.Name)
+	}
+	if source.FS == nil {
+		return fmt.Errorf("catalog %s: filesystem is nil", source.Name)
+	}
+	if source.Root == "." || source.Root == "" || !fs.ValidPath(source.Root) {
+		return fmt.Errorf("catalog %s: asset root is invalid", source.Name)
+	}
+	if strings.TrimSpace(source.ExpectedBackendID) == "" {
+		return fmt.Errorf("catalog %s: expected backend ID is blank", source.Name)
+	}
+	return validateLayout(source)
+}
+
+func validateLayout(source Source) error {
+	manifestPath := path.Join(source.Root, "backend.json")
+	profilesRoot := path.Join(source.Root, "profiles")
+	return fs.WalkDir(source.FS, source.Root, func(assetPath string, entry fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if assetPath == source.Root {
+			if !entry.IsDir() {
+				return fmt.Errorf("catalog %s: invalid asset path %s", source.Name, assetPath)
+			}
+			return nil
+		}
+		if entry.IsDir() {
+			if assetPath == profilesRoot || strings.HasPrefix(assetPath, profilesRoot+"/") {
+				return nil
+			}
+			return fmt.Errorf("catalog %s: invalid asset path %s", source.Name, assetPath)
+		}
+		if assetPath == manifestPath && entry.Type().IsRegular() {
+			return nil
+		}
+		if strings.HasPrefix(assetPath, profilesRoot+"/") && entry.Type().IsRegular() && strings.HasSuffix(assetPath, ".yml") {
+			return nil
+		}
+		return fmt.Errorf("catalog %s: invalid asset path %s", source.Name, assetPath)
+	})
+}
+
+func loadBackend(source Source) (domain.Backend, error) {
+	data, err := fs.ReadFile(source.FS, path.Join(source.Root, "backend.json"))
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: %w", source.Name, err)
+	}
+	type manifest struct {
+		SchemaVersion    *int            `json:"schema_version"`
+		ID               *string         `json:"id"`
+		Endpoint         *string         `json:"endpoint"`
+		APIKeyEnv        *string         `json:"api_key_env"`
+		ConcurrencyLimit *int            `json:"concurrency_limit"`
+		QueueCapacity    *int            `json:"queue_capacity"`
+		ExtraParams      json.RawMessage `json:"extra_params"`
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.DisallowUnknownFields()
+	var value manifest
+	if err := decoder.Decode(&value); err != nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: invalid manifest", source.Name)
+	}
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: invalid manifest", source.Name)
+	}
+	if value.SchemaVersion == nil || *value.SchemaVersion != 1 || value.ID == nil || value.Endpoint == nil || value.APIKeyEnv == nil || value.ConcurrencyLimit == nil || value.QueueCapacity == nil || value.ExtraParams == nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: required field is missing or unsupported", source.Name)
+	}
+	if *value.ID != source.ExpectedBackendID {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend ID does not match expected ID", source.Name)
+	}
+	if strings.TrimSpace(*value.APIKeyEnv) == "" {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: api key environment variable must not be blank", source.Name)
+	}
+	extraParams, err := decodeExtraParams(value.ExtraParams)
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: invalid extra parameters", source.Name)
+	}
+	if err := rejectSecretKeys(extraParams); err != nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: prohibited extra parameter key", source.Name)
+	}
+	normalized, err := backend.NormalizeDefinition(domain.Backend{ID: *value.ID, Endpoint: *value.Endpoint, APIKeyEnv: *value.APIKeyEnv, ExtraParams: extraParams, ConcurrencyLimit: *value.ConcurrencyLimit, QueueCapacity: *value.QueueCapacity, QueueCapacitySet: true})
+	if err != nil {
+		return domain.Backend{}, fmt.Errorf("catalog %s: backend.json: invalid backend definition", source.Name)
+	}
+	return normalized, nil
+}
+
+func decodeExtraParams(data []byte) (map[string]any, error) {
+	if bytes.Equal(bytes.TrimSpace(data), []byte("null")) {
+		return nil, nil
+	}
+	decoder := json.NewDecoder(bytes.NewReader(data))
+	decoder.UseNumber()
+	var value map[string]any
+	if err := decoder.Decode(&value); err != nil || value == nil {
+		return nil, errors.New("extra parameters must be an object or null")
+	}
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		return nil, errors.New("extra parameters must contain exactly one JSON value")
+	}
+	return value, nil
+}
+
+func containsField(fields []string, target string) bool {
+	for _, field := range fields {
+		if field == target {
+			return true
+		}
+	}
+	return false
+}
+
+func rejectSecretKeys(value map[string]any) error {
+	return rejectSecretValue(value)
+}
+
+func rejectSecretValue(value any) error {
+	switch value := value.(type) {
+	case map[string]any:
+		for key, child := range value {
+			switch strings.ToLower(key) {
+			case "api_key", "apikey", "authorization", "credential", "credentials", "password", "secret", "token", "access_token":
+				return errors.New("prohibited key")
+			}
+			if err := rejectSecretValue(child); err != nil {
+				return err
+			}
+		}
+	case []any:
+		for _, child := range value {
+			if err := rejectSecretValue(child); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}

internal/catalog/catalog_test.go

@@ -0,0 +1,356 @@
+package catalog
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/fs"
+	"strings"
+	"testing"
+	"testing/fstest"
+
+	openrouter "gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2"
+	rakestrawhome "gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2"
+)
+
+func TestLoadPublishedCatalogs(t *testing.T) {
+	loaded, err := Load(
+		Source{Name: "OpenRouter", ExpectedBackendID: "openrouter", FS: openrouter.FS(), Root: openrouter.Root},
+		Source{Name: "Rakestrawhome", ExpectedBackendID: "rakestrawhome", FS: rakestrawhome.FS(), Root: rakestrawhome.Root},
+	)
+	if err != nil {
+		t.Fatalf("load published catalogs: %v", err)
+	}
+	if loaded.Profiles == nil || len(loaded.profileIDs) == 0 {
+		t.Fatalf("published catalogs have no usable profiles: %#v", loaded)
+	}
+	if _, err := loaded.Profiles.GetProfile(context.Background(), "gemini-flash-latest"); err != nil {
+		t.Fatalf("load maintained standard-profile base: %v", err)
+	}
+
+	expectedBackends := map[string]struct {
+		endpoint         string
+		apiKeyEnv        string
+		concurrencyLimit int
+		queueCapacity    int
+	}{
+		"openrouter": {
+			endpoint:         "https://openrouter.ai/api/v1",
+			apiKeyEnv:        "OPENROUTER_API_KEY",
+			concurrencyLimit: 16,
+			queueCapacity:    1024,
+		},
+		"rakestrawhome": {
+			endpoint:         "https://inference.ai.rakestrawhome.com/v1",
+			apiKeyEnv:        "RAKESTRAWHOME_INFERENCE_API_KEY",
+			concurrencyLimit: 4,
+			queueCapacity:    1024,
+		},
+	}
+	if len(loaded.Backends) != len(expectedBackends) {
+		t.Fatalf("published backend count = %d, want %d", len(loaded.Backends), len(expectedBackends))
+	}
+	for _, definition := range loaded.Backends {
+		expected, found := expectedBackends[definition.ID]
+		if !found {
+			t.Fatalf("unexpected published backend %q", definition.ID)
+		}
+		if definition.Endpoint != expected.endpoint ||
+			definition.APIKeyEnv != expected.apiKeyEnv ||
+			definition.ConcurrencyLimit != expected.concurrencyLimit ||
+			definition.QueueCapacity != expected.queueCapacity ||
+			!definition.QueueCapacitySet ||
+			definition.ExtraParams != nil {
+			t.Fatalf("unexpected published backend definition: %#v", definition)
+		}
+	}
+}
+
+func TestLoadRejectsInvalidSources(t *testing.T) {
+	for name, sources := range map[string][]Source{
+		"none":       nil,
+		"blank name": {{Name: " ", ExpectedBackendID: "openrouter", FS: openrouter.FS(), Root: openrouter.Root}},
+		"duplicate name": {
+			{Name: "same", ExpectedBackendID: "openrouter", FS: openrouter.FS(), Root: openrouter.Root},
+			{Name: "same", ExpectedBackendID: "rakestrawhome", FS: rakestrawhome.FS(), Root: rakestrawhome.Root},
+		},
+		"nil filesystem":         {{Name: "missing", ExpectedBackendID: "openrouter", Root: openrouter.Root}},
+		"invalid root":           {{Name: "invalid-root", ExpectedBackendID: "openrouter", FS: openrouter.FS(), Root: "."}},
+		"blank expected backend": {{Name: "blank-backend", ExpectedBackendID: " ", FS: openrouter.FS(), Root: openrouter.Root}},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if _, err := Load(sources...); err == nil {
+				t.Fatal("expected error")
+			}
+		})
+	}
+}
+
+func TestLoadRejectsInvalidLayouts(t *testing.T) {
+	tests := map[string]func(fstest.MapFS){
+		"unexpected file": func(fsys fstest.MapFS) {
+			fsys["catalog/notes.txt"] = &fstest.MapFile{Data: []byte("unexpected")}
+		},
+		"unexpected directory": func(fsys fstest.MapFS) {
+			fsys["catalog/unexpected"] = &fstest.MapFile{Mode: fs.ModeDir}
+		},
+		"nonregular manifest": func(fsys fstest.MapFS) {
+			fsys["catalog/backend.json"].Mode = fs.ModeSymlink
+		},
+		"wrong profile extension": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/extra.yaml"] = &fstest.MapFile{Data: []byte(validProfile("extra", "one"))}
+		},
+		"nonregular profile": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Mode = fs.ModeSymlink
+		},
+	}
+	for name, mutate := range tests {
+		t.Run(name, func(t *testing.T) {
+			fsys := validCatalogFS("one")
+			mutate(fsys)
+			if _, err := Load(testSource("one", fsys)); err == nil {
+				t.Fatal("expected invalid layout error")
+			}
+		})
+	}
+}
+
+func TestLoadRejectsInvalidManifests(t *testing.T) {
+	tests := map[string]string{
+		"malformed":             `{`,
+		"trailing value":        validManifest("one", "TEST_API_KEY", "null") + `{}`,
+		"missing fields":        `{"schema_version":1,"id":"one"}`,
+		"unsupported version":   strings.Replace(validManifest("one", "TEST_API_KEY", "null"), `"schema_version":1`, `"schema_version":2`, 1),
+		"unknown field":         strings.Replace(validManifest("one", "TEST_API_KEY", "null"), `"extra_params":null`, `"extra_params":null,"unknown":true`, 1),
+		"blank API key env":     validManifest("one", "   ", "null"),
+		"invalid API key env":   validManifest("one", "LEAK-MARKER", "null"),
+		"invalid endpoint":      strings.Replace(validManifest("one", "TEST_API_KEY", "null"), `https://one.example/v1`, `ftp://leak-marker.invalid/v1`, 1),
+		"zero concurrency":      strings.Replace(validManifest("one", "TEST_API_KEY", "null"), `"concurrency_limit":2`, `"concurrency_limit":0`, 1),
+		"non-object parameters": validManifest("one", "TEST_API_KEY", `[]`),
+		"secret parameter":      validManifest("one", "TEST_API_KEY", `{"nested":{"token":"leak-marker"}}`),
+	}
+	for name, manifest := range tests {
+		t.Run(name, func(t *testing.T) {
+			fsys := validCatalogFS("one")
+			fsys["catalog/backend.json"].Data = []byte(manifest)
+			_, err := Load(testSource("one", fsys))
+			if err == nil {
+				t.Fatal("expected invalid manifest error")
+			}
+			if strings.Contains(strings.ToLower(err.Error()), "leak-marker") {
+				t.Fatalf("catalog error exposed manifest content: %v", err)
+			}
+		})
+	}
+}
+
+func TestLoadPreservesManifestJSONNumbers(t *testing.T) {
+	fsys := validCatalogFS("one")
+	fsys["catalog/backend.json"].Data = []byte(validManifest(
+		"one",
+		"TEST_API_KEY",
+		`{"large":9007199254740993,"nested":[1.25]}`,
+	))
+	loaded, err := Load(testSource("one", fsys))
+	if err != nil {
+		t.Fatalf("load catalog: %v", err)
+	}
+	if got := loaded.Backends[0].ExtraParams["large"]; got != json.Number("9007199254740993") {
+		t.Fatalf("large JSON integer = %#v, want preserved json.Number", got)
+	}
+	nested := loaded.Backends[0].ExtraParams["nested"].([]any)
+	if nested[0] != json.Number("1.25") {
+		t.Fatalf("nested JSON number = %#v, want preserved json.Number", nested[0])
+	}
+}
+
+func TestLoadRejectsInvalidCatalogProfiles(t *testing.T) {
+	tests := map[string]func(fstest.MapFS){
+		"empty": func(fsys fstest.MapFS) {
+			delete(fsys, "catalog/profiles/one-profile.yml")
+			fsys["catalog/profiles"] = &fstest.MapFile{Mode: fs.ModeDir}
+		},
+		"malformed": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte("id: [")
+		},
+		"raw API key": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "one") + "api_key: leak-marker\n")
+		},
+		"endpoint field": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "one") + "endpoint: ''\n")
+		},
+		"API key environment field": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "one") + "api_key_env: ''\n")
+		},
+		"owner mismatch": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "other"))
+		},
+		"missing base": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte("id: one-profile\nbase_profile: leak-marker\n")
+		},
+		"cyclic base": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte("id: one-profile\nbase_profile: second\n")
+			fsys["catalog/profiles/second.yml"] = &fstest.MapFile{Data: []byte("id: second\nbase_profile: one-profile\n")}
+		},
+		"secret profile parameter": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "one") + "extra_params:\n  nested:\n    password: leak-marker\n")
+		},
+		"unknown field is redacted": func(fsys fstest.MapFS) {
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile("one-profile", "one") + "leak_marker: leak-marker\n")
+		},
+	}
+	for name, mutate := range tests {
+		t.Run(name, func(t *testing.T) {
+			fsys := validCatalogFS("one")
+			mutate(fsys)
+			_, err := Load(testSource("one", fsys))
+			if err == nil {
+				t.Fatal("expected invalid profile error")
+			}
+			if strings.Contains(strings.ToLower(err.Error()), "leak-marker") {
+				t.Fatalf("catalog error exposed profile content: %v", err)
+			}
+		})
+	}
+}
+
+func TestLoadReservesPromptkitProfilePrefixForCatalogs(t *testing.T) {
+	tests := map[string]struct {
+		profileID string
+		wantError bool
+	}{
+		"maintained name": {
+			profileID: "promptkit-openrouter-standard",
+			wantError: true,
+		},
+		"other reserved name": {
+			profileID: "promptkit-example",
+			wantError: true,
+		},
+		"ordinary name": {
+			profileID: "ordinary-profile",
+		},
+	}
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			fsys := validCatalogFS("one")
+			fsys["catalog/profiles/one-profile.yml"].Data = []byte(validProfile(test.profileID, "one"))
+
+			_, err := Load(testSource("one", fsys))
+			if (err != nil) != test.wantError {
+				t.Fatalf("Load() error = %v, want error %t", err, test.wantError)
+			}
+			if err != nil && !strings.Contains(err.Error(), "catalog one: one-profile.yml") {
+				t.Fatalf("Load() error = %v, want catalog source and path context", err)
+			}
+		})
+	}
+}
+
+func TestLoadRejectsCrossCatalogConflicts(t *testing.T) {
+	t.Run("duplicate backend", func(t *testing.T) {
+		second := catalogFS("one", map[string]string{
+			"catalog/profiles/second.yml": validProfile("second", "one"),
+		}, "null")
+		_, err := Load(
+			Source{Name: "first", ExpectedBackendID: "one", FS: validCatalogFS("one"), Root: "catalog"},
+			Source{Name: "second", ExpectedBackendID: "one", FS: second, Root: "catalog"},
+		)
+		if err == nil {
+			t.Fatal("expected duplicate backend error")
+		}
+	})
+
+	t.Run("duplicate profile", func(t *testing.T) {
+		first := catalogFS("one", map[string]string{
+			"catalog/profiles/shared.yml": validProfile("shared", "one"),
+		}, "null")
+		second := catalogFS("two", map[string]string{
+			"catalog/profiles/shared.yml": validProfile("shared", "two"),
+		}, "null")
+		_, err := Load(testSource("one", first), testSource("two", second))
+		if err == nil {
+			t.Fatal("expected duplicate profile error")
+		}
+	})
+
+	t.Run("cross-catalog base", func(t *testing.T) {
+		first := catalogFS("one", map[string]string{
+			"catalog/profiles/base.yml": validProfile("base", "one"),
+		}, "null")
+		second := catalogFS("two", map[string]string{
+			"catalog/profiles/child.yml": "id: child\nbase_profile: base\n",
+		}, "null")
+		_, err := Load(testSource("one", first), testSource("two", second))
+		if err == nil {
+			t.Fatal("expected cross-catalog base error")
+		}
+	})
+}
+
+func TestLoadReturnsDefensiveCatalogValues(t *testing.T) {
+	fsys := catalogFS("one", map[string]string{
+		"catalog/profiles/one-profile.yml": validProfile("one-profile", "one") + "extra_params:\n  nested:\n    value: profile\n",
+	}, `{"nested":{"value":"backend"}}`)
+	loaded, err := Load(testSource("one", fsys))
+	if err != nil {
+		t.Fatalf("load catalog: %v", err)
+	}
+	loaded.Backends[0].ExtraParams["nested"].(map[string]any)["value"] = "changed"
+	profileValue, err := loaded.Profiles.GetProfile(context.Background(), "one-profile")
+	if err != nil {
+		t.Fatalf("load profile: %v", err)
+	}
+	profileValue.ExtraParams["nested"].(map[string]any)["value"] = "changed"
+
+	again, err := Load(testSource("one", fsys))
+	if err != nil {
+		t.Fatalf("reload catalog: %v", err)
+	}
+	if got := again.Backends[0].ExtraParams["nested"].(map[string]any)["value"]; got != "backend" {
+		t.Fatalf("backend mutation escaped returned set: %#v", got)
+	}
+	againProfile, err := loaded.Profiles.GetProfile(context.Background(), "one-profile")
+	if err != nil {
+		t.Fatalf("reload profile: %v", err)
+	}
+	if got := againProfile.ExtraParams["nested"].(map[string]any)["value"]; got != "profile" {
+		t.Fatalf("profile mutation escaped returned value: %#v", got)
+	}
+}
+
+func testSource(id string, fsys fs.FS) Source {
+	return Source{Name: id, ExpectedBackendID: id, FS: fsys, Root: "catalog"}
+}
+
+func validCatalogFS(id string) fstest.MapFS {
+	return catalogFS(id, map[string]string{
+		"catalog/profiles/" + id + "-profile.yml": validProfile(id+"-profile", id),
+	}, "null")
+}
+
+func catalogFS(id string, profiles map[string]string, extraParams string) fstest.MapFS {
+	fsys := fstest.MapFS{
+		"catalog/backend.json": &fstest.MapFile{Data: []byte(validManifest(id, "TEST_API_KEY", extraParams))},
+	}
+	for name, content := range profiles {
+		fsys[name] = &fstest.MapFile{Data: []byte(content)}
+	}
+	return fsys
+}
+
+func validManifest(id, apiKeyEnv, extraParams string) string {
+	return fmt.Sprintf(
+		`{"schema_version":1,"id":%q,"endpoint":%q,"api_key_env":%q,"concurrency_limit":2,"queue_capacity":3,"extra_params":%s}`,
+		id,
+		"https://"+id+".example/v1",
+		apiKeyEnv,
+		extraParams,
+	)
+}
+
+func validProfile(id, backendID string) string {
+	return fmt.Sprintf("id: %s\nbackend: %s\nmodel: test-model\n", id, backendID)
+}
+
+var _ fs.FS = openrouter.FS()

internal/defaults/defaults.go

@@ -14,21 +14,12 @@ const (
 	ContentTypeApplicationJSON = "application/json"
 	OpenAIChatCompletionsPath  = "/chat/completions"
 
-	ExecutionDefaultTemperature    = 0.0
-	ExecutionDefaultMaxTokens      = 0
-	ExecutionDefaultTopP           = 1.0
 	ExecutionDefaultTimeoutSeconds = 600
-)
-
-var (
-	LLMRequestTimeoutDefault = 10 * time.Minute
+	LLMRequestTimeoutDefault       = 10 * time.Minute
 )
 
 func ExecutionTargetDefault() domain.ExecutionTarget {
 	return domain.ExecutionTarget{
-		Temperature:    ExecutionDefaultTemperature,
-		MaxTokens:      ExecutionDefaultMaxTokens,
-		TopP:           ExecutionDefaultTopP,
 		TimeoutSeconds: ExecutionDefaultTimeoutSeconds,
 	}
 }

internal/domain/domain.go

@@ -60,15 +60,18 @@ type CacheControl struct {
 
 // RunRequest represents a request to generate a single artifact.
 type RunRequest struct {
-	PromptID      string
-	PromptVersion string
-	ProfileID     string
-	APIKey        string `json:"-" yaml:"-"`
-	Inputs        map[string]ArtifactRef
-	Vars          map[string]string
-	Execution     *ExecutionTargetOverride
-	Validation    *OutputContract
-	Metadata      map[string]string
+	PromptID         string
+	PromptVersion    string
+	ProfileID        string
+	SessionID        string
+	APIKey           string `json:"-" yaml:"-"`
+	Inputs           map[string]ArtifactRef
+	Vars             map[string]string
+	Execution        *ExecutionTargetOverride
+	Validation       *OutputContract
+	AppendedMessages []RenderedMessage
+	TransientRetries *int
+	Observer         ExecutionObserver `json:"-"`
 }
 
 // RunResult represents the complete result of a prompt execution run.
@@ -80,8 +83,10 @@ type RunResult struct {
 	PromptID             string
 	PromptVersion        string
 	PromptHash           string
+	SessionID            string
 	RenderedPromptHash   string
 	SelectedProfileID    string
+	SelectedBackendID    string
 	ModelName            string
 	Endpoint             string
 	EffectiveModelParams ExecutionTarget
@@ -95,21 +100,22 @@ type RunResult struct {
 // PreparedRun contains pre-LLM execution state from the prepare/render phase.
 // It must never include resolved API key values, model output, or validation data.
 type PreparedRun struct {
-	PromptID             string                  `json:"prompt_id"`
-	PromptVersion        string                  `json:"prompt_version,omitempty"`
-	PromptHash           string                  `json:"prompt_hash,omitempty"`
-	SelectedProfileID    string                  `json:"selected_profile_id"`
-	EffectiveModelParams ExecutionTarget         `json:"effective_model_params"`
-	TargetPresence       ExecutionTargetPresence `json:"-"`
-	OutputContract       OutputContract          `json:"output_contract"`
-	StructuredOutput     *StructuredOutputSpec   `json:"structured_output,omitempty"`
-	InputHashes          map[string]string       `json:"input_hashes,omitempty"`
-	SessionID            string                  `json:"session_id,omitempty"`
-	RenderedPromptHash   string                  `json:"rendered_prompt_hash"`
-	Messages             []RenderedMessage       `json:"messages"`
-	StartTime            time.Time               `json:"start_time,omitempty"`
-	EndTime              time.Time               `json:"end_time,omitempty"`
-	DurationMS           int64                   `json:"duration_ms,omitempty"`
+	PromptID             string
+	PromptVersion        string
+	PromptHash           string
+	SelectedProfileID    string
+	SelectedBackendID    string
+	EffectiveModelParams ExecutionTarget
+	TargetPresence       ExecutionTargetPresence
+	OutputContract       OutputContract
+	StructuredOutput     *StructuredOutputSpec
+	InputHashes          map[string]string
+	SessionID            string
+	RenderedPromptHash   string
+	Messages             []RenderedMessage
+	StartTime            time.Time
+	EndTime              time.Time
+	DurationMS           int64
 }
 
 // ArtifactRef represents a reference to an input artifact.
@@ -142,6 +148,16 @@ type PromptDefinition struct {
 	Validation     OutputContract          `yaml:"validation"`
 }
 
+// PromptInspection is the resolved result of exact prompt inspection.
+type PromptInspection struct {
+	PromptID         string
+	PromptVersion    string
+	PromptHash       string
+	DefaultProfileID string
+	Inputs           []PromptInput
+	OutputContract   OutputContract
+}
+
 // PromptInput describes one named input expected by a prompt definition.
 type PromptInput struct {
 	Name        string `yaml:"name"`
@@ -158,9 +174,29 @@ type PromptMessageTemplate struct {
 	CacheControl *CacheControl `yaml:"cache_control,omitempty" json:"cache_control,omitempty"`
 }
 
+// Backend describes reusable OpenAI-compatible connection defaults.
+type Backend struct {
+	ID               string
+	Endpoint         string
+	APIKeyEnv        string
+	ExtraParams      map[string]any
+	ConcurrencyLimit int
+	QueueCapacity    int
+	QueueCapacitySet bool
+}
+
+// BackendCapacityPolicy describes normalized run and generation capacity for
+// one limited backend.
+type BackendCapacityPolicy struct {
+	ConcurrencyLimit int
+	QueueCapacity    int
+}
+
 // ExecutionProfile describes how and where to execute a model.
 type ExecutionProfile struct {
 	ID              string         `yaml:"id"`
+	BaseProfileID   string         `yaml:"base_profile"`
+	BackendID       string         `yaml:"backend"`
 	Endpoint        string         `yaml:"endpoint"`
 	Model           string         `yaml:"model"`
 	Temperature     float64        `yaml:"temperature"`
@@ -183,7 +219,7 @@ type ExecutionTargetOverride struct {
 	TopP            *float64       `json:"top_p,omitempty"`
 	TimeoutSeconds  *int           `json:"timeout_seconds,omitempty"`
 	ServiceTier     string         `json:"service_tier,omitempty"`
-	ReasoningEffort string         `json:"reasoning_effort,omitempty"`
+	ReasoningEffort *string        `json:"reasoning_effort,omitempty"`
 	APIKeyEnv       string         `json:"api_key_env,omitempty"`
 	ExtraParams     map[string]any `json:"extra_params,omitempty"`
 }
@@ -199,6 +235,7 @@ type ExecutionTargetPresence struct {
 
 // ExecutionTarget represents effective model runtime settings for a run.
 type ExecutionTarget struct {
+	BackendID       string         `yaml:"backend" json:"backend_id,omitempty"`
 	Endpoint        string         `yaml:"endpoint" json:"endpoint"`
 	Model           string         `yaml:"model" json:"model"`
 	Temperature     float64        `yaml:"temperature" json:"temperature"`
@@ -213,6 +250,13 @@ type ExecutionTarget struct {
 	ExtraParams     map[string]any `yaml:"extra_params" json:"extra_params"`
 }
 
+// ProfileInspection is the resolved result of exact profile inspection.
+type ProfileInspection struct {
+	ProfileID            string
+	EffectiveModelParams ExecutionTarget
+	APIKeyRequired       bool
+}
+
 // OutputContract defines the requirements for the output artifact.
 type OutputContract struct {
 	Format         OutputFormat   `yaml:"format"`
@@ -240,6 +284,8 @@ type GenerateRequest struct {
 	Target           ExecutionTarget
 	TargetPresence   ExecutionTargetPresence
 	StructuredOutput *StructuredOutputSpec
+	TransientRetries uint64
+	Generation       uint64
 }
 
 // StructuredOutputType indicates which provider-level output mode is requested.
@@ -264,8 +310,18 @@ type StructuredOutputJSONSpec struct {
 
 // GenerateResponse is the response received from the LLM client.
 type GenerateResponse struct {
-	Content string
-	Usage   TokenUsage
+	Content       string
+	Usage         TokenUsage
+	UsagePresence *TokenUsagePresence
+}
+
+// TokenUsagePresence records which token fields a provider reported.
+type TokenUsagePresence struct {
+	PromptTokens     bool
+	CompletionTokens bool
+	TotalTokens      bool
+	CachedTokens     bool
+	CacheWriteTokens bool
 }
 
 // TokenUsage tracks token consumption.

internal/domain/endpoint.go

@@ -0,0 +1,39 @@
+package domain
+
+import (
+	"errors"
+	"net/url"
+	"strings"
+)
+
+// NormalizeOpenAICompatibleBaseEndpoint trims and validates a source-neutral
+// OpenAI-compatible provider base endpoint.
+func NormalizeOpenAICompatibleBaseEndpoint(endpoint string) (string, error) {
+	endpoint = strings.TrimSpace(endpoint)
+	if endpoint == "" {
+		return "", errors.New("endpoint must not be blank")
+	}
+	if strings.Contains(endpoint, "#") {
+		return "", errors.New("endpoint must not contain a fragment")
+	}
+
+	parsed, err := url.Parse(endpoint)
+	if err != nil {
+		return "", errors.New("endpoint must be a valid URL")
+	}
+	parsed.Scheme = strings.ToLower(parsed.Scheme)
+	if parsed.Scheme != "http" && parsed.Scheme != "https" {
+		return "", errors.New("endpoint must use http or https")
+	}
+	if !parsed.IsAbs() || parsed.Hostname() == "" {
+		return "", errors.New("endpoint must be absolute and include a host")
+	}
+	if parsed.User != nil {
+		return "", errors.New("endpoint must not contain user information")
+	}
+	if parsed.RawQuery != "" || parsed.ForceQuery {
+		return "", errors.New("endpoint must not contain a query string")
+	}
+
+	return parsed.String(), nil
+}

internal/domain/endpoint_test.go

@@ -0,0 +1,47 @@
+package domain
+
+import "testing"
+
+func TestNormalizeOpenAICompatibleBaseEndpoint(t *testing.T) {
+	tests := []struct {
+		name     string
+		endpoint string
+		want     string
+		wantErr  bool
+	}{
+		{name: "http host", endpoint: "http://provider.example", want: "http://provider.example"},
+		{name: "https nested path and whitespace", endpoint: "  HTTPS://provider.example/api/openai/v1  ", want: "https://provider.example/api/openai/v1"},
+		{name: "IPv4 host and port", endpoint: "http://127.0.0.1:8080/v1", want: "http://127.0.0.1:8080/v1"},
+		{name: "IPv6 host and port", endpoint: "https://[::1]:8443/v1", want: "https://[::1]:8443/v1"},
+		{name: "repeated trailing slashes", endpoint: "https://provider.example/v1///", want: "https://provider.example/v1///"},
+		{name: "blank", endpoint: " \t\n ", wantErr: true},
+		{name: "relative path", endpoint: "/api/v1", wantErr: true},
+		{name: "scheme relative", endpoint: "//provider.example/v1", wantErr: true},
+		{name: "missing host", endpoint: "https:///v1", wantErr: true},
+		{name: "unsupported scheme", endpoint: "ftp://provider.example/v1", wantErr: true},
+		{name: "user information", endpoint: "https://user:secret@provider.example/v1", wantErr: true},
+		{name: "query", endpoint: "https://provider.example/v1?mode=chat", wantErr: true},
+		{name: "empty query", endpoint: "https://provider.example/v1?", wantErr: true},
+		{name: "fragment", endpoint: "https://provider.example/v1#chat", wantErr: true},
+		{name: "empty fragment", endpoint: "https://provider.example/v1#", wantErr: true},
+		{name: "malformed URL", endpoint: "https://provider.example/%zz", wantErr: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := NormalizeOpenAICompatibleBaseEndpoint(tc.endpoint)
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("expected endpoint error, got %q", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("normalize endpoint: %v", err)
+			}
+			if got != tc.want {
+				t.Fatalf("normalized endpoint = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}

internal/domain/execution_settings.go

@@ -0,0 +1,34 @@
+package domain
+
+import (
+	"errors"
+	"math"
+	"time"
+)
+
+const maxExecutionTimeoutSeconds int64 = math.MaxInt64 / int64(time.Second)
+
+// ValidateExecutionTargetSettings validates source-neutral execution-setting
+// invariants on a resolved target.
+func ValidateExecutionTargetSettings(target ExecutionTarget) error {
+	if !isFinite(target.Temperature) || target.Temperature < 0 || target.Temperature > 2 {
+		return errors.New("temperature must be finite and between 0 and 2")
+	}
+	if target.MaxTokens < 0 {
+		return errors.New("max_tokens must be greater than or equal to 0")
+	}
+	if !isFinite(target.TopP) || target.TopP < 0 || target.TopP > 1 {
+		return errors.New("top_p must be finite and between 0 and 1")
+	}
+	if target.TimeoutSeconds < 0 {
+		return errors.New("timeout_seconds must be greater than or equal to 0")
+	}
+	if int64(target.TimeoutSeconds) > maxExecutionTimeoutSeconds {
+		return errors.New("timeout_seconds exceeds the maximum supported duration")
+	}
+	return nil
+}
+
+func isFinite(value float64) bool {
+	return !math.IsNaN(value) && !math.IsInf(value, 0)
+}

internal/domain/execution_settings_test.go

@@ -0,0 +1,73 @@
+package domain
+
+import (
+	"math"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestValidateExecutionTargetSettings(t *testing.T) {
+	valid := ExecutionTarget{
+		Temperature:    1,
+		MaxTokens:      1,
+		TopP:           0.5,
+		TimeoutSeconds: 1,
+	}
+
+	type testCase struct {
+		name    string
+		change  func(*ExecutionTarget)
+		wantErr string
+	}
+	tests := []testCase{
+		{name: "temperature lower boundary", change: func(v *ExecutionTarget) { v.Temperature = 0 }},
+		{name: "temperature finite lower neighbor", change: func(v *ExecutionTarget) { v.Temperature = math.Nextafter(0, 1) }},
+		{name: "temperature finite upper neighbor", change: func(v *ExecutionTarget) { v.Temperature = math.Nextafter(2, 0) }},
+		{name: "temperature upper boundary", change: func(v *ExecutionTarget) { v.Temperature = 2 }},
+		{name: "temperature below lower boundary", change: func(v *ExecutionTarget) { v.Temperature = math.Nextafter(0, math.Inf(-1)) }, wantErr: "temperature"},
+		{name: "temperature above upper boundary", change: func(v *ExecutionTarget) { v.Temperature = math.Nextafter(2, math.Inf(1)) }, wantErr: "temperature"},
+		{name: "temperature NaN", change: func(v *ExecutionTarget) { v.Temperature = math.NaN() }, wantErr: "temperature"},
+		{name: "temperature positive infinity", change: func(v *ExecutionTarget) { v.Temperature = math.Inf(1) }, wantErr: "temperature"},
+		{name: "temperature negative infinity", change: func(v *ExecutionTarget) { v.Temperature = math.Inf(-1) }, wantErr: "temperature"},
+		{name: "max tokens lower boundary", change: func(v *ExecutionTarget) { v.MaxTokens = 0 }},
+		{name: "max tokens finite neighbor", change: func(v *ExecutionTarget) { v.MaxTokens = 1 }},
+		{name: "max tokens below lower boundary", change: func(v *ExecutionTarget) { v.MaxTokens = -1 }, wantErr: "max_tokens"},
+		{name: "top p lower boundary", change: func(v *ExecutionTarget) { v.TopP = 0 }},
+		{name: "top p finite lower neighbor", change: func(v *ExecutionTarget) { v.TopP = math.Nextafter(0, 1) }},
+		{name: "top p finite upper neighbor", change: func(v *ExecutionTarget) { v.TopP = math.Nextafter(1, 0) }},
+		{name: "top p upper boundary", change: func(v *ExecutionTarget) { v.TopP = 1 }},
+		{name: "top p below lower boundary", change: func(v *ExecutionTarget) { v.TopP = math.Nextafter(0, math.Inf(-1)) }, wantErr: "top_p"},
+		{name: "top p above upper boundary", change: func(v *ExecutionTarget) { v.TopP = math.Nextafter(1, math.Inf(1)) }, wantErr: "top_p"},
+		{name: "top p NaN", change: func(v *ExecutionTarget) { v.TopP = math.NaN() }, wantErr: "top_p"},
+		{name: "top p positive infinity", change: func(v *ExecutionTarget) { v.TopP = math.Inf(1) }, wantErr: "top_p"},
+		{name: "top p negative infinity", change: func(v *ExecutionTarget) { v.TopP = math.Inf(-1) }, wantErr: "top_p"},
+		{name: "timeout lower boundary", change: func(v *ExecutionTarget) { v.TimeoutSeconds = 0 }},
+		{name: "timeout finite neighbor", change: func(v *ExecutionTarget) { v.TimeoutSeconds = 1 }},
+		{name: "timeout below lower boundary", change: func(v *ExecutionTarget) { v.TimeoutSeconds = -1 }, wantErr: "timeout_seconds"},
+	}
+	if strconv.IntSize == 64 {
+		durationLimit := maxExecutionTimeoutSeconds
+		tests = append(tests,
+			testCase{name: "timeout duration boundary", change: func(v *ExecutionTarget) { v.TimeoutSeconds = int(durationLimit) }},
+			testCase{name: "timeout above duration boundary", change: func(v *ExecutionTarget) { v.TimeoutSeconds = int(durationLimit) + 1 }, wantErr: "timeout_seconds"},
+		)
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			target := valid
+			tt.change(&target)
+			err := ValidateExecutionTargetSettings(target)
+			if tt.wantErr == "" {
+				if err != nil {
+					t.Fatalf("validate execution settings: %v", err)
+				}
+				return
+			}
+			if err == nil || !strings.Contains(err.Error(), tt.wantErr) {
+				t.Fatalf("error = %v, want diagnostic containing %q", err, tt.wantErr)
+			}
+		})
+	}
+}

internal/domain/message.go

@@ -0,0 +1,82 @@
+package domain
+
+import (
+	"errors"
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	RoleDeveloper = "developer"
+	RoleSystem    = "system"
+	RoleUser      = "user"
+	RoleAssistant = "assistant"
+)
+
+// NormalizeMessageRole validates and canonicalizes a provider-bound chat role.
+func NormalizeMessageRole(role string) (string, error) {
+	if !utf8.ValidString(role) {
+		return "", errors.New("message role must be valid UTF-8")
+	}
+
+	normalized := strings.ToLower(strings.TrimSpace(role))
+	switch normalized {
+	case RoleDeveloper, RoleSystem, RoleUser, RoleAssistant:
+		return normalized, nil
+	default:
+		return "", errors.New("message role must be developer, system, user, or assistant")
+	}
+}
+
+// NormalizeCacheControl validates, canonicalizes, and copies cache metadata.
+func NormalizeCacheControl(control *CacheControl) (*CacheControl, error) {
+	if control == nil {
+		return nil, nil
+	}
+	if !utf8.ValidString(string(control.Type)) {
+		return nil, errors.New("cache control type must be valid UTF-8")
+	}
+	if !utf8.ValidString(control.TTL) {
+		return nil, errors.New("cache control ttl must be valid UTF-8")
+	}
+
+	cacheType := strings.TrimSpace(string(control.Type))
+	if cacheType == "" {
+		return nil, errors.New("cache control type is required")
+	}
+	if CacheControlType(cacheType) != CacheControlEphemeral {
+		return nil, errors.New("unsupported type")
+	}
+
+	ttl := strings.TrimSpace(control.TTL)
+	if ttl != "" && ttl != "1h" {
+		return nil, errors.New("unsupported ttl")
+	}
+
+	return &CacheControl{Type: CacheControlType(cacheType), TTL: ttl}, nil
+}
+
+// CloneRenderedMessages returns a deep copy of rendered messages.
+func CloneRenderedMessages(messages []RenderedMessage) []RenderedMessage {
+	cloned := make([]RenderedMessage, len(messages))
+	copyRenderedMessages(cloned, messages)
+	return cloned
+}
+
+// ConcatRenderedMessages returns an independently owned concatenation of messages.
+func ConcatRenderedMessages(prefix, suffix []RenderedMessage) []RenderedMessage {
+	messages := make([]RenderedMessage, len(prefix)+len(suffix))
+	copyRenderedMessages(messages, prefix)
+	copyRenderedMessages(messages[len(prefix):], suffix)
+	return messages
+}
+
+func copyRenderedMessages(destination, source []RenderedMessage) {
+	for index, message := range source {
+		destination[index] = message
+		if message.CacheControl != nil {
+			cacheControl := *message.CacheControl
+			destination[index].CacheControl = &cacheControl
+		}
+	}
+}

internal/domain/message_test.go

@@ -0,0 +1,121 @@
+package domain
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestNormalizeMessageRole(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		want    string
+		wantErr bool
+	}{
+		{name: "developer", input: RoleDeveloper, want: RoleDeveloper},
+		{name: "system", input: RoleSystem, want: RoleSystem},
+		{name: "user", input: RoleUser, want: RoleUser},
+		{name: "assistant", input: RoleAssistant, want: RoleAssistant},
+		{name: "surrounding whitespace and mixed case", input: " \u2003UsEr\u2003 ", want: RoleUser},
+		{name: "blank", input: " \t\n ", wantErr: true},
+		{name: "tool", input: "tool", wantErr: true},
+		{name: "function", input: "function", wantErr: true},
+		{name: "custom", input: "custom-role", wantErr: true},
+		{name: "invalid UTF-8", input: string([]byte{0xff}), wantErr: true},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got, err := NormalizeMessageRole(test.input)
+			if test.wantErr {
+				if err == nil {
+					t.Fatal("expected an error")
+				}
+				if strings.Contains(err.Error(), test.input) {
+					t.Fatalf("error exposed the input: %v", err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("NormalizeMessageRole() error = %v", err)
+			}
+			if got != test.want {
+				t.Fatalf("NormalizeMessageRole() = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
+func TestNormalizeCacheControl(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   *CacheControl
+		want    *CacheControl
+		wantErr bool
+	}{
+		{name: "nil", input: nil, want: nil},
+		{
+			name:  "canonical values",
+			input: &CacheControl{Type: CacheControlEphemeral, TTL: "1h"},
+			want:  &CacheControl{Type: CacheControlEphemeral, TTL: "1h"},
+		},
+		{
+			name:  "trims values",
+			input: &CacheControl{Type: " ephemeral ", TTL: " 1h\t"},
+			want:  &CacheControl{Type: CacheControlEphemeral, TTL: "1h"},
+		},
+		{name: "empty type", input: &CacheControl{}, wantErr: true},
+		{name: "unsupported type", input: &CacheControl{Type: "persistent"}, wantErr: true},
+		{name: "unsupported ttl", input: &CacheControl{Type: CacheControlEphemeral, TTL: "5m"}, wantErr: true},
+		{name: "invalid type UTF-8", input: &CacheControl{Type: CacheControlType(string([]byte{0xff}))}, wantErr: true},
+		{name: "invalid ttl UTF-8", input: &CacheControl{Type: CacheControlEphemeral, TTL: string([]byte{0xff})}, wantErr: true},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got, err := NormalizeCacheControl(test.input)
+			if test.wantErr {
+				if err == nil {
+					t.Fatal("expected an error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("NormalizeCacheControl() error = %v", err)
+			}
+			if got == nil || test.want == nil {
+				if got != test.want {
+					t.Fatalf("NormalizeCacheControl() = %#v, want %#v", got, test.want)
+				}
+				return
+			}
+			if *got != *test.want {
+				t.Fatalf("NormalizeCacheControl() = %#v, want %#v", got, test.want)
+			}
+			if got == test.input {
+				t.Fatal("normalized cache control aliases its input")
+			}
+		})
+	}
+}
+
+func TestRenderedMessageCloning(t *testing.T) {
+	prefix := []RenderedMessage{{Role: RoleSystem, Content: "prefix", CacheControl: &CacheControl{Type: CacheControlEphemeral, TTL: "1h"}}}
+	suffix := []RenderedMessage{{Role: RoleUser, Content: " suffix "}, {Role: RoleAssistant, Content: "", CacheControl: &CacheControl{Type: CacheControlEphemeral}}}
+
+	cloned := CloneRenderedMessages(prefix)
+	combined := ConcatRenderedMessages(prefix, suffix)
+	if len(combined) != 3 || combined[0].Content != "prefix" || combined[1].Content != " suffix " || combined[2].Content != "" {
+		t.Fatalf("unexpected combined messages: %#v", combined)
+	}
+	if cloned[0].CacheControl == prefix[0].CacheControl || combined[0].CacheControl == prefix[0].CacheControl || combined[2].CacheControl == suffix[1].CacheControl {
+		t.Fatal("cloned cache controls alias their inputs")
+	}
+
+	prefix[0].Content = "changed"
+	prefix[0].CacheControl.TTL = ""
+	suffix[1].CacheControl.Type = "changed"
+	if cloned[0].Content != "prefix" || cloned[0].CacheControl.TTL != "1h" || combined[0].Content != "prefix" || combined[0].CacheControl.TTL != "1h" || combined[2].CacheControl.Type != CacheControlEphemeral {
+		t.Fatalf("cloned messages changed with their inputs: cloned=%#v combined=%#v", cloned, combined)
+	}
+}

internal/domain/observation.go

@@ -0,0 +1,90 @@
+package domain
+
+import "time"
+
+// ExecutionObserver receives one immutable metadata event synchronously.
+type ExecutionObserver func(ExecutionEvent)
+
+type ExecutionEventKind string
+
+const (
+	ExecutionStarted    ExecutionEventKind = "started"
+	ExecutionAttempt    ExecutionEventKind = "attempt"
+	ExecutionRetryDelay ExecutionEventKind = "retry_delay"
+	ExecutionFinished   ExecutionEventKind = "finished"
+)
+
+type ExecutionOutcome string
+
+const (
+	ExecutionOutcomeSuccess       ExecutionOutcome = "success"
+	ExecutionOutcomeInvalidOutput ExecutionOutcome = "invalid_output"
+	ExecutionOutcomeError         ExecutionOutcome = "error"
+)
+
+type ExecutionFailureKind string
+
+const (
+	ExecutionFailureNone              ExecutionFailureKind = ""
+	ExecutionFailureCanceled          ExecutionFailureKind = "canceled"
+	ExecutionFailureDeadline          ExecutionFailureKind = "deadline"
+	ExecutionFailureTransport         ExecutionFailureKind = "transport"
+	ExecutionFailureProviderStatus    ExecutionFailureKind = "provider_status"
+	ExecutionFailureMalformedResponse ExecutionFailureKind = "malformed_response"
+	ExecutionFailureCapacity          ExecutionFailureKind = "capacity"
+	ExecutionFailureInvalidConfig     ExecutionFailureKind = "invalid_config"
+	ExecutionFailureInvalidRequest    ExecutionFailureKind = "invalid_request"
+	ExecutionFailurePromptNotFound    ExecutionFailureKind = "prompt_not_found"
+	ExecutionFailureProfileNotFound   ExecutionFailureKind = "profile_not_found"
+	ExecutionFailurePromptLoad        ExecutionFailureKind = "prompt_load"
+	ExecutionFailureProfileLoad       ExecutionFailureKind = "profile_load"
+	ExecutionFailureArtifactLoad      ExecutionFailureKind = "artifact_load"
+	ExecutionFailurePromptRender      ExecutionFailureKind = "prompt_render"
+	ExecutionFailureValidation        ExecutionFailureKind = "validation"
+	ExecutionFailureGeneration        ExecutionFailureKind = "generation"
+	ExecutionFailureOther             ExecutionFailureKind = "other"
+)
+
+// ObservedTokenCount distinguishes omitted usage from reported zero.
+type ObservedTokenCount struct {
+	Value    int
+	Known    bool
+	Complete bool
+}
+
+// ObservedTokenUsage reports presence-aware token counts.
+type ObservedTokenUsage struct {
+	PromptTokens     ObservedTokenCount
+	CompletionTokens ObservedTokenCount
+	TotalTokens      ObservedTokenCount
+	CachedTokens     ObservedTokenCount
+	CacheWriteTokens ObservedTokenCount
+}
+
+// ExecutionEvent contains metadata only; it carries no mutable containers or
+// error values. Nonterminal events leave aggregate counters at zero.
+type ExecutionEvent struct {
+	Kind               ExecutionEventKind
+	RunID              string
+	Time               time.Time
+	PromptID           string
+	PromptVersion      string
+	ProfileID          string
+	BackendID          string
+	Model              string
+	Generation         uint64
+	Attempt            uint64
+	Dispatched         bool
+	CapacityWait       time.Duration
+	GenerationDuration time.Duration
+	RetryDelay         time.Duration
+	Duration           time.Duration
+	Outcome            ExecutionOutcome
+	Failure            ExecutionFailureKind
+	StatusCode         int
+	RetriesExhausted   bool
+	Usage              ObservedTokenUsage
+	Attempts           uint64
+	TransientRetries   uint64
+	RepairCalls        uint64
+}

internal/domain/output_contract.go

@@ -0,0 +1,38 @@
+package domain
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+const maxOutputRepairAttempts = 3
+
+// ValidateOutputContract validates source-neutral output-contract invariants.
+func ValidateOutputContract(contract OutputContract) error {
+	switch contract.Format {
+	case FormatText, FormatMarkdown, FormatJSON:
+	default:
+		return fmt.Errorf("invalid output format: %q", contract.Format)
+	}
+
+	switch contract.ValidationMode {
+	case ValidationNone, ValidationBasic, ValidationJSON, ValidationJSONSchema:
+	default:
+		return fmt.Errorf("invalid validation mode: %q", contract.ValidationMode)
+	}
+
+	if contract.ValidationMode == ValidationJSONSchema && strings.TrimSpace(contract.SchemaPath) == "" {
+		return errors.New("schema_path is required when validation_mode is json_schema")
+	}
+	if contract.RepairAttempts < 0 {
+		return errors.New("repair_attempts must be greater than or equal to 0")
+	}
+	if contract.RepairAttempts > maxOutputRepairAttempts {
+		return fmt.Errorf("repair_attempts must be less than or equal to %d", maxOutputRepairAttempts)
+	}
+	if contract.ValidationMode == ValidationNone && contract.RepairAttempts > 0 {
+		return errors.New("repair_attempts requires basic, json, or json_schema validation")
+	}
+	return nil
+}

internal/domain/output_contract_test.go

@@ -0,0 +1,87 @@
+package domain
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestValidateOutputContract(t *testing.T) {
+	valid := OutputContract{
+		Format:         FormatText,
+		ValidationMode: ValidationNone,
+	}
+
+	tests := []struct {
+		name    string
+		change  func(*OutputContract)
+		wantErr string
+	}{
+		{name: "text format", change: func(c *OutputContract) { c.Format = FormatText }},
+		{name: "markdown format", change: func(c *OutputContract) { c.Format = FormatMarkdown }},
+		{name: "json format", change: func(c *OutputContract) { c.Format = FormatJSON }},
+		{name: "empty format", change: func(c *OutputContract) { c.Format = "" }, wantErr: "format"},
+		{name: "unsupported format", change: func(c *OutputContract) { c.Format = OutputFormat("binary") }, wantErr: "format"},
+		{name: "none validation", change: func(c *OutputContract) { c.ValidationMode = ValidationNone }},
+		{name: "basic validation", change: func(c *OutputContract) { c.ValidationMode = ValidationBasic }},
+		{name: "json validation", change: func(c *OutputContract) { c.ValidationMode = ValidationJSON }},
+		{name: "json schema validation", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSONSchema
+			c.SchemaPath = "schema.json"
+		}},
+		{name: "empty validation mode", change: func(c *OutputContract) { c.ValidationMode = "" }, wantErr: "validation mode"},
+		{name: "unsupported validation mode", change: func(c *OutputContract) { c.ValidationMode = ValidationMode("unknown") }, wantErr: "validation mode"},
+		{name: "negative repair attempts", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationBasic
+			c.RepairAttempts = -1
+		}, wantErr: "repair_attempts"},
+		{name: "zero repair attempts", change: func(c *OutputContract) { c.RepairAttempts = 0 }},
+		{name: "one repair attempt", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationBasic
+			c.RepairAttempts = 1
+		}},
+		{name: "maximum repair attempts", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSON
+			c.RepairAttempts = 3
+		}},
+		{name: "too many repair attempts", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSONSchema
+			c.SchemaPath = "schema.json"
+			c.RepairAttempts = 4
+		}, wantErr: "repair_attempts"},
+		{name: "none validation with repair attempts", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationNone
+			c.RepairAttempts = 1
+		}, wantErr: "repair_attempts"},
+		{name: "json schema empty path", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSONSchema
+			c.SchemaPath = ""
+		}, wantErr: "schema_path"},
+		{name: "json schema whitespace path", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSONSchema
+			c.SchemaPath = " \t "
+		}, wantErr: "schema_path"},
+		{name: "json schema nonblank path", change: func(c *OutputContract) {
+			c.ValidationMode = ValidationJSONSchema
+			c.SchemaPath = " schema.json "
+		}},
+		{name: "non-schema empty path", change: func(c *OutputContract) { c.SchemaPath = "" }},
+		{name: "non-schema populated path", change: func(c *OutputContract) { c.SchemaPath = "ignored.json" }},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			contract := valid
+			tt.change(&contract)
+			err := ValidateOutputContract(contract)
+			if tt.wantErr == "" {
+				if err != nil {
+					t.Fatalf("validate output contract: %v", err)
+				}
+				return
+			}
+			if err == nil || !strings.Contains(err.Error(), tt.wantErr) {
+				t.Fatalf("error = %v, want diagnostic containing %q", err, tt.wantErr)
+			}
+		})
+	}
+}

internal/domain/prepared_run_test.go

@@ -1,141 +0,0 @@
-package domain
-
-import (
-	"encoding/json"
-	"strings"
-	"testing"
-)
-
-func TestPreparedRunJSONDoesNotIncludeSecretValues(t *testing.T) {
-	const envName = "PROMPTKIT_TEST_API_KEY"
-	const secret = "super-secret-value"
-	t.Setenv(envName, secret)
-
-	prepared := PreparedRun{
-		PromptID:          "prompt.id",
-		PromptVersion:     "v1",
-		PromptHash:        "prompt-hash",
-		SelectedProfileID: "local-fast",
-		EffectiveModelParams: ExecutionTarget{
-			Endpoint:  "http://llm/v1",
-			Model:     "gpt-test",
-			APIKeyEnv: envName,
-			APIKey:    secret,
-		},
-		InputHashes:        map[string]string{"transcript": "hash-1"},
-		RenderedPromptHash: "rendered-hash",
-		Messages: []RenderedMessage{
-			{Role: "system", Content: "You are helpful."},
-			{Role: "user", Content: "Summarize this."},
-		},
-	}
-
-	b, err := json.Marshal(prepared)
-	if err != nil {
-		t.Fatalf("marshal failed: %v", err)
-	}
-
-	out := string(b)
-	if strings.Contains(out, secret) {
-		t.Fatalf("prepared run JSON unexpectedly contains secret value: %s", out)
-	}
-	if !strings.Contains(out, `"api_key_env":"`+envName+`"`) {
-		t.Fatalf("prepared run JSON should include api_key_env name: %s", out)
-	}
-
-	var top map[string]any
-	if err := json.Unmarshal(b, &top); err != nil {
-		t.Fatalf("unmarshal failed: %v", err)
-	}
-
-	for _, forbidden := range []string{"raw_output", "validation", "artifact"} {
-		if _, ok := top[forbidden]; ok {
-			t.Fatalf("prepared run JSON should not include %q", forbidden)
-		}
-	}
-}
-
-func TestPreparedRunJSONIncludesMessageCacheControlOnlyWhenPresent(t *testing.T) {
-	prepared := PreparedRun{
-		PromptID:          "prompt.id",
-		SelectedProfileID: "local-fast",
-		EffectiveModelParams: ExecutionTarget{
-			Endpoint: "http://llm/v1",
-			Model:    "gpt-test",
-		},
-		RenderedPromptHash: "rendered-hash",
-		Messages: []RenderedMessage{
-			{
-				Role:    "system",
-				Content: "You are helpful.",
-				CacheControl: &CacheControl{
-					Type: CacheControlEphemeral,
-					TTL:  "1h",
-				},
-			},
-			{Role: "user", Content: "Summarize this."},
-		},
-	}
-
-	b, err := json.Marshal(prepared)
-	if err != nil {
-		t.Fatalf("marshal failed: %v", err)
-	}
-
-	var decoded struct {
-		Messages []map[string]any `json:"messages"`
-	}
-	if err := json.Unmarshal(b, &decoded); err != nil {
-		t.Fatalf("unmarshal failed: %v", err)
-	}
-	if len(decoded.Messages) != 2 {
-		t.Fatalf("expected 2 messages, got %d", len(decoded.Messages))
-	}
-
-	cacheControl, ok := decoded.Messages[0]["cache_control"].(map[string]any)
-	if !ok {
-		t.Fatalf("expected cache_control on first message, got %#v", decoded.Messages[0])
-	}
-	if cacheControl["type"] != string(CacheControlEphemeral) || cacheControl["ttl"] != "1h" {
-		t.Fatalf("unexpected cache_control payload: %#v", cacheControl)
-	}
-	if _, ok := decoded.Messages[1]["cache_control"]; ok {
-		t.Fatalf("expected second message to omit cache_control, got %#v", decoded.Messages[1])
-	}
-}
-
-func TestPreparedRunJSONIncludesSessionIDOnlyWhenPresent(t *testing.T) {
-	prepared := PreparedRun{
-		PromptID:          "prompt.id",
-		SelectedProfileID: "local-fast",
-		EffectiveModelParams: ExecutionTarget{
-			Endpoint: "http://llm/v1",
-			Model:    "gpt-test",
-		},
-		SessionID:          "session-123",
-		RenderedPromptHash: "rendered-hash",
-		Messages:           []RenderedMessage{{Role: "user", Content: "Summarize this."}},
-	}
-
-	b, err := json.Marshal(prepared)
-	if err != nil {
-		t.Fatalf("marshal failed: %v", err)
-	}
-
-	var decoded map[string]any
-	if err := json.Unmarshal(b, &decoded); err != nil {
-		t.Fatalf("unmarshal failed: %v", err)
-	}
-	if decoded["session_id"] != "session-123" {
-		t.Fatalf("expected session_id in prepared run JSON, got %#v", decoded["session_id"])
-	}
-
-	prepared.SessionID = ""
-	b, err = json.Marshal(prepared)
-	if err != nil {
-		t.Fatalf("marshal failed: %v", err)
-	}
-	if strings.Contains(string(b), "session_id") {
-		t.Fatalf("expected empty session_id to be omitted, got %s", b)
-	}
-}

internal/domain/retries.go

@@ -0,0 +1,15 @@
+package domain
+
+import "fmt"
+
+// ResolveTransientRetries selects a nonnegative retry budget. A nil selection
+// inherits the supplied default.
+func ResolveTransientRetries(defaultBudget uint64, selection *int) (uint64, error) {
+	if selection == nil {
+		return defaultBudget, nil
+	}
+	if *selection < 0 {
+		return 0, fmt.Errorf("transient retries must not be negative")
+	}
+	return uint64(*selection), nil
+}

internal/domain/session.go

@@ -0,0 +1,22 @@
+package domain
+
+import (
+	"fmt"
+	"strings"
+	"unicode/utf8"
+)
+
+// NormalizeSessionID applies the shared session identifier rule.
+func NormalizeSessionID(raw string) (string, error) {
+	if !utf8.ValidString(raw) {
+		return "", fmt.Errorf("session_id must contain valid UTF-8")
+	}
+	normalized := strings.TrimSpace(raw)
+	if normalized == "" {
+		return "", nil
+	}
+	if length := utf8.RuneCountInString(normalized); length > SessionIDMaxLength {
+		return "", fmt.Errorf("session_id length %d exceeds maximum %d", length, SessionIDMaxLength)
+	}
+	return normalized, nil
+}

internal/domain/session_test.go

@@ -0,0 +1,60 @@
+package domain
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestNormalizeSessionID(t *testing.T) {
+	tests := []struct {
+		name            string
+		raw             string
+		want            string
+		wantErrContains string
+	}{
+		{
+			name: "trims surrounding Unicode whitespace",
+			raw:  "\u2003 session-123 \u2003",
+			want: "session-123",
+		},
+		{
+			name: "blank input is omitted",
+			raw:  " \t\u2003 ",
+			want: "",
+		},
+		{
+			name: "maximum Unicode length is accepted",
+			raw:  strings.Repeat("界", SessionIDMaxLength),
+			want: strings.Repeat("界", SessionIDMaxLength),
+		},
+		{
+			name:            "one Unicode code point over maximum is rejected",
+			raw:             strings.Repeat("界", SessionIDMaxLength+1),
+			wantErrContains: "exceeds maximum",
+		},
+		{name: "invalid UTF-8 before valid content", raw: string([]byte{0xff}) + "session", wantErrContains: "valid UTF-8"},
+		{name: "invalid UTF-8 within valid content", raw: "ses" + string([]byte{0xff}) + "sion", wantErrContains: "valid UTF-8"},
+		{name: "invalid UTF-8 after valid content", raw: "session" + string([]byte{0xff}), wantErrContains: "valid UTF-8"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := NormalizeSessionID(tt.raw)
+			if tt.wantErrContains != "" {
+				if err == nil {
+					t.Fatal("expected normalization error")
+				}
+				if !strings.Contains(err.Error(), tt.wantErrContains) {
+					t.Fatalf("expected diagnostic containing %q, got %v", tt.wantErrContains, err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("normalize session id: %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("normalized session id = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}

internal/engine/engine.go

@@ -0,0 +1,285 @@
+// Package engine assembles Promptkit's internal execution components.
+package engine
+
+import (
+	"context"
+	"fmt"
+	"io/fs"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	openrouter "gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2"
+	rakestrawhome "gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2"
+	"gitea.maximumdirect.net/eric/promptkit/internal/artifact"
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+	"gitea.maximumdirect.net/eric/promptkit/internal/catalog"
+	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/generation"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
+	"gitea.maximumdirect.net/eric/promptkit/internal/prompt"
+	"gitea.maximumdirect.net/eric/promptkit/internal/promptdef"
+	"gitea.maximumdirect.net/eric/promptkit/internal/usecase"
+	"gitea.maximumdirect.net/eric/promptkit/internal/validate"
+)
+
+// Config carries construction settings selected by the public facade.
+type Config struct {
+	PromptDir        string
+	ProfileDir       string
+	SchemaDir        string
+	Timeout          time.Duration
+	HTTPClient       *http.Client
+	TransientRetries *int
+}
+
+// Options collects construction choices from the public facade.
+type Options struct {
+	llmClient             llm.Client
+	artifactReader        artifact.Reader
+	promptDefinitions     promptdef.Repository
+	profiles              profile.Repository
+	fallbackProfiles      profile.Repository
+	memoryProfiles        profile.Repository
+	backends              []domain.Backend
+	validator             validate.Validator
+	promptSource          bool
+	profileSource         bool
+	fallbackProfileSource bool
+	memorySource          bool
+	validatorSource       bool
+	artifactSource        bool
+}
+
+// SetLLMClient selects the client collaborator for one engine.
+func (o *Options) SetLLMClient(client llm.Client) { o.llmClient = client }
+
+// SetArtifactReader selects the artifact collaborator for one engine.
+func (o *Options) SetArtifactReader(reader artifact.Reader) {
+	o.artifactReader = reader
+	o.artifactSource = true
+}
+
+// SetPromptFS selects a prompt source rooted in fsys.
+func (o *Options) SetPromptFS(fsys fs.FS, root string) error {
+	if err := validateSourceFS(fsys, root); err != nil {
+		return err
+	}
+	o.promptDefinitions = promptdef.NewFSRepository(fsys, root)
+	o.promptSource = true
+	return nil
+}
+
+// SetPromptFile selects a single prompt file.
+func (o *Options) SetPromptFile(path string) error {
+	fsys, root, directory, err := fileSource(path)
+	if err != nil {
+		return err
+	}
+	o.promptDefinitions = promptdef.NewFileRepository(fsys, root, directory)
+	o.promptSource = true
+	return nil
+}
+
+// SetProfileFS selects an ordinary profile source rooted in fsys.
+func (o *Options) SetProfileFS(fsys fs.FS, root string) error {
+	if err := validateSourceFS(fsys, root); err != nil {
+		return err
+	}
+	o.profiles = profile.NewFSRepository(fsys, root)
+	o.profileSource = true
+	return nil
+}
+
+// SetProfileFile selects a single ordinary profile file.
+func (o *Options) SetProfileFile(path string) error {
+	fsys, root, _, err := fileSource(path)
+	if err != nil {
+		return err
+	}
+	o.profiles = profile.NewFSRepository(fsys, root)
+	o.profileSource = true
+	return nil
+}
+
+// SetFallbackProfileFS selects a fallback profile source rooted in fsys.
+func (o *Options) SetFallbackProfileFS(fsys fs.FS, root string) error {
+	if err := validateSourceFS(fsys, root); err != nil {
+		return err
+	}
+	o.fallbackProfiles = profile.NewFSRepository(fsys, root)
+	o.fallbackProfileSource = true
+	return nil
+}
+
+// SetMemoryProfiles validates and stores application-owned profile definitions.
+func (o *Options) SetMemoryProfiles(definitions []domain.ExecutionProfile) error {
+	repository, err := profile.NewMemoryRepository(definitions)
+	if err != nil {
+		return err
+	}
+	o.memoryProfiles = repository
+	o.memorySource = true
+	return nil
+}
+
+// AddBackend appends one backend registration.
+func (o *Options) AddBackend(backend domain.Backend) { o.backends = append(o.backends, backend) }
+
+// SetSchemaFS selects a schema source rooted in fsys.
+func (o *Options) SetSchemaFS(fsys fs.FS, root string) error {
+	if err := validateSourceFS(fsys, root); err != nil {
+		return err
+	}
+	o.validator = validate.NewFSValidator(fsys, root)
+	o.validatorSource = true
+	return nil
+}
+
+// SetSchemaFile selects a single schema file.
+func (o *Options) SetSchemaFile(path string) error {
+	fsys, root, _, err := fileSource(path)
+	if err != nil {
+		return err
+	}
+	o.validator = validate.NewFSValidator(fsys, root)
+	o.validatorSource = true
+	return nil
+}
+
+// Engine forwards domain operations to the single assembled use-case runner.
+type Engine struct {
+	runner *usecase.Runner
+}
+
+// New assembles an engine from facade-selected configuration and collaborators.
+func New(cfg Config, options Options) (*Engine, error) {
+	defaultRetries, err := domain.ResolveTransientRetries(2, cfg.TransientRetries)
+	if err != nil {
+		return nil, err
+	}
+	promptDefinitions := options.promptDefinitions
+	if !options.promptSource {
+		if strings.TrimSpace(cfg.PromptDir) == "" {
+			return nil, fmt.Errorf("prompt directory is required")
+		}
+		promptDefinitions = promptdef.NewFilesystemRepository(cfg.PromptDir)
+	}
+
+	maintained, err := catalog.Load(
+		catalog.Source{Name: "OpenRouter", ExpectedBackendID: backend.OpenRouterID, FS: openrouter.FS(), Root: openrouter.Root},
+		catalog.Source{Name: "Rakestrawhome", ExpectedBackendID: backend.RakestrawHomeID, FS: rakestrawhome.FS(), Root: rakestrawhome.Root},
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load maintained catalogs: %w", err)
+	}
+
+	maintainedProfiles, err := newMaintainedProfileRepository(maintained.Profiles, maintained.Backends)
+	if err != nil {
+		return nil, fmt.Errorf("failed to construct Promptkit-maintained profiles: %w", err)
+	}
+
+	profiles := newProfileRepository(cfg.ProfileDir, options, maintainedProfiles)
+	registry, err := backend.NewRegistry(maintained.Backends, options.backends)
+	if err != nil {
+		return nil, fmt.Errorf("failed to construct backend registry: %w", err)
+	}
+	manager, err := capacity.NewManager(registry.CapacityPolicies())
+	if err != nil {
+		return nil, fmt.Errorf("failed to construct backend capacity manager: %w", err)
+	}
+
+	validator := options.validator
+	if !options.validatorSource {
+		schemaDir := cfg.SchemaDir
+		if strings.TrimSpace(schemaDir) == "" {
+			schemaDir = defaults.SchemaDirDefault
+		}
+		validator = validate.NewStandardValidator(schemaDir)
+	}
+	var client llm.Client
+	if options.llmClient == nil {
+		builtIn, newErr := llm.NewOpenAICompatibleClient(llm.OpenAICompatibleConfig{Timeout: cfg.Timeout, HTTPClient: cfg.HTTPClient})
+		if newErr != nil {
+			return nil, newErr
+		}
+		client = generation.NewBuiltIn(manager, builtIn)
+	} else {
+		client = generation.NewInjected(manager, options.llmClient)
+	}
+	reader := options.artifactReader
+	if !options.artifactSource {
+		reader = artifact.NewCompositeReader()
+	}
+
+	return &Engine{runner: usecase.NewRunnerWithRepairer(promptDefinitions, profiles, registry, reader, prompt.NewGoRenderer(), client, validator, usecase.NewDefaultOutputRepairer(client), manager, defaultRetries)}, nil
+}
+
+func newProfileRepository(profileDir string, options Options, maintained profile.Repository) profile.Repository {
+	repository := maintained
+	if options.fallbackProfileSource {
+		repository = profile.NewOverlayRepository(options.fallbackProfiles, repository)
+	}
+	if options.profileSource {
+		repository = profile.NewOverlayRepository(options.profiles, repository)
+	} else if strings.TrimSpace(profileDir) != "" {
+		repository = profile.NewOverlayRepository(profile.NewFilesystemRepository(profileDir), repository)
+	}
+	if options.memorySource {
+		repository = profile.NewOverlayRepository(options.memoryProfiles, repository)
+	}
+	return profile.NewResolvingRepository(repository)
+}
+
+func validateSourceFS(fsys fs.FS, root string) error {
+	if fsys == nil {
+		return fmt.Errorf("source filesystem is nil")
+	}
+	if strings.TrimSpace(root) == "" {
+		return fmt.Errorf("source root is required")
+	}
+	return nil
+}
+
+func fileSource(name string) (fs.FS, string, string, error) {
+	if strings.TrimSpace(name) == "" {
+		return nil, "", "", fmt.Errorf("source path is required")
+	}
+	directory := filepath.Dir(name)
+	base := filepath.Base(name)
+	if base == "." || base == string(filepath.Separator) {
+		return nil, "", "", fmt.Errorf("source path must name a file")
+	}
+	info, err := os.Stat(name)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("failed to access source file %q: %w", name, err)
+	}
+	if info.IsDir() {
+		return nil, "", "", fmt.Errorf("source path %q must be a file", name)
+	}
+	return os.DirFS(directory), filepath.ToSlash(base), directory, nil
+}
+
+func (e *Engine) InspectPrompt(ctx context.Context, id, version string) (*domain.PromptInspection, error) {
+	return e.runner.InspectPrompt(ctx, id, version)
+}
+func (e *Engine) InspectProfile(ctx context.Context, id string) (*domain.ProfileInspection, error) {
+	return e.runner.InspectProfile(ctx, id)
+}
+func (e *Engine) Prepare(ctx context.Context, request domain.RunRequest) (*domain.PreparedRun, error) {
+	return e.runner.Prepare(ctx, request)
+}
+func (e *Engine) PrepareExecution(ctx context.Context, request domain.RunRequest) (*usecase.PreparedExecution, error) {
+	return e.runner.PrepareExecution(ctx, request)
+}
+func (e *Engine) Run(ctx context.Context, request domain.RunRequest) (*domain.RunResult, error) {
+	return e.runner.Run(ctx, request)
+}
+func (e *Engine) RunPrepared(ctx context.Context, prepared *usecase.PreparedExecution) (*domain.RunResult, error) {
+	return e.runner.RunPrepared(ctx, prepared)
+}

internal/engine/maintained_profiles.go

@@ -0,0 +1,50 @@
+package engine
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
+)
+
+func maintainedProfileDefinitions() []domain.ExecutionProfile {
+	return []domain.ExecutionProfile{
+		{
+			ID:            "promptkit-openrouter-standard",
+			BaseProfileID: "gemini-flash-latest",
+		},
+		{
+			ID:        "promptkit-openrouter-auto",
+			BackendID: backend.OpenRouterID,
+			Model:     "openrouter/auto",
+		},
+	}
+}
+
+func newMaintainedProfileRepository(catalogProfiles profile.Repository, maintainedBackends []domain.Backend) (profile.Repository, error) {
+	definitions := maintainedProfileDefinitions()
+	owned, err := profile.NewMemoryRepository(definitions)
+	if err != nil {
+		return nil, fmt.Errorf("create Promptkit-maintained profiles: %w", err)
+	}
+
+	combined := profile.NewOverlayRepository(owned, catalogProfiles)
+	resolved := profile.NewResolvingRepository(combined)
+	registry, err := backend.NewRegistry(maintainedBackends, nil)
+	if err != nil {
+		return nil, fmt.Errorf("construct maintained backend registry: %w", err)
+	}
+	for _, definition := range definitions {
+		effective, err := resolved.GetProfile(context.Background(), definition.ID)
+		if err != nil {
+			return nil, fmt.Errorf("resolve Promptkit-maintained profile %q: %w", definition.ID, err)
+		}
+		if _, err := registry.GetBackend(effective.BackendID); err != nil {
+			return nil, fmt.Errorf("Promptkit-maintained profile %q selects unavailable backend %q: %w", definition.ID, effective.BackendID, err)
+		}
+	}
+
+	return combined, nil
+}

internal/engine/maintained_profiles_test.go

@@ -0,0 +1,78 @@
+package engine
+
+import (
+	"context"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
+)
+
+func TestNewMaintainedProfileRepository(t *testing.T) {
+	newCatalogProfiles := func(t *testing.T, definitions []domain.ExecutionProfile) profile.Repository {
+		t.Helper()
+		repository, err := profile.NewMemoryRepository(definitions)
+		if err != nil {
+			t.Fatalf("create catalog profiles: %v", err)
+		}
+		return repository
+	}
+	newBackend := func(id string) domain.Backend {
+		return domain.Backend{ID: id, Endpoint: "https://" + id + ".example/v1", APIKeyEnv: "TEST_API_KEY"}
+	}
+
+	t.Run("resolves inherited and direct definitions", func(t *testing.T) {
+		repository, err := newMaintainedProfileRepository(
+			newCatalogProfiles(t, []domain.ExecutionProfile{{
+				ID:        "gemini-flash-latest",
+				BackendID: backend.OpenRouterID,
+				Model:     "catalog-selected-model",
+			}}),
+			[]domain.Backend{newBackend(backend.OpenRouterID)},
+		)
+		if err != nil {
+			t.Fatalf("create maintained profiles: %v", err)
+		}
+
+		resolved := profile.NewResolvingRepository(repository)
+		standard, err := resolved.GetProfile(context.Background(), "promptkit-openrouter-standard")
+		if err != nil {
+			t.Fatalf("resolve inherited profile: %v", err)
+		}
+		if standard.BackendID != backend.OpenRouterID || standard.Model != "catalog-selected-model" {
+			t.Fatalf("unexpected inherited profile: %#v", standard)
+		}
+
+		auto, err := resolved.GetProfile(context.Background(), "promptkit-openrouter-auto")
+		if err != nil {
+			t.Fatalf("resolve direct profile: %v", err)
+		}
+		definitions := maintainedProfileDefinitions()
+		if auto.BackendID != definitions[1].BackendID || auto.Model != definitions[1].Model {
+			t.Fatalf("unexpected direct profile: %#v", auto)
+		}
+	})
+
+	t.Run("rejects a missing inherited base", func(t *testing.T) {
+		if _, err := newMaintainedProfileRepository(
+			newCatalogProfiles(t, nil),
+			[]domain.Backend{newBackend(backend.OpenRouterID)},
+		); err == nil {
+			t.Fatal("expected missing base error")
+		}
+	})
+
+	t.Run("rejects an unavailable effective backend", func(t *testing.T) {
+		if _, err := newMaintainedProfileRepository(
+			newCatalogProfiles(t, []domain.ExecutionProfile{{
+				ID:        "gemini-flash-latest",
+				BackendID: "other",
+				Model:     "catalog-selected-model",
+			}}),
+			[]domain.Backend{newBackend("other")},
+		); err == nil {
+			t.Fatal("expected unavailable backend error")
+		}
+	})
+}

internal/filecatalog/catalog.go

@@ -36,7 +36,8 @@ func FindYAMLFiles(ctx context.Context, root string) ([]string, error) {
 	return files, err
 }
 
-// FindFSYAMLFiles returns sorted paths for .yaml and .yml files under root in fsys.
+// FindFSYAMLFiles returns root itself when it names a file. For a directory
+// root, it returns sorted paths for .yaml and .yml files beneath that root.
 func FindFSYAMLFiles(ctx context.Context, fsys fs.FS, root string) ([]string, error) {
 	cleanRoot := CleanFSRoot(root)
 	var files []string
@@ -52,6 +53,10 @@ func FindFSYAMLFiles(ctx context.Context, fsys fs.FS, root string) ([]string, er
 		if d.IsDir() {
 			return nil
 		}
+		if name == cleanRoot {
+			files = append(files, name)
+			return nil
+		}
 		if !IsYAMLFile(d.Name()) {
 			return nil
 		}
@@ -71,10 +76,10 @@ func RelativePath(root string, filePath string) string {
 	return filepath.Clean(rel)
 }
 
-// CleanFSRoot normalizes a root path for use with fs.FS.
+// CleanFSRoot normalizes a root path for use with fs.FS while preserving
+// nonblank leading and trailing whitespace.
 func CleanFSRoot(root string) string {
-	root = strings.TrimSpace(root)
-	if root == "" || root == "." {
+	if strings.TrimSpace(root) == "" || root == "." {
 		return "."
 	}
 	return path.Clean(root)
@@ -97,22 +102,21 @@ func DisplayPath(root string, name string) string {
 // ResolveFSPath resolves userPath from baseDir and keeps it inside root.
 func ResolveFSPath(root string, baseDir string, userPath string) (string, string, error) {
 	cleanRoot := CleanFSRoot(root)
-	cleanBase := path.Clean(strings.TrimSpace(baseDir))
-	if cleanBase == "" {
+	cleanBase := path.Clean(baseDir)
+	if strings.TrimSpace(baseDir) == "" {
 		cleanBase = cleanRoot
 	}
 	if !containsFSPath(cleanRoot, cleanBase) {
 		return "", "", fmt.Errorf("base path %q is outside source root %q", cleanBase, cleanRoot)
 	}
 
-	cleanUserPath := strings.TrimSpace(userPath)
-	if cleanUserPath == "" {
+	if strings.TrimSpace(userPath) == "" {
 		return "", "", fmt.Errorf("path is required")
 	}
-	cleanUserPath = path.Clean(cleanUserPath)
-	if path.IsAbs(cleanUserPath) {
+	if path.IsAbs(userPath) {
 		return "", "", fmt.Errorf("path %q must be relative", userPath)
 	}
+	cleanUserPath := path.Clean(userPath)
 
 	resolved := path.Clean(path.Join(cleanBase, cleanUserPath))
 	if !containsFSPath(cleanRoot, resolved) {
@@ -130,13 +134,6 @@ func containsFSPath(root string, name string) bool {
 	return name == root || strings.HasPrefix(name, strings.TrimSuffix(root, "/")+"/")
 }
 
-// Stem strips .yaml or .yml from a file name.
-func Stem(name string) string {
-	name = strings.TrimSuffix(name, ".yaml")
-	name = strings.TrimSuffix(name, ".yml")
-	return name
-}
-
 func IsYAMLFile(name string) bool {
 	return strings.HasSuffix(name, ".yaml") || strings.HasSuffix(name, ".yml")
 }

internal/filecatalog/catalog_test.go

@@ -54,7 +54,7 @@ func TestFindFSYAMLFilesNestedSortedAndFiltered(t *testing.T) {
 		"other/ignored.yaml":        &fstest.MapFile{Data: []byte("id: ignored")},
 	}
 
-	got, err := FindFSYAMLFiles(context.Background(), fsys, " prompts ")
+	got, err := FindFSYAMLFiles(context.Background(), fsys, "prompts")
 	if err != nil {
 		t.Fatalf("expected no error, got %v", err)
 	}
@@ -98,8 +98,11 @@ func TestCleanFSRoot(t *testing.T) {
 		want string
 	}{
 		{name: "empty", root: "", want: "."},
+		{name: "whitespace only", root: " \t ", want: "."},
 		{name: "dot", root: ".", want: "."},
-		{name: "trimmed", root: " prompts/../profiles ", want: "profiles"},
+		{name: "cleaned", root: "prompts/../profiles", want: "profiles"},
+		{name: "leading whitespace preserved", root: " profiles", want: " profiles"},
+		{name: "trailing whitespace preserved", root: "profiles ", want: "profiles "},
 	}
 
 	for _, tc := range tests {
@@ -158,6 +161,22 @@ func TestResolveFSPath(t *testing.T) {
 			wantPath:    "prompts/shared/user.tmpl",
 			wantDisplay: "shared/user.tmpl",
 		},
+		{
+			name:        "leading whitespace preserved",
+			root:        "prompts",
+			baseDir:     "prompts/nested",
+			userPath:    " user.tmpl",
+			wantPath:    "prompts/nested/ user.tmpl",
+			wantDisplay: "nested/ user.tmpl",
+		},
+		{
+			name:        "trailing whitespace preserved",
+			root:        "prompts",
+			baseDir:     "prompts/nested",
+			userPath:    "user.tmpl ",
+			wantPath:    "prompts/nested/user.tmpl ",
+			wantDisplay: "nested/user.tmpl ",
+		},
 		{
 			name:     "escape rejected",
 			root:     "prompts",
@@ -218,26 +237,6 @@ func TestResolveFSPath(t *testing.T) {
 	}
 }
 
-func TestStemStripsYAMLExtensions(t *testing.T) {
-	tests := []struct {
-		name string
-		in   string
-		want string
-	}{
-		{name: "yaml", in: "prompt.yaml", want: "prompt"},
-		{name: "yml", in: "profile.yml", want: "profile"},
-		{name: "other", in: "file.txt", want: "file.txt"},
-	}
-
-	for _, tc := range tests {
-		t.Run(tc.name, func(t *testing.T) {
-			if got := Stem(tc.in); got != tc.want {
-				t.Fatalf("expected %q, got %q", tc.want, got)
-			}
-		})
-	}
-}
-
 func TestIsYAMLFile(t *testing.T) {
 	tests := []struct {
 		name string

internal/generation/coordinator.go

@@ -0,0 +1,294 @@
+// Package generation coordinates model attempts, backend permits, and bounded
+// built-in HTTP retries for one generation request.
+package generation
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"math/rand/v2"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+	"gitea.maximumdirect.net/eric/promptkit/internal/observation"
+)
+
+const (
+	initialBackoff = 500 * time.Millisecond
+	maximumBackoff = 8 * time.Second
+)
+
+// Coordinator implements the internal model client using the existing backend
+// capacity manager. Exactly one of builtIn and injected is selected.
+type Coordinator struct {
+	manager  *capacity.Manager
+	builtIn  *llm.OpenAICompatibleClient
+	injected llm.Client
+	now      func() time.Time
+	jitter   func(time.Duration) time.Duration
+	wait     func(context.Context, time.Duration) error
+}
+
+// NewBuiltIn selects the built-in HTTP retry path.
+func NewBuiltIn(manager *capacity.Manager, client *llm.OpenAICompatibleClient) *Coordinator {
+	return &Coordinator{manager: manager, builtIn: client, now: time.Now, jitter: randomJitter, wait: waitContext}
+}
+
+// NewInjected selects one opaque client dispatch with no automatic retry.
+func NewInjected(manager *capacity.Manager, client llm.Client) *Coordinator {
+	return &Coordinator{manager: manager, injected: client, now: time.Now, jitter: randomJitter, wait: waitContext}
+}
+
+// ExhaustedError retains the final eligible status failure and the number of
+// attempts actually dispatched.
+type ExhaustedError struct {
+	attempts uint64
+	cause    error
+}
+
+func (e *ExhaustedError) Error() string {
+	if e == nil {
+		return "transient model retries exhausted"
+	}
+	return fmt.Sprintf("transient model retries exhausted after %d attempts", e.attempts)
+}
+
+func (e *ExhaustedError) Unwrap() error {
+	if e == nil {
+		return nil
+	}
+	return e.cause
+}
+
+func (e *ExhaustedError) Attempts() uint64 {
+	if e == nil {
+		return 0
+	}
+	return e.attempts
+}
+
+// Generate executes either one opaque client call or a frozen built-in HTTP
+// sequence with one permit per actual dispatch.
+func (c *Coordinator) Generate(ctx context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error) {
+	if c.injected != nil {
+		return c.generateInjected(ctx, req)
+	}
+	prepared, err := c.builtIn.PrepareGeneration(req)
+	if err != nil {
+		return nil, err
+	}
+
+	var attempts, retriesUsed uint64
+	recorder := observation.FromContext(ctx)
+	generation := req.Generation
+	if generation == 0 {
+		generation = 1
+	}
+	for {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		ordinal := attempts + 1
+		outcome, dispatched, capacityWait, generationDuration := c.execute(ctx, req.Target.BackendID, prepared)
+		if dispatched {
+			attempts++
+		}
+		if recorder != nil {
+			recorder.Attempt(observation.AttemptData{Generation: generation, Attempt: ordinal,
+				Dispatched: dispatched, CapacityWait: capacityWait, GenerationDuration: generationDuration,
+				Outcome: attemptOutcome(outcome.Err), Failure: attemptFailure(outcome.Err),
+				StatusCode: outcome.StatusCode, Usage: outcome.Usage, UsagePresence: outcome.UsagePresence})
+		}
+		if outcome.Err == nil {
+			if err := ctx.Err(); err != nil {
+				return nil, err
+			}
+			return outcome.Response, nil
+		}
+		if !dispatched || !eligibleStatus(outcome) {
+			return nil, outcome.Err
+		}
+		if retriesUsed == req.TransientRetries {
+			if retriesUsed == 0 {
+				return nil, outcome.Err
+			}
+			return nil, &ExhaustedError{attempts: attempts, cause: outcome.Err}
+		}
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		retryOrdinal := retriesUsed + 1
+		delay := retryDelay(c.backoff(retryOrdinal), outcome.RetryNotBefore, c.now())
+		waitStart := c.now()
+		waitErr := c.wait(ctx, delay)
+		if recorder != nil {
+			recorder.Delay(observation.DelayData{Generation: generation, Attempt: attempts,
+				Elapsed: elapsed(waitStart, c.now()), Failure: attemptFailure(waitErr)})
+		}
+		if waitErr != nil {
+			return nil, waitErr
+		}
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		retriesUsed++
+	}
+}
+
+func (c *Coordinator) generateInjected(ctx context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error) {
+	recorder := observation.FromContext(ctx)
+	generation := req.Generation
+	if generation == 0 {
+		generation = 1
+	}
+	start := c.now()
+	release, err := c.manager.Acquire(ctx, req.Target.BackendID)
+	capacityWait := c.capacityWait(req.Target.BackendID, start)
+	if err != nil {
+		if recorder != nil {
+			recorder.Attempt(observation.AttemptData{Generation: generation, Attempt: 1, CapacityWait: capacityWait, Outcome: domain.ExecutionOutcomeError, Failure: attemptFailure(err)})
+		}
+		return nil, err
+	}
+	defer release()
+	if err := ctx.Err(); err != nil {
+		release()
+		if recorder != nil {
+			recorder.Attempt(observation.AttemptData{Generation: generation, Attempt: 1, CapacityWait: capacityWait, Outcome: domain.ExecutionOutcomeError, Failure: attemptFailure(err)})
+		}
+		return nil, err
+	}
+	dispatchStart := c.now()
+	response, err := c.injected.Generate(ctx, req)
+	duration := elapsed(dispatchStart, c.now())
+	if err == nil && response == nil {
+		err = llm.ErrMalformedResponse
+	}
+	release()
+	if recorder != nil {
+		data := observation.AttemptData{Generation: generation, Attempt: 1, Dispatched: true, CapacityWait: capacityWait, GenerationDuration: duration,
+			Outcome: attemptOutcome(err), Failure: attemptFailure(err)}
+		if err == nil {
+			data.Usage = response.Usage
+			data.UsagePresence = response.UsagePresence
+		}
+		recorder.Attempt(data)
+	}
+	if err != nil {
+		return nil, err
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	return response, nil
+}
+
+func (c *Coordinator) execute(ctx context.Context, backendID string, prepared *llm.PreparedGeneration) (outcome llm.AttemptOutcome, dispatched bool, capacityWait, generationDuration time.Duration) {
+	start := c.now()
+	release, err := c.manager.Acquire(ctx, backendID)
+	capacityWait = c.capacityWait(backendID, start)
+	if err != nil {
+		return llm.AttemptOutcome{Err: err}, false, capacityWait, 0
+	}
+	defer release()
+	if err := ctx.Err(); err != nil {
+		return llm.AttemptOutcome{Err: err}, false, capacityWait, 0
+	}
+	dispatchStart := c.now()
+	outcome = prepared.Execute(ctx)
+	return outcome, true, capacityWait, elapsed(dispatchStart, c.now())
+}
+
+func (c *Coordinator) capacityWait(backendID string, start time.Time) time.Duration {
+	if !c.manager.Limited(backendID) {
+		return 0
+	}
+	return elapsed(start, c.now())
+}
+
+func elapsed(start, end time.Time) time.Duration {
+	if d := end.Sub(start); d > 0 {
+		return d
+	}
+	return 0
+}
+
+func attemptOutcome(err error) domain.ExecutionOutcome {
+	if err == nil {
+		return domain.ExecutionOutcomeSuccess
+	}
+	return domain.ExecutionOutcomeError
+}
+
+func attemptFailure(err error) domain.ExecutionFailureKind {
+	if err == nil {
+		return domain.ExecutionFailureNone
+	}
+	if errors.Is(err, context.Canceled) {
+		return domain.ExecutionFailureCanceled
+	}
+	if errors.Is(err, context.DeadlineExceeded) {
+		return domain.ExecutionFailureDeadline
+	}
+	if errors.Is(err, llm.ErrUnexpectedStatus) {
+		return domain.ExecutionFailureProviderStatus
+	}
+	if errors.Is(err, llm.ErrTransport) {
+		return domain.ExecutionFailureTransport
+	}
+	if errors.Is(err, llm.ErrMalformedResponse) {
+		return domain.ExecutionFailureMalformedResponse
+	}
+	if errors.Is(err, llm.ErrInvalidRequest) {
+		return domain.ExecutionFailureInvalidRequest
+	}
+	return domain.ExecutionFailureGeneration
+}
+
+func eligibleStatus(outcome llm.AttemptOutcome) bool {
+	if !errors.Is(outcome.Err, llm.ErrUnexpectedStatus) {
+		return false
+	}
+	switch outcome.StatusCode {
+	case 429, 500, 502, 503, 504:
+		return true
+	default:
+		return false
+	}
+}
+
+func (c *Coordinator) backoff(ordinal uint64) time.Duration {
+	base := initialBackoff
+	for step := uint64(1); step < ordinal && base < maximumBackoff; step++ {
+		base *= 2
+	}
+	half := base / 2
+	return half + c.jitter(half)
+}
+
+func retryDelay(local time.Duration, notBefore, now time.Time) time.Duration {
+	if providerDelay := notBefore.Sub(now); providerDelay > local {
+		return providerDelay
+	}
+	return local
+}
+
+func randomJitter(max time.Duration) time.Duration {
+	return time.Duration(rand.Int64N(int64(max) + 1))
+}
+
+func waitContext(ctx context.Context, delay time.Duration) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	timer := time.NewTimer(delay)
+	defer timer.Stop()
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-timer.C:
+		return ctx.Err()
+	}
+}

internal/generation/coordinator_test.go

@@ -0,0 +1,278 @@
+package generation
+
+import (
+	"context"
+	"errors"
+	"io"
+	"math"
+	"net/http"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+)
+
+type transportFunc func(*http.Request) (*http.Response, error)
+
+func (f transportFunc) RoundTrip(req *http.Request) (*http.Response, error) { return f(req) }
+
+func response(status int, body string) *http.Response {
+	return &http.Response{StatusCode: status, Body: io.NopCloser(strings.NewReader(body)), Header: make(http.Header)}
+}
+
+func testRequest(retries uint64) domain.GenerateRequest {
+	return domain.GenerateRequest{
+		Prompt:           domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: "user", Content: "hello"}}},
+		Target:           domain.ExecutionTarget{BackendID: "limited", Endpoint: "https://example.invalid/v1", Model: "model"},
+		TransientRetries: retries,
+	}
+}
+
+func testCoordinator(t *testing.T, transport transportFunc) *Coordinator {
+	t.Helper()
+	manager, err := capacity.NewManager(map[string]domain.BackendCapacityPolicy{
+		"limited": {ConcurrencyLimit: 1, QueueCapacity: 1},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	client, err := llm.NewOpenAICompatibleClient(llm.OpenAICompatibleConfig{HTTPClient: &http.Client{Transport: transport}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	coordinator := NewBuiltIn(manager, client)
+	coordinator.jitter = func(time.Duration) time.Duration { return 0 }
+	coordinator.wait = func(ctx context.Context, _ time.Duration) error { return ctx.Err() }
+	return coordinator
+}
+
+func TestBuiltInRetryEligibilityAndExhaustion(t *testing.T) {
+	for _, tc := range []struct {
+		status   int
+		eligible bool
+	}{
+		{status: 429, eligible: true}, {status: 500, eligible: true},
+		{status: 502, eligible: true}, {status: 503, eligible: true},
+		{status: 504, eligible: true}, {status: 400}, {status: 501},
+	} {
+		t.Run(http.StatusText(tc.status), func(t *testing.T) {
+			calls := 0
+			coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) {
+				calls++
+				if calls == 1 {
+					return response(tc.status, `{"error":{}}`), nil
+				}
+				return response(200, `{"choices":[{"message":{"content":"ok"}}]}`), nil
+			})
+			result, err := coordinator.Generate(context.Background(), testRequest(1))
+			if tc.eligible {
+				if err != nil || result == nil || result.Content != "ok" || calls != 2 {
+					t.Fatalf("result=%+v, error=%v, calls=%d", result, err, calls)
+				}
+			} else if result != nil || err == nil || calls != 1 {
+				t.Fatalf("result=%+v, error=%v, calls=%d", result, err, calls)
+			}
+		})
+	}
+
+	for _, budget := range []uint64{0, 2} {
+		calls := 0
+		coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) {
+			calls++
+			return response(503, `{"error":{}}`), nil
+		})
+		_, err := coordinator.Generate(context.Background(), testRequest(budget))
+		var exhausted *ExhaustedError
+		if !errors.Is(err, llm.ErrUnexpectedStatus) || calls != int(budget+1) || errors.As(err, &exhausted) != (budget > 0) {
+			t.Fatalf("budget=%d calls=%d error=%v", budget, calls, err)
+		}
+		if budget > 0 && exhausted.Attempts() != budget+1 {
+			t.Fatalf("attempts=%d", exhausted.Attempts())
+		}
+	}
+
+	calls := 0
+	coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) {
+		calls++
+		if calls == 1 {
+			return response(503, `{"error":{}}`), nil
+		}
+		return response(400, `{"error":{}}`), nil
+	})
+	_, err := coordinator.Generate(context.Background(), testRequest(3))
+	var exhausted *ExhaustedError
+	if calls != 2 || !errors.Is(err, llm.ErrUnexpectedStatus) || errors.As(err, &exhausted) {
+		t.Fatalf("later permanent failure: calls=%d, error=%v", calls, err)
+	}
+}
+
+func TestBuiltInRetryWaitHonorsContextAndProviderMinimum(t *testing.T) {
+	when := time.Date(2026, 9, 23, 12, 0, 0, 0, time.UTC)
+	coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) { return response(503, `{"error":{}}`), nil })
+	if got := coordinator.backoff(1); got != 250*time.Millisecond {
+		t.Fatalf("first backoff=%v", got)
+	}
+	if got := coordinator.backoff(math.MaxUint64); got != 4*time.Second {
+		t.Fatalf("capped backoff=%v", got)
+	}
+	coordinator.jitter = func(max time.Duration) time.Duration { return max }
+	if got := coordinator.backoff(math.MaxUint64); got != 8*time.Second {
+		t.Fatalf("maximum equal jitter=%v", got)
+	}
+	if got := retryDelay(500*time.Millisecond, when.Add(3*time.Second), when); got != 3*time.Second {
+		t.Fatalf("provider minimum=%v", got)
+	}
+	if got := retryDelay(500*time.Millisecond, when.Add(-time.Second), when); got != 500*time.Millisecond {
+		t.Fatalf("past provider minimum=%v", got)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	calls := 0
+	coordinator = testCoordinator(t, func(*http.Request) (*http.Response, error) {
+		calls++
+		return response(503, `{"error":{}}`), nil
+	})
+	coordinator.wait = func(ctx context.Context, delay time.Duration) error {
+		if delay < 250*time.Millisecond {
+			t.Fatalf("delay=%v", delay)
+		}
+		cancel()
+		return ctx.Err()
+	}
+	_, err := coordinator.Generate(ctx, testRequest(2))
+	if !errors.Is(err, context.Canceled) || calls != 1 {
+		t.Fatalf("canceled wait: error=%v calls=%d", err, calls)
+	}
+}
+
+func TestBuiltInRetryUsesSeparateAttemptDeadlines(t *testing.T) {
+	var contexts []context.Context
+	coordinator := testCoordinator(t, func(req *http.Request) (*http.Response, error) {
+		contexts = append(contexts, req.Context())
+		if len(contexts) == 1 {
+			return response(503, `{"error":{}}`), nil
+		}
+		return response(200, `{"choices":[{"message":{"content":"ok"}}]}`), nil
+	})
+	req := testRequest(1)
+	req.Target.TimeoutSeconds = 1
+	if _, err := coordinator.Generate(context.Background(), req); err != nil {
+		t.Fatal(err)
+	}
+	if len(contexts) != 2 || contexts[0] == contexts[1] {
+		t.Fatalf("attempt contexts=%d", len(contexts))
+	}
+	for _, ctx := range contexts {
+		if _, ok := ctx.Deadline(); !ok || !errors.Is(ctx.Err(), context.Canceled) {
+			t.Fatalf("attempt deadline/error=%t/%v", ok, ctx.Err())
+		}
+	}
+}
+
+func TestCanceledCapacityWaitDispatchesNothing(t *testing.T) {
+	calls := 0
+	coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) {
+		calls++
+		return response(200, `{"choices":[{"message":{"content":"ok"}}]}`), nil
+	})
+	release, err := coordinator.manager.Acquire(context.Background(), "limited")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer release()
+	ctx, cancel := context.WithCancel(context.Background())
+	result := make(chan error, 1)
+	go func() { _, err := coordinator.Generate(ctx, testRequest(2)); result <- err }()
+	cancel()
+	if err := <-result; !errors.Is(err, context.Canceled) || calls != 0 {
+		t.Fatalf("capacity cancellation: error=%v calls=%d", err, calls)
+	}
+}
+
+func TestBuiltInRetryFreesPermitAndFreezesCredential(t *testing.T) {
+	const envName = "PROMPTKIT_GENERATION_RETRY_TEST_KEY"
+	t.Setenv(envName, "first-key")
+	var calls atomic.Int64
+	var firstAuth, retryAuth string
+	coordinator := testCoordinator(t, func(req *http.Request) (*http.Response, error) {
+		switch calls.Add(1) {
+		case 1:
+			firstAuth = req.Header.Get("Authorization")
+			return response(503, `{"error":{}}`), nil
+		case 2:
+			return response(200, `{"choices":[{"message":{"content":"other"}}]}`), nil
+		default:
+			retryAuth = req.Header.Get("Authorization")
+			return response(200, `{"choices":[{"message":{"content":"retry"}}]}`), nil
+		}
+	})
+	entered := make(chan struct{})
+	resume := make(chan struct{})
+	coordinator.wait = func(ctx context.Context, _ time.Duration) error {
+		close(entered)
+		select {
+		case <-resume:
+			return ctx.Err()
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+	}
+	req := testRequest(1)
+	req.Target.APIKeyEnv = envName
+	first := make(chan error, 1)
+	go func() { _, err := coordinator.Generate(context.Background(), req); first <- err }()
+	<-entered
+	t.Setenv(envName, "later-key")
+	other, err := coordinator.Generate(context.Background(), testRequest(0))
+	if err != nil || other == nil || other.Content != "other" {
+		t.Fatalf("other call while backoff blocked = %+v, %v", other, err)
+	}
+	close(resume)
+	if err := <-first; err != nil {
+		t.Fatal(err)
+	}
+	if calls.Load() != 3 || firstAuth != "Bearer first-key" || retryAuth != firstAuth {
+		t.Fatalf("calls=%d, first auth=%q, retry auth=%q", calls.Load(), firstAuth, retryAuth)
+	}
+}
+
+func TestInjectedClientDispatchesOnceAndReleasesAfterPanic(t *testing.T) {
+	manager, err := capacity.NewManager(map[string]domain.BackendCapacityPolicy{"limited": {ConcurrencyLimit: 1}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	client := &injectedClient{panicFirst: true}
+	coordinator := NewInjected(manager, client)
+	func() {
+		defer func() {
+			if recover() == nil {
+				t.Fatal("expected injected panic")
+			}
+		}()
+		_, _ = coordinator.Generate(context.Background(), testRequest(5))
+	}()
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	result, err := coordinator.Generate(ctx, testRequest(5))
+	if err != nil || result == nil || client.calls != 2 {
+		t.Fatalf("after panic result=%+v error=%v calls=%d", result, err, client.calls)
+	}
+}
+
+type injectedClient struct {
+	calls      int
+	panicFirst bool
+}
+
+func (c *injectedClient) Generate(context.Context, domain.GenerateRequest) (*domain.GenerateResponse, error) {
+	c.calls++
+	if c.panicFirst && c.calls == 1 {
+		panic("injected panic")
+	}
+	return &domain.GenerateResponse{Content: "ok"}, nil
+}

internal/generation/observation_test.go

@@ -0,0 +1,201 @@
+package generation
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/observation"
+)
+
+func recordEvents(t *testing.T, ctx context.Context, events *[]domain.ExecutionEvent) context.Context {
+	t.Helper()
+	recorder, err := observation.New(func(event domain.ExecutionEvent) { *events = append(*events, event) })
+	if err != nil {
+		t.Fatal(err)
+	}
+	return observation.WithRecorder(ctx, recorder)
+}
+
+func TestObservedRetryAndExhaustion(t *testing.T) {
+	for _, status := range []int{200, 503} {
+		calls := 0
+		coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) {
+			calls++
+			if calls == 1 || status == 503 {
+				return response(503, `{"error":{}}`), nil
+			}
+			return response(200, `{"choices":[{"message":{"content":"ok"}}],"usage":{"prompt_tokens":0,"completion_tokens":2}}`), nil
+		})
+		var events []domain.ExecutionEvent
+		ctx := recordEvents(t, context.Background(), &events)
+		_, err := coordinator.Generate(ctx, testRequest(1))
+		if status == 200 && err != nil {
+			t.Fatal(err)
+		}
+		if status == 503 {
+			var exhausted *ExhaustedError
+			if !errors.As(err, &exhausted) {
+				t.Fatalf("error=%v", err)
+			}
+		}
+		if len(events) != 3 || events[0].Kind != domain.ExecutionAttempt || events[1].Kind != domain.ExecutionRetryDelay || events[2].Kind != domain.ExecutionAttempt {
+			t.Fatalf("events=%+v", events)
+		}
+		if events[0].Attempt != 1 || events[1].Attempt != 1 || events[2].Attempt != 2 || !events[0].Dispatched || !events[2].Dispatched {
+			t.Fatalf("indexes=%+v", events)
+		}
+		if events[0].Failure != domain.ExecutionFailureProviderStatus || events[1].RetryDelay < 0 {
+			t.Fatalf("first=%+v delay=%+v", events[0], events[1])
+		}
+		if status == 200 && (!events[2].Usage.PromptTokens.Known || events[2].Usage.PromptTokens.Value != 0 || events[2].Usage.TotalTokens.Known) {
+			t.Fatalf("usage=%+v", events[2].Usage)
+		}
+	}
+}
+
+func TestObservedInterruptedWaitAndCanceledCapacity(t *testing.T) {
+	coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) { return response(503, `{"error":{}}`), nil })
+	ctx, cancel := context.WithCancel(context.Background())
+	var events []domain.ExecutionEvent
+	ctx = recordEvents(t, ctx, &events)
+	coordinator.wait = func(ctx context.Context, _ time.Duration) error { cancel(); return ctx.Err() }
+	_, err := coordinator.Generate(ctx, testRequest(1))
+	if !errors.Is(err, context.Canceled) || len(events) != 2 || events[1].Kind != domain.ExecutionRetryDelay || events[1].Failure != domain.ExecutionFailureCanceled {
+		t.Fatalf("error=%v events=%+v", err, events)
+	}
+
+	coordinator = testCoordinator(t, func(*http.Request) (*http.Response, error) { t.Fatal("unexpected dispatch"); return nil, nil })
+	release, err := coordinator.manager.Acquire(context.Background(), "limited")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer release()
+	ctx, cancel = context.WithCancel(context.Background())
+	events = nil
+	ctx = recordEvents(t, ctx, &events)
+	entered := make(chan struct{})
+	ctx = &notifyingContext{Context: ctx, entered: entered}
+	done := make(chan error, 1)
+	go func() { _, err := coordinator.Generate(ctx, testRequest(0)); done <- err }()
+	<-entered
+	cancel()
+	if err := <-done; !errors.Is(err, context.Canceled) {
+		t.Fatalf("error=%v", err)
+	}
+	if len(events) != 1 || events[0].Dispatched || events[0].Failure != domain.ExecutionFailureCanceled {
+		t.Fatalf("events=%+v", events)
+	}
+}
+
+type notifyingContext struct {
+	context.Context
+	entered chan struct{}
+}
+
+func (c *notifyingContext) Done() <-chan struct{} {
+	select {
+	case <-c.entered:
+	default:
+		close(c.entered)
+	}
+	return c.Context.Done()
+}
+
+func TestObservedCallbackReleasesPermitAndCanCancelRetry(t *testing.T) {
+	coordinator := testCoordinator(t, func(*http.Request) (*http.Response, error) { return response(503, `{"error":{}}`), nil })
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	var events []domain.ExecutionEvent
+	recorder, err := observation.New(func(event domain.ExecutionEvent) {
+		events = append(events, event)
+		if event.Kind != domain.ExecutionAttempt {
+			return
+		}
+		permitCtx, stop := context.WithTimeout(context.Background(), time.Second)
+		defer stop()
+		release, err := coordinator.manager.Acquire(permitCtx, "limited")
+		if err != nil {
+			t.Errorf("callback could not acquire permit: %v", err)
+		} else {
+			release()
+		}
+		cancel()
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = coordinator.Generate(observation.WithRecorder(ctx, recorder), testRequest(2))
+	if !errors.Is(err, context.Canceled) || len(events) != 1 {
+		t.Fatalf("error=%v events=%+v", err, events)
+	}
+}
+
+type fixedClient struct {
+	response *domain.GenerateResponse
+	err      error
+}
+
+func (c fixedClient) Generate(context.Context, domain.GenerateRequest) (*domain.GenerateResponse, error) {
+	return c.response, c.err
+}
+
+func TestObservedInjectedUsageAndRepairGeneration(t *testing.T) {
+	manager, err := capacity.NewManager(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var events []domain.ExecutionEvent
+	ctx := recordEvents(t, context.Background(), &events)
+	legacy := NewInjected(manager, fixedClient{response: &domain.GenerateResponse{Usage: domain.TokenUsage{PromptTokens: 3}}})
+	if _, err := legacy.Generate(ctx, testRequest(4)); err != nil {
+		t.Fatal(err)
+	}
+	presence := &domain.TokenUsagePresence{CompletionTokens: true}
+	repair := NewInjected(manager, fixedClient{response: &domain.GenerateResponse{UsagePresence: presence}})
+	req := testRequest(4)
+	req.Generation = 2
+	if _, err := repair.Generate(ctx, req); err != nil {
+		t.Fatal(err)
+	}
+	if len(events) != 2 || !events[0].Usage.PromptTokens.Known || events[0].Usage.CompletionTokens.Known || !events[1].Usage.CompletionTokens.Known || events[1].Usage.CompletionTokens.Value != 0 || events[1].Usage.PromptTokens.Known {
+		t.Fatalf("events=%+v", events)
+	}
+	if events[1].Generation != 2 || events[1].Attempt != 1 {
+		t.Fatalf("repair indexes=%+v", events[1])
+	}
+}
+
+func TestObservedSuccessfulGenerationBeforeRepairFailure(t *testing.T) {
+	manager, err := capacity.NewManager(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var events []domain.ExecutionEvent
+	recorder, err := observation.New(func(event domain.ExecutionEvent) { events = append(events, event) })
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx := observation.WithRecorder(context.Background(), recorder)
+	initial := NewInjected(manager, fixedClient{response: &domain.GenerateResponse{Usage: domain.TokenUsage{PromptTokens: 5}}})
+	if _, err := initial.Generate(ctx, testRequest(0)); err != nil {
+		t.Fatal(err)
+	}
+	repair := NewInjected(manager, fixedClient{err: errors.New("repair unavailable")})
+	req := testRequest(0)
+	req.Generation = 2
+	if _, err := repair.Generate(ctx, req); err == nil {
+		t.Fatal("expected repair failure")
+	}
+	recorder.Finish(observation.FinishData{Outcome: domain.ExecutionOutcomeError, Failure: domain.ExecutionFailureGeneration})
+	if len(events) != 3 || events[0].Outcome != domain.ExecutionOutcomeSuccess || events[1].Outcome != domain.ExecutionOutcomeError || events[2].Attempts != 2 || events[2].RepairCalls != 1 {
+		t.Fatalf("events=%+v", events)
+	}
+	if got := events[2].Usage.PromptTokens; got.Value != 5 || !got.Known || got.Complete {
+		t.Fatalf("prompt usage=%+v", got)
+	}
+}