Finish audit remediation and prepare v0.6.0

README.md

@@ -33,6 +33,15 @@ boundary and constraints that framework work must preserve.
 
 ## Release Guidance
 
+Consumers upgrading from `v0.5.0` to `v0.6.0` should read the
+[v0.6.0 changelog and migration guide](docs/releases/v0.6.0.md).
+
+Earlier adopters 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).
 

backends.go

@@ -34,7 +34,8 @@ type Backend struct {
 	// 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.
+	// 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

capacity_contract_test.go

@@ -60,7 +60,18 @@ func TestEngineRejectsRunBeforeCompletionWhenAdmissionIsFull(t *testing.T) {
 
 	awaitCapacitySignal(t, reader.entered, "first artifact read")
 
-	result, err := engine.Run(context.Background(), capacityInputRequest("http://second.example/v1"))
+	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)
 	}
@@ -70,6 +81,21 @@ func TestEngineRejectsRunBeforeCompletionWhenAdmissionIsFull(t *testing.T) {
 	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)
 	}
@@ -174,6 +200,19 @@ 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,
@@ -181,7 +220,8 @@ func TestCapacityExceededSentinelContract(t *testing.T) {
 		promptkit.ErrValidation,
 	} {
 		if errors.Is(promptkit.ErrCapacityExceeded, unrelated) ||
-			errors.Is(unrelated, promptkit.ErrCapacityExceeded) {
+			errors.Is(unrelated, promptkit.ErrCapacityExceeded) ||
+			errors.Is(populatedCapacityErr, unrelated) {
 			t.Fatalf("ErrCapacityExceeded aliases unrelated sentinel %v", unrelated)
 		}
 	}

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

@@ -170,6 +170,40 @@ 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,

doc.go

@@ -3,25 +3,28 @@
 //
 // Applications construct an [Engine] with [NewEngine], select filesystem or
 // in-memory sources and optional engine-scoped [Backend] registrations, and
-// call [Engine.Prepare], [Engine.PrepareExecution], [Engine.Run], or
-// [Engine.RunPrepared]. Concrete registries, repositories, validators, and the
-// built-in OpenAI-compatible client remain internal implementation details.
+// 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 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.
+// 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. 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.
+// 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. Returned structured errors are likewise caller-owned and may
+// be mutated without affecting engine state or another error.
 //
 // # Security and sensitive data
 //
@@ -47,11 +50,12 @@
 // [GenerateResponse], [ExecutionTargetPresence], and the string value types
 // used by those values.
 //
-// Construction and handle values, including [Config], [Backend], [RunRequest],
-// [ArtifactRef], [ExecutionTargetOverride], [Profile],
-// [OpenAICompatibleProfileConfig], and [PreparedExecution], do not have stable
-// JSON representations. Direct API keys are nevertheless excluded from JSON
-// for every public value.
+// Construction, inspection, handle, and error values, including [Config],
+// [Backend], [RunRequest], [ArtifactRef], [ExecutionTargetOverride], [Profile],
+// [OpenAICompatibleProfileConfig], [ProfileInspection],
+// [PromptInputDefinition], [PromptInspection], [PreparedExecution], and
+// [CapacityError], do not have stable JSON representations. Direct API keys
+// are nevertheless excluded from JSON for every public value.
 //
 // JSON timestamps use time.Time's RFC 3339 encoding and are omitted when zero.
 // PreparedRun and RunResult durations are encoded as integer milliseconds in

docs/consumers/pkg-promptkit.md

@@ -40,6 +40,60 @@ validation, and default transport behavior. Source discovery, format
 validation, and profile precedence are defined by the
 [framework format reference](../formats.md).
 
+## Supply Embedded Application Defaults
+
+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:
+
+```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,
@@ -128,13 +182,41 @@ 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 profiles, built-ins, schemas,
-and framework defaults.
+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`.
 
+### 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 != "" {
+	// Apply application policy for the named environment variable.
+} 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. Inspection reports credential requirements but leaves the
+timing of credential enforcement to the application. The method's
+[GoDoc](../../engine.go) owns its exact result and error contract.
+
 ### Set A Per-Run Session And Reasoning
 
 Supply a direct session ID when one prompt should be correlated with a
@@ -325,6 +407,11 @@ When a limited backend has admitted all active and waiting calls, handle
 ```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 policy: shed work, report overload, or retry later.
 }
 ```
@@ -332,8 +419,9 @@ if errors.Is(err, promptkit.ErrCapacityExceeded) {
 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
-[`Engine.Run` and error GoDoc](../../engine.go) owns exact error and
-cancellation identities.
+[`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.
 
 ## Application Boundary
 

docs/development.md

@@ -45,11 +45,17 @@ 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:
+This section is the canonical local validation workflow for Promptkit. Run
+every command from the repository root before accepting a change. The test
+suite and maintained examples are deterministic, offline, and require no real
+provider credentials.
+
+### Tests, Analysis, Build, And Examples
+
+Run the ordinary and race-enabled suites, static analysis, the build, and both
+maintained consumer examples:
 
 ```sh
 go test ./...
@@ -57,85 +63,171 @@ go test -race ./...
 go vet ./...
 go build ./...
 go run ./examples/go-library/prepare
+go run ./examples/go-library/run
 ```
 
-Check formatting across every tracked Go file:
+Both examples must exit successfully. Review their JSON output: preparation
+must report the selected offline prompt, profile, model, and message count;
+execution must report the deterministic generated output, successful
+validation, selected offline model, and usage. Neither command may contact a
+provider or require credentials.
+
+### Go Formatting
+
+Check every tracked Go file. The final command must succeed and the captured
+list must be empty:
 
 ```sh
-gofmt -l $(git ls-files '*.go')
+unformatted=$(
+    git ls-files '*.go' |
+        while IFS= read -r go_file
+        do
+            gofmt -l "$go_file"
+        done
+)
+test -z "$unformatted"
 ```
 
-The formatting command must produce no paths. Follow every added or changed
-Markdown link and confirm its target exists. Finally, check whitespace:
+### Local Markdown Links
+
+Use the Python standard library to verify every repository-relative Markdown
+target and local heading fragment. The check is offline and prints nothing on
+success:
+
+```sh
+python3 - <<'PY'
+from pathlib import Path
+import re
+import subprocess
+import sys
+from urllib.parse import unquote
+
+root = Path.cwd().resolve()
+markdown_files = [
+    root / name
+    for name in subprocess.check_output(
+        ["git", "ls-files", "*.md"], text=True
+    ).splitlines()
+]
+link_pattern = re.compile(r"!?\[[^]]*\]\(([^)]+)\)")
+heading_pattern = re.compile(r"^#{1,6}\s+(.+?)\s*#*\s*$")
+scheme_pattern = re.compile(r"^[a-z][a-z0-9+.-]*:", re.IGNORECASE)
+
+
+def markdown_lines(path):
+    in_fence = False
+    fence = ""
+    for line in path.read_text(encoding="utf-8").splitlines():
+        stripped = line.lstrip()
+        marker = stripped[:3]
+        if marker in {"```", "~~~"}:
+            if not in_fence:
+                in_fence = True
+                fence = marker
+            elif marker == fence:
+                in_fence = False
+                fence = ""
+            continue
+        if not in_fence:
+            yield line
+
+
+anchor_cache = {}
+
+
+def anchors(path):
+    if path in anchor_cache:
+        return anchor_cache[path]
+    found = set()
+    counts = {}
+    for line in markdown_lines(path):
+        match = heading_pattern.match(line)
+        if not match:
+            continue
+        heading = re.sub(r"<[^>]+>", "", match.group(1)).replace("`", "")
+        base = re.sub(r"[^\w\- ]", "", heading.lower()).replace(" ", "-")
+        count = counts.get(base, 0)
+        counts[base] = count + 1
+        found.add(base if count == 0 else f"{base}-{count}")
+    anchor_cache[path] = found
+    return found
+
+
+failures = []
+for source in markdown_files:
+    text = "\n".join(markdown_lines(source))
+    for match in link_pattern.finditer(text):
+        target = match.group(1).strip()
+        if target.startswith("<") and target.endswith(">"):
+            target = target[1:-1]
+        if scheme_pattern.match(target) or target.startswith("//"):
+            continue
+        path_text, separator, fragment = target.partition("#")
+        destination = source if not path_text else source.parent / unquote(path_text)
+        try:
+            destination = destination.resolve()
+            destination.relative_to(root)
+        except ValueError:
+            failures.append(f"{source.relative_to(root)}: escapes repository: {target}")
+            continue
+        if not destination.exists():
+            failures.append(f"{source.relative_to(root)}: missing target: {target}")
+            continue
+        if separator and destination.suffix.lower() == ".md":
+            fragment = unquote(fragment).lower()
+            if fragment not in anchors(destination):
+                failures.append(f"{source.relative_to(root)}: missing anchor: {target}")
+
+if failures:
+    print("\n".join(failures), file=sys.stderr)
+    raise SystemExit(1)
+PY
+```
+
+### Repository Hygiene And Review
+
+Reject an active Go workspace, tracked workspace files, a vendor tree, or a
+module replacement:
+
+```sh
+case "$(go env GOWORK)" in
+    ''|off) ;;
+    *) printf '%s\n' 'an active Go workspace is not allowed' >&2; exit 1 ;;
+esac
+test -z "$(git ls-files go.work go.work.sum)"
+test ! -e vendor
+if grep -Eq '^[[:space:]]*replace([[:space:]]|\()' go.mod
+then
+    printf '%s\n' 'go.mod contains a replacement' >&2
+    exit 1
+fi
+```
+
+Check whitespace in both unstaged and staged changes. List ignored files and
+scan tracked content for common credential forms:
 
 ```sh
 git diff --check
+git diff --cached --check
+test -z "$(git ls-files --others --ignored --exclude-standard)"
+credential_pattern='-----BEGIN ([A-Z0-9]+ )?PRIV''ATE KEY-----|AKI''A[0-9A-Z]{16}|gh[pousr]_[A-Za-z0-9]{36,}|sk-[A-Za-z0-9]{32,}'
+if git grep -nEI -e "$credential_pattern" -- .
+then
+    printf '%s\n' 'possible credential found' >&2
+    exit 1
+fi
 ```
 
-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.
+Inspect `git status --short --untracked-files=all` and the complete diff before
+accepting a change. The status may contain only the intended source changes
+during development. Reject credentials, private keys, environment files,
+generated binaries, test or coverage output, downloaded assets, template
+residue, and any other artifact that does not belong in source control. The
+credential scan catches common forms but does not replace inspection of the
+actual change.
 
-## Focused Validation
-
-Use focused checks while iterating, then run the complete validation sequence
-before accepting the change. The root package supports:
+After committing the accepted change, require a clean candidate:
 
 ```sh
-go test .
-go vet .
-go build .
+test -z "$(git status --porcelain)"
 ```
-
-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.

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:
@@ -81,9 +87,16 @@ Each message has a non-empty `role` and 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
@@ -151,9 +164,9 @@ extra_params:
 
 | Field | Required | Meaning |
 | --- | --- | --- |
-| `id` | yes | Non-empty profile identifier. IDs must be unique within one source. |
-| `backend` | unless `endpoint` is present | Backend registry ID. It is trimmed and registry membership is checked when the profile is prepared. |
-| `endpoint` | unless `backend` is present | Non-empty OpenAI-compatible base URL, including an API version path when required. When both connection fields are present, this overrides the backend endpoint without changing backend identity. |
+| `id` | yes | Profile identifier, trimmed before selection and publication. It must be non-empty after trimming and unique within one source after normalization. |
+| `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. |
@@ -178,30 +191,33 @@ GoDoc.
 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;
+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 profile strings replace backend defaults, and non-empty request
 strings replace both. Request reasoning is the exception: a nil
@@ -219,18 +235,25 @@ 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. embedded built-in 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.
 
 ## Built-In Profile Catalog
 
@@ -238,8 +261,8 @@ Every built-in selects the `openrouter` backend. The engine's built-in backend
 registry supplies `https://openrouter.ai/api/v1` and the environment-variable
 name `OPENROUTER_API_KEY`, so individual profiles contain only model and
 generation settings. Built-in profile files do not repeat those connection
-values. A custom or in-memory profile with the same profile ID takes
-precedence.
+values. A configured, application fallback, or in-memory profile with the same
+profile ID takes precedence.
 
 | Provider | ID | Model |
 | --- | --- | --- |

docs/integrations/openai-compatible-chat.md

@@ -14,10 +14,16 @@ that produce these outbound settings.
 
 Generation sends an HTTP `POST` with `Content-Type: application/json`.
 Before the client is called, the engine resolves framework, backend, profile,
-and request values into one execution target. A non-empty endpoint from that
-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.
+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
@@ -53,8 +59,9 @@ never also sent as a session header.
 
 The client conditionally includes:
 
-- `temperature`, `max_tokens`, and `top_p` when non-zero or explicitly
-  present;
+- `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,
@@ -81,13 +88,29 @@ 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 non-empty message content 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, empty first-choice content, and size
+overflow are malformed responses and return no partial result.
+
+For a non-2xx status, the error includes the status code but never the provider
+response body. Promptkit does not yet parse provider error envelopes; bounded
+non-success parsing belongs to the
+[structured-generation-error roadmap](../roadmap/structured-generation-errors.md).
+
+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.
 
 ## Timeout And Cancellation
 
@@ -102,5 +125,7 @@ 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

@@ -38,10 +38,10 @@ output contract, but before schema loading, artifact loading, or rendering.
 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 the
-internal `ErrCapacityExceeded` identity. The root facade maps that identity to
-the public error without treating it as an invalid request or generation
-failure.
+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
@@ -56,7 +56,10 @@ reserve another bounded slot.
 
 `NewClient` wraps the engine's selected internal model client after public
 client adaptation or built-in client construction. Initial generation and the
-default repairer receive the same wrapper.
+default repairer receive the same wrapper. Their requests retain the same
+effective backend, credential, numeric-presence metadata, and structured-output
+settings, so scheduling does not change provider omission semantics between
+calls.
 
 For each `Generate` call, the wrapper selects a pool from the request's
 effective backend ID. An unlimited call passes directly to the next client. A
@@ -71,7 +74,9 @@ other backend IDs.
 
 The wrapper passes generation requests, responses, and collaborator errors
 through unchanged. It owns scheduling only; the concrete model client remains
-responsible for provider transport behavior.
+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.
 
 ## Cancellation And Release
 

docs/internal/llm.md

@@ -25,16 +25,20 @@ and request precedence. 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.
 
-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:
+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 then:
 
-1. validates request-level timeout and endpoint requirements;
+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;
+6. performs the outbound request under the applicable deadlines; and
+7. decodes one strictly framed, size-bounded response object and maps its first
+   choice and token usage.
 
 `internal/llm` owns the set of reserved OpenAI-compatible request fields used
 when validating extra parameters. Backend registration consumes the same rule
@@ -65,9 +69,28 @@ 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.
 
-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.
+
+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. Non-success
+responses remain status-only; bounded provider error-envelope parsing belongs
+to the
+[structured-generation-error roadmap](../roadmap/structured-generation-errors.md).
+
+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
 
@@ -75,7 +98,11 @@ 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. The root transport contract test
-also verifies that resolved backend settings reach this client without
-serializing backend identity. All use local test servers or test transports;
-the default suite makes no live or paid provider requests.
+cancellation, endpoint selection and composition, pre-transport rejection, and
+bounded single-document response framing, closure, and response-body
+suppression. The root
+transport contract tests also verify 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/overview.md

@@ -11,23 +11,23 @@ contributor workflow and validation.
 
 | Component | Implemented responsibility | References |
 | --- | --- | --- |
-| Root `promptkit` package | Provides the supported engine facade, source, backend-registration, and injection options, public request and result values, opaque prepared-execution handles, profile construction, extension interfaces, value conversion, redacted formatting, public error mapping, and engine-local assembly. | [Package GoDoc](../../doc.go), [prepared execution](../../prepared_execution.go), [backend API](../../backends.go), [engine assembly](../../engine.go) |
+| Root `promptkit` package | Provides the supported engine facade, source, backend-registration, and injection options, public request, result, prompt-inspection, and profile-inspection values, opaque prepared-execution handles, profile construction, extension interfaces, value conversion, redacted formatting, typed capacity errors, public error mapping, and engine-local profile-source assembly including application fallbacks. | [Package GoDoc](../../doc.go), [prepared execution](../../prepared_execution.go), [backend API](../../backends.go), [engine assembly](../../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) |
 | `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) |
 | `internal/backend` | Constructs each engine's immutable registry from the built-in OpenRouter definition 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/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. | [Domain declarations](../../internal/domain/domain.go) |
+| `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/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 JSON-compatible extra-parameter and prepared-schema trees while preserving supported concrete value types. | [JSON values](../../internal/jsonvalue/jsonvalue.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, including backend selection, 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 profile catalog, whose entries select OpenRouter, 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/builtin` | Embeds the built-in profile catalog, whose entries select OpenRouter. | [Built-in catalog](../formats.md#built-in-profile-catalog), [repository](../../internal/profile/builtin/repository.go) |
 | `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 and creates frozen validation plans for prepared execution. | [Framework formats](../formats.md#schemas), [internal sources and validation](sources.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 response decoding, authentication, deadline handling, and ownership of the OpenAI-compatible reserved request-field policy. | [Internal model client](llm.md) |
-| `internal/usecase` | Resolves backend, profile, and request settings and coordinates preparation, ordinary execution, and one-attempt prepared execution across internal sources, rendering, artifact loading, generation, validation, capacity, and optional repair. | [Internal runner](runner.md), [prepared-execution implementation](../../internal/usecase/prepared_execution.go) |
+| `internal/usecase` | Resolves prompt definitions and hashes, profiles, backends, and targets for exact inspection and request settings for preparation, and coordinates ordinary execution and one-attempt prepared execution across internal sources, rendering, artifact loading, operation-local validation plans, generation, capacity, and optional repair. | [Internal runner](runner.md), [prepared-execution implementation](../../internal/usecase/prepared_execution.go) |
 
 The root package assembles these internal components without exposing their
 representations. Consumers depend only on the root facade.

docs/internal/runner.md

@@ -20,14 +20,43 @@ and override semantics consumed by the runner.
 profiles, backend resolution, artifacts, rendering, model generation, and
 validation. The root engine supplies one immutable registry containing the
 built-in backend and validated consumer additions, one engine-local run
-admitter, and a model client wrapped by the same capacity manager. Schema
-documents are loaded through the validator's optional schema-loader interface.
+admitter, and a model client wrapped by the same capacity manager. Validation
+plans and provider-facing schema metadata come from the validator's preparation
+interface.
 An output repairer can be injected internally, but the ordinary runner
 constructor does not enable one.
 
 Each invocation carries its state in request, prepared-run, and result values.
 The runner has no durable run or session store.
 
+## Shared Prompt Selection
+
+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.
+
+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
@@ -41,14 +70,16 @@ performs only the work needed to validate routing and admission:
 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 the effective output contract without loading its schema; and
+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. load structured-output schema metadata when required;
+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;
@@ -59,7 +90,10 @@ profile, or backend:
 `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.
+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. Endpoint overrides do not change
@@ -90,8 +124,17 @@ 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. Invalid generated content remains a validation
-result; an inability to perform validation is an operational error.
+and validates that artifact with the plan compiled during completion. Invalid
+generated content remains a validation result; an inability to perform
+validation is an operational error.
+
+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
@@ -101,20 +144,27 @@ each actual generation call.
 
 When an internal repairer is present, a JSON or JSON Schema content failure can
 trigger bounded repair attempts. Repair receives the effective execution
-target and session ID, validation errors, prior output, and structured-output
-specification. The default repairer uses the same wrapped client 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. This capability remains internal and is not a public
-option.
+target, explicit numeric-presence bits, credential, backend identity, session
+ID, validation errors, prior output, and structured-output specification. One
+request constructor supplies those common fields to initial and repair
+generation while their rendered prompts remain intentionally distinct. The
+default repairer uses the same wrapped client 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.
+This capability remains internal and is not a public option.
 
 A successful result includes the output artifact and raw output, validation
 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, including backend identity, reaches generation and any
-repair attempt.
+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 usage.
 
 ## Failure Categories
 
@@ -124,18 +174,21 @@ validation failures. Wrapping preserves the package identities mapped by the
 public facade and retains collaborator identities where they are part of the
 internal contract.
 
-Admission capacity exhaustion retains the internal capacity identity and adds
-the selected backend ID as context. 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.
+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.
+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,
@@ -147,8 +200,9 @@ The [runner tests](../../internal/usecase/runner_test.go) own preparation order,
 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, shared initial/repair capacity, credentials and redaction,
-error categories, artifact metadata, usage, and timing. The
+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,
 waiter, and wrapped-client tests.
 

docs/internal/sources.md

@@ -12,9 +12,26 @@ 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.
+
+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:
@@ -23,29 +40,56 @@ 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. Strict
-YAML decoding recognizes the optional `backend` field, trims its value, and
-requires a model plus at least one non-blank backend or endpoint. Loading does
-not check registry membership because the available registry belongs to the
-assembled engine; the runner checks membership during preparation.
+operating-system filesystem or an `fs.FS`. 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 the
+optional `backend` field, trims its value, and requires a model plus at least
+one non-blank backend or endpoint. 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. Every embedded
-profile selects `openrouter` and inherits its endpoint and credential
-environment-variable name from the built-in backend registry rather than
-repeating those values. Profile behavior is owned by the
-[profile repository tests](../../internal/profile/repository_test.go), while
-catalog completeness, the backend-selection invariant, duplicate IDs, and
-overlay behavior are owned by the
+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 root engine assembles profile repositories in precedence order: in-memory
+profiles, one ordinary configured source, an application fallback source, then
+the embedded built-in catalog. An explicit file or `fs.FS` profile source
+replaces `Config.ProfileDir` within the ordinary configured-source category.
+
+Exact profile inspection performs one point-in-time lookup through those
+profile sources and checks the resolved target without reading prompt, input,
+or schema sources. It does not retain that lookup for a later execution.
+
+`internal/profile/builtin` embeds the maintained built-in profile catalog.
+Every embedded profile selects `openrouter` and inherits its endpoint and
+credential environment-variable name from the built-in backend registry rather
+than repeating those values. Profile loading and overlay behavior are owned by
+the [profile repository tests](../../internal/profile/repository_test.go),
+while catalog completeness, the backend-selection invariant, and duplicate IDs
+are owned by the
 [built-in repository tests](../../internal/profile/builtin/repository_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
@@ -57,8 +101,17 @@ 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
-control into the rendered prompt. The
+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 carries
+message roles, session IDs, and cache control into the rendered prompt. The
 [renderer tests](../../internal/prompt/renderer_test.go) own rendering behavior.
 
 ## Schemas And Output Validation
@@ -68,22 +121,35 @@ 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.
 
-For executable preparation, the built-in validators create a frozen validation
-plan. None, basic, and JSON modes retain the effective output contract without
-source access. JSON Schema mode loads the root document, resolves and compiles
-every transitive reference during preparation, and retains the compiled
-validator. The provider-facing structured-output metadata uses that same
-captured root document.
+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.
 
-`PrepareExecution` also completes prompt and profile selection, artifact
-loading and hashing, session and message rendering, and target resolution.
-`RunPrepared` uses the retained source-derived state and validation plan; it
-does not reopen prompt, profile, input, or schema sources and does not rerender
-the request. By contrast, ordinary `Prepare` produces an inspection value only:
-a later `Run` performs its own source resolution and preparation.
+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,
-frozen-reference behavior, and content-failure behavior. Prepared execution
+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/policy/architecture.md

@@ -19,8 +19,8 @@ results, public values, extension interfaces, profiles, and error sentinels.
 
 The implemented internal components consist of:
 
-- `internal/domain`, which owns framework data values shared by later internal
-  components;
+- `internal/domain`, which owns framework data values and source-neutral
+  invariants shared by later internal components;
 - `internal/backend`, which owns validated immutable OpenAI-compatible backend
   definitions and the built-in OpenRouter definition;
 - `internal/capacity`, which owns engine-local bounded run admission and
@@ -92,6 +92,13 @@ 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
 
 Scriptorium is a downstream application that consumes Promptkit through

docs/policy/testing.md

@@ -50,19 +50,18 @@ Examples of appropriate seams include clocks, randomness, subprocesses, remote A
 ## 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.
+Maintainers run the complete local workflow in the
+[development guide](../development.md#maintainer-validation) before accepting
+changes. That guide is the canonical owner of exact commands, formatting,
+documentation-link validation, and repository-hygiene checks.
 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
-```
+Maintainer validation must include ordinary and race-enabled package tests,
+static analysis, a complete build, and execution of both maintained offline
+consumer examples. The preparation example protects assembled preparation and
+inspection behavior. The execution example separately protects assembled
+`Run`, injected-client, validation, usage, and result behavior.
 
 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 +87,9 @@ 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 and execution 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

docs/release.md

@@ -106,48 +106,12 @@ gitea.maximumdirect.net/eric/promptkit 1.25.5
 promptkit gitea.maximumdirect.net/eric/promptkit
 ```
 
-Run the complete maintainer 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. This command must produce no output:
-
-```sh
-unformatted=$(
-    git ls-files '*.go' |
-        while IFS= read -r go_file
-        do
-            gofmt -l "$go_file"
-        done
-)
-test -z "$unformatted"
-```
-
-Follow every maintained Markdown link and confirm that its local or published
-target exists. Review the repository for generated binaries, test or coverage
-output, credentials, template residue, downloaded assets, and other files that
-do not belong in source control.
-
-Recheck module and repository hygiene, whitespace, and the clean checkout:
-
-```sh
-test -z "$(git ls-files go.work go.work.sum)"
-test ! -e vendor
-if grep -Eq '^[[:space:]]*replace([[:space:]]|\()' go.mod
-then
-    printf '%s\n' 'go.mod contains a replacement' >&2
-    exit 1
-fi
-git diff --check
-test -z "$(git status --porcelain)"
-```
+As a release prerequisite, run the complete
+[maintainer validation workflow](development.md#maintainer-validation) against
+the clean candidate. Do not substitute a partial command list: the development
+guide owns the tests, race checks, analysis, build, both offline examples,
+formatting, Markdown links, generated-output and credential review, and
+repository hygiene. Record the successful workflow result with the candidate.
 
 ## Write The Release Note
 

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/roadmap/concurrency.md

@@ -1,237 +0,0 @@
-# Backend-Specific Concurrency Management
-
-**Status:** Complete.
-
-## Purpose
-
-This roadmap defines the scope and target end state for engine-local,
-backend-specific concurrency management. It records the intended capability,
-consumer value, and important policy choices.
-
-This document is planning material, not a description of current behavior.
-Current exported contracts remain owned by Go declarations and GoDoc, backend
-registration guidance by the
-[consumer guide](../consumers/pkg-promptkit.md#configure-a-local-openai-compatible-endpoint),
-and
-implemented orchestration by the
-[internal runner document](../internal/runner.md).
-
-## Motivation
-
-Different model backends can sustain very different request loads. A local
-network endpoint may need a small concurrency limit, while OpenRouter can
-usually accept substantially more simultaneous work. Requiring every consumer
-to build its own semaphores and queues would duplicate routing knowledge,
-create inconsistent cancellation behavior, and make it easy for one caller to
-bypass the intended backend limit.
-
-Promptkit should own this coordination because it already resolves each run to
-an engine-scoped backend identity and owns every model-generation call made by
-the runner. Consumers should continue submitting ready-to-run requests through
-the synchronous API, including concurrently from multiple goroutines, without
-implementing their own backend scheduler.
-
-The buffered queue is a safety boundary, not an ordinary throughput
-restriction. Its primary purpose is to prevent a bug or unintended submission
-loop from creating an unbounded in-memory backlog.
-
-## Scope
-
-The feature will add optional concurrency policy to registered backends and
-coordinate `Run` calls against independent per-backend capacity pools.
-
-Each policy has two distinct controls:
-
-- an active-generation limit, which protects the backend from too many
-  simultaneous model requests; and
-- a bounded waiting capacity, which protects the process from admitting an
-  unbounded backlog.
-
-Concurrency policy belongs to a backend registration. It is not a profile
-model parameter and cannot be overridden per run. Profiles select the policy
-through their backend ID, while a profile or request endpoint override remains
-in the selected backend's pool.
-
-`Prepare` does not call a model and will remain outside concurrency admission.
-
-## Defaults And Configuration
-
-The built-in OpenRouter backend will use:
-
-- an active-generation limit of 16; and
-- a waiting capacity of 1024.
-
-The waiting default is intentionally generous. Reaching it should indicate
-abnormal submission pressure rather than normal application behavior.
-
-Consumer-registered backends will remain unlimited unless the consumer
-configures an active-generation limit. When a consumer enables a limit and
-does not specify waiting capacity, the waiting capacity will default to 1024.
-Consumers may configure a different bounded capacity, including zero when
-they want no admitted backlog beyond the active-limit-sized run set.
-
-The public representation must distinguish an omitted waiting capacity from
-an explicit zero.
-
-Endpoint-only profiles have no backend registration from which to obtain
-policy and will remain unlimited. A future engine-wide or endpoint-keyed
-policy can be considered separately if consumers demonstrate that need.
-
-Invalid limits or capacities will fail engine construction as invalid
-configuration. Policy values will be copied into engine-owned immutable state
-along with the rest of the backend registration.
-
-## Admission And Execution Behavior
-
-`Run` remains a synchronous, wait-for-result operation. Concurrent callers may
-block inside `Run` while waiting for their selected backend, then receive the
-ordinary result or error from that invocation.
-
-For a configured pool, the active-generation limit plus the waiting capacity
-defines the maximum number of concurrent `Run` invocations that Promptkit will
-accept for that backend. A waiting capacity of zero therefore accepts no more
-runs than the active limit. Admission is immediate: a call either reserves one
-of those bounded slots or receives the capacity error. An accepted run may
-then wait internally for active-generation capacity.
-
-For a limited backend, Promptkit will bound the number of accepted runs before
-expensive artifact loading, prompt rendering, and large defensive copies where
-practical. Lightweight prompt, profile, and backend resolution may occur first
-when it is required to identify the correct capacity pool. This pre-admission
-resolution must not become a second execution-precedence path with behavior
-that can drift from `Prepare`.
-
-An accepted run retains its admission until it completes or fails. Every
-actual model-generation call for that run must separately observe the
-backend's active-generation limit. This includes:
-
-- the initial generation;
-- every output-repair generation; and
-- calls made through either the built-in or an injected model client.
-
-Preparation and output validation should not hold an active-generation permit.
-A repair remains part of its already-admitted run, but reacquires active
-generation capacity so repairs cannot exceed the backend limit. It must not be
-rejected merely because new runs filled the waiting queue after its initial
-generation.
-
-Within one backend pool, waiting generation calls should be served in FIFO
-order, subject to canceled calls being removed. Different backend pools make
-progress independently; a saturated local backend must not consume
-OpenRouter's active or waiting capacity.
-
-The feature will not promise ordering across backend pools or completion order
-among admitted runs.
-
-## Capacity Failure And Cancellation
-
-When a backend's bounded waiting capacity is full, a new `Run` call will fail
-promptly rather than waiting outside the bounded admission system. The public
-API will expose a recognizable capacity-exhaustion error identity distinct
-from invalid configuration, invalid requests, and model-client failures.
-Rejected calls return no partial result and do not invoke the model client.
-
-Waiting within the admitted backlog or for active-generation capacity must
-honor the caller's context. Cancellation or deadline expiry will:
-
-- stop waiting promptly;
-- release any admission or generation capacity held by that invocation;
-- preserve the applicable context error identity; and
-- avoid invoking the model client if cancellation wins before generation
-  starts.
-
-Capacity must also be released after preparation, generation, validation,
-repair, or collaborator failure. One failed or canceled run must not reduce
-the backend's future usable capacity.
-
-Elapsed `Run` timing will include time spent waiting after the call is
-accepted. `PreparedRun` timing will continue to describe preparation rather
-than queue waiting.
-
-## Engine And Client Boundaries
-
-All pools and queued state belong to one `Engine`. Separate engines do not
-share capacity, even when they register the same backend ID or endpoint. The
-feature introduces no process-global scheduler.
-
-The engine will apply policy consistently to the built-in model client and an
-injected `LLMClient`. Consumers calling their own client outside Promptkit are
-outside this boundary. Injected clients remain responsible for their internal
-thread safety and cancellation behavior.
-
-Backend policy is keyed by the resolved backend ID rather than endpoint text.
-This preserves stable routing when a selected backend's endpoint is overridden
-and avoids accidentally combining unrelated registrations that happen to use
-the same URL.
-
-## Queue Lifetime And Observability
-
-Admission state is buffered, ephemeral, and in-process. It is not persisted
-and has no survival guarantee across engine disposal or process termination.
-Promptkit will not introduce background job ownership or require consumers to
-start or stop workers.
-
-The initial feature does not require public queue-depth metrics, callbacks, or
-inspection APIs. Capacity errors and ordinary call timing provide the
-consumer-visible behavior. Operational observability can be added later
-without coupling the scheduling mechanism to an application logging or
-metrics system.
-
-## Compatibility
-
-Consumer-registered backends and endpoint-only profiles remain unlimited
-unless concurrency is explicitly configured, preserving their existing
-behavior.
-
-The built-in OpenRouter backend will change from unlimited concurrency to a
-limit of 16 with a bounded waiting capacity of 1024. Ordinary synchronous
-calls remain unchanged, while unusually high concurrent use may now wait or
-return the capacity error. This behavioral change must be identified in the
-release notes for the version that publishes it.
-
-Adding backend policy fields and a public capacity error is otherwise
-additive. The change will use a pre-`v1` minor release under Promptkit's
-[release policy](../release.md#release-model).
-
-## Non-Goals
-
-This scope does not include:
-
-- asynchronous job handles, polling, or detached result delivery;
-- durable or cross-process queues;
-- persistence or recovery across engine or process shutdown;
-- priorities, scheduling weights, or consumer-defined fairness classes;
-- automatic retries, backoff, rate-limit interpretation, or provider quota
-  discovery;
-- token-per-minute or request-per-minute rate limiting;
-- dynamic reconfiguration after engine construction;
-- per-profile or per-run concurrency overrides;
-- endpoint-keyed pooling for profiles without a backend ID;
-- process-global coordination across engines;
-- application worker lifecycle, logging, tracing, or metrics policy; or
-- changes to prompt, profile, schema, or model-provider wire formats.
-
-## Target End State
-
-This roadmap reaches its target end state when:
-
-- each engine independently coordinates configured backend capacity;
-- the built-in OpenRouter backend allows 16 active generations and up to 1024
-  waiting runs;
-- consumer backends can opt into their own active and waiting limits while
-  remaining unlimited by default;
-- endpoint overrides retain the selected backend's capacity pool and
-  endpoint-only profiles remain unlimited;
-- synchronous `Run` callers wait for and receive their ordinary result;
-- admission is bounded before expensive preparation work where practical;
-- every initial and repair generation observes the backend's active limit
-  without serializing preparation or validation;
-- a full waiting queue returns a recognizable capacity error without invoking
-  the model client;
-- cancellation and all failure paths promptly release capacity and preserve
-  context error identity;
-- built-in and injected model clients receive the same scheduling behavior;
-- pools remain ephemeral, engine-scoped, and independent across backend IDs;
-  and
-- current-state GoDoc, consumer, internal, and release documentation describe
-  the implemented behavior once it lands.

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

@@ -12,6 +12,9 @@ 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.
@@ -23,6 +26,8 @@ selected.
 - 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.
 
@@ -33,36 +38,33 @@ consumers.
 
 ## Ideas
 
-Prompt-independent profile inspection has been selected for active planning in
-the [focused feature roadmap](profile-inspection.md). The remaining ideas are
-still available for future selection.
+### Public bounded output repair
 
-### Prompt-definition inspection
+After the codebase-audit remediations are complete, Promptkit should make its
+bounded output-repair capability available through the public engine. A
+consumer should be able to request a limited number of corrective generation
+attempts when JSON or JSON Schema output fails content validation, without
+having to reproduce Promptkit's generation, validation, capacity, and result-
+accounting orchestration.
 
-Provide exact prompt-definition lookup without rendering, placeholder inputs,
-profile resolution, or model generation, as requested by
-[Weatherreporter](weatherreporter-promptkit-wishlist.md#priority-2-prompt-definition-inspection).
+- Repair is validation recovery, not a general provider retry, failover, or
+  backoff policy. Transport failures, cancellation, and operational schema or
+  validation errors must retain their ordinary error behavior.
+- Repair must stop after the first valid result or the configured attempt
+  bound. Exhausting the bound should preserve the final invalid result and its
+  validation diagnostics rather than inventing success.
+- Initial generation and every repair attempt must use the same resolved
+  backend, effective execution settings and presence semantics, session,
+  credential boundary, structured-output contract, and backend-capacity
+  policy.
+- Results should report the number of repair attempts and cumulative usage for
+  every model call made by the run.
+- Ordinary and prepared execution should expose coherent behavior, including
+  cancellation, frozen prepared state, error identity, and capacity lifetime.
 
-- Return caller-owned identity, version, input definitions, default-profile,
-  output-contract, and opaque definition-equality information.
-- Apply ordinary prompt-source precedence and exact ID/version selection.
-- Validate the selected definition and referenced prompt content
-  structurally, without returning source bodies or rendered messages.
-- Leave complete cross-source corpus validation and enumeration outside the
-  initial inspection contract.
-
-### Structured capacity errors
-
-Add safe structured context to backend admission rejection, as requested by
-[Notarius](notarius-promptkit-wishlist.md#priority-4-structured-capacity-errors)
-and
-[Weatherreporter](weatherreporter-promptkit-wishlist.md#structured-capacity-errors).
-
-- Preserve compatibility with `errors.Is(err, ErrCapacityExceeded)`.
-- Support `errors.As` to obtain the stable backend ID.
-- Do not expose endpoints, credential configuration or values, request
-  content, or speculative retry timing.
-- Keep retry and backoff policy with downstream consumers.
+Select this work only after the accepted audit findings affecting shared
+execution invariants, validation, orchestration, transport, and repair
+internals have been remediated.
 
 ## Entry Format
 

docs/roadmap/implementation.md

@@ -1,670 +0,0 @@
-# Prompt-Independent Profile Inspection Implementation Plan
-
-**Status:** Ready for implementation.
-
-## Purpose
-
-This document is the decision-complete implementation plan for
-[prompt-independent profile inspection](profile-inspection.md). It is written
-for a coding agent that will implement each stage in order.
-
-The feature roadmap owns the motivation, consumer workflow, policy choices,
-compatibility requirements, non-goals, and target end state. This document
-owns the concrete design, file-level changes, implementation sequence, test
-ownership, documentation work, validation commands, and completion gates.
-
-## Implementation Rules
-
-- Complete the stages in order. Keep the repository compiling and the focused
-  tests passing at every stage boundary.
-- Preserve unrelated working-tree changes. In particular, retain the accepted
-  feature roadmap and the corresponding future-roadmap and downstream-wishlist
-  edits that may already be uncommitted.
-- Follow every policy under `docs/policy/`, the task-specific reading guide in
-  `docs/development.md`, and the accepted behavior in
-  `profile-inspection.md`.
-- Keep the supported API in the root `promptkit` package. Profile repositories,
-  backend resolution, and target assembly remain below Go's `internal/`
-  boundary.
-- Reuse the exact profile-source, backend-membership, and execution-target
-  precedence used by `Prepare`, `PrepareExecution`, and `Run`. Do not create a
-  second profile loader, backend registry, or target-merging implementation.
-- Preserve the observable behavior and error ordering of existing preparation
-  and execution methods. The new inspection operation must not require a
-  prompt, prompt default profile, request override, credential value, capacity
-  admission, model client, renderer, artifact reader, schema source, or
-  validator.
-- Treat structural validation as the existing profile, backend, and effective
-  target invariants. Do not add new endpoint URL policy, provider
-  connectivity checks, reserved-extra-parameter policy, credential syntax, or
-  file-format validation rules as part of this feature.
-- Never read, retain, return, format, or log an environment credential value.
-  The result may contain only the effective environment-variable name and the
-  direct-key-required boolean.
-- Return caller-owned public values. In particular, nested
-  `ExecutionTarget.ExtraParams` maps, slices, and objects must not alias
-  engine-owned state or another inspection result.
-- Keep tests lean and behavior-focused. Reuse existing profile repository,
-  backend registry, target precedence, and preparation tests rather than
-  duplicating their complete matrices.
-- Update exact contracts in GoDoc with the exported declarations. Update
-  current-state consumer, format, and internal documentation only after the
-  corresponding code exists.
-- Do not add release notes, change a module version, create a release, or tag a
-  commit as part of this work.
-
-## Fixed Design
-
-### Public API
-
-Add this root-package value immediately after `ExecutionTarget` in `types.go`:
-
-```go
-// ProfileInspection is the caller-owned result of Engine.InspectProfile.
-// The exact GoDoc is specified below.
-type ProfileInspection struct {
-	ProfileID            string
-	EffectiveModelParams ExecutionTarget
-	APIKeyRequired       bool
-}
-```
-
-Add this method to `Engine` in `engine.go`, immediately before `Prepare`:
-
-```go
-func (e *Engine) InspectProfile(
-	ctx context.Context,
-	profileID string,
-) (*ProfileInspection, error)
-```
-
-Do not accept `RunRequest`, `ExecutionTargetOverride`, an API key, an
-environment override, or options on this method. Exact inspection of one
-explicit profile ID is the complete operation.
-
-`ProfileInspection` has no stable JSON contract. Do not add JSON tags,
-`MarshalJSON`, `UnmarshalJSON`, or a custom string representation. Ordinary Go
-encoding of the exported fields is not prohibited, but consumers must not be
-promised compatibility for that encoding.
-
-The exact type and method GoDoc must establish:
-
-- surrounding whitespace is trimmed from `profileID`; the resulting nonblank
-  ID is looked up exactly and case-sensitively;
-- the result applies the engine's ordinary in-memory, configured-source, and
-  built-in profile precedence;
-- `EffectiveModelParams` contains framework defaults overlaid by the selected
-  backend and then the selected profile, with no request override;
-- `EffectiveModelParams.BackendID` is empty for endpoint-only profiles;
-- `EffectiveModelParams.APIKeyEnv` is an environment-variable name and never
-  its value;
-- `APIKeyRequired` means a direct request credential is required and is
-  mutually exclusive with a nonblank effective `APIKeyEnv`;
-- the method never derives an ID from a prompt's `default_profile`;
-- the method performs no prompt lookup, rendering, artifact or schema work,
-  backend admission, provider connectivity check, or model generation;
-- credential availability is not checked, so an absent or blank named
-  environment variable is not an error;
-- the returned value and all nested mutable values are caller-owned;
-- filesystem-backed inspection is a point-in-time lookup and does not freeze
-  a profile for a later execution;
-- a nil engine matches `ErrInvalidConfig`;
-- a blank 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 observed during profile loading matches `ErrProfileLoad` while
-  preserving the context error through `errors.Is`; and
-- the method returns no partial result on error.
-
-Update the `Engine` type GoDoc to include `InspectProfile` among the operations
-safe for concurrent calls. Do not imply that injected collaborators become
-safe when their existing contracts do not provide that guarantee.
-
-Update `doc.go` in the same stage:
-
-- include `Engine.InspectProfile` in the package's operation list;
-- include inspection in the concurrency and caller-ownership summary; and
-- list `ProfileInspection` among construction and inspection values without a
-  stable JSON representation.
-
-Do not add `ProfileInspection` to the stable JSON list.
-
-### Internal Result
-
-Add this internal value to `internal/domain/domain.go` near
-`ExecutionProfile` and `ExecutionTarget`:
-
-```go
-// ProfileInspection is the resolved result of exact profile inspection.
-type ProfileInspection struct {
-	ProfileID            string
-	EffectiveModelParams ExecutionTarget
-	APIKeyRequired       bool
-}
-```
-
-Do not add JSON or YAML tags. The internal value is a use-case result, not a
-file format or persistence contract.
-
-Add a root conversion in `convert.go`:
-
-```go
-func fromDomainProfileInspection(
-	inspection *domain.ProfileInspection,
-) *ProfileInspection
-```
-
-The conversion must:
-
-- return `nil` for a nil internal value;
-- copy the scalar fields;
-- convert the target through the existing `fromDomainExecutionTarget`; and
-- therefore use the existing recursive `copyAnyMap` boundary for nested extra
-  parameters.
-
-Do not add `APIKeyRequired` to the public `ExecutionTarget`. Keeping the
-requirement on `ProfileInspection` preserves the existing stable JSON and
-general execution-target contract.
-
-### Shared Profile Selection
-
-Add `internal/usecase/profile_inspection.go`. Define one private selection
-value:
-
-```go
-type resolvedProfileSelection struct {
-	id      string
-	profile *domain.ExecutionProfile
-	backend *domain.Backend
-}
-```
-
-Add a private runner helper:
-
-```go
-func (r *Runner) resolveProfileSelection(
-	ctx context.Context,
-	profileID string,
-) (*resolvedProfileSelection, error)
-```
-
-The helper must perform these operations in order:
-
-1. trim surrounding whitespace from `profileID`;
-2. reject a blank result with `ErrInvalidRequest`;
-3. reject a nil runner profile repository with `ErrProfileLoad` rather than
-   panicking;
-4. call the existing `profile.Repository.GetProfile` exactly once;
-5. wrap every repository error with `ErrProfileLoad` while preserving the
-   underlying error with `%w`;
-6. reject a nil profile returned without an error as `ErrProfileLoad`;
-7. make a value copy of the selected profile before normalization so the
-   runner does not mutate repository-owned state;
-8. trim the copied profile's backend ID;
-9. when that ID is nonblank, resolve it exactly once through the existing
-   `BackendResolver`, preserving the current unknown-backend
-   `ErrProfileLoad` wrapping and backend ID context; and
-10. return the normalized exact ID, copied profile, and optional defensive
-    backend value.
-
-Do not inspect all sources, enumerate profiles, expose a source path, fall back
-after a malformed higher-precedence match, or infer a backend from an endpoint
-or model.
-
-Refactor the profile-loading and backend-resolution block in
-`Runner.resolvePreparation` to call `resolveProfileSelection`. Leave prompt
-selection, prompt default-profile selection, prompt hashing, target overrides,
-request credentials, output-contract resolution, artifact work, and all later
-ordering where they currently occur.
-
-This refactor must preserve:
-
-- explicit request profile selection over prompt `default_profile`;
-- the existing `ErrProfileRequired` result when neither exists;
-- exact repository and backend lookup behavior;
-- existing public not-found versus profile-load classification;
-- request override precedence and target-presence tracking;
-- credential checking during ordinary preparation; and
-- current `Prepare`, `PrepareExecution`, `Run`, and `RunPrepared` behavior.
-
-### Shared Target Resolution And Structural Validation
-
-Continue using the existing `resolveExecutionTarget` for framework, backend,
-profile, and optional request precedence. Do not duplicate or move the
-individual merge rules into the inspection code.
-
-Extract the two existing effective-target requiredness checks from
-`resolvePreparation` into a private pure helper:
-
-```go
-func validateResolvedExecutionTarget(
-	target domain.ExecutionTarget,
-) error
-```
-
-It checks only that the trimmed endpoint and model are nonblank and returns a
-plain descriptive error. It does not validate URL syntax, contact the
-endpoint, validate credentials, or introduce new parameter rules.
-
-`resolvePreparation` calls this helper at the same current point: after
-request override resolution and direct API-key assignment, and before
-`validateAPIKey`. It wraps a failure with `ErrInvalidRequest`, preserving
-ordinary preparation behavior.
-
-Add the internal inspection method:
-
-```go
-func (r *Runner) InspectProfile(
-	ctx context.Context,
-	profileID string,
-) (*domain.ProfileInspection, error)
-```
-
-It performs these operations:
-
-1. trim and reject a blank ID as `ErrInvalidRequest`;
-2. if the supplied context is already canceled, return an error wrapping both
-   `ErrProfileLoad` and `ctx.Err()` without touching the repository;
-3. call `resolveProfileSelection`;
-4. call `resolveExecutionTarget` with the selected backend, selected profile,
-   and a nil request override;
-5. wrap any target-resolution error with `ErrProfileLoad`;
-6. call `validateResolvedExecutionTarget` and wrap a failure with
-   `ErrProfileLoad`;
-7. defensively clear `target.APIKey`;
-8. copy `target.APIKeyRequired` into the result's `APIKeyRequired`; and
-9. return the normalized profile ID and effective target.
-
-Do not call `validateAPIKey`, `os.Getenv`, prompt repositories, artifact
-readers, renderers, validators, capacity admission, output repair, or the
-model client. Do not populate request target-presence state.
-
-The internal `ExecutionTarget` may retain its private `APIKeyRequired` field;
-the root conversion intentionally omits that private field from the public
-target and publishes the separate inspection boolean.
-
-### Root Facade And Error Mapping
-
-`Engine.InspectProfile` follows the existing facade pattern:
-
-1. reject a nil engine or nil runner with `ErrInvalidConfig`;
-2. pass the context and string ID directly to `Runner.InspectProfile`;
-3. map internal failures through the existing `mapPublicError`; and
-4. convert a successful result with `fromDomainProfileInspection`.
-
-No request conversion is needed. Do not add a public sentinel or typed error.
-
-The existing error mapping already has the required ordering:
-
-- an underlying `profile.ErrProfileNotFound` maps to
-  `ErrProfileNotFound` before the enclosing use-case `ErrProfileLoad` is
-  considered;
-- other use-case `ErrProfileLoad` failures map to `ErrProfileLoad`; and
-- `usecase.ErrInvalidRequest` maps to `ErrInvalidRequest`.
-
-Do not reorder or otherwise change `errors.go` unless a focused test proves
-that the existing mapping does not meet this plan. Preserve underlying
-repository, backend, and context errors through `errors.Is`.
-
-### Credentials, Ownership, And Concurrency
-
-Inspection has no input through which a direct credential value can enter.
-Backend and file-profile `APIKeyEnv` values remain names only. An in-memory
-profile with `APIKeyRequired` clears an inherited backend environment name
-through the existing target merge behavior.
-
-The implementation must succeed for:
-
-- a backend or profile naming an unset environment variable;
-- a backend or profile naming an environment variable whose value is blank;
-- an in-memory profile requiring a direct key when no key is supplied; and
-- a profile requiring no credential.
-
-The result expresses these effective states:
-
-| `EffectiveModelParams.APIKeyEnv` | `APIKeyRequired` | Meaning |
-| --- | --- | --- |
-| nonblank | `false` | The profile resolves to the named environment source. |
-| blank | `true` | A later execution must supply a direct key or explicit request environment override. |
-| blank | `false` | The resolved target declares no credential requirement. |
-
-The implementation must never produce a successful public result with both a
-nonblank `APIKeyEnv` and `APIKeyRequired == true`.
-
-Public ownership is enforced at the root conversion boundary. A consumer may
-mutate the returned target and arbitrarily nested JSON-compatible extra
-parameters without affecting:
-
-- the engine registry or profile repository;
-- a later `InspectProfile` call;
-- `Prepare`, prepared execution, or `Run`; or
-- another result already returned to a caller.
-
-No new mutable engine state, cache, global registry, lock, or goroutine is
-needed. Concurrency safety follows from the existing immutable registry and
-repository contracts plus per-call values.
-
-### Test Ownership
-
-Add focused internal tests in
-`internal/usecase/profile_inspection_test.go`. Use small repository and backend
-fakes already present in the package where practical; do not build a parallel
-fixture framework.
-
-The internal tests own:
-
-- blank-ID rejection;
-- pre-canceled context classification without repository access;
-- one exact profile and backend lookup;
-- framework-default, backend, and profile target precedence through the
-  existing resolver;
-- endpoint-only behavior;
-- effective environment-name reporting without availability checks;
-- direct-key-required behavior clearing an inherited backend environment
-  name;
-- missing-profile and unknown-backend wrapping; and
-- nil repository, nil returned profile, and invalid resolved target defenses
-  only if these cases are not already cheaply covered through existing runner
-  fakes.
-
-Keep the internal matrix compact. Profile parser tests continue to own YAML,
-duplicates, raw-key rejection, ranges, and source discovery. Backend tests
-continue to own registration validation. Existing target tests continue to
-own every merge field and numeric override boundary.
-
-Add external-package public contract tests in `public_contract_test.go`. They
-own:
-
-- the exported method and result shape through normal Go use;
-- a nil engine returning `ErrInvalidConfig`;
-- blank, missing, malformed, and unknown-backend public error identities,
-  including that not-found does not also match `ErrProfileLoad`;
-- a pre-canceled inspection preserving both `ErrProfileLoad` and the context
-  error without consulting the profile repository;
-- successful inspection with an absent credential environment value;
-- no prompt dependency, demonstrated with an empty configured prompt
-  `fs.FS`;
-- no model invocation, using the existing deterministic fake client;
-- the three credential-requirement result states;
-- an endpoint-only profile's empty backend ID;
-- deep caller ownership of nested extra parameters across repeated
-  inspections; and
-- representative equivalence between `InspectProfile.EffectiveModelParams`
-  and `Prepare.EffectiveModelParams` for the same engine, profile, and source
-  state with no request execution override.
-
-Combine closely related assertions into a few readable behavioral tests.
-Do not add a JSON golden test because `ProfileInspection` deliberately has no
-stable JSON contract. Do not duplicate the complete repository-precedence,
-target-field, parser-error, or credential-execution suites at the root layer.
-
-Existing tests that must continue passing without semantic edits include:
-
-- profile repository and built-in fallback tests;
-- backend registry defensive-copy and lookup tests;
-- execution-target precedence tests;
-- `Prepare` and `Run` profile/backend equivalence tests;
-- prepared-execution snapshot and credential tests; and
-- public error mapping tests.
-
-### Documentation Ownership
-
-After the implementation and public tests pass, update current-state
-documentation:
-
-- `docs/consumers/pkg-promptkit.md`: add a concise task-oriented section near
-  profile selection showing `Engine.InspectProfile`, explaining when to use it
-  instead of a synthetic `Prepare`, how to interpret `APIKeyEnv` and
-  `APIKeyRequired`, and that credential enforcement timing remains
-  application policy. Link to the exact GoDoc rather than restating every
-  error and field contract.
-- `docs/formats.md`: update profile selection and backend-membership wording
-  so exact inspection is recognized as another consumer of the existing
-  source and profile precedence. Do not redefine the exported method here.
-- `docs/internal/runner.md`: describe the shared profile-selection boundary
-  and explain that inspection stops after structural target resolution,
-  before credential availability and all prompt-dependent work.
-- `docs/internal/sources.md`: record that exact profile inspection performs
-  one point-in-time profile-source lookup without reading prompt, input, or
-  schema sources, and replace any ambiguous use of “inspection value” for
-  `PreparedRun` with “preparation value.”
-- `docs/internal/overview.md`: add profile inspection to the existing root
-  facade and `internal/usecase` responsibility descriptions. Do not add a new
-  component or package row.
-- `docs/roadmap/future.md`: remove the statement that profile inspection is in
-  active planning and leave the remaining unselected ideas intact.
-- `docs/roadmap/notarius-promptkit-wishlist.md` and
-  `docs/roadmap/weatherreporter-promptkit-wishlist.md`: change the profile
-  inspection disposition from accepted planning to implemented behavior and
-  link to the durable consumer guidance or GoDoc rather than treating the
-  roadmap as current-state documentation.
-- `docs/roadmap/profile-inspection.md`: change its status to `Complete` only
-  after the code, tests, current-state documentation, and full validation are
-  complete.
-- `docs/roadmap/implementation.md`: change its status to `Complete` only after
-  every completion gate in this plan is satisfied.
-
-Do not update release guidance in this feature implementation. A later release
-pass decides whether the change warrants a supplemental release document.
-
-## Stage 1: Implement Shared Internal Profile Resolution
-
-### Objective
-
-Add the internal inspection result and operation, share profile/backend
-selection and structural target validation with ordinary preparation, and
-prove the internal behavior without publishing the root API yet.
-
-### Implementation Prompt
-
-Implement only Stage 1 of
-`docs/roadmap/implementation.md`. Read the complete feature roadmap and the
-implementation rules and fixed design above before editing.
-
-1. Add `domain.ProfileInspection` to `internal/domain/domain.go` without
-   serialization tags.
-2. Add `internal/usecase/profile_inspection.go` with
-   `resolvedProfileSelection`, `resolveProfileSelection`,
-   `validateResolvedExecutionTarget`, and `Runner.InspectProfile` exactly as
-   specified.
-3. Refactor `Runner.resolvePreparation` in `internal/usecase/runner.go` to use
-   the shared selection and target-validation helpers while preserving its
-   current ordering, error classification, target overrides, credentials, and
-   results.
-4. Add lean behavioral tests in
-   `internal/usecase/profile_inspection_test.go`.
-5. Run the focused validation below and repair regressions before ending the
-   stage.
-
-Do not add the root public type or method, update current-state documentation,
-or alter profile formats, backend registration, credential availability,
-capacity, model-client, or provider behavior in this stage.
-
-### Focused Validation
-
-Run:
-
-```sh
-gofmt -w internal/domain/domain.go \
-  internal/usecase/profile_inspection.go \
-  internal/usecase/profile_inspection_test.go \
-  internal/usecase/runner.go
-go test ./internal/usecase ./internal/profile ./internal/profile/builtin \
-  ./internal/backend
-go test ./internal/usecase -run \
-  'TestRunner(InspectProfile|Prepare|Run|PrepareExecution|RunPrepared)'
-go vet ./internal/usecase ./internal/profile ./internal/backend
-```
-
-### Completion Gate
-
-Stage 1 is complete only when:
-
-- inspection reaches profile and backend resolution without any prompt or
-  execution collaborator;
-- profile/backend selection is shared with ordinary preparation;
-- target merging and requiredness checks are shared rather than duplicated;
-- inspection does not check credential values or capacity;
-- internal errors preserve the required identities;
-- the ordinary preparation and execution tests still pass without weakened
-  assertions; and
-- no root public API or current-state documentation claims the feature yet.
-
-## Stage 2: Publish The Root Facade And Public Contract
-
-### Objective
-
-Expose the minimal caller-owned inspection API through `Engine`, preserve
-public error and JSON compatibility, and protect the consumer-visible
-contract.
-
-### Implementation Prompt
-
-Implement only Stage 2 of
-`docs/roadmap/implementation.md` after Stage 1 satisfies its completion gate.
-Re-read the fixed public API, error, credential, ownership, and test sections
-before editing.
-
-1. Add `ProfileInspection` and its exact GoDoc to `types.go` immediately after
-   `ExecutionTarget`. Do not add JSON tags or change `ExecutionTarget`.
-2. Add `fromDomainProfileInspection` to `convert.go` using
-   `fromDomainExecutionTarget`.
-3. Add `Engine.InspectProfile` and its exact GoDoc to `engine.go` immediately
-   before `Prepare`.
-4. Update `Engine` GoDoc to include concurrent inspection.
-5. Update the package GoDoc in `doc.go` for operation discovery, concurrency,
-   ownership, and the non-stable JSON classification.
-6. Add compact external-package contract coverage in
-   `public_contract_test.go`, using existing fixtures and fakes where they
-   remain clear.
-7. Confirm that the existing `errors.go` mapping meets the plan; do not change
-   it unless a required public identity test fails for a genuine mapping
-   reason.
-8. Run the focused validation below and repair regressions before ending the
-   stage.
-
-Do not add enumeration, request overrides, profile fingerprints, JSON
-stability, prompt inspection, environment credential checks, caching, or
-current-state prose documentation in this stage.
-
-### Focused Validation
-
-Run:
-
-```sh
-gofmt -w doc.go types.go convert.go engine.go public_contract_test.go
-go test .
-go test ./internal/usecase
-go test . -run 'Test(InspectProfile|.*Profile.*PublicError|.*Profile.*Contract)'
-go vet .
-go build .
-```
-
-If the repository's actual focused test names differ, use the implemented test
-names rather than weakening or skipping the intended assertions.
-
-### Completion Gate
-
-Stage 2 is complete only when:
-
-- a consumer can call `Engine.InspectProfile` through the root package;
-- the result contains only the normalized ID, caller-owned effective target,
-  and direct-key-required signal;
-- no credential value can enter the result;
-- environment, direct, and no-credential states are unambiguous;
-- nil, blank, missing, malformed, unknown-backend, and cancellation errors
-  have the required public identities;
-- not-found remains distinct from profile-load failure;
-- the effective target matches ordinary preparation absent request overrides;
-- repeated calls and caller mutation cannot alter engine-owned state;
-- no stable JSON or new error contract was introduced; and
-- existing public preparation, execution, and stable JSON tests remain
-  unchanged and passing.
-
-## Stage 3: Update Documentation And Validate The Repository
-
-### Objective
-
-Make implemented profile inspection discoverable in its canonical
-documentation, reconcile temporary roadmap state, and complete full repository
-validation.
-
-### Implementation Prompt
-
-Implement only Stage 3 of
-`docs/roadmap/implementation.md` after Stages 1 and 2 satisfy their completion
-gates.
-
-1. Update `docs/consumers/pkg-promptkit.md`, `docs/formats.md`,
-   `docs/internal/runner.md`, `docs/internal/sources.md`, and
-   `docs/internal/overview.md` according to the documentation ownership
-   section above.
-2. Update the future catalog and both downstream wishlist dispositions so they
-   no longer describe profile inspection as merely accepted work.
-3. Check every changed Markdown link and confirm its file and heading target.
-4. Run the full validation sequence below.
-5. Only after every check passes, set the feature roadmap and this
-   implementation plan to `**Status:** Complete.`
-6. Re-run `git diff --check` after the status edits.
-
-Do not add release notes, an example program, a new public package, or a
-duplicate API reference. Keep detailed contracts in GoDoc and task-oriented
-usage in the consumer guide.
-
-### Full Validation
-
-Run from the repository root:
-
-```sh
-gofmt -w internal/domain/domain.go \
-  internal/usecase/profile_inspection.go \
-  internal/usecase/profile_inspection_test.go \
-  internal/usecase/runner.go \
-  doc.go types.go convert.go engine.go public_contract_test.go
-gofmt -l $(git ls-files '*.go')
-go test ./...
-go test -race ./...
-go vet ./...
-go build ./...
-go run ./examples/go-library/prepare
-git diff --check
-git status --short
-```
-
-The `gofmt -l` command must print no paths. The maintained example must remain
-offline and must not require a real credential or provider.
-
-Inspect the final diff and confirm:
-
-- only files required by this feature and pre-existing user changes are
-  present;
-- no credential values, private infrastructure details, workspace files,
-  local replacements, generated binaries, or unrelated formatting changes
-  were added;
-- the public declarations and GoDoc own exact API behavior;
-- current-state documentation describes only implemented behavior and links
-  to canonical owners;
-- roadmap documents contain future scope or completion status rather than a
-  duplicate current API reference; and
-- no release, commit, or tag was created.
-
-### Completion Gate
-
-The implementation is complete only when:
-
-- every Stage 1 and Stage 2 gate remains satisfied;
-- the complete ordinary and race-enabled suites pass;
-- vet, build, formatting, the maintained offline example, Markdown links, and
-  whitespace checks pass;
-- consumer, format, internal, future, and wishlist documentation are
-  consistent with the implemented boundary;
-- both roadmap statuses are `Complete`;
-- the working tree contains no unintended files or changes; and
-- the repository is ready for maintainer review without a commit or release
-  having been created by this plan.
-
-## Open Questions
-
-None. The accepted feature roadmap and the fixed decisions above fully specify
-the implementation boundary.

docs/roadmap/local-backend.md

@@ -1,163 +0,0 @@
-# Local Backend Convenience
-
-**Status:** Complete.
-
-## Purpose
-
-Make the common case of using a local OpenAI-compatible endpoint concise and
-easy to discover without introducing implicit configuration or a separate
-backend abstraction.
-
-The existing `Backend` type and registry remain the canonical, fully
-configurable interface. A small convenience constructor will cover the usual
-local-network case, while improved consumer documentation will make it clear
-when an endpoint-only profile, the convenience constructor, or a complete
-`Backend` value is appropriate.
-
-## Motivation
-
-Consumers can already use a local endpoint by setting `Profile.Endpoint`, or
-register one as a backend with `WithBackend`. The first option is concise but
-does not provide shared backend-level concurrency control. The second supports
-the complete backend feature set but requires consumers to understand and
-populate several fields for a common configuration.
-
-Most consumers adding a local backend need only:
-
-- a stable backend ID;
-- an OpenAI-compatible endpoint; and
-- a concurrency limit appropriate for the local server.
-
-Promptkit should provide a direct path for that case while keeping all
-configuration explicit and preserving the full registry interface for
-advanced needs.
-
-## Consumer Paths
-
-Documentation should present three progressively more configurable paths:
-
-1. Set `Profile.Endpoint` when a profile only needs to target a local endpoint
-   and does not need shared backend policy.
-2. Use the local-backend convenience constructor when profiles should share a
-   named local endpoint and its concurrency limit.
-3. Construct a complete `Backend` value when the consumer needs a custom
-   backend ID, authentication, extra request parameters, an explicit queue
-   capacity, or multiple local backends.
-
-These are complementary interfaces. The convenience constructor must return an
-ordinary `Backend`, so it does not create a second configuration model.
-
-## Public Convenience API
-
-The public package should expose:
-
-```go
-const BackendLocal = "local"
-
-func LocalBackend(endpoint string, concurrencyLimit int) Backend
-```
-
-`LocalBackend` should return a `Backend` with:
-
-- `ID` set to `BackendLocal`;
-- `Endpoint` set to the supplied endpoint;
-- `ConcurrencyLimit` set to the supplied limit; and
-- all other fields left at their zero values.
-
-The returned value is passed to `WithBackend` and follows the same copying,
-normalization, validation, and registration rules as any consumer-constructed
-`Backend`.
-
-The constructor should be a transparent value constructor. It should not read
-environment variables, mutate global state, register the backend, validate
-arguments independently, or create profiles. Consumers may inspect or modify
-the returned value before registration, although documentation should direct
-substantially customized configurations to the full `Backend` form.
-
-## Identity and Registration
-
-`BackendLocal` is a conventional ID used by the convenience constructor. It is
-not pre-registered and should not become a specially reserved registry ID.
-Consumers remain responsible for registering the returned backend with
-`WithBackend` and naming it from profiles through `BackendID`.
-
-This distinction preserves compatibility with consumers that may already
-register their own backend using the ID `"local"`. Normal duplicate-ID rules
-still apply if a consumer attempts to register more than one backend with that
-ID.
-
-Consumers that need multiple local endpoints should choose distinct IDs and
-use complete `Backend` values rather than the single conventional helper ID.
-
-## Concurrency and Queue Semantics
-
-The constructor must preserve the existing backend concurrency contract:
-
-- a positive concurrency limit bounds simultaneous requests and uses the
-  existing default queue capacity because `QueueCapacity` remains `nil`;
-- a zero concurrency limit leaves the backend unconstrained; and
-- a negative concurrency limit is rejected through the existing engine
-  configuration validation path.
-
-The constructor should not select a hidden default concurrency limit. Local
-servers vary substantially in capacity, so the consumer should make this
-choice explicitly.
-
-## Documentation
-
-The final documentation state has two canonical surfaces:
-
-- Public Go documentation describes the exact contract of
-  `BackendLocal` and `LocalBackend`, including their conventional,
-  non-pre-registered nature.
-- The [promptkit consumer guide](../consumers/pkg-promptkit.md) includes
-  a task-oriented local-endpoint section that shows the three consumer paths,
-  explains the decision between them, and provides concise examples of the
-  endpoint-only and convenience-constructor forms.
-
-The consumer guide continues to document the full `Backend` interface as
-the advanced path rather than attempting to reproduce every configuration
-variation through convenience APIs.
-
-## Compatibility
-
-This feature is additive:
-
-- existing endpoint-only profiles continue to work unchanged;
-- existing `Backend` values and `WithBackend` registrations remain the
-  canonical general-purpose interface;
-- existing registrations using the literal ID `"local"` remain valid; and
-- OpenRouter defaults and all other backend behavior remain unchanged.
-
-No consumer is required to adopt the convenience constructor.
-
-## Non-Goals
-
-This work does not include:
-
-- pre-registering or implicitly enabling a local backend;
-- discovering a local endpoint, API key, or concurrency limit from environment
-  variables;
-- adding local-backend fields to `Config`;
-- selecting a default local model or creating a profile automatically;
-- adding a combined backend-and-profile constructor;
-- adding convenience parameters for API keys, extra request parameters, or
-  queue capacity;
-- replacing or redesigning the backend registry;
-- adding support for non-OpenAI-compatible local APIs; or
-- changing backend routing, scheduling, or queue behavior.
-
-## Target End State
-
-After this work:
-
-- consumers with a simple one-profile local endpoint can continue to configure
-  it directly on the profile;
-- consumers needing a shared local endpoint and concurrency policy can express
-  it with one `LocalBackend` call and register the returned value normally;
-- consumers with advanced or multiple-local-backend requirements have a clear
-  path to the complete `Backend` interface;
-- all local configuration remains explicit, inspectable, and compatible with
-  dependency injection; and
-- canonical documentation makes the simplest suitable interface easy to find
-  without obscuring the underlying registry model.

docs/roadmap/notarius-promptkit-wishlist.md

@@ -1,358 +0,0 @@
-# Notarius PromptKit Wishlist
-
-## Purpose
-
-This document records features and interface changes that would be useful
-additions to PromptKit from the perspective of the maintainers of Notarius, a
-downstream application that consumes PromptKit.
-
-PromptKit v0.3.0 provides the capabilities Notarius currently needs. None of
-the ideas below blocks current Notarius development. They are opportunities to
-reduce downstream workarounds, improve integration correctness, and make
-PromptKit more ergonomic for applications with configuration validation,
-debugging, checkpointing, and operational-observability requirements.
-
-The examples are API sketches intended to communicate the desired capability,
-not prescriptive names or finalized Go contracts.
-
-## Priority 1: Atomic Execution With Prepared Details
-
-**Disposition:** Covered by the accepted
-[executable preparation handles](prepared-execution.md) roadmap. The shared
-two-phase capability should provide the required single-preparation
-consistency; a separate `RunDetailed` method is not cataloged initially.
-
-### Downstream need
-
-Notarius needs both:
-
-- the completed `RunResult`; and
-- the rendered messages, effective output contract, hashes, and other
-  preparation details exposed by `PreparedRun`.
-
-Notarius uses the prepared details to construct redaction-aware debug bundles
-and retain enough information to diagnose model behavior.
-
-### Current integration
-
-Notarius currently calls `Engine.Prepare` and then `Engine.Run` with the same
-request. Because `Run` performs preparation internally, a successful request
-resolves and prepares the same work twice.
-
-This duplicates profile resolution, input hashing, schema loading, and prompt
-rendering. It also creates a theoretical consistency window in which a
-filesystem-backed prompt, profile, schema, or input could change between the
-explicit preparation and the preparation performed by `Run`.
-
-### Requested capability
-
-Add an opt-in execution method that prepares exactly once and returns both the
-prepared details and completed result:
-
-```go
-type RunReport struct {
-	Prepared PreparedRun
-	Result   RunResult
-}
-
-func (e *Engine) RunDetailed(
-	ctx context.Context,
-	req RunRequest,
-) (*RunReport, error)
-```
-
-The exact names are flexible. The important contract is that preparation
-occurs once and that the returned prepared state describes the execution that
-produced the returned result.
-
-Existing `Prepare` and `Run` behavior should remain available for consumers
-that need only one side of the operation.
-
-### Design considerations
-
-- Keep this API additive and preserve the existing simple `Run` workflow.
-- Return caller-owned copies under PromptKit's existing ownership rules.
-- Define whether any prepared details are available after an operational
-  generation or validation error. Notarius does not require partial results
-  for the initial use case, but an explicit contract would be valuable.
-- Preserve cancellation and backend-admission semantics.
-- Do not add all prepared content directly to `RunResult`. Rendered prompt
-  content can be large and sensitive, and consumers should opt in to receiving
-  it.
-
-### Value to Notarius
-
-This is the highest-value wishlist item. It would remove duplicate work from
-every successful PromptKit-backed call and ensure that retained debug material
-corresponds atomically to the actual execution.
-
-## Priority 2: Prompt-Independent Profile Inspection
-
-**Disposition:** Covered by the accepted
-[prompt-independent profile inspection](profile-inspection.md) roadmap.
-
-### Downstream need
-
-Notarius validates configured pipeline profile IDs before beginning a run. It
-needs to determine whether:
-
-- a profile exists;
-- its referenced backend is registered;
-- its execution target can be resolved; and
-- it declares a credential requirement that the application may need to
-  enforce.
-
-This validation should not require model generation.
-
-### Current integration
-
-Notarius constructs a synthetic prompt using `testing/fstest.MapFS`, supplies a
-dummy transcript, and calls `Engine.Prepare` solely to exercise profile and
-backend resolution. This works, but prompt preparation is serving as a
-substitute for a profile-inspection interface.
-
-### Requested capability
-
-Add a prompt-independent profile-resolution API, for example:
-
-```go
-type ResolvedProfile struct {
-	ProfileID       string
-	BackendID       string
-	EffectiveTarget ExecutionTarget
-	APIKeyEnv       string
-}
-
-func (e *Engine) ResolveProfile(
-	ctx context.Context,
-	profileID string,
-) (ResolvedProfile, error)
-```
-
-The returned shape may differ, but it should provide enough information for a
-consumer to validate an explicit profile selection without inventing a prompt
-or supplying placeholder inputs.
-
-### Design considerations
-
-- Resolve built-in, file-backed, and programmatic profiles using normal
-  PromptKit precedence.
-- Validate that a referenced backend registration exists.
-- Do not resolve, retain, or expose credential values.
-- Report credential requirements, such as an environment-variable name, so
-  the consuming application can decide whether availability is required at
-  configuration-validation time or only at execution time.
-- Return caller-owned values.
-- Preserve typed or sentinel error classification for missing and invalid
-  profiles.
-- Consider accepting an `ExecutionTargetOverride` if consumers need to inspect
-  the same effective target that a run-level override would produce.
-- Enumeration of all profiles is not required for the Notarius use case; exact
-  lookup by ID is sufficient.
-
-### Value to Notarius
-
-This would eliminate a synthetic production-only prompt fixture and establish
-a direct, supported contract for configuration-time profile and backend
-validation.
-
-## Priority 3: Semantic Execution-Target Fingerprints
-
-**Disposition:** Deferred until prompt-independent profile inspection defines
-the resolved target whose configuration identity would be fingerprinted.
-
-### Downstream need
-
-Notarius checkpoints model-backed pipeline stages. A checkpoint must not be
-reused when generation-affecting PromptKit configuration changes.
-
-Notarius therefore needs a stable equality signal for the effective profile
-and backend target used by a pipeline.
-
-### Current integration
-
-Notarius currently constructs this identity itself from:
-
-- a manually maintained marker for the PromptKit release and built-in profile
-  catalog;
-- raw hashes of configured profile files; and
-- a separate hash of the configured conventional local-backend endpoint.
-
-This is safe but conservative and coupled to PromptKit details. Raw file
-hashing also invalidates checkpoints for semantically irrelevant YAML changes,
-such as comments or formatting.
-
-### Requested capability
-
-Expose an opaque semantic digest for a resolved profile and its effective
-generation target. It could be returned by the proposed profile-resolution
-API:
-
-```go
-type ResolvedProfile struct {
-	ProfileID       string
-	BackendID       string
-	EffectiveTarget ExecutionTarget
-	ExecutionDigest string
-}
-```
-
-Alternatively, PromptKit could expose a dedicated method such as
-`ProfileExecutionDigest(profileID)`.
-
-### Desired equality semantics
-
-The digest should change when generation-affecting state changes, including:
-
-- resolved model and endpoint;
-- backend routing identity;
-- backend request defaults and extra parameters;
-- profile generation parameters; and
-- the semantic identity of any selected built-in profile.
-
-The digest should not incorporate:
-
-- credential values;
-- concurrency or queue capacity;
-- filesystem source paths;
-- YAML comments or formatting; or
-- other settings that affect scheduling or source representation without
-  changing the generation target.
-
-The credential environment-variable name may need to participate if changing
-it can select a materially different provider account or target. PromptKit
-should define this deliberately while continuing to exclude the resolved
-secret value.
-
-### Design considerations
-
-- Treat the digest as an opaque equality value rather than a public encoding
-  of internal structures.
-- Document which categories of change affect equality.
-- Include a versioned semantic marker internally so PromptKit can deliberately
-  invalidate old digests when its resolution semantics change.
-- Prefer a per-profile digest over a digest of every profile known to an
-  engine. Notarius generally knows which profiles a resolved pipeline uses.
-- Do not require consumers to know PromptKit's built-in catalog version.
-
-### Value to Notarius
-
-This would let Notarius remove its PromptKit release marker and raw
-profile-source fingerprinting, reduce unnecessary checkpoint invalidation, and
-delegate execution-target equality to the component that owns target
-resolution.
-
-## Priority 4: Structured Capacity Errors
-
-**Disposition:** Accepted into the
-[future catalog](future.md#structured-capacity-errors).
-
-### Downstream need
-
-Notarius translates PromptKit backend-capacity rejection into a
-provider-neutral application error. When multiple backends are active,
-operators would benefit from knowing which backend rejected admission without
-parsing an error string or exposing endpoint details.
-
-### Current integration
-
-PromptKit provides the useful `ErrCapacityExceeded` sentinel. Notarius can
-classify the failure reliably, but it retains only a sanitized diagnostic
-string as additional context.
-
-### Requested capability
-
-Add a typed error that continues to match `ErrCapacityExceeded`:
-
-```go
-type CapacityError struct {
-	BackendID string
-}
-
-func (e *CapacityError) Is(target error) bool {
-	return target == ErrCapacityExceeded
-}
-```
-
-The exact implementation may use `Unwrap` or another idiomatic mechanism. The
-important properties are compatibility with `errors.Is` and discoverability
-through `errors.As`.
-
-### Design considerations
-
-- Include the stable backend ID.
-- Do not expose the backend endpoint, credential environment, credential
-  value, request content, or other sensitive configuration.
-- Consider including the configured concurrency and queue limits if they are
-  useful and safe, but backend identity alone provides most of the downstream
-  value.
-- Add a retry delay only if PromptKit can provide a meaningful value. A full
-  queue does not necessarily imply a reliable `Retry-After` duration.
-- Keep retry and backoff policy with the consuming application. PromptKit
-  should classify the admission failure rather than silently retry it.
-
-### Value to Notarius
-
-This would improve operational diagnostics and future metrics while preserving
-the provider-neutral error boundary used by Notarius.
-
-## Capabilities PromptKit Already Provides Well
-
-The current PromptKit boundary is sufficient for Notarius's implemented
-behavior. In particular, PromptKit already provides:
-
-- filesystem, `fs.FS`, and programmatic prompt, profile, and schema sources;
-- offline preparation without model execution;
-- structured output and content validation;
-- direct session propagation;
-- tri-state per-run reasoning overrides;
-- selected profile, backend, model, endpoint, effective parameters, hashes, and
-  token-usage provenance;
-- endpoint-only profiles;
-- the conventional `local` backend helper;
-- arbitrary engine-scoped `Backend` registrations;
-- backend authentication environment names, extra parameters, concurrency
-  limits, and queue-capacity policies;
-- provider-client and artifact-reader extension interfaces;
-- context cancellation; and
-- useful public error sentinels, including profile absence and capacity
-  exhaustion.
-
-The wishlist does not imply that Notarius needs PromptKit to broaden its core
-responsibilities. It primarily asks for more direct access to information and
-operations that PromptKit already computes internally.
-
-## Responsibilities That Should Remain In Notarius
-
-The following concerns belong to the downstream application and should not
-move into PromptKit for the sake of Notarius:
-
-- pipeline staging, dependencies, and generated references;
-- application-wide scheduling across providers and backends;
-- module and validation retry policy;
-- checkpoints, resume, and recomputation;
-- durable run artifacts and manifests;
-- D&D prompts, schemas, extractors, validators, and normalizers;
-- Notarius configuration-file parsing and precedence;
-- domain-specific prompt-cache prefix policy; and
-- application-specific redaction, retention, and debug-bundle policy.
-
-PromptKit's complete `Backend` API already supports custom IDs, multiple local
-endpoints, authentication, extra parameters, and explicit queue policies.
-Whether Notarius exposes those capabilities in its own configuration is an
-application-policy decision, not an upstream PromptKit gap.
-
-## Suggested Upstream Sequence
-
-If the PromptKit team chooses to pursue these ideas, the most useful order for
-Notarius would be:
-
-1. Add atomic execution that returns prepared details and the completed result.
-2. Add prompt-independent profile inspection.
-3. Add a semantic execution-target digest, preferably as part of profile
-   inspection.
-4. Add a typed capacity error carrying backend identity.
-
-The first two address concrete workarounds in current Notarius code. The third
-would improve checkpoint correctness and reduce coupling. The fourth is
-operational polish.

docs/roadmap/prepared-execution.md

@@ -1,280 +0,0 @@
-# Executable Preparation Handles
-
-**Status:** Complete.
-
-## Purpose
-
-Allow a consumer to prepare one exact Promptkit execution, inspect and retain
-its credential-redacted public preparation details, and later execute that
-already-prepared work without resolving or rendering the request again.
-
-This provides a supported preflight-before-generation boundary for
-[Weatherreporter](weatherreporter-promptkit-wishlist.md#priority-1-executable-preparation-handles)
-and removes the duplicate `Prepare`-then-`Run` workaround described by
-[Notarius](notarius-promptkit-wishlist.md#priority-1-atomic-execution-with-prepared-details).
-
-## Motivation
-
-`Engine.Prepare` currently returns the provenance and rendered details that
-consumers need for debugging, persistence, and preflight checks. `Engine.Run`
-then performs its own preparation before generation. A consumer that needs
-both values must therefore prepare the same logical request twice.
-
-That workaround duplicates source loading, input hashing, schema work, and
-template rendering. It also permits filesystem-backed prompts, profiles,
-schemas, or inputs to change between the public preparation and the
-preparation that actually produces the result.
-
-Promptkit already owns the complete preparation and execution pipeline. An
-opt-in prepared-execution handle should expose the missing boundary without
-putting rendered content into every `RunResult` or moving persistence policy
-into the library.
-
-## Consumer Workflow
-
-The target public workflow is:
-
-```go
-prepared, err := engine.PrepareExecution(ctx, request)
-if err != nil {
-	// Handle preparation failure.
-	return
-}
-defer prepared.Discard()
-
-details := prepared.Details()
-// Persist or inspect a consumer-selected safe subset of details.
-
-result, err := engine.RunPrepared(ctx, prepared)
-```
-
-The target public surface is:
-
-```go
-type PreparedExecution struct {
-	// Opaque Promptkit-owned state.
-}
-
-func (e *Engine) PrepareExecution(
-	ctx context.Context,
-	req RunRequest,
-) (*PreparedExecution, error)
-
-func (p *PreparedExecution) Details() PreparedRun
-
-func (p *PreparedExecution) Discard()
-
-func (e *Engine) RunPrepared(
-	ctx context.Context,
-	prepared *PreparedExecution,
-) (*RunResult, error)
-```
-
-The declarations and GoDoc will own the exact implemented contract. The
-important public shape is an opaque handle, caller-owned `PreparedRun`
-details, an explicit discard operation, and execution through the engine that
-created the handle.
-
-## Prepared Snapshot
-
-`PrepareExecution` performs complete preparation without model generation or
-backend-capacity admission. It applies the same request validation, source
-precedence, backend and profile resolution, credential requirement checks,
-output-contract resolution, artifact loading, hashing, schema loading,
-session resolution, and rendering behavior as `Prepare`.
-
-A successful handle freezes all source-derived state required for later
-execution, including:
-
-- the selected prompt definition, profile, and backend identity;
-- the complete effective execution target and request-field presence;
-- rendered messages and effective session ID;
-- prompt, rendered-prompt, and input hashes;
-- the effective output contract and provider-facing structured-output
-  constraint; and
-- private validation state sufficient to validate generated output without
-  reopening schema files or `fs.FS` resources, including required schema
-  references.
-
-After `PrepareExecution` succeeds, changes to prompt, profile, schema, input,
-or request-owned data cannot change what `RunPrepared` sends to the model or
-how it validates the generated output.
-
-The handle retains an internal snapshot independent from values returned by
-`Details`. Mutating a returned `PreparedRun`, its maps, slices, messages, or
-schema values does not affect later execution. Each `Details` call returns a
-fresh caller-owned copy under the existing `PreparedRun` ownership and stable
-JSON rules.
-
-## Handle Lifecycle
-
-A `PreparedExecution` is:
-
-- created only by a successful `PrepareExecution` call;
-- bound to the exact `Engine` that created it;
-- valid for one `RunPrepared` invocation;
-- safe for repeated `Details` calls;
-- intentionally opaque and without a supported JSON representation; and
-- in-process state rather than a durable or restartable job.
-
-`RunPrepared` atomically claims a valid handle before beginning the execution
-attempt. A second or concurrent invocation fails without starting another
-execution, including when the first invocation ended in cancellation, capacity
-rejection, generation failure, or operational validation failure. Copies of
-the public handle share the same one-attempt state and cannot bypass this rule.
-
-A nil, zero-value, foreign-engine, discarded, already-claimed, or already-used
-handle is invalid. `RunPrepared` reports these lifecycle errors through the
-ordinary public invalid-request category. A failed foreign-engine invocation
-does not consume a handle that remains valid for its owning engine.
-
-`Discard` idempotently makes an unclaimed handle unavailable for execution and
-drops Promptkit's references to secret-bearing or execution-only state.
-`RunPrepared` performs the same cleanup automatically after claiming a handle.
-Credential-redacted public preparation details remain available after discard,
-success, or failure so consumers can retain diagnostics. Promptkit does not
-promise secure erasure of Go string memory.
-
-Lifecycle transitions are concurrency-safe. When `RunPrepared` and `Discard`
-race, exactly one claims the ready handle. `Discard` is not an execution
-cancellation mechanism and does not interrupt an attempt that has already
-claimed the handle; consumers cancel that attempt through its context.
-
-## Credentials And Sensitive Data
-
-`Details` has the same security contract as `PreparedRun`: it can contain
-rendered messages, schemas, identifiers, and hashes, but never a resolved API
-key value. Consumers remain responsible for selecting, redacting, storing, and
-retaining any persisted preparation material.
-
-A direct `RunRequest.APIKey` is retained only in opaque execution state until
-the handle is run or discarded. It is never added to details, hashes, JSON,
-`String`, or `GoString` output.
-
-An environment-variable name is frozen as part of the effective target, but
-its credential value is not captured for the lifetime of the handle.
-`PrepareExecution` applies the existing preparation-time availability check.
-`RunPrepared` rechecks availability before admission, and the selected model
-client uses the environment value visible during execution. This preserves
-current secret ownership and avoids retaining an environment credential while
-a consumer persists preflight material.
-
-The opaque handle must not expose retained request data or credentials through
-default formatting, JSON, or error messages.
-
-## Admission, Cancellation, And Execution
-
-`PrepareExecution` never reserves backend admission or an active-generation
-permit. Its context governs preparation only; cancellation after it returns
-does not invalidate the handle.
-
-`RunPrepared` uses its own context for credential revalidation, backend
-admission, active-generation waiting, model generation, output validation, and
-any internal repair. Admission occurs when `RunPrepared` begins so a consumer
-cannot occupy bounded capacity while inspecting or persisting preparation
-details.
-
-For a limited backend, the admission lease covers the complete prepared
-execution attempt after admission: generation, validation, internal repair,
-and every success or failure exit. Actual generation continues to use the
-backend's FIFO active-generation permit. Existing capacity error identity,
-cancellation behavior, and release guarantees remain in force.
-
-Because a prepared handle is one-attempt, cancellation or capacity rejection
-does not make it reusable. Retry and backoff policy remains with the consumer,
-which may create a new prepared handle when another attempt is appropriate.
-
-## Results And Failures
-
-On success, `RunPrepared` returns the existing caller-owned `RunResult`. Its
-source-derived provenance must match `Details`, including prompt identity and
-hash, rendered-prompt hash, session ID, selected profile and backend,
-effective target, and input hashes.
-
-`RunResult.StartTime`, `EndTime`, and `Duration` describe the
-`RunPrepared` execution attempt. They exclude preparation time and any delay
-while the consumer retained the handle. Preparation timing remains in
-`PreparedRun`.
-
-Preparation failure returns no handle. After successful preparation,
-`RunPrepared` retains the existing rule that an operational failure returns no
-partial `RunResult`; the consumer already has independent preparation details.
-A completed content-validation failure remains a successful result with
-`ValidationFailed`.
-
-`PrepareExecution` preserves the public error categories of `Prepare`.
-`RunPrepared` preserves applicable invalid-request, credential, capacity,
-generation, validation, collaborator, and cancellation identities without
-reintroducing source-loading or rendering failures from frozen state.
-
-## Compatibility And Existing Workflows
-
-This feature is additive:
-
-- `Prepare` remains the simple preparation-only operation;
-- `Run` remains the simple prepare-and-execute operation with its current
-  early-admission and error-ordering behavior;
-- `PreparedRun` and `RunResult` retain their existing stable JSON
-  representations;
-- model-client and artifact-reader extension interfaces remain unchanged; and
-- backend routing, concurrency limits, queue capacities, and provider wire
-  behavior remain unchanged.
-
-The new workflow may share internal machinery with `Prepare` and `Run`, but it
-must not change their observable behavior merely to simplify implementation.
-
-## Documentation
-
-The completed documentation set has these ownership boundaries:
-
-- exported declarations and GoDoc own the exact handle, method, lifecycle,
-  ownership, concurrency, credential, error, and cancellation contracts;
-- the promptkit consumer guide explains when to use `Prepare`, `Run`, or the
-  two-phase prepared-execution workflow; and
-- internal runner, source-validation, capacity, and model-client documentation
-  describe the implemented collaborator boundaries without duplicating public
-  contracts.
-
-No release document is part of the feature implementation itself. Release
-guidance is prepared only when the resulting public API is selected for
-publication.
-
-## Non-Goals
-
-This work does not include:
-
-- serializable, durable, resumable, or cross-process execution handles;
-- reuse for multiple consumer-initiated executions;
-- concurrent execution of one handle;
-- capacity reservation during preparation;
-- a background task queue, priorities, worker lifecycle, or job status;
-- retry, backoff, or provider failover policy;
-- a separate `RunDetailed` convenience method;
-- adding preparation details or rendered messages to every `RunResult`;
-- prompt or profile inspection APIs;
-- structured capacity or generation errors;
-- freezing environment-variable credential values for the handle lifetime;
-- snapshotting provider state or mutable behavior inside an injected
-  `LLMClient`;
-- allowing target, validation, session, variable, or input overrides after
-  preparation; or
-- changing existing `Prepare`, `Run`, file-format, provider-request, or stable
-  JSON contracts.
-
-## Target End State
-
-After this work:
-
-- consumers can perform and persist preflight before starting provider work;
-- one prepared handle executes exactly the source-derived prompt, target,
-  schema, inputs, session, and messages described by its public details;
-- execution never reloads or rerenders consumer sources;
-- direct credentials remain confined to opaque, explicitly discardable state;
-- environment credentials are not retained across the preflight boundary;
-- backend capacity is reserved only when execution begins;
-- one handle can start at most one execution attempt, including any internal
-  repair calls owned by that attempt;
-- preparation details remain available after execution success or failure;
-- existing simple `Prepare` and `Run` consumers remain unaffected; and
-- Promptkit continues to own reusable execution mechanics without taking on
-  downstream persistence, redaction, retry, or job-management policy.

docs/roadmap/profile-inspection.md

@@ -1,246 +0,0 @@
-# Prompt-Independent Profile Inspection
-
-**Status:** Accepted.
-
-## Purpose
-
-Allow consumers to look up one execution profile by ID and inspect its
-structurally resolved model target without selecting a prompt, supplying
-placeholder inputs, checking credential availability, or invoking a model.
-
-This provides a direct configuration-validation boundary for
-[Notarius](notarius-promptkit-wishlist.md#priority-2-prompt-independent-profile-inspection)
-and
-[Weatherreporter](weatherreporter-promptkit-wishlist.md#priority-3-prompt-independent-profile-inspection).
-
-## Motivation
-
-Both downstream consumers need to reject invalid configured profile IDs before
-starting application work. They currently have to construct a synthetic prompt
-and call `Engine.Prepare` merely to exercise profile loading, backend lookup,
-and execution-target resolution.
-
-That workaround couples profile validation to unrelated prompt definitions,
-fixture inputs, rendering, schema behavior, and current credential
-availability. Promptkit already owns profile precedence, backend membership,
-and target resolution, so it should expose that cohesive capability directly.
-
-## Consumer Workflow
-
-The target public workflow is:
-
-```go
-inspection, err := engine.InspectProfile(ctx, profileID)
-if err != nil {
-	// Reject or report the configured profile.
-	return
-}
-
-target := inspection.EffectiveModelParams
-if target.APIKeyEnv != "" {
-	// Apply application policy for the named environment variable.
-}
-```
-
-The target public surface is:
-
-```go
-type ProfileInspection struct {
-	ProfileID           string
-	EffectiveModelParams ExecutionTarget
-	APIKeyRequired      bool
-}
-
-func (e *Engine) InspectProfile(
-	ctx context.Context,
-	profileID string,
-) (*ProfileInspection, error)
-```
-
-The declarations and GoDoc will own the exact implemented contract. The
-important public shape is exact lookup through the existing engine, one
-caller-owned inspection value, the resolved `ExecutionTarget`, and an explicit
-signal for a direct API-key requirement.
-
-`EffectiveModelParams.BackendID` identifies the selected registered backend
-and remains empty for endpoint-only profiles.
-`EffectiveModelParams.APIKeyEnv` reports the effective credential environment
-variable name. `APIKeyRequired` reports that the profile requires a direct
-request credential instead. These states are mutually exclusive after normal
-profile and backend precedence is applied.
-
-`ProfileInspection` does not need a stable JSON representation. Consumers that
-persist application configuration or diagnostics can select the fields their
-own format requires.
-
-## Lookup And Precedence
-
-`InspectProfile` requires a non-blank explicit profile ID. It trims surrounding
-whitespace and otherwise performs the same case-sensitive exact lookup used by
-ordinary execution.
-
-Lookup applies the engine's normal profile-source precedence:
-
-- programmatic profiles supplied through `WithProfiles`;
-- the configured file, directory, or `fs.FS` profile source; and
-- the built-in profile catalog.
-
-A valid higher-precedence match shadows a lower-precedence profile with the
-same ID. A malformed or unreadable higher-precedence match fails rather than
-silently falling back. The
-[profile format reference](../formats.md#profile-definitions) remains the
-canonical owner of profile-source and file-format behavior.
-
-Inspection never derives a profile ID from a prompt's `default_profile`; the
-caller is inspecting one explicitly named profile.
-
-## Structural Resolution
-
-Inspection loads and validates the selected profile, verifies that a named
-backend exists in the engine's immutable backend registry, and applies normal
-framework-default, backend, and profile precedence to produce the effective
-target.
-
-For the same engine state and profile ID, with no per-run execution override,
-the inspected target must match the target that ordinary preparation would
-resolve before applying request credentials and checking their availability.
-This equivalence must use one shared resolution path rather than a second set
-of precedence rules.
-
-Structural resolution includes:
-
-- backend routing identity;
-- endpoint and model;
-- sampling, token, timeout, service-tier, and reasoning settings;
-- the effective credential environment-variable name or direct-key
-  requirement; and
-- deeply copied provider-specific extra parameters.
-
-Inspection returns the effective target rather than a raw profile definition.
-This keeps framework and backend defaults visible to consumers without
-creating a second public profile-loading interface.
-
-The result does not include request-override presence because no
-`ExecutionTargetOverride` participates in inspection.
-
-## Credentials And Sensitive Data
-
-Inspection reports credential requirements but never resolves, retains, or
-returns a credential value.
-
-The operation does not read the named environment variable and succeeds when
-that variable is absent or blank. It accepts neither a direct API key nor an
-API-key environment override. Consumers decide whether credential availability
-must be enforced during application configuration, while `Prepare`,
-`PrepareExecution`, `Run`, and `RunPrepared` retain their execution-time
-credential contracts.
-
-Error messages, formatting, and returned values must not expose environment
-values or other resolved secrets. Existing restrictions against raw API keys
-in profile sources remain unchanged.
-
-## Ownership, Consistency, And Concurrency
-
-Each successful call returns a caller-owned snapshot. Mutating the returned
-target or any nested extra-parameter map or slice cannot affect the engine,
-later inspection, or later execution.
-
-Inspection is safe to call concurrently under the engine's existing immutable
-registry and repository contracts. It does not mutate profile sources or
-cache a result globally.
-
-For filesystem-backed sources, an inspection describes the state observed by
-that call. It does not freeze the profile for a later `Run`; a source may
-change between operations. Consumers requiring an exact preflight-to-execution
-snapshot should use the existing prepared-execution workflow.
-
-## Errors And Cancellation
-
-The operation uses existing public error categories:
-
-- a blank profile ID matches `ErrInvalidRequest`;
-- an absent exact ID matches `ErrProfileNotFound` and not `ErrProfileLoad`;
-- read, decode, validation, and source-selection failures match
-  `ErrProfileLoad`; and
-- an unknown referenced backend or an invalid structurally resolved target
-  matches `ErrProfileLoad`.
-
-Errors should preserve useful underlying collaborator and context identities
-through `errors.Is` where the existing facade does so, without exposing
-internal package types. Context cancellation governs inspection and no partial
-inspection result is returned on failure.
-
-Missing credential values are not inspection errors. The operation cannot
-return capacity or model-generation failures because it performs neither
-backend admission nor generation.
-
-## Compatibility And Boundaries
-
-This feature is additive. Existing profile formats, source precedence,
-backend registration, `Prepare`, prepared execution, and `Run` behavior remain
-unchanged.
-
-The method belongs on the root `Engine` facade. Profile repositories and the
-backend registry remain internal implementation details, and no new public
-repository interface is introduced.
-
-Inspection does not require prompt lookup, rendering, artifact loading, schema
-loading, validation, backend-capacity admission, or model-client access.
-Engine construction retains its ordinary configuration requirements; this
-feature does not introduce a separate profile-only engine.
-
-## Documentation
-
-The completed documentation set has these ownership boundaries:
-
-- exported declarations and GoDoc own the exact method, result, ownership,
-  credential, error, and cancellation contracts;
-- the promptkit consumer guide explains configuration-time profile inspection
-  and distinguishes it from `Prepare` and prepared execution;
-- the profile format reference continues to own profile fields and source
-  precedence; and
-- internal documentation describes shared profile and target resolution
-  without duplicating public contracts.
-
-## Non-Goals
-
-This work does not include:
-
-- enumerating or searching profiles;
-- returning raw profile definitions or profile source paths;
-- accepting per-run execution overrides, direct API keys, or API-key
-  environment overrides;
-- checking environment-variable contents or other credential availability;
-- semantic execution-target fingerprints or profile hashes;
-- prompt-definition inspection or prompt default-profile resolution;
-- full-corpus validation across every profile source;
-- freezing a filesystem-backed profile for later execution;
-- exposing backend concurrency limits, queue state, or capacity policy;
-- model generation, provider health checks, or endpoint connectivity tests;
-- dynamic backend or profile registration after engine construction; or
-- changing current profile, backend, prepared-execution, or stable JSON
-  contracts.
-
-## Target End State
-
-After this work:
-
-- consumers can validate one configured profile without inventing a prompt or
-  placeholder inputs;
-- lookup observes ordinary programmatic, configured-source, and built-in
-  precedence;
-- a successful result proves that the profile exists, is valid, references a
-  registered backend when applicable, and resolves to a structurally valid
-  effective target;
-- the inspected target matches ordinary preparation for the same profile and
-  engine state before per-run overrides and credential availability checks;
-- credential requirements are visible without reading or exposing credential
-  values;
-- returned targets and nested data are caller-owned;
-- inspection performs no rendering, source loading unrelated to the profile,
-  capacity admission, or model work;
-- existing execution workflows and compatibility contracts remain unchanged;
-  and
-- Promptkit owns reusable profile validation while downstream applications
-  retain configuration policy, persistence, logging, and credential-timing
-  decisions.

docs/roadmap/structured-generation-errors.md

@@ -0,0 +1,71 @@
+# Structured Generation Errors
+
+## Purpose
+
+Promptkit should give downstream applications actionable, machine-readable
+details when the built-in OpenAI-compatible client receives a non-success HTTP
+response. Today the client reports only the status code and discards the
+provider response body. This makes ordinary configuration failures—such as an
+unsupported strict JSON Schema keyword—unnecessarily difficult to diagnose.
+
+## Target End State
+
+Failures from the built-in transport are available through a public typed error
+that works with `errors.As` while continuing to match `ErrLLMGenerate` through
+`errors.Is`. The error should expose:
+
+- the HTTP status code;
+- a normalized provider error code or type when supplied; and
+- a bounded provider message extracted from a recognized OpenAI-compatible
+  JSON error envelope.
+
+The ordinary `Error()` string should remain safe and concise: it should include
+the status and provider code or type, but not automatically include the
+provider message. Consumers that deliberately want the provider's diagnostic
+text can retrieve it from the typed error and apply their own disclosure and
+logging policy.
+
+This contract should be available for both ordinary and prepared execution.
+Errors returned by injected model clients must continue to preserve their own
+identity and should not be converted into fabricated HTTP details.
+
+## Safety And Compatibility Boundaries
+
+- Never expose the raw response body, response headers, endpoint, credentials,
+  request messages, schema document, or generated content through this API.
+- Read only a small fixed maximum response body, reject malformed or
+  unrecognized envelopes, normalize invalid UTF-8 and control characters, and
+  cap every retained diagnostic field independently.
+- Treat the extracted provider message as untrusted and potentially sensitive:
+  its GoDoc must tell consumers not to log or display it without applying their
+  own policy.
+- Preserve the existing generic behavior when a response is empty, non-JSON,
+  oversized, or does not match a recognized error envelope.
+- Do not assign retryability from an HTTP status. Promptkit supplies facts;
+  downstream applications retain retry and presentation policy.
+
+## Recommended API Direction
+
+Prefer one immutable public `GenerationError` value, constructed internally and
+carrying accessors for HTTP status, provider code or type, and provider message.
+This keeps the exact representation evolvable while giving consumers an
+idiomatic `errors.As` contract. Public Go declarations and GoDoc should own the
+final exact names and semantics.
+
+The internal OpenAI-compatible client should parse only the conventional
+top-level `error` envelope and pass normalized details through the use-case and
+public error-mapping layers. The integration documentation should continue to
+own wire behavior; the public declarations should own the consumer contract.
+
+## Acceptance Criteria
+
+- A downstream consumer can distinguish a provider HTTP 400 from other
+  generation failures and obtain a bounded provider explanation when present.
+- The typed error still satisfies `errors.Is(err, ErrLLMGenerate)`.
+- Existing cancellation, capacity, validation, and injected-client error
+  identities remain unchanged.
+- Tests cover recognized string and numeric provider codes, absent and malformed
+  envelopes, oversized bodies and fields, control characters, and error-chain
+  behavior without making live provider requests.
+- Current-state GoDoc and the OpenAI-compatible integration and internal-client
+  documents are updated only when the implementation lands.

docs/roadmap/weatherreporter-promptkit-wishlist.md

@@ -1,468 +0,0 @@
-# Weatherreporter PromptKit Wishlist
-
-## Purpose
-
-This document records features and interface changes that would be useful
-additions to PromptKit from the perspective of the maintainers of
-Weatherreporter, a downstream application planning to replace its Scriptorium
-CLI integration with PromptKit.
-
-PromptKit v0.3.0 provides the capabilities Weatherreporter needs for the
-migration. None of the ideas below is a hard adoption requirement. They are
-opportunities to avoid duplicate preparation, validate configuration earlier,
-improve durable failure diagnostics, and make the integration more direct.
-
-The examples are API sketches intended to communicate the desired capability,
-not prescriptive names or finalized Go contracts. The related
-[Notarius PromptKit wishlist](notarius-promptkit-wishlist.md) proposes several
-overlapping features from another downstream consumer's perspective.
-
-## Priority 1: Executable Preparation Handles
-
-**Disposition:** Accepted into the
-[executable preparation handles](prepared-execution.md) feature roadmap.
-
-### Downstream need
-
-Weatherreporter treats prompt preparation as a durable preflight boundary. It
-needs to:
-
-1. prepare the exact request that will be executed;
-2. persist a safe preparation record before starting the provider call; and
-3. execute without reloading or rerendering prompt, profile, schema, or input
-   sources.
-
-Persisting preflight before generation leaves useful evidence when a provider
-call fails or the process is interrupted during generation.
-
-### Current integration option
-
-With PromptKit v0.3.0, Weatherreporter can call `Engine.Prepare`, save selected
-fields from the returned `PreparedRun`, and then call `Engine.Run` with the
-same request. Because `Run` performs preparation internally, the work is
-repeated.
-
-Weatherreporter plans to use embedded prompt and schema files plus immutable
-inline input bytes, which removes most of the consistency risk. An external
-profile file or directory can still change between the two calls, and the
-second preparation remains unnecessary work.
-
-The atomic `RunDetailed` operation proposed by the
-[Notarius wishlist](notarius-promptkit-wishlist.md#priority-1-atomic-execution-with-prepared-details)
-would guarantee that returned preparation details describe the completed
-execution. However, returning those details only after generation would not
-preserve Weatherreporter's preflight-before-generation persistence boundary.
-
-### Requested capability
-
-Add an opt-in two-phase API that returns a prepared execution handle:
-
-```go
-prepared, err := engine.PrepareExecution(ctx, request)
-if err != nil {
-	// Handle preparation failure.
-}
-
-details := prepared.Details()
-// Persist a consumer-selected safe preparation record.
-
-result, err := engine.RunPrepared(ctx, prepared)
-```
-
-The exact names and shapes are flexible. The important contract is that
-`RunPrepared` executes the already prepared prompt and does not reload or
-rerender its prompt, profile, schema, or input sources.
-
-`Details` should return the same caller-owned public preparation information
-currently represented by `PreparedRun`. The execution handle may retain opaque
-engine-owned state needed to invoke the model and validate the response.
-
-### Design considerations
-
-- Keep `Prepare` and `Run` available for consumers that do not need a
-  two-phase execution boundary.
-- Bind a prepared handle to the engine that constructed it.
-- Define whether a handle is one-shot, reusable, or safe for concurrent use.
-  A one-shot contract may be the safest initial design.
-- Do not give the opaque handle a stable JSON representation.
-- Do not expose or serialize resolved credential values through `Details`.
-- Define how a direct request API key is retained and released when an opaque
-  handle must carry it until execution.
-- Preserve caller-owned copies for all public details.
-- Make context cancellation and backend admission timing explicit.
-- Document whether profile credential environment values are resolved during
-  preparation or execution.
-- Ensure an execution error does not invalidate the public details already
-  returned to the consumer.
-- Consider whether an atomic `RunDetailed` can share the same internal
-  prepared-execution implementation.
-
-### Value to Weatherreporter
-
-This is the highest-value upstream addition. It would preserve
-Weatherreporter's durable preflight behavior, remove duplicate work, eliminate
-the remaining source-consistency window, and ensure that persisted provenance
-describes the actual execution.
-
-## Priority 2: Prompt-Definition Inspection
-
-**Disposition:** Accepted into the
-[future catalog](future.md#prompt-definition-inspection).
-
-### Downstream need
-
-Weatherreporter has a fixed registry of seven report definitions. Each report
-selects a prompt ID and one of two output workflows:
-
-- direct Markdown; or
-- structured generated text followed by application-owned domain validation
-  and Markdown template rendering.
-
-Weatherreporter will embed the PromptKit prompt definitions and private
-response schemas that implement those reports. It needs to validate that the
-report registry and embedded prompt corpus agree before weather collection or
-provider execution.
-
-### Current integration option
-
-Weatherreporter can maintain synthetic data-package fixtures and call
-`Engine.Prepare` for every report prompt during tests. Runtime validation can
-also occur through the ordinary per-report preparation stage.
-
-This works, but it requires complete placeholder inputs and profile resolution
-when the application primarily wants to inspect prompt identity and declared
-contracts.
-
-### Requested capability
-
-Add exact prompt-definition lookup without rendering or generation:
-
-```go
-type PromptInfo struct {
-	PromptID         string
-	PromptVersion    string
-	PromptHash       string
-	DefaultProfileID string
-	Inputs           []InputDefinition
-	OutputContract   OutputContract
-}
-
-func (e *Engine) ResolvePrompt(
-	ctx context.Context,
-	promptID string,
-	promptVersion string,
-) (PromptInfo, error)
-```
-
-The exact returned shape may differ. Weatherreporter needs enough information
-to verify prompt existence, version selection, declared inputs, default
-profile identity, output format, validation mode, and schema selection without
-supplying synthetic prompt input.
-
-### Design considerations
-
-- Use ordinary PromptKit prompt-source precedence and exact ID/version
-  selection.
-- Fully load and structurally validate the selected prompt definition.
-- Validate referenced prompt content files without rendering their templates.
-- Resolve and validate the selected output contract and schema reference where
-  practical.
-- Return an opaque prompt-definition equality value rather than raw source
-  bytes.
-- Do not return rendered messages, schema bodies, profile credentials, or
-  another source of sensitive content.
-- Preserve typed or sentinel errors for missing and invalid prompts.
-- Return caller-owned values.
-- Enumeration of all known prompts is not required for Weatherreporter; exact
-  lookup is sufficient.
-
-### Value to Weatherreporter
-
-This would let Weatherreporter directly verify that every report prompt
-exists, requires the curated `data_package` input, and declares the expected
-Markdown or JSON Schema output contract. It would reduce synthetic test setup
-and move failures ahead of weather collection.
-
-## Priority 3: Prompt-Independent Profile Inspection
-
-**Disposition:** Covered by the accepted
-[prompt-independent profile inspection](profile-inspection.md) roadmap.
-
-### Downstream need
-
-Weatherreporter will allow operators to select an external PromptKit profile
-source and may allow an explicit profile override. It should reject a missing
-profile, unknown backend, malformed execution target, or unsatisfied credential
-requirement before collecting weather data or writing report artifacts.
-
-### Current integration option
-
-Weatherreporter can validate an explicit profile by preparing one embedded
-prompt with fixture input. Prompts that use their own default profiles can be
-validated during their normal preparation stage.
-
-This couples configuration validation to one prompt and requires placeholder
-input even when only profile and backend resolution are relevant.
-
-### Requested capability
-
-The prompt-independent `ResolveProfile` API proposed by the
-[Notarius wishlist](notarius-promptkit-wishlist.md#priority-2-prompt-independent-profile-inspection)
-would satisfy this need. It should resolve built-in, file-backed, and
-programmatic profiles, validate backend membership, report credential
-requirements without resolving credential values, and preserve typed error
-classification.
-
-### Additional Weatherreporter considerations
-
-- An explicit application profile override should be inspectable without
-  selecting a report prompt.
-- A prompt-definition inspection result may expose its default profile ID so
-  Weatherreporter can inspect that profile separately.
-- Inspection should distinguish structural profile validity from current
-  credential availability so configuration validation can apply explicit
-  application policy.
-- An optional execution-target override should be considered only if it
-  describes the same target that a later run will use.
-
-### Value to Weatherreporter
-
-This would improve fail-fast configuration validation and give operator-facing
-errors direct profile and backend context. It is valuable but not required for
-the initial migration.
-
-## Priority 4: Eager Source Validation
-
-**Disposition:** Deferred until prompt and profile inspection have been used
-to determine whether a broader engine-wide validation operation is still
-needed.
-
-### Downstream need
-
-PromptKit deliberately defers reading and validating filesystem and `fs.FS`
-prompt, profile, and schema content until a request needs it. Weatherreporter
-has a small fixed embedded prompt corpus and one optional external profile
-source. It would benefit from an explicit offline validation operation for
-tests, startup diagnostics, and configuration checks.
-
-### Current integration option
-
-Weatherreporter can prepare every report prompt with fixture inputs and inspect
-any explicit profiles individually. That provides strong coverage but requires
-consumer-maintained traversal and synthetic material.
-
-### Requested capability
-
-Consider an opt-in source-validation operation:
-
-```go
-type SourceValidationOptions struct {
-	RequireCredentials bool
-}
-
-func (e *Engine) ValidateSources(
-	ctx context.Context,
-	opts SourceValidationOptions,
-) error
-```
-
-The operation should eagerly discover and structurally validate the configured
-prompt, profile, and schema sources without model generation.
-
-### Design considerations
-
-- Keep deferred validation as the normal `NewEngine` behavior.
-- Make eager validation an explicit consumer choice.
-- Validate duplicate IDs and versions, strict YAML decoding, referenced content
-  files, profile/backend membership, schema syntax, and schema references.
-- Distinguish structural credential declarations from current environment
-  availability.
-- Do not read or expose credential values when credential availability is not
-  requested.
-- Preserve source-specific public error identities and useful path context.
-- Respect context cancellation during filesystem discovery and schema work.
-- Consider whether exact prompt and profile inspection APIs already provide a
-  smaller sufficient surface before adding an engine-wide operation.
-
-### Value to Weatherreporter
-
-This would simplify offline corpus checks and catch malformed operator profile
-sources before report work begins. It is helpful but lower priority than exact
-prompt and profile inspection.
-
-## Priority 5: Structured Generation Errors
-
-**Disposition:** Deferred pending stronger downstream demand and a narrower
-design that does not duplicate prepared provenance or impose HTTP-specific
-fields on injected model clients.
-
-### Downstream need
-
-Weatherreporter preserves redacted, inspectable failure receipts for report
-runs. When model generation fails operationally, it needs to classify the
-failure and retain safe execution context without parsing error prose.
-
-Prompt preparation already supplies selected profile, backend, and model
-identity. Provider status classification would add useful operator context,
-especially when the built-in OpenAI-compatible client receives a non-success
-HTTP status.
-
-### Current integration option
-
-PromptKit exposes `ErrLLMGenerate` and preserves injected client errors through
-`errors.Is`. Weatherreporter can reliably classify generation failure and use
-its preparation record for profile, backend, and model provenance. Any further
-diagnostic detail remains a redacted error string.
-
-### Requested capability
-
-Consider a typed generation error that continues to match `ErrLLMGenerate`:
-
-```go
-type GenerationError struct {
-	BackendID string
-	Model     string
-	StatusCode int
-}
-```
-
-The exact fields may differ. The useful contract is safe structured context
-available through `errors.As`, while `errors.Is(err, ErrLLMGenerate)` remains
-compatible.
-
-### Design considerations
-
-- Include only fields that PromptKit knows reliably and can expose safely.
-- Treat an HTTP status as optional because injected model clients may not use
-  HTTP.
-- Do not expose provider response bodies, endpoints, credential environment
-  names, credential values, request content, or generated content.
-- Do not make a structured error a second source of prompt/profile provenance
-  already present in a prepared execution.
-- Preserve injected client error identity.
-- Keep retry and backoff policy with the consuming application.
-
-### Value to Weatherreporter
-
-This would improve durable failure receipts and troubleshooting, particularly
-for built-in transport failures. It is not required if preparation details and
-the existing sentinel remain available.
-
-## Lower-Priority Shared Wishlist Items
-
-### Structured Capacity Errors
-
-**Disposition:** Accepted into the
-[future catalog](future.md#structured-capacity-errors).
-
-The typed capacity error proposed by the
-[Notarius wishlist](notarius-promptkit-wishlist.md#priority-4-structured-capacity-errors)
-would improve Weatherreporter diagnostics by exposing the stable backend ID
-without parsing error text.
-
-Weatherreporter currently generates batch reports sequentially and constructs
-one engine per invocation, so engine-local capacity exhaustion is unlikely in
-the initial design. The feature would become more valuable if report
-generation later becomes concurrent or PromptKit engines become longer-lived.
-It should not block adoption.
-
-### Semantic Execution-Target Fingerprints
-
-**Disposition:** Deferred until prompt-independent profile inspection defines
-the resolved target whose configuration identity would be fingerprinted.
-
-The semantic target digest proposed by the
-[Notarius wishlist](notarius-promptkit-wishlist.md#priority-3-semantic-execution-target-fingerprints)
-would provide a compact equality signal for audit metadata.
-
-Weatherreporter does not currently reuse LLM-dependent checkpoints. Its Recent
-Changes behavior compares deterministic module snapshots rather than generated
-reports, so the digest has no immediate cache-correctness role. Existing
-PromptKit result metadata is sufficient for the initial integration. A digest
-would still be useful provenance and future-proofing, but it is not a
-migration priority.
-
-## Capabilities PromptKit Already Provides Well
-
-PromptKit v0.3.0 already provides the essential Weatherreporter integration
-surface:
-
-- importable in-process engine construction;
-- filesystem, `fs.FS`, and programmatic prompt, profile, and schema sources;
-- offline preparation without model execution;
-- versioned prompt selection;
-- text, Markdown, JSON, and JSON Schema output contracts;
-- single-pass output validation with raw output retained after completed
-  validation failure;
-- inline input artifacts with provenance URIs and input hashes;
-- selected profile, backend, model, effective target, prompt hashes, timing,
-  and token-usage provenance;
-- endpoint-only profiles and engine-scoped backend registration;
-- injected model-client and artifact-reader interfaces;
-- caller cancellation, generation timeout, and transport timeout behavior; and
-- public error sentinels for configuration, prompt, profile, artifact,
-  validation, capacity, and generation failures.
-
-These capabilities are sufficient for Weatherreporter to adopt PromptKit
-without waiting for new upstream work.
-
-## Responsibilities That Should Remain In Weatherreporter
-
-The following concerns belong to Weatherreporter and should not move into
-PromptKit:
-
-- report definitions, valid periods, batches, and output naming;
-- application prompt content and private report response schemas;
-- deterministic weather facts, modules, and Recent Changes;
-- curated `data_package` construction and persistence;
-- generated-text domain validation and Markdown template rendering;
-- managed artifact paths, atomic writes, metadata, and inspection commands;
-- preparation, execution, raw-output, and failure-receipt schemas;
-- CLI configuration loading and precedence;
-- debug enablement, redaction, placement, sensitivity, and retention;
-- distributor notification;
-- batch continuation and any future retry policy; and
-- application-level compatibility and migration policy.
-
-## Suggested Upstream Sequence
-
-If the PromptKit team chooses to pursue these ideas, the most useful order for
-Weatherreporter would be:
-
-1. Add executable preparation handles, ideally sharing implementation with an
-   atomic detailed-run API.
-2. Add prompt-definition inspection.
-3. Add prompt-independent profile inspection.
-4. Consider eager source validation after evaluating whether the two exact
-   inspection APIs are sufficient.
-5. Add structured generation errors.
-6. Add structured capacity errors and semantic execution-target fingerprints
-   as lower-priority operational improvements.
-
-The first item removes the only material integration workaround. Prompt and
-profile inspection improve fail-fast validation. The remaining items improve
-ergonomics and diagnostics.
-
-## Adoption Sequencing
-
-Weatherreporter should not wait for the complete wishlist. PromptKit v0.3.0 is
-already sufficient when Weatherreporter:
-
-- embeds immutable prompt and schema assets;
-- supplies immutable inline data-package bytes;
-- constructs one engine per CLI invocation;
-- calls `Prepare` and `Run` with the same request; and
-- keeps PromptKit behind a weatherreporter-owned adapter contract.
-
-If executable preparation handles are scheduled for a near-term PromptKit
-release, Weatherreporter may defer only its final adapter implementation to
-avoid implementing and then removing duplicate preparation. Prompt corpus
-retrieval, application-contract design, configuration work, embedded assets,
-state contracts, and offline fixtures can proceed independently.
-
-If the feature is not scheduled, Weatherreporter can adopt v0.3.0 and keep the
-duplicate `Prepare` and `Run` sequence inside its adapter. A later PromptKit
-upgrade would remain localized behind that neutral boundary.
-
-Prompt inspection, profile inspection, source validation, structured errors,
-capacity details, and semantic fingerprints should not gate adoption.

engine.go

@@ -65,8 +65,8 @@ var (
 	ErrPromptRender = errors.New("failed to render prompt")
 	// ErrCapacityExceeded identifies a Run or RunPrepared rejected because the
 	// selected backend already admitted ConcurrencyLimit + QueueCapacity calls.
-	// It is not an invalid request, an LLM or provider rate-limit response, or
-	// ErrLLMGenerate.
+	// 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. Errors returned by an injected LLMClient remain available
@@ -78,14 +78,15 @@ var (
 	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.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.
+// 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
 }
@@ -97,9 +98,10 @@ type Config struct {
 	// It is required unless a WithPromptFS or WithPromptFile option supplies the
 	// prompt source.
 	PromptDir string
-	// ProfileDir is an optional directory whose profiles take precedence over
-	// embedded built-in profiles. An empty value selects only built-ins unless
-	// profile options are also supplied.
+	// ProfileDir is an optional ordinary configured source whose profiles take
+	// precedence over application fallback and embedded built-in profiles. An
+	// empty value selects the lower-precedence sources unless a profile-source
+	// option supplies the ordinary source.
 	ProfileDir string
 	// SchemaDir is the root for JSON Schema files. An empty value uses the
 	// current directory. WithSchemaFS or WithSchemaFile replaces this source.
@@ -118,12 +120,12 @@ type Config struct {
 // Option customizes engine construction.
 //
 // NewEngine applies options in argument order and ignores nil options. Within
-// each prompt-source, 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.
+// 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
 }
@@ -139,11 +141,13 @@ type engineOptions struct {
 	artifactReader        artifactadapter.Reader
 	promptDefs            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
@@ -215,7 +219,7 @@ func WithPromptFile(path string) Option {
 		if err != nil {
 			return err
 		}
-		options.promptDefs = promptdef.NewFSRepository(fsys, root)
+		options.promptDefs = promptdef.NewFileRepository(fsys, root, filepath.Dir(path))
 		options.promptSource = true
 		return nil
 	})
@@ -223,12 +227,12 @@ func WithPromptFile(path string) Option {
 
 // 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.
-// 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.
+// 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 {
@@ -245,11 +249,12 @@ func WithProfileFS(fsys fs.FS, root string) Option {
 
 // 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. 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.
+// 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)
@@ -262,8 +267,41 @@ func WithProfileFile(path string) Option {
 	})
 }
 
+// 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 embedded built-in
+// 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 {
+		if fsys == nil {
+			return ErrInvalidConfig
+		}
+		if strings.TrimSpace(root) == "" {
+			return ErrInvalidConfig
+		}
+		options.fallbackProfiles = profile.NewFSRepository(fsys, root)
+		options.fallbackProfileSource = true
+		return nil
+	})
+}
+
 // 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 validates and copies every profile. IDs must be unique within one
 // call. An invalid profile, duplicate ID, or unsupported ExtraParams value
@@ -349,13 +387,7 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 		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)
-	}
+	profiles := newProfileRepository(cfg.ProfileDir, options)
 
 	backendRegistry, err := backend.NewRegistry(options.backends)
 	if err != nil {
@@ -408,26 +440,132 @@ func NewEngine(cfg Config, opts ...Option) (*Engine, error) {
 	}, nil
 }
 
+func newProfileRepository(profileDir string, options engineOptions) profile.Repository {
+	repository := builtin.NewRepository()
+
+	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 repository
+}
+
 func fileSource(name string) (fs.FS, string, error) {
-	cleanName := strings.TrimSpace(name)
-	if cleanName == "" {
+	if strings.TrimSpace(name) == "" {
 		return nil, "", ErrInvalidConfig
 	}
-	dir := filepath.Dir(cleanName)
-	base := filepath.Base(cleanName)
-	if base == "." || base == string(filepath.Separator) || strings.TrimSpace(base) == "" {
+	dir := filepath.Dir(name)
+	base := filepath.Base(name)
+	if base == "." || base == string(filepath.Separator) {
 		return nil, "", ErrInvalidConfig
 	}
-	info, err := os.Stat(cleanName)
+	info, err := os.Stat(name)
 	if err != nil {
-		return nil, "", fmt.Errorf("%w: failed to access source file %q: %v", ErrInvalidConfig, cleanName, err)
+		return nil, "", fmt.Errorf("%w: failed to access source file %q: %v", ErrInvalidConfig, name, err)
 	}
 	if info.IsDir() {
-		return nil, "", fmt.Errorf("%w: source path %q must be a file", ErrInvalidConfig, cleanName)
+		return nil, "", fmt.Errorf("%w: source path %q must be a file", ErrInvalidConfig, name)
 	}
 	return os.DirFS(dir), filepath.ToSlash(base), nil
 }
 
+// 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.runner == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	inspection, err := e.runner.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.runner == nil {
+		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)
+	}
+
+	inspection, err := e.runner.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.
 //
 // Prepare selects the prompt and profile, resolves any selected backend and
@@ -504,9 +642,10 @@ func (e *Engine) PrepareExecution(ctx context.Context, req RunRequest) (*Prepare
 // single-pass even when OutputContract.RepairAttempts is positive.
 //
 // Run can return every error category documented by [Engine.Prepare], plus
-// ErrCapacityExceeded and ErrLLMGenerate. ErrCapacityExceeded identifies
-// rejection before artifacts, schemas, rendering, or model generation because
-// the selected backend's admission capacity is full; it does not match
+// ErrCapacityExceeded and ErrLLMGenerate. 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. Errors from injected clients remain
 // available through errors.Is. Cancellation while waiting for model-generation
 // capacity matches both ErrLLMGenerate and the context error. Cancellation
@@ -547,9 +686,11 @@ func (e *Engine) Run(ctx context.Context, req RunRequest) (*RunResult, error) {
 //
 // RunPrepared can return ErrInvalidRequest, ErrAPIKeyEnvMissing,
 // ErrCapacityExceeded, ErrLLMGenerate, or ErrValidation as applicable while
-// preserving documented collaborator and context identities. A completed
-// content-validation rejection is returned in RunResult, not as an
-// operational error. An operational error returns no partial RunResult.
+// preserving documented collaborator and context identities. An engine
+// admission rejection is discoverable as [CapacityError] and still matches
+// ErrCapacityExceeded. A completed content-validation rejection is returned
+// in RunResult, not as an operational error. An operational error returns no
+// partial RunResult.
 func (e *Engine) RunPrepared(ctx context.Context, prepared *PreparedExecution) (*RunResult, error) {
 	if e == nil || e.runner == nil {
 		return nil, fmt.Errorf("%w: engine is nil", ErrInvalidConfig)

errors.go

@@ -3,6 +3,7 @@ package promptkit
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
 	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
@@ -14,6 +15,11 @@ 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}
+	}
 	publicErr := publicErrorFor(err)
 	if publicErr == nil {
 		return err

errors_internal_test.go

@@ -20,3 +20,31 @@ func TestMapPublicErrorPreservesGenerationCancellation(t *testing.T) {
 		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)
+	}
+}

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) {
-	reader := NewCompositeReader()
-	ctx := context.Background()
-
-	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)
-		}
-	})
-
-	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)
-		}
-	})
-
-	t.Run("unsupported ref type", func(t *testing.T) {
-		ref := domain.ArtifactRef{
+func TestCompositeReaderRejectsUnsupportedReferences(t *testing.T) {
+	_, err := NewCompositeReader().Read(context.Background(), 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")
+		t.Fatalf("expected ErrUnsupportedRefType, got %v", err)
+	}
+}
+
+func TestCompositeReaderSourceParityAndOpaqueHashes(t *testing.T) {
+	reader := NewCompositeReader()
+	hashes := make(map[string]string)
+	tests := []struct {
+		name    string
+		content string
+	}{
+		{name: "empty", content: ""},
+		{name: "ordinary", content: "same content"},
+		{name: "changed", content: "changed content"},
+	}
+
+	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)
+			}
+
+			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,
+				},
+			}
+
+			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) {
+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}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
 			ctx, cancel := context.WithCancel(context.Background())
 			cancel()
 
-	_, err := NewCompositeReader().Read(ctx, domain.ArtifactRef{
-		Type: domain.ArtifactRefInline,
-		Body: "ignored",
+			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)
+			}
 		})
-	if !errors.Is(err, context.Canceled) {
-		t.Fatalf("expected context cancellation, got %v", 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

@@ -5,7 +5,6 @@ package backend
 import (
 	"errors"
 	"fmt"
-	"net/url"
 	"regexp"
 	"sort"
 	"strings"
@@ -109,10 +108,11 @@ func (r *Registry) CapacityPolicies() map[string]domain.BackendCapacityPolicy {
 }
 
 func normalizeBackend(definition domain.Backend) (domain.Backend, error) {
-	definition.Endpoint = strings.TrimSpace(definition.Endpoint)
-	if err := validateEndpoint(definition.Endpoint); err != nil {
+	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) {
@@ -182,31 +182,3 @@ func normalizeBackend(definition domain.Backend) (domain.Backend, error) {
 	definition.ExtraParams = extraParams
 	return definition, nil
 }
-
-func validateEndpoint(endpoint string) error {
-	if endpoint == "" {
-		return errors.New("must not be blank")
-	}
-	if strings.Contains(endpoint, "#") {
-		return errors.New("must not contain a fragment")
-	}
-
-	parsed, err := url.Parse(endpoint)
-	if err != nil {
-		return fmt.Errorf("must be a valid URL: %w", err)
-	}
-	scheme := strings.ToLower(parsed.Scheme)
-	if scheme != "http" && scheme != "https" {
-		return errors.New("must use http or https")
-	}
-	if !parsed.IsAbs() || parsed.Hostname() == "" {
-		return errors.New("must be absolute and include a host")
-	}
-	if parsed.User != nil {
-		return errors.New("must not contain user information")
-	}
-	if parsed.RawQuery != "" || parsed.ForceQuery {
-		return errors.New("must not contain a query string")
-	}
-	return nil
-}

internal/capacity/manager_test.go

@@ -124,6 +124,11 @@ func TestManagerAdmissionHonorsContextAndUnlimitedBackends(t *testing.T) {
 	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()

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
 )
 
 func ExecutionTargetDefault() domain.ExecutionTarget {
 	return domain.ExecutionTarget{
-		Temperature:    ExecutionDefaultTemperature,
-		MaxTokens:      ExecutionDefaultMaxTokens,
-		TopP:           ExecutionDefaultTopP,
 		TimeoutSeconds: ExecutionDefaultTimeoutSeconds,
 	}
 }

internal/domain/domain.go

@@ -97,22 +97,22 @@ 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"`
-	SelectedBackendID    string                  `json:"selected_backend_id,omitempty"`
-	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.
@@ -145,6 +145,16 @@ 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"`
@@ -236,6 +246,13 @@ 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"`

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/output_contract.go

@@ -0,0 +1,30 @@
+package domain
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// 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")
+	}
+	return nil
+}

internal/domain/output_contract_test.go

@@ -0,0 +1,68 @@
+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.RepairAttempts = -1 }, wantErr: "repair_attempts"},
+		{name: "zero repair attempts", change: func(c *OutputContract) { c.RepairAttempts = 0 }},
+		{name: "positive repair attempts", change: func(c *OutputContract) { c.RepairAttempts = 1 }},
+		{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/session.go

@@ -8,6 +8,9 @@ import (
 
 // 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

internal/domain/session_test.go

@@ -10,7 +10,7 @@ func TestNormalizeSessionID(t *testing.T) {
 		name            string
 		raw             string
 		want            string
-		wantErr bool
+		wantErrContains string
 	}{
 		{
 			name: "trims surrounding Unicode whitespace",
@@ -30,19 +30,22 @@ func TestNormalizeSessionID(t *testing.T) {
 		{
 			name:            "one Unicode code point over maximum is rejected",
 			raw:             strings.Repeat("界", SessionIDMaxLength+1),
-			wantErr: true,
+			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.wantErr {
+			if tt.wantErrContains != "" {
 				if err == nil {
 					t.Fatal("expected normalization error")
 				}
-				if !strings.Contains(err.Error(), "exceeds maximum") {
-					t.Fatalf("expected useful length diagnostic, got %v", err)
+				if !strings.Contains(err.Error(), tt.wantErrContains) {
+					t.Fatalf("expected diagnostic containing %q, got %v", tt.wantErrContains, err)
 				}
 				return
 			}

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/jsonvalue/jsonvalue.go

@@ -1,5 +1,5 @@
-// Package jsonvalue validates and defensively copies JSON-compatible value
-// trees used by configuration, request, and prepared-state boundaries.
+// Package jsonvalue validates and defensively copies bounded JSON-compatible
+// value trees used by configuration, request, and prepared-state boundaries.
 package jsonvalue
 
 import (
@@ -8,29 +8,39 @@ import (
 	"math"
 	"reflect"
 	"sort"
-	"strconv"
 )
 
-const maxSafeJSONInteger = 1<<53 - 1
+const (
+	maxContainerDepth = 100
+	maxProducedNodes  = 100_000
+)
 
 type visit struct {
 	typ reflect.Type
 	ptr uintptr
 }
 
+type traversalState struct {
+	active        map[visit]struct{}
+	producedNodes int
+}
+
 // Copy validates and deeply copies a JSON-compatible value while preserving
-// compatible concrete map, slice, array, scalar, and number types.
+// compatible concrete map, slice, array, scalar, and number types. It rejects
+// cycles and values that exceed the package's traversal limits.
 func Copy(src any) (any, error) {
-	return copyValue(reflect.ValueOf(src), "value", make(map[visit]struct{}), true)
+	return copyValue(reflect.ValueOf(src), "value", newTraversalState(), true, 0)
 }
 
 // CopyMap validates and deeply copies an extra-parameter map while preserving
-// compatible concrete map, slice, array, scalar, and number types.
+// compatible concrete map, slice, array, scalar, and number types. It rejects
+// empty object keys, cycles, and values that exceed the package's traversal
+// limits.
 func CopyMap(src map[string]any) (map[string]any, error) {
 	if src == nil {
 		return nil, nil
 	}
-	copied, err := copyValue(reflect.ValueOf(src), "extra_params", make(map[visit]struct{}), false)
+	copied, err := copyValue(reflect.ValueOf(src), "extra_params", newTraversalState(), false, 0)
 	if err != nil {
 		return nil, err
 	}
@@ -44,71 +54,90 @@ func CopyMap(src map[string]any) (map[string]any, error) {
 func copyValue(
 	value reflect.Value,
 	path string,
-	seen map[visit]struct{},
+	state *traversalState,
 	allowEmptyMapKeys bool,
+	containerDepth int,
 ) (any, error) {
-	if !value.IsValid() {
+	resolved, cleanup, isNull, err := state.resolveIndirection(value, path)
+	if err != nil {
+		return nil, err
+	}
+	defer cleanup()
+	if isNull {
+		if err := state.produceNode(path); err != nil {
+			return nil, err
+		}
 		return nil, nil
 	}
-	if value.Kind() == reflect.Interface {
-		if value.IsNil() {
-			return nil, nil
-		}
-		return copyValue(value.Elem(), path, seen, allowEmptyMapKeys)
-	}
+	value = resolved
 	if !value.CanInterface() {
 		return nil, fmt.Errorf("%s: value cannot be copied", path)
 	}
 	if number, ok := value.Interface().(json.Number); ok {
-		if _, err := json.Marshal(number); err != nil {
+		if !validJSONNumber(number) {
 			return nil, fmt.Errorf("%s: invalid JSON number", path)
 		}
-		f, err := strconv.ParseFloat(number.String(), 64)
-		if err != nil || math.IsNaN(f) || math.IsInf(f, 0) {
-			return nil, fmt.Errorf("%s: invalid JSON number", path)
+		if err := state.produceNode(path); err != nil {
+			return nil, err
 		}
 		return number, nil
 	}
 
 	switch value.Kind() {
 	case reflect.Bool, reflect.String:
+		if err := state.produceNode(path); err != nil {
+			return nil, err
+		}
 		return value.Interface(), nil
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		if value.Int() < -maxSafeJSONInteger || value.Int() > maxSafeJSONInteger {
-			return nil, fmt.Errorf("%s: integer is outside the JSON-safe range", path)
+		if err := state.produceNode(path); err != nil {
+			return nil, err
 		}
 		return value.Interface(), nil
 	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		if value.Uint() > maxSafeJSONInteger {
-			return nil, fmt.Errorf("%s: integer is outside the JSON-safe range", path)
+		if err := state.produceNode(path); err != nil {
+			return nil, err
 		}
 		return value.Interface(), nil
 	case reflect.Float32, reflect.Float64:
-		number := value.Convert(reflect.TypeOf(float64(0))).Float()
+		number := value.Float()
 		if math.IsNaN(number) || math.IsInf(number, 0) {
 			return nil, fmt.Errorf("%s: floating-point value must be finite", path)
 		}
+		if err := state.produceNode(path); err != nil {
+			return nil, err
+		}
 		return value.Interface(), nil
-	case reflect.Pointer:
+	case reflect.Map:
 		if value.IsNil() {
+			if err := state.produceNode(path); err != nil {
+				return nil, err
+			}
 			return nil, nil
 		}
-		current := visit{typ: value.Type(), ptr: value.Pointer()}
-		if _, ok := seen[current]; ok {
-			return nil, fmt.Errorf("%s: cyclic value is not supported", path)
+		nextDepth, err := state.enterContainer(path, containerDepth)
+		if err != nil {
+			return nil, err
 		}
-		seen[current] = struct{}{}
-		defer delete(seen, current)
-		return copyValue(value.Elem(), path, seen, allowEmptyMapKeys)
-	case reflect.Map:
-		return copyMapValue(value, path, seen, allowEmptyMapKeys)
+		return copyMapValue(value, path, state, allowEmptyMapKeys, nextDepth)
 	case reflect.Slice:
 		if value.IsNil() {
+			if err := state.produceNode(path); err != nil {
+				return nil, err
+			}
 			return nil, nil
 		}
-		return copySequenceValue(value, path, seen, allowEmptyMapKeys)
+		nextDepth, err := state.enterContainer(path, containerDepth)
+		if err != nil {
+			return nil, err
+		}
+		return copySequenceValue(value, path, state, allowEmptyMapKeys, nextDepth)
 	case reflect.Array:
-		return copySequenceValue(value, path, seen, allowEmptyMapKeys)
+		nextDepth, err := state.enterContainer(path, containerDepth)
+		if err != nil {
+			return nil, err
+		}
+		return copySequenceValue(value, path, state, allowEmptyMapKeys, nextDepth)
 	default:
 		return nil, fmt.Errorf("%s: unsupported JSON value type %s", path, value.Type())
 	}
@@ -117,22 +146,26 @@ func copyValue(
 func copyMapValue(
 	value reflect.Value,
 	path string,
-	seen map[visit]struct{},
+	state *traversalState,
 	allowEmptyMapKeys bool,
+	containerDepth int,
 ) (any, error) {
-	if value.IsNil() {
-		return nil, nil
-	}
 	if value.Type().Key().Kind() != reflect.String {
 		return nil, fmt.Errorf("%s: map key type %s is not supported", path, value.Type().Key())
 	}
+	if err := state.produceNode(path); err != nil {
+		return nil, err
+	}
+	if err := state.ensureChildCapacity(path, value.Len()); err != nil {
+		return nil, err
+	}
 
 	current := visit{typ: value.Type(), ptr: value.Pointer()}
-	if _, ok := seen[current]; ok {
+	if _, ok := state.active[current]; ok {
 		return nil, fmt.Errorf("%s: cyclic value is not supported", path)
 	}
-	seen[current] = struct{}{}
-	defer delete(seen, current)
+	state.active[current] = struct{}{}
+	defer delete(state.active, current)
 
 	keys := value.MapKeys()
 	sort.Slice(keys, func(i, j int) bool {
@@ -152,7 +185,13 @@ func copyMapValue(
 		if name == "" && !allowEmptyMapKeys {
 			return nil, fmt.Errorf("%s: map key must not be empty", path)
 		}
-		copied, err := copyValue(value.MapIndex(key), path+"."+name, seen, allowEmptyMapKeys)
+		copied, err := copyValue(
+			value.MapIndex(key),
+			path+"."+name,
+			state,
+			allowEmptyMapKeys,
+			containerDepth,
+		)
 		if err != nil {
 			return nil, err
 		}
@@ -190,17 +229,25 @@ func copyMapValue(
 func copySequenceValue(
 	value reflect.Value,
 	path string,
-	seen map[visit]struct{},
+	state *traversalState,
 	allowEmptyMapKeys bool,
+	containerDepth int,
 ) (any, error) {
+	if err := state.produceNode(path); err != nil {
+		return nil, err
+	}
+	if err := state.ensureChildCapacity(path, value.Len()); err != nil {
+		return nil, err
+	}
+
 	var current visit
 	if value.Kind() == reflect.Slice {
 		current = visit{typ: value.Type(), ptr: value.Pointer()}
-		if _, ok := seen[current]; ok {
+		if _, ok := state.active[current]; ok {
 			return nil, fmt.Errorf("%s: cyclic value is not supported", path)
 		}
-		seen[current] = struct{}{}
-		defer delete(seen, current)
+		state.active[current] = struct{}{}
+		defer delete(state.active, current)
 	}
 
 	values := make([]any, value.Len())
@@ -210,8 +257,9 @@ func copySequenceValue(
 		copied, err := copyValue(
 			value.Index(i),
 			fmt.Sprintf("%s[%d]", path, i),
-			seen,
+			state,
 			allowEmptyMapKeys,
+			containerDepth,
 		)
 		if err != nil {
 			return nil, err
@@ -248,6 +296,73 @@ func copySequenceValue(
 	return out, nil
 }
 
+func validJSONNumber(number json.Number) bool {
+	var parsed json.Number
+	if err := json.Unmarshal([]byte(number.String()), &parsed); err != nil {
+		return false
+	}
+	return parsed.String() == number.String()
+}
+
+func newTraversalState() *traversalState {
+	return &traversalState{active: make(map[visit]struct{})}
+}
+
+func (state *traversalState) produceNode(path string) error {
+	if state.producedNodes >= maxProducedNodes {
+		return fmt.Errorf("%s: JSON value work limit exceeded", path)
+	}
+	state.producedNodes++
+	return nil
+}
+
+func (state *traversalState) enterContainer(path string, depth int) (int, error) {
+	depth++
+	if depth > maxContainerDepth {
+		return 0, fmt.Errorf("%s: JSON container depth limit exceeded", path)
+	}
+	return depth, nil
+}
+
+func (state *traversalState) ensureChildCapacity(path string, count int) error {
+	if count > maxProducedNodes-state.producedNodes {
+		return fmt.Errorf("%s: JSON value work limit exceeded", path)
+	}
+	return nil
+}
+
+func (state *traversalState) resolveIndirection(
+	value reflect.Value,
+	path string,
+) (reflect.Value, func(), bool, error) {
+	var visits []visit
+	cleanup := func() {
+		for _, current := range visits {
+			delete(state.active, current)
+		}
+	}
+
+	for value.IsValid() && (value.Kind() == reflect.Interface || value.Kind() == reflect.Pointer) {
+		if value.IsNil() {
+			return reflect.Value{}, cleanup, true, nil
+		}
+		if value.Kind() == reflect.Pointer {
+			current := visit{typ: value.Type(), ptr: value.Pointer()}
+			if _, ok := state.active[current]; ok {
+				cleanup()
+				return reflect.Value{}, nil, false, fmt.Errorf("%s: cyclic value is not supported", path)
+			}
+			state.active[current] = struct{}{}
+			visits = append(visits, current)
+		}
+		value = value.Elem()
+	}
+	if !value.IsValid() {
+		return reflect.Value{}, cleanup, true, nil
+	}
+	return value, cleanup, false, nil
+}
+
 func canAssignNil(typ reflect.Type) bool {
 	switch typ.Kind() {
 	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:

internal/jsonvalue/jsonvalue_test.go

@@ -1,112 +1,332 @@
-package jsonvalue_test
+package jsonvalue
 
 import (
 	"encoding/json"
 	"math"
 	"reflect"
+	"strings"
 	"testing"
-
-	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
 )
 
-func TestCopyMapPreservesTypesAndIsolatesMutations(t *testing.T) {
-	nested := map[string]int{"limit": 2}
-	sequence := []string{"one", "two"}
-	input := map[string]any{
-		"count":    int64(7),
-		"number":   json.Number("-1.25e+2"),
-		"nested":   nested,
-		"sequence": sequence,
-	}
-
-	copied, err := jsonvalue.CopyMap(input)
-	if err != nil {
-		t.Fatalf("copy map: %v", err)
-	}
-	nested["limit"] = 99
-	sequence[0] = "changed"
-	input["added"] = true
-
-	if got, ok := copied["count"].(int64); !ok || got != 7 {
-		t.Fatalf("integer type or value changed: %#v", copied["count"])
-	}
-	if got, ok := copied["number"].(json.Number); !ok || got != "-1.25e+2" {
-		t.Fatalf("JSON number type or value changed: %#v", copied["number"])
-	}
-	if got := copied["nested"].(map[string]int)["limit"]; got != 2 {
-		t.Fatalf("nested map was not isolated: %d", got)
-	}
-	if got := copied["sequence"].([]string)[0]; got != "one" {
-		t.Fatalf("sequence was not isolated: %q", got)
-	}
-	if _, ok := copied["added"]; ok {
-		t.Fatalf("top-level map was not isolated: %#v", copied)
-	}
-}
-
-func TestCopyAllowsEmptyObjectKeysAndIsolatesMutations(t *testing.T) {
-	nested := map[string]any{"": []any{"original"}}
-
-	copiedValue, err := jsonvalue.Copy(nested)
-	if err != nil {
-		t.Fatalf("copy value: %v", err)
-	}
-	nested[""].([]any)[0] = "changed"
-
-	copied := copiedValue.(map[string]any)
-	if got := copied[""].([]any)[0]; got != "original" {
-		t.Fatalf("copied value was not isolated: %v", got)
-	}
-}
-
-func TestCopyMapRejectsInvalidValues(t *testing.T) {
-	cyclicMap := map[string]any{}
-	cyclicMap["self"] = cyclicMap
-	cyclicSlice := []any{nil}
-	cyclicSlice[0] = cyclicSlice
+type (
+	namedBool    bool
+	namedString  string
+	namedInt64   int64
+	namedUint64  uint64
+	namedFloat32 float32
+	namedFloat64 float64
+	namedKey     string
+	namedMap     map[namedKey]namedInt64
+	namedSlice   []namedString
+	namedArray   [1]map[string]int
+)
 
+func TestCopyPreservesSupportedScalarAndNumberTypes(t *testing.T) {
+	maxInt := int(^uint(0) >> 1)
+	minInt := -maxInt - 1
 	tests := []struct {
 		name  string
 		value any
 	}{
-		{name: "empty nested key", value: map[string]int{"": 1}},
-		{name: "non-string map key", value: map[int]string{1: "one"}},
-		{name: "unsupported value", value: make(chan int)},
-		{name: "cyclic map", value: cyclicMap},
-		{name: "cyclic slice", value: cyclicSlice},
-		{name: "NaN", value: math.NaN()},
-		{name: "positive infinity", value: math.Inf(1)},
-		{name: "unsafe signed integer", value: int64(1 << 53)},
-		{name: "unsafe unsigned integer", value: uint64(1 << 53)},
+		{name: "bool", value: true},
+		{name: "named bool", value: namedBool(true)},
+		{name: "string", value: "value"},
+		{name: "named string", value: namedString("value")},
+		{name: "int", value: minInt},
+		{name: "int8", value: int8(-1 << 7)},
+		{name: "int16", value: int16(-1 << 15)},
+		{name: "int32", value: int32(-1 << 31)},
+		{name: "int64", value: int64(-1 << 63)},
+		{name: "named int64", value: namedInt64(1<<63 - 1)},
+		{name: "uint", value: ^uint(0)},
+		{name: "uint8", value: ^uint8(0)},
+		{name: "uint16", value: ^uint16(0)},
+		{name: "uint32", value: ^uint32(0)},
+		{name: "uint64", value: ^uint64(0)},
+		{name: "uintptr", value: ^uintptr(0)},
+		{name: "named uint64", value: namedUint64(^uint64(0))},
+		{name: "float32", value: float32(1.25)},
+		{name: "float64", value: float64(-2.5e100)},
+		{name: "named float32", value: namedFloat32(3.5)},
+		{name: "named float64", value: namedFloat64(-4.5e200)},
+		{name: "JSON number integer", value: json.Number("18446744073709551615")},
+		{name: "JSON number fraction", value: json.Number("-1.25e+2")},
+		{name: "JSON number beyond float64", value: json.Number("1e9999")},
 	}
 
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
-			if _, err := jsonvalue.CopyMap(map[string]any{"value": tc.value}); err == nil {
+			got, err := Copy(tc.value)
+			if err != nil {
+				t.Fatalf("copy value: %v", err)
+			}
+			if !reflect.DeepEqual(got, tc.value) {
+				t.Fatalf("value or concrete type changed: got %#v (%T), want %#v (%T)", got, got, tc.value, tc.value)
+			}
+		})
+	}
+}
+
+func TestCopyRejectsInvalidNumbers(t *testing.T) {
+	tests := []struct {
+		name  string
+		value any
+	}{
+		{name: "float32 NaN", value: float32(math.NaN())},
+		{name: "float64 NaN", value: math.NaN()},
+		{name: "named float NaN", value: namedFloat64(math.NaN())},
+		{name: "positive infinity", value: math.Inf(1)},
+		{name: "negative infinity", value: math.Inf(-1)},
+		{name: "empty JSON number", value: json.Number("")},
+		{name: "leading zero JSON number", value: json.Number("01")},
+		{name: "leading plus JSON number", value: json.Number("+1")},
+		{name: "trailing decimal JSON number", value: json.Number("1.")},
+		{name: "leading decimal JSON number", value: json.Number(".1")},
+		{name: "non-number JSON number", value: json.Number("NaN")},
+		{name: "spaced JSON number", value: json.Number(" 1")},
+		{name: "quoted JSON number", value: json.Number(`"1"`)},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if _, err := Copy(tc.value); err == nil {
 				t.Fatal("expected validation error")
 			}
 		})
 	}
 }
 
-func TestCopyMapValidatesJSONNumberSyntaxAndRange(t *testing.T) {
-	for _, number := range []json.Number{"0", "-1", "1.25", "-1.25e+2"} {
-		t.Run("valid "+number.String(), func(t *testing.T) {
-			got, err := jsonvalue.CopyMap(map[string]any{"value": number})
-			if err != nil {
-				t.Fatalf("copy valid JSON number: %v", err)
+func TestCopyPreservesCompatibleCollectionsAndNilEmptyDistinctions(t *testing.T) {
+	collections := []struct {
+		name  string
+		value any
+	}{
+		{name: "unnamed map", value: map[string]int{"limit": 2}},
+		{name: "named map", value: namedMap{"limit": 2}},
+		{name: "unnamed slice", value: []string{"one", "two"}},
+		{name: "named slice", value: namedSlice{"one", "two"}},
+		{name: "unnamed array", value: [2]int{1, 2}},
+		{name: "named array", value: namedArray{{"limit": 2}}},
+		{name: "empty map", value: map[string]int{}},
+		{name: "empty named map", value: namedMap{}},
+		{name: "empty slice", value: []string{}},
+		{name: "empty named slice", value: namedSlice{}},
+		{name: "empty array", value: [0]string{}},
 	}
-			if !reflect.DeepEqual(got["value"], number) {
-				t.Fatalf("JSON number changed: got %#v want %#v", got["value"], number)
+
+	for _, tc := range collections {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := Copy(tc.value)
+			if err != nil {
+				t.Fatalf("copy collection: %v", err)
+			}
+			if !reflect.DeepEqual(got, tc.value) || reflect.TypeOf(got) != reflect.TypeOf(tc.value) {
+				t.Fatalf("collection changed: got %#v (%T), want %#v (%T)", got, got, tc.value, tc.value)
+			}
+			kind := reflect.ValueOf(got).Kind()
+			if (kind == reflect.Map || kind == reflect.Slice) && reflect.ValueOf(got).IsNil() {
+				t.Fatal("non-nil collection became nil")
 			}
 		})
 	}
 
-	for _, number := range []json.Number{"", "01", "+1", "1.", ".1", "1e9999", "not-a-number"} {
-		t.Run("invalid "+number.String(), func(t *testing.T) {
-			if _, err := jsonvalue.CopyMap(map[string]any{"value": number}); err == nil {
-				t.Fatal("expected invalid JSON number error")
+	var nilMap map[string]int
+	var nilSlice []string
+	var nilPointer *namedInt64
+	for _, value := range []any{nil, nilMap, nilSlice, nilPointer} {
+		got, err := Copy(value)
+		if err != nil {
+			t.Fatalf("copy null value: %v", err)
+		}
+		if got != nil {
+			t.Fatalf("null value became %#v (%T)", got, got)
+		}
+	}
+
+	gotNil, err := CopyMap(nil)
+	if err != nil || gotNil != nil {
+		t.Fatalf("nil CopyMap result = %#v, %v", gotNil, err)
+	}
+	gotEmpty, err := CopyMap(map[string]any{})
+	if err != nil || gotEmpty == nil || len(gotEmpty) != 0 {
+		t.Fatalf("empty CopyMap result = %#v, %v", gotEmpty, err)
+	}
+}
+
+func TestCopyHandlesIndirectionAndIsolatesNestedMutations(t *testing.T) {
+	integer := namedInt64(7)
+	nestedMap := namedMap{"limit": 2}
+	nestedSlice := namedSlice{"original"}
+	nestedArray := namedArray{{"limit": 3}}
+	shared := []any{map[string]int{"value": 4}}
+	input := map[string]any{
+		"integer": &integer,
+		"map":     nestedMap,
+		"slice":   nestedSlice,
+		"array":   nestedArray,
+		"first":   shared,
+		"second":  shared,
+	}
+
+	copiedValue, err := Copy(input)
+	if err != nil {
+		t.Fatalf("copy mixed tree: %v", err)
+	}
+	copied := copiedValue.(map[string]any)
+	nestedMap["limit"] = 20
+	nestedSlice[0] = "changed"
+	nestedArray[0]["limit"] = 30
+	shared[0].(map[string]int)["value"] = 40
+
+	if got, ok := copied["integer"].(namedInt64); !ok || got != 7 {
+		t.Fatalf("pointer target changed: %#v", copied["integer"])
+	}
+	if got := copied["map"].(namedMap)["limit"]; got != 2 {
+		t.Fatalf("nested map aliased input: %d", got)
+	}
+	if got := copied["slice"].(namedSlice)[0]; got != "original" {
+		t.Fatalf("nested slice aliased input: %q", got)
+	}
+	if got := copied["array"].(namedArray)[0]["limit"]; got != 3 {
+		t.Fatalf("nested array aliased input: %d", got)
+	}
+	first := copied["first"].([]any)
+	second := copied["second"].([]any)
+	if got := first[0].(map[string]int)["value"]; got != 4 {
+		t.Fatalf("shared child aliased input: %d", got)
+	}
+	first[0].(map[string]int)["value"] = 99
+	if got := second[0].(map[string]int)["value"]; got != 4 {
+		t.Fatalf("repeated acyclic value shared copied output: %d", got)
+	}
+}
+
+func TestCopyAndCopyMapApplyDistinctEmptyKeyRules(t *testing.T) {
+	nested := map[string]any{"": []any{"original"}}
+	copiedValue, err := Copy(nested)
+	if err != nil {
+		t.Fatalf("Copy rejected empty schema key: %v", err)
+	}
+	nested[""].([]any)[0] = "changed"
+	if got := copiedValue.(map[string]any)[""].([]any)[0]; got != "original" {
+		t.Fatalf("copied schema value was not isolated: %v", got)
+	}
+
+	_, err = CopyMap(map[string]any{"nested": map[string]any{"": true}})
+	if err == nil || !strings.Contains(err.Error(), "extra_params.nested") {
+		t.Fatalf("CopyMap empty-key error = %v", err)
+	}
+}
+
+func TestCopyRejectsUnsupportedValuesAndActiveCycles(t *testing.T) {
+	cyclicMap := map[string]any{}
+	cyclicMap["self"] = cyclicMap
+	cyclicSlice := []any{nil}
+	cyclicSlice[0] = cyclicSlice
+	var cyclicPointer any
+	cyclicPointer = &cyclicPointer
+
+	tests := []struct {
+		name     string
+		value    any
+		wantPath string
+	}{
+		{name: "non-string map key", value: map[int]string{1: "one"}, wantPath: "value"},
+		{name: "unsupported channel", value: make(chan int), wantPath: "value"},
+		{name: "deterministic map path", value: map[string]any{"z": make(chan int), "a": make(chan int)}, wantPath: "value.a"},
+		{name: "cyclic map", value: cyclicMap, wantPath: "value.self"},
+		{name: "cyclic slice", value: cyclicSlice, wantPath: "value[0]"},
+		{name: "cyclic pointer", value: cyclicPointer, wantPath: "value"},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Copy(tc.value)
+			if err == nil || !strings.Contains(err.Error(), tc.wantPath) {
+				t.Fatalf("error = %v, want structural path %q", err, tc.wantPath)
 			}
 		})
 	}
 }
+
+func TestCopyEnforcesContainerDepth(t *testing.T) {
+	tests := []struct {
+		name    string
+		depth   int
+		wantErr bool
+	}{
+		{name: "just below", depth: maxContainerDepth - 1},
+		{name: "at limit", depth: maxContainerDepth},
+		{name: "over limit", depth: maxContainerDepth + 1, wantErr: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Copy(alternatingContainers(tc.depth))
+			if tc.wantErr {
+				if err == nil || !strings.HasPrefix(err.Error(), "value") || !strings.Contains(err.Error(), "container depth limit") {
+					t.Fatalf("depth error = %v", err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("copy depth %d: %v", tc.depth, err)
+			}
+		})
+	}
+}
+
+func TestCopyEnforcesProducedNodeBudgetForRepeatedAcyclicValues(t *testing.T) {
+	shared := []any{true}
+	sharedOccurrences := (maxProducedNodes - 2) / 2
+	justBelow := repeatedValues(shared, sharedOccurrences, 0)
+	atLimit := repeatedValues(shared, sharedOccurrences, 1)
+	overLimit := repeatedValues(shared, sharedOccurrences, 2)
+
+	for name, value := range map[string]any{
+		"just below": justBelow,
+		"at limit":   atLimit,
+	} {
+		t.Run(name, func(t *testing.T) {
+			if _, err := Copy(value); err != nil {
+				t.Fatalf("copy value within work budget: %v", err)
+			}
+		})
+	}
+
+	_, err := Copy(overLimit)
+	if err == nil || !strings.HasPrefix(err.Error(), "value[") || !strings.Contains(err.Error(), "value work limit") {
+		t.Fatalf("work-budget error = %v", err)
+	}
+
+	_, err = Copy(make([]any, maxProducedNodes))
+	if err == nil || !strings.HasPrefix(err.Error(), "value:") || !strings.Contains(err.Error(), "value work limit") {
+		t.Fatalf("flat work-budget error = %v", err)
+	}
+}
+
+func alternatingContainers(depth int) any {
+	var value any = true
+	for level := 0; level < depth; level++ {
+		switch level % 3 {
+		case 0:
+			value = map[string]any{"child": value}
+		case 1:
+			value = []any{value}
+		default:
+			value = [1]any{value}
+		}
+	}
+	return value
+}
+
+func repeatedValues(shared []any, occurrences, leadingScalars int) []any {
+	values := make([]any, 0, leadingScalars+occurrences)
+	for i := 0; i < leadingScalars; i++ {
+		values = append(values, false)
+	}
+	for i := 0; i < occurrences; i++ {
+		values = append(values, shared)
+	}
+	return values
+}

internal/llm/openai_compatible_client.go

@@ -25,6 +25,20 @@ var (
 	ErrMalformedResponse = errors.New("malformed llm response")
 )
 
+const maxOpenAIChatResponseBytes int64 = 16 << 20
+
+type requestFailedError struct {
+	cause error
+}
+
+func (e *requestFailedError) Error() string {
+	return ErrRequestFailed.Error()
+}
+
+func (e *requestFailedError) Unwrap() []error {
+	return []error{ErrRequestFailed, e.cause}
+}
+
 type OpenAICompatibleConfig struct {
 	BaseURL    string
 	Model      string
@@ -39,9 +53,11 @@ type OpenAICompatibleClient struct {
 }
 
 func NewOpenAICompatibleClient(cfg OpenAICompatibleConfig) (*OpenAICompatibleClient, error) {
-	baseURL := strings.TrimSpace(cfg.BaseURL)
-	if baseURL != "" {
-		if _, err := url.ParseRequestURI(baseURL); err != nil {
+	baseURL := ""
+	if strings.TrimSpace(cfg.BaseURL) != "" {
+		var err error
+		baseURL, err = domain.NormalizeOpenAICompatibleBaseEndpoint(cfg.BaseURL)
+		if err != nil {
 			return nil, fmt.Errorf("%w: invalid base URL: %v", ErrInvalidConfig, err)
 		}
 	}
@@ -63,25 +79,29 @@ func NewOpenAICompatibleClient(cfg OpenAICompatibleConfig) (*OpenAICompatibleCli
 	}
 
 	return &OpenAICompatibleClient{
-		baseURL:      strings.TrimRight(baseURL, "/"),
+		baseURL:      baseURL,
 		defaultModel: cfg.Model,
 		httpClient:   client,
 	}, nil
 }
 
 func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error) {
-	if req.Target.TimeoutSeconds < 0 {
-		return nil, fmt.Errorf("%w: timeout_seconds must be greater than or equal to 0", ErrInvalidRequest)
+	if err := domain.ValidateExecutionTargetSettings(req.Target); err != nil {
+		return nil, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
 	}
 
-	endpoint := strings.TrimSpace(req.Target.Endpoint)
-	if endpoint == "" {
-		endpoint = c.baseURL
+	selectedEndpoint := req.Target.Endpoint
+	if strings.TrimSpace(selectedEndpoint) == "" {
+		selectedEndpoint = c.baseURL
 	}
-	if endpoint == "" {
-		return nil, fmt.Errorf("%w: endpoint is required", ErrInvalidRequest)
+	endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(selectedEndpoint)
+	if err != nil {
+		return nil, fmt.Errorf("%w: invalid endpoint: %v", ErrInvalidRequest, err)
+	}
+	endpoint, err = url.JoinPath(endpoint, defaults.OpenAIChatCompletionsPath)
+	if err != nil {
+		return nil, fmt.Errorf("%w: invalid endpoint path: %v", ErrInvalidRequest, err)
 	}
-	endpoint = strings.TrimRight(endpoint, "/") + defaults.OpenAIChatCompletionsPath
 
 	wireReq, err := openAIChatRequestFromGenerateRequest(req, c.defaultModel)
 	if err != nil {
@@ -130,7 +150,7 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 
 	httpResp, err := httpClient.Do(httpReq)
 	if err != nil {
-		return nil, fmt.Errorf("%w: %v", ErrRequestFailed, err)
+		return nil, &requestFailedError{cause: err}
 	}
 	defer httpResp.Body.Close()
 
@@ -138,10 +158,13 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 		_, _ = io.Copy(io.Discard, io.LimitReader(httpResp.Body, 4096))
 		return nil, fmt.Errorf("%w: status=%d", ErrUnexpectedStatus, httpResp.StatusCode)
 	}
+	if httpResp.ContentLength > maxOpenAIChatResponseBytes {
+		return nil, openAIChatResponseTooLargeError()
+	}
 
-	var wireResp openAIChatResponse
-	if err := json.NewDecoder(httpResp.Body).Decode(&wireResp); err != nil {
-		return nil, fmt.Errorf("%w: failed to decode response: %v", ErrMalformedResponse, err)
+	wireResp, err := decodeOpenAIChatResponse(httpResp.Body)
+	if err != nil {
+		return nil, err
 	}
 
 	if len(wireResp.Choices) == 0 {
@@ -164,6 +187,46 @@ func (c *OpenAICompatibleClient) Generate(ctx context.Context, req domain.Genera
 	}, nil
 }
 
+func decodeOpenAIChatResponse(body io.Reader) (openAIChatResponse, error) {
+	limited := &io.LimitedReader{
+		R: body,
+		N: maxOpenAIChatResponseBytes + 1,
+	}
+	decoder := json.NewDecoder(limited)
+
+	var response openAIChatResponse
+	if err := decoder.Decode(&response); err != nil {
+		if limited.N == 0 {
+			return openAIChatResponse{}, openAIChatResponseTooLargeError()
+		}
+		return openAIChatResponse{}, fmt.Errorf("%w: failed to decode response", ErrMalformedResponse)
+	}
+	if limited.N == 0 {
+		return openAIChatResponse{}, openAIChatResponseTooLargeError()
+	}
+
+	var trailing any
+	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
+		if limited.N == 0 {
+			return openAIChatResponse{}, openAIChatResponseTooLargeError()
+		}
+		return openAIChatResponse{}, fmt.Errorf("%w: response contains trailing data", ErrMalformedResponse)
+	}
+	if limited.N == 0 {
+		return openAIChatResponse{}, openAIChatResponseTooLargeError()
+	}
+
+	return response, nil
+}
+
+func openAIChatResponseTooLargeError() error {
+	return fmt.Errorf(
+		"%w: response exceeds %d-byte limit",
+		ErrMalformedResponse,
+		maxOpenAIChatResponseBytes,
+	)
+}
+
 func openAIChatRequestFromGenerateRequest(req domain.GenerateRequest, defaultModel string) (openAIChatRequest, error) {
 	model := strings.TrimSpace(req.Target.Model)
 	if model == "" {

internal/profile/builtin/repository.go

@@ -2,7 +2,6 @@ package builtin
 
 import (
 	"embed"
-	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
 )
@@ -15,17 +14,3 @@ var assets embed.FS
 func NewRepository() profile.Repository {
 	return profile.NewFSRepository(assets, assetRoot)
 }
-
-func NewRepositoryWithPrimary(primary profile.Repository) profile.Repository {
-	if primary == nil {
-		return NewRepository()
-	}
-	return profile.NewOverlayRepository(primary, NewRepository())
-}
-
-func NewRepositoryWithDirectory(dir string) profile.Repository {
-	if strings.TrimSpace(dir) == "" {
-		return NewRepository()
-	}
-	return NewRepositoryWithPrimary(profile.NewFilesystemRepository(dir))
-}

internal/profile/builtin/repository_test.go

@@ -2,14 +2,11 @@ package builtin
 
 import (
 	"context"
-	"errors"
 	"io/fs"
 	"strings"
 	"testing"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
-	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
-	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
 	"gopkg.in/yaml.v3"
 )
 
@@ -91,53 +88,3 @@ func loadBuiltInProfileIDs(t *testing.T) map[string]string {
 	}
 	return ids
 }
-
-func TestRepositoryWithPrimaryUsesPrimaryBeforeBuiltIns(t *testing.T) {
-	repo := NewRepositoryWithPrimary(staticProfileRepo{
-		profiles: map[string]string{"mistral-small-3": "custom-model"},
-	})
-
-	p, err := repo.GetProfile(context.Background(), "mistral-small-3")
-	if err != nil {
-		t.Fatalf("expected profile to load, got %v", err)
-	}
-	if p.Model != "custom-model" {
-		t.Fatalf("expected primary profile to override built-in, got %+v", p)
-	}
-}
-
-func TestRepositoryWithPrimaryFallsBackToBuiltIns(t *testing.T) {
-	repo := NewRepositoryWithPrimary(staticProfileRepo{})
-
-	p, err := repo.GetProfile(context.Background(), "mistral-small-3")
-	if err != nil {
-		t.Fatalf("expected built-in profile to load, got %v", err)
-	}
-	if p.ID != "mistral-small-3" {
-		t.Fatalf("unexpected profile: %+v", p)
-	}
-}
-
-func TestRepositoryWithPrimaryDoesNotFallBackAfterPrimaryError(t *testing.T) {
-	repo := NewRepositoryWithPrimary(staticProfileRepo{err: profile.ErrInvalidProfile})
-
-	_, err := repo.GetProfile(context.Background(), "mistral-small-3")
-	if !errors.Is(err, profile.ErrInvalidProfile) {
-		t.Fatalf("expected primary error, got %v", err)
-	}
-}
-
-type staticProfileRepo struct {
-	profiles map[string]string
-	err      error
-}
-
-func (r staticProfileRepo) GetProfile(_ context.Context, id string) (*domain.ExecutionProfile, error) {
-	if r.err != nil {
-		return nil, r.err
-	}
-	if model, ok := r.profiles[id]; ok {
-		return &domain.ExecutionProfile{ID: id, Endpoint: "http://primary/v1", Model: model}, nil
-	}
-	return nil, profile.ErrProfileNotFound
-}

internal/profile/filesystem_repository.go

@@ -5,13 +5,14 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"os"
-	"path"
 	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
 	"gitea.maximumdirect.net/eric/promptkit/internal/filecatalog"
+	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
 	"gopkg.in/yaml.v3"
 )
 
@@ -73,7 +74,8 @@ func (r *overlayRepository) GetProfile(ctx context.Context, id string) (*domain.
 }
 
 func loadProfile(ctx context.Context, fsys fs.FS, root string, id string) (*domain.ExecutionProfile, error) {
-	if strings.TrimSpace(id) == "" {
+	id = strings.TrimSpace(id)
+	if id == "" {
 		return nil, fmt.Errorf("%w: profile id is required", ErrInvalidProfile)
 	}
 	if fsys == nil {
@@ -94,42 +96,50 @@ func loadProfile(ctx context.Context, fsys fs.FS, root string, id string) (*doma
 		}
 
 		relPath := filecatalog.DisplayPath(root, fullPath)
-		fileMatch := filecatalog.Stem(path.Base(fullPath)) == id
 		data, err := fs.ReadFile(fsys, fullPath)
 		if err != nil {
 			return nil, fmt.Errorf("failed to read profile file %s: %w", relPath, err)
 		}
-		metadata := readProfileFileMetadata(data)
-		idMatch := fileMatch || metadata.id == id
+		metadata, metadataErr := readProfileFileMetadata(data)
+		idMatch := metadata.matchesID(id)
+		if metadataErr != nil {
+			if idMatch {
+				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidYAML, relPath, metadataErr)
+			}
+			continue
+		}
 		if metadata.hasRawAPIKey {
 			if idMatch {
 				return nil, fmt.Errorf("%w: %s", ErrRawAPIKeyNotAllowed, relPath)
 			}
 			continue
 		}
-
-		var prof domain.ExecutionProfile
-		decoder := yaml.NewDecoder(bytes.NewReader(data))
-		decoder.KnownFields(true)
-		if err := decoder.Decode(&prof); err != nil {
-			if idMatch {
-				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidYAML, relPath, err)
-			}
+		if !idMatch {
 			continue
 		}
 
+		prof, err := decodeProfile(data)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %s: %v", ErrInvalidYAML, relPath, err)
+		}
+
+		prof.ID = strings.TrimSpace(prof.ID)
 		if prof.ID != id {
 			continue
 		}
 		prof.BackendID = strings.TrimSpace(prof.BackendID)
-		if err := validateProfile(&prof); err != nil {
+		prof.ExtraParams, err = jsonvalue.CopyMap(prof.ExtraParams)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %s: %v", ErrInvalidProfile, relPath, err)
+		}
+		if err := normalizeAndValidateProfile(prof); err != nil {
 			if errors.Is(err, ErrRawAPIKeyNotAllowed) {
 				return nil, fmt.Errorf("%w: %s", err, relPath)
 			}
 			return nil, fmt.Errorf("%w: %s: %v", ErrInvalidProfile, relPath, err)
 		}
 		matches = append(matches, profileMatch{
-			profile: &prof,
+			profile: prof,
 			path:    relPath,
 		})
 	}
@@ -155,15 +165,36 @@ type profileMatch struct {
 }
 
 type profileFileMetadata struct {
-	id           string
+	ids          []string
 	hasRawAPIKey bool
 }
 
-func readProfileFileMetadata(data []byte) profileFileMetadata {
+func readProfileFileMetadata(data []byte) (profileFileMetadata, error) {
+	decoder := yaml.NewDecoder(bytes.NewReader(data))
 	var node yaml.Node
-	if err := yaml.NewDecoder(bytes.NewReader(data)).Decode(&node); err != nil {
-		return profileFileMetadata{}
+	if err := decoder.Decode(&node); err != nil {
+		return profileFileMetadata{}, err
 	}
+	metadata := profileMetadataFromNode(&node)
+	documentCount := 1
+	for {
+		var trailing yaml.Node
+		err := decoder.Decode(&trailing)
+		if errors.Is(err, io.EOF) {
+			if documentCount == 1 {
+				return metadata, nil
+			}
+			return metadata, errors.New("profile file must contain exactly one YAML document")
+		}
+		if err != nil {
+			return metadata, err
+		}
+		documentCount++
+		metadata.merge(profileMetadataFromNode(&trailing))
+	}
+}
+
+func profileMetadataFromNode(node *yaml.Node) profileFileMetadata {
 	if node.Kind != yaml.DocumentNode || len(node.Content) == 0 {
 		return profileFileMetadata{}
 	}
@@ -178,7 +209,7 @@ func readProfileFileMetadata(data []byte) profileFileMetadata {
 		value := mapping.Content[i+1]
 		switch key.Value {
 		case "id":
-			metadata.id = strings.TrimSpace(value.Value)
+			metadata.ids = append(metadata.ids, strings.TrimSpace(value.Value))
 		case "api_key":
 			metadata.hasRawAPIKey = true
 		}
@@ -186,29 +217,68 @@ func readProfileFileMetadata(data []byte) profileFileMetadata {
 	return metadata
 }
 
-func validateProfile(p *domain.ExecutionProfile) error {
+func (m profileFileMetadata) matchesID(id string) bool {
+	for _, candidate := range m.ids {
+		if candidate == id {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *profileFileMetadata) merge(other profileFileMetadata) {
+	m.ids = append(m.ids, other.ids...)
+	m.hasRawAPIKey = m.hasRawAPIKey || other.hasRawAPIKey
+}
+
+func decodeProfile(data []byte) (*domain.ExecutionProfile, error) {
+	var prof domain.ExecutionProfile
+	decoder := yaml.NewDecoder(bytes.NewReader(data))
+	decoder.KnownFields(true)
+	if err := decoder.Decode(&prof); err != nil {
+		return nil, err
+	}
+	if err := requireYAMLStreamEnd(decoder); err != nil {
+		return nil, err
+	}
+	return &prof, nil
+}
+
+func requireYAMLStreamEnd(decoder *yaml.Decoder) error {
+	var trailing yaml.Node
+	err := decoder.Decode(&trailing)
+	if errors.Is(err, io.EOF) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	return errors.New("profile file must contain exactly one YAML document")
+}
+
+func normalizeAndValidateProfile(p *domain.ExecutionProfile) error {
 	if strings.TrimSpace(p.ID) == "" {
 		return errors.New("id is required")
 	}
-	if strings.TrimSpace(p.BackendID) == "" && strings.TrimSpace(p.Endpoint) == "" {
+	p.Endpoint = strings.TrimSpace(p.Endpoint)
+	if strings.TrimSpace(p.BackendID) == "" && p.Endpoint == "" {
 		return errors.New("backend or endpoint is required")
 	}
+	if p.Endpoint != "" {
+		endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(p.Endpoint)
+		if err != nil {
+			return err
+		}
+		p.Endpoint = endpoint
+	}
 	if strings.TrimSpace(p.Model) == "" {
 		return errors.New("model is required")
 	}
 
-	if p.Temperature < 0 || p.Temperature > 2 {
-		return errors.New("temperature must be between 0 and 2")
-	}
-	if p.MaxTokens < 0 {
-		return errors.New("max_tokens must be greater than or equal to 0")
-	}
-	if p.TopP < 0 || p.TopP > 1 {
-		return errors.New("top_p must be between 0 and 1")
-	}
-	if p.TimeoutSeconds < 0 {
-		return errors.New("timeout_seconds must be greater than or equal to 0")
-	}
-
-	return nil
+	return domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{
+		Temperature:    p.Temperature,
+		MaxTokens:      p.MaxTokens,
+		TopP:           p.TopP,
+		TimeoutSeconds: p.TimeoutSeconds,
+	})
 }

internal/profile/repository_benchmark_test.go

@@ -0,0 +1,58 @@
+package profile
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"testing/fstest"
+)
+
+func BenchmarkProfileRepositoryLookup(b *testing.B) {
+	for _, size := range []int{10, 1000} {
+		b.Run(fmt.Sprintf("catalog-%d", size), func(b *testing.B) {
+			files := fstest.MapFS{
+				"target.yaml": profileMapFile(`
+id: target
+endpoint: http://localhost:8000/v1
+model: target-model
+extra_params:
+  selected: true
+`),
+			}
+			metadataNames := []string{"target.yaml"}
+			for i := 1; i < size; i++ {
+				name := fmt.Sprintf("profile-%04d.yaml", i)
+				files[name] = profileMapFile(fmt.Sprintf(`
+id: profile-%04d
+endpoint: http://localhost:8000/v1
+model: unrelated-model
+temperature: 0.5
+max_tokens: 500
+extra_params:
+  provider:
+    order:
+      - first
+      - second
+`, i))
+				metadataNames = append(metadataNames, name)
+			}
+
+			fsys := &recordingProfileFS{FS: files}
+			repo := NewFSRepository(fsys, ".")
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				if _, err := repo.GetProfile(context.Background(), "target"); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.StopTimer()
+
+			for _, name := range metadataNames {
+				if got := fsys.openCount(name); got != b.N {
+					b.Fatalf("metadata %q opens = %d, want %d", name, got, b.N)
+				}
+			}
+		})
+	}
+}

internal/profile/repository_test.go

@@ -2,11 +2,13 @@ package profile
 
 import (
 	"context"
-	"encoding/json"
 	"errors"
+	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"testing"
 	"testing/fstest"
 
@@ -61,7 +63,7 @@ func TestFilesystemRepository_GetProfile(t *testing.T) {
 			wantErr      bool
 		}{
 			{name: "backend only", connection: "backend: '  openrouter  '", wantBackend: "openrouter"},
-			{name: "endpoint only", connection: "endpoint: http://localhost:8000/v1", wantEndpoint: "http://localhost:8000/v1"},
+			{name: "endpoint only", connection: "endpoint: '  https://localhost:8000/nested/v1  '", wantEndpoint: "https://localhost:8000/nested/v1"},
 			{name: "both", connection: "backend: openrouter\nendpoint: http://localhost:8000/v1", wantBackend: "openrouter", wantEndpoint: "http://localhost:8000/v1"},
 			{name: "neither", wantErr: true},
 			{name: "blank backend", connection: "backend: '   '", wantErr: true},
@@ -126,63 +128,6 @@ temperature: 0.1
 		}
 	})
 
-	t.Run("valid profile with JSON-compatible extra params", func(t *testing.T) {
-		writeProfileTestFile(t, filepath.Join(tmpDir, "json-extra-params.yaml"), `
-id: json-extra-params
-endpoint: http://localhost:8000/v1
-model: nested-model
-extra_params:
-  string_value: enabled
-  number_value: 42
-  boolean_value: true
-  object_value:
-    nested: value
-    count: 2
-  array_value:
-    - first
-    - 3
-    - false
-`)
-
-		p, err := repo.GetProfile(ctx, "json-extra-params")
-		if err != nil {
-			t.Fatalf("expected no error, got %v", err)
-		}
-
-		var got map[string]any
-		encoded, err := json.Marshal(p.ExtraParams)
-		if err != nil {
-			t.Fatalf("expected extra_params to marshal as JSON, got %v", err)
-		}
-		if err := json.Unmarshal(encoded, &got); err != nil {
-			t.Fatalf("expected extra_params JSON to decode, got %v", err)
-		}
-
-		if got["string_value"] != "enabled" {
-			t.Fatalf("unexpected string extra param: %#v", got["string_value"])
-		}
-		if got["number_value"] != float64(42) {
-			t.Fatalf("unexpected number extra param: %#v", got["number_value"])
-		}
-		if got["boolean_value"] != true {
-			t.Fatalf("unexpected boolean extra param: %#v", got["boolean_value"])
-		}
-		objectValue, ok := got["object_value"].(map[string]any)
-		if !ok {
-			t.Fatalf("expected object extra param, got %#v", got["object_value"])
-		}
-		if objectValue["nested"] != "value" || objectValue["count"] != float64(2) {
-			t.Fatalf("unexpected object extra param: %#v", objectValue)
-		}
-		arrayValue, ok := got["array_value"].([]any)
-		if !ok {
-			t.Fatalf("expected array extra param, got %#v", got["array_value"])
-		}
-		if len(arrayValue) != 3 || arrayValue[0] != "first" || arrayValue[1] != float64(3) || arrayValue[2] != false {
-			t.Fatalf("unexpected array extra param: %#v", arrayValue)
-		}
-	})
-
 	t.Run("duplicate profile IDs fail as ambiguous", func(t *testing.T) {
 		writeProfileTestFile(t, filepath.Join(tmpDir, "duplicate-profile-a.yaml"), `
 id: duplicate-profile
@@ -245,10 +190,10 @@ api_key: secret
 		}
 	})
 
-	t.Run("invalid yaml", func(t *testing.T) {
+	t.Run("unidentifiable invalid yaml is unrelated", func(t *testing.T) {
 		_, err := repo.GetProfile(ctx, "invalid_yaml")
-		if !errors.Is(err, ErrInvalidYAML) {
-			t.Fatalf("expected ErrInvalidYAML, got %v", err)
+		if !errors.Is(err, ErrProfileNotFound) {
+			t.Fatalf("expected ErrProfileNotFound, got %v", err)
 		}
 	})
 
@@ -274,14 +219,14 @@ api_key: secret
 	})
 
 	t.Run("unknown field", func(t *testing.T) {
-		_, err := repo.GetProfile(ctx, "unknown_field")
+		_, err := repo.GetProfile(ctx, "unknown-field")
 		if !errors.Is(err, ErrInvalidYAML) {
 			t.Fatalf("expected ErrInvalidYAML for strict decode unknown field, got %v", err)
 		}
 	})
 
 	t.Run("raw api_key rejected", func(t *testing.T) {
-		_, err := repo.GetProfile(ctx, "raw_api_key")
+		_, err := repo.GetProfile(ctx, "raw-api-key")
 		if !errors.Is(err, ErrRawAPIKeyNotAllowed) {
 			t.Fatalf("expected ErrRawAPIKeyNotAllowed, got %v", err)
 		}
@@ -406,6 +351,513 @@ model: second
 	})
 }
 
+func TestProfileRepositoriesRejectInvalidEndpoints(t *testing.T) {
+	tests := []struct {
+		name        string
+		endpoint    string
+		withBackend bool
+	}{
+		{name: "relative", endpoint: "/v1"},
+		{name: "missing host", endpoint: "https:///v1"},
+		{name: "unsupported scheme", endpoint: "ftp://provider.example/v1"},
+		{name: "user information", endpoint: "https://user@provider.example/v1"},
+		{name: "query", endpoint: "https://provider.example/v1?mode=chat"},
+		{name: "fragment", endpoint: "https://provider.example/v1#chat"},
+		{name: "backend with invalid override", endpoint: "/v1", withBackend: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			backend := ""
+			if tc.withBackend {
+				backend = "backend: openrouter\n"
+			}
+			repo := NewFSRepository(fstest.MapFS{
+				"profiles/invalid.yaml": profileMapFile(fmt.Sprintf(
+					"id: invalid-endpoint\nmodel: model\n%sendpoint: %q\n",
+					backend,
+					tc.endpoint,
+				)),
+			}, "profiles")
+
+			_, err := repo.GetProfile(context.Background(), "invalid-endpoint")
+			if !errors.Is(err, ErrInvalidProfile) {
+				t.Fatalf("expected ErrInvalidProfile, got %v", err)
+			}
+		})
+	}
+}
+
+func TestProfileRepositoriesValidateExtraParams(t *testing.T) {
+	const validProfile = `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: model
+extra_params:
+  string_value: enabled
+  object_value:
+    nested: true
+  array_value:
+    - first
+    - 3
+`
+	tests := []struct {
+		name        string
+		definition  string
+		wantErr     bool
+		diagnostics []string
+	}{
+		{name: "valid nested values", definition: validProfile},
+		{
+			name: "empty key",
+			definition: `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: model
+extra_params:
+  "": value
+`,
+			wantErr:     true,
+			diagnostics: []string{"extra_params", "key must not be empty"},
+		},
+		{
+			name: "non-finite value",
+			definition: `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: model
+extra_params:
+  invalid: .nan
+`,
+			wantErr:     true,
+			diagnostics: []string{"extra_params.invalid", "must be finite"},
+		},
+		{
+			name: "nested non-finite value",
+			definition: `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: model
+extra_params:
+  outer:
+    invalid: .inf
+`,
+			wantErr:     true,
+			diagnostics: []string{"extra_params.outer.invalid", "must be finite"},
+		},
+		{
+			name: "unsupported decoded value",
+			definition: `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: model
+extra_params:
+  timestamp: 2026-08-11T12:34:56Z
+`,
+			wantErr:     true,
+			diagnostics: []string{"extra_params.timestamp", "unsupported JSON value type"},
+		},
+		{
+			name:        "excessive nesting",
+			definition:  deeplyNestedExtraParamsProfile(101),
+			wantErr:     true,
+			diagnostics: []string{"extra_params", "JSON container depth limit exceeded"},
+		},
+	}
+
+	for _, source := range profileRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				repo := source.newRepository(t, map[string]string{"selected.yaml": tc.definition})
+				got, err := repo.GetProfile(context.Background(), "selected-profile")
+				if tc.wantErr {
+					if !errors.Is(err, ErrInvalidProfile) {
+						t.Fatalf("expected ErrInvalidProfile, got %v", err)
+					}
+					if !strings.Contains(err.Error(), "selected.yaml") {
+						t.Fatalf("expected source path in error, got %v", err)
+					}
+					for _, diagnostic := range tc.diagnostics {
+						if !strings.Contains(err.Error(), diagnostic) {
+							t.Fatalf("expected error to contain %q, got %v", diagnostic, err)
+						}
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load valid profile: %v", err)
+				}
+				if got.ExtraParams["string_value"] != "enabled" {
+					t.Fatalf("unexpected copied extra params: %#v", got.ExtraParams)
+				}
+				objectValue, objectOK := got.ExtraParams["object_value"].(map[string]any)
+				arrayValue, arrayOK := got.ExtraParams["array_value"].([]any)
+				if !objectOK || objectValue["nested"] != true ||
+					!arrayOK || len(arrayValue) != 2 || arrayValue[0] != "first" || arrayValue[1] != 3 {
+					t.Fatalf("unexpected copied nested extra params: %#v", got.ExtraParams)
+				}
+			})
+		}
+	}
+}
+
+func TestProfileRepositoriesSelectCanonicalYAMLID(t *testing.T) {
+	const validProfile = `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected-model
+`
+	tests := []struct {
+		name        string
+		files       map[string]string
+		wantErr     error
+		diagnostics []string
+	}{
+		{
+			name: "same stem unknown field with different id is unrelated",
+			files: map[string]string{
+				"selected-profile.yaml": `
+id: unrelated-profile
+endpoint: http://localhost:8000/v1
+model: unrelated
+unknown: true
+`,
+				"valid.yaml": validProfile,
+			},
+		},
+		{
+			name: "same stem unidentifiable yaml is unrelated",
+			files: map[string]string{
+				"selected-profile.yaml": "id: [",
+				"valid.yaml":            validProfile,
+			},
+		},
+		{
+			name: "same stem raw key with different id is unrelated",
+			files: map[string]string{
+				"selected-profile.yaml": `
+id: unrelated-profile
+endpoint: http://localhost:8000/v1
+model: unrelated
+api_key: secret
+`,
+				"valid.yaml": validProfile,
+			},
+		},
+		{
+			name: "leading and trailing whitespace is normalized",
+			files: map[string]string{
+				"padded.yaml": `
+id: "  selected-profile  "
+endpoint: http://localhost:8000/v1
+model: selected-model
+`,
+			},
+		},
+		{
+			name: "blank id is unrelated",
+			files: map[string]string{
+				"selected-profile.yaml": `
+id: "   "
+endpoint: http://localhost:8000/v1
+model: unrelated
+`,
+			},
+			wantErr: ErrProfileNotFound,
+		},
+		{
+			name: "normalized duplicates are ambiguous",
+			files: map[string]string{
+				"first.yaml": validProfile,
+				"nested/second.yaml": `
+id: " selected-profile "
+endpoint: http://localhost:8000/v1
+model: duplicate
+`,
+			},
+			wantErr:     ErrInvalidProfile,
+			diagnostics: []string{"duplicate execution profile id", "first.yaml", "nested/second.yaml"},
+		},
+		{
+			name: "selected unknown field is authoritative",
+			files: map[string]string{
+				"malformed.yaml": `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected-model
+unknown: true
+`,
+			},
+			wantErr:     ErrInvalidYAML,
+			diagnostics: []string{"malformed.yaml"},
+		},
+		{
+			name: "selected raw key is authoritative",
+			files: map[string]string{
+				"insecure.yaml": `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected-model
+api_key: secret
+`,
+			},
+			wantErr:     ErrRawAPIKeyNotAllowed,
+			diagnostics: []string{"insecure.yaml"},
+		},
+		{
+			name: "selected identity in an additional document is authoritative",
+			files: map[string]string{
+				"additional-document.yaml": `
+---
+---
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected-model
+`,
+			},
+			wantErr:     ErrInvalidYAML,
+			diagnostics: []string{"additional-document.yaml", "exactly one YAML document"},
+		},
+	}
+
+	for _, source := range profileRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				repo := source.newRepository(t, tc.files)
+				got, err := repo.GetProfile(context.Background(), " selected-profile ")
+				if tc.wantErr != nil {
+					if !errors.Is(err, tc.wantErr) {
+						t.Fatalf("expected %v, got %v", tc.wantErr, err)
+					}
+					for _, diagnostic := range tc.diagnostics {
+						if !strings.Contains(err.Error(), diagnostic) {
+							t.Fatalf("expected error to contain %q, got %v", diagnostic, err)
+						}
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load selected profile: %v", err)
+				}
+				if got.ID != "selected-profile" || got.Model != "selected-model" {
+					t.Fatalf("unexpected selected profile: %+v", got)
+				}
+			})
+		}
+	}
+}
+
+func TestProfileRepositoriesRequireOneYAMLDocument(t *testing.T) {
+	const profile = `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected-model
+`
+	tests := []struct {
+		name    string
+		suffix  string
+		wantErr bool
+	}{
+		{name: "comments and trailing whitespace", suffix: "\n# trailing comment\n\n"},
+		{name: "second populated document", suffix: "\n---\nid: another\n", wantErr: true},
+		{name: "second empty document", suffix: "\n---\n", wantErr: true},
+		{name: "malformed trailing yaml", suffix: "\n---\n[", wantErr: true},
+		{name: "raw key in trailing document", suffix: "\n---\napi_key: secret\n", wantErr: true},
+	}
+
+	for _, source := range profileRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				repo := source.newRepository(t, map[string]string{"definition.yaml": profile + tc.suffix})
+				got, err := repo.GetProfile(context.Background(), "selected-profile")
+				if tc.wantErr {
+					if !errors.Is(err, ErrInvalidYAML) {
+						t.Fatalf("expected ErrInvalidYAML, got %v", err)
+					}
+					if !strings.Contains(err.Error(), "definition.yaml") {
+						t.Fatalf("expected source path in error, got %v", err)
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load one-document profile: %v", err)
+				}
+				if got.ID != "selected-profile" {
+					t.Fatalf("unexpected profile: %+v", got)
+				}
+			})
+		}
+	}
+}
+
+func TestProfileRepositoriesPreserveOverlayFallbackRules(t *testing.T) {
+	fallback := staticProfileRepo{profiles: map[string]*domain.ExecutionProfile{
+		"selected-profile": {ID: "selected-profile", Endpoint: "http://fallback", Model: "fallback-model"},
+	}}
+	tests := []struct {
+		name      string
+		files     map[string]string
+		wantModel string
+		wantErr   error
+	}{
+		{
+			name: "same stem malformed different id falls back",
+			files: map[string]string{
+				"selected-profile.yaml": `
+id: unrelated-profile
+endpoint: http://localhost:8000/v1
+model: unrelated
+unknown: true
+`,
+			},
+			wantModel: "fallback-model",
+		},
+		{
+			name: "blank id falls back",
+			files: map[string]string{
+				"selected-profile.yaml": `
+id: "   "
+endpoint: http://localhost:8000/v1
+model: unrelated
+`,
+			},
+			wantModel: "fallback-model",
+		},
+		{
+			name: "selected malformed profile stops fallback",
+			files: map[string]string{
+				"other-name.yaml": `
+id: selected-profile
+endpoint: http://localhost:8000/v1
+model: selected
+unknown: true
+`,
+			},
+			wantErr: ErrInvalidYAML,
+		},
+	}
+
+	for _, source := range profileRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				primary := source.newRepository(t, tc.files)
+				got, err := NewOverlayRepository(primary, fallback).GetProfile(context.Background(), "selected-profile")
+				if tc.wantErr != nil {
+					if !errors.Is(err, tc.wantErr) {
+						t.Fatalf("expected %v, got %v", tc.wantErr, err)
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load fallback profile: %v", err)
+				}
+				if got.Model != tc.wantModel {
+					t.Fatalf("model = %q, want %q", got.Model, tc.wantModel)
+				}
+			})
+		}
+	}
+}
+
+func TestProfileRepositoryReadsSourcesFreshOnEveryLookup(t *testing.T) {
+	newSource := func() (*recordingProfileFS, Repository) {
+		fsys := &recordingProfileFS{FS: fstest.MapFS{
+			"target.yaml": profileMapFile(`
+id: target
+endpoint: http://localhost:8000/v1
+model: target-model
+`),
+			"unrelated.yaml": profileMapFile(`
+id: unrelated
+endpoint: http://localhost:8000/v1
+model: unrelated-model
+`),
+		}}
+		return fsys, NewFSRepository(fsys, ".")
+	}
+
+	t.Run("selected source", func(t *testing.T) {
+		fsys, repo := newSource()
+		for lookup := 1; lookup <= 2; lookup++ {
+			got, err := repo.GetProfile(context.Background(), "target")
+			if err != nil {
+				t.Fatalf("lookup %d: %v", lookup, err)
+			}
+			if got.Model != "target-model" {
+				t.Fatalf("lookup %d model = %q", lookup, got.Model)
+			}
+			for _, name := range []string{"target.yaml", "unrelated.yaml"} {
+				if count := fsys.openCount(name); count != lookup {
+					t.Fatalf("%s opens after lookup %d = %d, want %d", name, lookup, count, lookup)
+				}
+			}
+		}
+	})
+
+	t.Run("overlay fallthrough", func(t *testing.T) {
+		primaryFS := &recordingProfileFS{FS: fstest.MapFS{
+			"unrelated.yaml": profileMapFile(`
+id: unrelated
+endpoint: http://localhost:8000/v1
+model: unrelated-model
+`),
+		}}
+		fallbackFS, fallback := newSource()
+		repo := NewOverlayRepository(NewFSRepository(primaryFS, "."), fallback)
+
+		for lookup := 1; lookup <= 2; lookup++ {
+			got, err := repo.GetProfile(context.Background(), "target")
+			if err != nil {
+				t.Fatalf("lookup %d: %v", lookup, err)
+			}
+			if got.Model != "target-model" {
+				t.Fatalf("lookup %d model = %q", lookup, got.Model)
+			}
+			if count := primaryFS.openCount("unrelated.yaml"); count != lookup {
+				t.Fatalf("primary opens after lookup %d = %d, want %d", lookup, count, lookup)
+			}
+			if count := fallbackFS.openCount("target.yaml"); count != lookup {
+				t.Fatalf("fallback opens after lookup %d = %d, want %d", lookup, count, lookup)
+			}
+		}
+	})
+}
+
+func TestProfileRepositoriesRejectInvalidExecutionSettings(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("operating-system filesystem", func(t *testing.T) {
+		dir := t.TempDir()
+		writeProfileTestFile(t, filepath.Join(dir, "invalid.yaml"), `
+id: invalid
+endpoint: http://localhost:8000/v1
+model: model
+temperature: .nan
+`)
+
+		_, err := NewFilesystemRepository(dir).GetProfile(ctx, "invalid")
+		if !errors.Is(err, ErrInvalidProfile) {
+			t.Fatalf("expected ErrInvalidProfile, got %v", err)
+		}
+	})
+
+	t.Run("fs.FS", func(t *testing.T) {
+		repo := NewFSRepository(fstest.MapFS{
+			"profiles/invalid.yaml": profileMapFile(`
+id: invalid
+endpoint: http://localhost:8000/v1
+model: model
+top_p: .inf
+`),
+		}, "profiles")
+
+		_, err := repo.GetProfile(ctx, "invalid")
+		if !errors.Is(err, ErrInvalidProfile) {
+			t.Fatalf("expected ErrInvalidProfile, got %v", err)
+		}
+	})
+}
+
 func TestOverlayRepository(t *testing.T) {
 	ctx := context.Background()
 	primaryProfile := &domain.ExecutionProfile{ID: "shared", Endpoint: "http://primary", Model: "primary"}
@@ -495,6 +947,77 @@ func TestOverlayRepository(t *testing.T) {
 	})
 }
 
+type profileRepositorySource struct {
+	name          string
+	newRepository func(t *testing.T, files map[string]string) Repository
+}
+
+type recordingProfileFS struct {
+	fs.FS
+	mu     sync.Mutex
+	opened []string
+}
+
+func (f *recordingProfileFS) Open(name string) (fs.File, error) {
+	f.mu.Lock()
+	f.opened = append(f.opened, name)
+	f.mu.Unlock()
+	return f.FS.Open(name)
+}
+
+func (f *recordingProfileFS) openCount(name string) int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	count := 0
+	for _, opened := range f.opened {
+		if opened == name {
+			count++
+		}
+	}
+	return count
+}
+
+func profileRepositorySources() []profileRepositorySource {
+	return []profileRepositorySource{
+		{
+			name: "operating system",
+			newRepository: func(t *testing.T, files map[string]string) Repository {
+				t.Helper()
+				root := t.TempDir()
+				for name, content := range files {
+					filePath := filepath.Join(root, filepath.FromSlash(name))
+					if err := os.MkdirAll(filepath.Dir(filePath), 0o755); err != nil {
+						t.Fatalf("create profile directory: %v", err)
+					}
+					writeProfileTestFile(t, filePath, content)
+				}
+				return NewFilesystemRepository(root)
+			},
+		},
+		{
+			name: "filesystem",
+			newRepository: func(t *testing.T, files map[string]string) Repository {
+				t.Helper()
+				fsys := make(fstest.MapFS, len(files))
+				for name, content := range files {
+					fsys[name] = profileMapFile(content)
+				}
+				return NewFSRepository(fsys, ".")
+			},
+		},
+	}
+}
+
+func deeplyNestedExtraParamsProfile(depth int) string {
+	var definition strings.Builder
+	definition.WriteString("id: selected-profile\nendpoint: http://localhost:8000/v1\nmodel: model\nextra_params:\n")
+	for level := 0; level < depth; level++ {
+		fmt.Fprintf(&definition, "%slevel_%d:\n", strings.Repeat("  ", level+1), level)
+	}
+	fmt.Fprintf(&definition, "%svalue: true\n", strings.Repeat("  ", depth+1))
+	return definition.String()
+}
+
 func profileMapFile(content string) *fstest.MapFile {
 	return &fstest.MapFile{Data: []byte(strings.TrimLeft(content, "\n"))}
 }

internal/prompt/go_renderer.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 	"text/template"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
@@ -18,6 +19,8 @@ var (
 	ErrInvalidMessageRole   = errors.New("invalid or empty message role")
 )
 
+const artifactTextChunkSize = 64 * 1024
+
 type goRenderer struct{}
 
 func NewGoRenderer() Renderer {
@@ -25,11 +28,13 @@ func NewGoRenderer() Renderer {
 }
 
 func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefinition, inputs map[string]*domain.Artifact, vars map[string]string) (*domain.RenderedPrompt, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
 	if definition == nil {
 		return nil, fmt.Errorf("%w: nil prompt definition", ErrRenderFailure)
 	}
 
-	// 1. Verify required inputs
 	for _, in := range definition.Inputs {
 		if !in.Required {
 			continue
@@ -40,44 +45,54 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 		}
 	}
 
-	// 2. Setup template functions
+	resolver := newArtifactTextResolver(ctx, inputs)
 	funcs := template.FuncMap{
-		"input": func(name string) (string, error) {
-			art, ok := inputs[name]
-			if !ok || art == nil {
-				return "", fmt.Errorf("%w: %s", ErrUnknownInput, name)
-			}
-			return string(art.Body), nil
-		},
+		"input": resolver.resolve,
 	}
 
-	sessionID, err := renderSessionID(definition.SessionID, funcs, vars)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	sessionID, err := renderSessionID(ctx, definition.SessionID, funcs, vars)
 	if err != nil {
 		return nil, err
 	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
 
-	var renderedMessages []domain.RenderedMessage
+	renderedMessages := make([]domain.RenderedMessage, 0, len(definition.Templates))
 
 	for i, tmplMsg := range definition.Templates {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
+		if err := ctx.Err(); err != nil {
+			return nil, err
 		}
 
 		if tmplMsg.Role == "" {
 			return nil, fmt.Errorf("%w: message %d", ErrInvalidMessageRole, i)
 		}
 
-		// Parse and execute template
-		tmpl, err := template.New(fmt.Sprintf("msg_%d", i)).Funcs(funcs).Option("missingkey=error").Parse(tmplMsg.Content)
-		if err != nil {
-			return nil, fmt.Errorf("%w: message %d: %v", ErrInvalidTemplate, i, err)
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		tmpl, parseErr := template.New(fmt.Sprintf("msg_%d", i)).Funcs(funcs).Option("missingkey=error").Parse(tmplMsg.Content)
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		if parseErr != nil {
+			return nil, fmt.Errorf("%w: message %d: %v", ErrInvalidTemplate, i, parseErr)
 		}
 
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
 		var buf bytes.Buffer
-		if err := tmpl.Execute(&buf, vars); err != nil {
-			return nil, fmt.Errorf("%w: message %d: %w", ErrRenderFailure, i, err)
+		executeErr := tmpl.Execute(&buf, vars)
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		if executeErr != nil {
+			return nil, fmt.Errorf("%w: message %d: %w", ErrRenderFailure, i, executeErr)
 		}
 
 		renderedMessages = append(renderedMessages, domain.RenderedMessage{
@@ -85,6 +100,13 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 			Content:      buf.String(),
 			CacheControl: cloneCacheControl(tmplMsg.CacheControl),
 		})
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := ctx.Err(); err != nil {
+		return nil, err
 	}
 
 	return &domain.RenderedPrompt{
@@ -93,15 +115,75 @@ func (r *goRenderer) Render(ctx context.Context, definition *domain.PromptDefini
 	}, nil
 }
 
-func renderSessionID(raw string, funcs template.FuncMap, vars map[string]string) (string, error) {
-	tmpl, err := template.New("session_id").Funcs(funcs).Option("missingkey=error").Parse(raw)
-	if err != nil {
-		return "", fmt.Errorf("%w: session_id: %v", ErrInvalidTemplate, err)
+type artifactTextResolver struct {
+	ctx        context.Context
+	inputs     map[string]*domain.Artifact
+	textByName map[string]string
+}
+
+func newArtifactTextResolver(ctx context.Context, inputs map[string]*domain.Artifact) *artifactTextResolver {
+	return &artifactTextResolver{
+		ctx:        ctx,
+		inputs:     inputs,
+		textByName: make(map[string]string),
+	}
+}
+
+func (r *artifactTextResolver) resolve(name string) (string, error) {
+	if err := r.ctx.Err(); err != nil {
+		return "", err
+	}
+	artifact, ok := r.inputs[name]
+	if !ok || artifact == nil {
+		return "", fmt.Errorf("%w: %s", ErrUnknownInput, name)
+	}
+	if text, ok := r.textByName[name]; ok {
+		return text, nil
 	}
 
+	var builder strings.Builder
+	builder.Grow(len(artifact.Body))
+	for start := 0; start < len(artifact.Body); start += artifactTextChunkSize {
+		if err := r.ctx.Err(); err != nil {
+			return "", err
+		}
+		end := min(start+artifactTextChunkSize, len(artifact.Body))
+		_, _ = builder.Write(artifact.Body[start:end])
+		if err := r.ctx.Err(); err != nil {
+			return "", err
+		}
+	}
+	if err := r.ctx.Err(); err != nil {
+		return "", err
+	}
+
+	text := builder.String()
+	r.textByName[name] = text
+	return text, nil
+}
+
+func renderSessionID(ctx context.Context, raw string, funcs template.FuncMap, vars map[string]string) (string, error) {
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+	tmpl, parseErr := template.New("session_id").Funcs(funcs).Option("missingkey=error").Parse(raw)
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+	if parseErr != nil {
+		return "", fmt.Errorf("%w: session_id: %v", ErrInvalidTemplate, parseErr)
+	}
+
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	var buf bytes.Buffer
-	if err := tmpl.Execute(&buf, vars); err != nil {
-		return "", fmt.Errorf("%w: session_id: %w", ErrRenderFailure, err)
+	executeErr := tmpl.Execute(&buf, vars)
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+	if executeErr != nil {
+		return "", fmt.Errorf("%w: session_id: %w", ErrRenderFailure, executeErr)
 	}
 
 	sessionID, err := domain.NormalizeSessionID(buf.String())

internal/prompt/renderer_test.go

@@ -1,6 +1,7 @@
 package prompt
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"strings"
@@ -228,6 +229,24 @@ func TestGoRenderer_Render(t *testing.T) {
 		}
 	})
 
+	t.Run("malformed rendered session id fails rendering", func(t *testing.T) {
+		def := &domain.PromptDefinition{
+			SessionID: "{{ .session_id }}",
+			Inputs:    []domain.PromptInput{{Name: "transcript", Required: true}},
+			Templates: []domain.PromptMessageTemplate{
+				{Role: "system", Content: "Speak in a {{.tone}} tone."},
+			},
+		}
+
+		_, err := renderer.Render(ctx, def, inputs, map[string]string{
+			"tone":       "concise",
+			"session_id": "session" + string([]byte{0xff}),
+		})
+		if !errors.Is(err, ErrRenderFailure) {
+			t.Fatalf("expected ErrRenderFailure, got %v", err)
+		}
+	})
+
 	t.Run("inserting required input artifact", func(t *testing.T) {
 		def := &domain.PromptDefinition{
 			Inputs: []domain.PromptInput{{Name: "transcript", Required: true}},
@@ -343,3 +362,186 @@ func TestGoRenderer_Render(t *testing.T) {
 		}
 	})
 }
+
+func TestGoRendererCancellation(t *testing.T) {
+	t.Run("before session parsing", func(t *testing.T) {
+		definition := &domain.PromptDefinition{
+			SessionID: "{{ malformed",
+			Templates: []domain.PromptMessageTemplate{
+				{Role: "user", Content: "not rendered"},
+			},
+		}
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+
+		result, err := NewGoRenderer().Render(ctx, definition, nil, nil)
+		if result != nil || !errors.Is(err, context.Canceled) {
+			t.Fatalf("result=%#v err=%v, want nil/context.Canceled", result, err)
+		}
+		if errors.Is(err, ErrInvalidTemplate) {
+			t.Fatalf("pre-canceled render parsed the malformed session: %v", err)
+		}
+
+		result, err = NewGoRenderer().Render(context.Background(), definition, nil, nil)
+		if result != nil || !errors.Is(err, ErrInvalidTemplate) {
+			t.Fatalf("active render result=%#v err=%v, want nil/ErrInvalidTemplate", result, err)
+		}
+	})
+
+	t.Run("during artifact text conversion", func(t *testing.T) {
+		ctx := newCancelOnCheckContext(3)
+		body := bytes.Repeat([]byte("x"), artifactTextChunkSize*2)
+		original := append([]byte(nil), body...)
+		resolver := newArtifactTextResolver(ctx, map[string]*domain.Artifact{
+			"document": {Body: body},
+		})
+
+		text, err := resolver.resolve("document")
+		if text != "" || !errors.Is(err, context.Canceled) {
+			t.Fatalf("text length=%d err=%v, want empty/context.Canceled", len(text), err)
+		}
+		if _, published := resolver.textByName["document"]; published {
+			t.Fatal("canceled conversion published partial artifact text")
+		}
+		if !bytes.Equal(body, original) {
+			t.Fatal("resolver mutated the artifact body")
+		}
+	})
+
+	t.Run("after final message execution", func(t *testing.T) {
+		definition := &domain.PromptDefinition{
+			Templates: []domain.PromptMessageTemplate{
+				{Role: "user", Content: "fully rendered"},
+			},
+		}
+		counter := &checkCountingContext{Context: context.Background()}
+		if _, err := NewGoRenderer().Render(counter, definition, nil, nil); err != nil {
+			t.Fatalf("count render checkpoints: %v", err)
+		}
+
+		// The final three checks occur after template execution, after the
+		// message is assembled, and immediately before publication.
+		ctx := newCancelOnCheckContext(counter.checks - 2)
+		result, err := NewGoRenderer().Render(ctx, definition, nil, nil)
+		if result != nil || !errors.Is(err, context.Canceled) {
+			t.Fatalf("result=%#v err=%v, want nil/context.Canceled", result, err)
+		}
+	})
+}
+
+func TestGoRendererArtifactTextLifecycle(t *testing.T) {
+	body := []byte{'a', 0xff, 'b', 0xfe}
+	original := append([]byte(nil), body...)
+	artifact := &domain.Artifact{Body: body}
+	inputs := map[string]*domain.Artifact{"document": artifact}
+	definition := &domain.PromptDefinition{
+		Templates: []domain.PromptMessageTemplate{
+			{Role: "user", Content: "{{input \"document\"}}|{{input \"document\"}}"},
+		},
+	}
+
+	first, err := NewGoRenderer().Render(context.Background(), definition, inputs, nil)
+	if err != nil {
+		t.Fatalf("first render: %v", err)
+	}
+	wantFirst := append(append(append([]byte(nil), body...), '|'), body...)
+	if !bytes.Equal([]byte(first.Messages[0].Content), wantFirst) {
+		t.Fatalf("rendered bytes=%v, want %v", []byte(first.Messages[0].Content), wantFirst)
+	}
+	if !bytes.Equal(body, original) {
+		t.Fatalf("renderer mutated artifact body: got %v want %v", body, original)
+	}
+
+	body[0] = 'z'
+	if bytes.Equal([]byte(first.Messages[0].Content), append(append(append([]byte(nil), body...), '|'), body...)) {
+		t.Fatal("completed render aliases the artifact body")
+	}
+	second, err := NewGoRenderer().Render(context.Background(), definition, inputs, nil)
+	if err != nil {
+		t.Fatalf("second render: %v", err)
+	}
+	wantSecond := append(append(append([]byte(nil), body...), '|'), body...)
+	if !bytes.Equal([]byte(second.Messages[0].Content), wantSecond) {
+		t.Fatalf("second render reused text from another call: got %v want %v", []byte(second.Messages[0].Content), wantSecond)
+	}
+
+	nilInputs := map[string]*domain.Artifact{"document": nil}
+	result, err := NewGoRenderer().Render(context.Background(), definition, nilInputs, nil)
+	if result != nil || !errors.Is(err, ErrUnknownInput) || !errors.Is(err, ErrRenderFailure) {
+		t.Fatalf("nil input result=%#v err=%v, want ErrUnknownInput and ErrRenderFailure", result, err)
+	}
+}
+
+func BenchmarkGoRendererArtifactReferences(b *testing.B) {
+	body := bytes.Repeat([]byte("document content "), (artifactTextChunkSize*4)/len("document content "))
+	inputs := map[string]*domain.Artifact{
+		"document": {Body: body},
+	}
+	tests := []struct {
+		name       string
+		definition *domain.PromptDefinition
+	}{
+		{
+			name: "one reference",
+			definition: &domain.PromptDefinition{
+				Templates: []domain.PromptMessageTemplate{
+					{Role: "user", Content: "{{input \"document\"}}"},
+				},
+			},
+		},
+		{
+			name: "repeated across session and messages",
+			definition: &domain.PromptDefinition{
+				SessionID: "document-{{len (input \"document\")}}",
+				Templates: []domain.PromptMessageTemplate{
+					{Role: "system", Content: "{{input \"document\"}}"},
+					{Role: "user", Content: "{{input \"document\"}} {{input \"document\"}}"},
+				},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		b.Run(tc.name, func(b *testing.B) {
+			renderer := NewGoRenderer()
+			b.ReportAllocs()
+			b.SetBytes(int64(len(body)))
+			for range b.N {
+				if _, err := renderer.Render(context.Background(), tc.definition, inputs, nil); err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+type checkCountingContext struct {
+	context.Context
+	checks int
+}
+
+func (c *checkCountingContext) Err() error {
+	c.checks++
+	return c.Context.Err()
+}
+
+type cancelOnCheckContext struct {
+	context.Context
+	cancel    context.CancelFunc
+	remaining int
+}
+
+func newCancelOnCheckContext(checks int) *cancelOnCheckContext {
+	ctx, cancel := context.WithCancel(context.Background())
+	return &cancelOnCheckContext{Context: ctx, cancel: cancel, remaining: checks}
+}
+
+func (c *cancelOnCheckContext) Err() error {
+	if c.Context.Err() == nil {
+		c.remaining--
+		if c.remaining == 0 {
+			c.cancel()
+		}
+	}
+	return c.Context.Err()
+}

internal/promptdef/content_source.go

@@ -0,0 +1,98 @@
+package promptdef
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/filecatalog"
+)
+
+type contentSourceRoot interface {
+	readContentFile(sourcePath string, contentFile string) (string, string, error)
+}
+
+type osContentSourceRoot struct {
+	root                string
+	sourcePathsRelative bool
+}
+
+func (r osContentSourceRoot) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	if strings.TrimSpace(contentFile) == "" {
+		return "", "", fmt.Errorf("path is required")
+	}
+	if filepath.IsAbs(contentFile) {
+		return "", "", fmt.Errorf("path %q must be relative", contentFile)
+	}
+
+	root, err := filepath.Abs(r.root)
+	if err != nil {
+		return "", "", fmt.Errorf("resolve source root %q: %w", r.root, err)
+	}
+	canonicalRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		return "", "", fmt.Errorf("resolve source root %q: %w", r.root, err)
+	}
+
+	promptPath := sourcePath
+	if r.sourcePathsRelative && !filepath.IsAbs(promptPath) {
+		promptPath = filepath.Join(root, filepath.FromSlash(promptPath))
+	} else {
+		promptPath, err = filepath.Abs(promptPath)
+		if err != nil {
+			return "", "", fmt.Errorf("resolve prompt source %q: %w", sourcePath, err)
+		}
+	}
+	resolvedPath := filepath.Clean(filepath.Join(filepath.Dir(promptPath), contentFile))
+	if !containsOSPath(root, resolvedPath) {
+		return "", "", fmt.Errorf("path %q escapes source root %q", contentFile, r.root)
+	}
+
+	canonicalPath, err := filepath.EvalSymlinks(resolvedPath)
+	if err != nil {
+		return "", "", err
+	}
+	if !containsOSPath(canonicalRoot, canonicalPath) {
+		return "", "", fmt.Errorf("path %q escapes source root %q", contentFile, r.root)
+	}
+
+	body, err := os.ReadFile(canonicalPath)
+	if err != nil {
+		return "", "", err
+	}
+	return string(body), resolvedPath, nil
+}
+
+type fsContentSourceRoot struct {
+	fsys fs.FS
+	root string
+}
+
+func (r fsContentSourceRoot) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	root := filecatalog.CleanFSRoot(r.root)
+	cleanSourcePath := path.Clean(sourcePath)
+	if cleanSourcePath == root {
+		root = path.Dir(root)
+	}
+
+	resolvedPath, _, err := filecatalog.ResolveFSPath(root, path.Dir(cleanSourcePath), contentFile)
+	if err != nil {
+		return "", "", err
+	}
+	body, err := fs.ReadFile(r.fsys, resolvedPath)
+	if err != nil {
+		return "", "", err
+	}
+	return string(body), resolvedPath, nil
+}
+
+func containsOSPath(root string, name string) bool {
+	relative, err := filepath.Rel(root, name)
+	if err != nil || filepath.IsAbs(relative) {
+		return false
+	}
+	return relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))
+}

internal/promptdef/filesystem_repository.go

@@ -5,14 +5,11 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
-	"os"
-	"path"
-	"path/filepath"
 	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
-	"gitea.maximumdirect.net/eric/promptkit/internal/filecatalog"
 	"gopkg.in/yaml.v3"
 )
 
@@ -22,13 +19,8 @@ var (
 	ErrInvalidPromptDefinition  = errors.New("invalid prompt definition configuration")
 )
 
-type filesystemRepository struct {
-	dir string
-}
-
-type fsRepository struct {
-	fsys fs.FS
-	root string
+type sourceRepository struct {
+	source promptDefinitionSource
 }
 
 type promptDefinitionFile struct {
@@ -69,19 +61,47 @@ type promptOutputContractFile struct {
 }
 
 func NewFilesystemRepository(dir string) Repository {
-	return &filesystemRepository{dir: dir}
+	return &sourceRepository{
+		source: osPromptSource{
+			root:        dir,
+			contentRoot: osContentSourceRoot{root: dir},
+		},
+	}
 }
 
 func NewFSRepository(fsys fs.FS, root string) Repository {
-	return &fsRepository{fsys: fsys, root: root}
+	return &sourceRepository{
+		source: fsPromptSource{
+			fsys:        fsys,
+			root:        root,
+			contentRoot: fsContentSourceRoot{fsys: fsys, root: root},
+		},
+	}
 }
 
-func (r *filesystemRepository) GetPromptDefinition(ctx context.Context, id string, version string) (*domain.PromptDefinition, error) {
+// NewFileRepository constructs a repository for one operating-system prompt file.
+func NewFileRepository(fsys fs.FS, file string, sourceDir string) Repository {
+	return &sourceRepository{
+		source: fsPromptSource{
+			fsys: fsys,
+			root: file,
+			contentRoot: osContentSourceRoot{
+				root:                sourceDir,
+				sourcePathsRelative: true,
+			},
+		},
+	}
+}
+
+func (r *sourceRepository) GetPromptDefinition(ctx context.Context, id string, version string) (*domain.PromptDefinition, error) {
 	if strings.TrimSpace(id) == "" {
 		return nil, fmt.Errorf("%w: prompt id is required", ErrInvalidPromptDefinition)
 	}
+	if r == nil || r.source == nil {
+		return nil, errors.New("failed to read prompt definition directory: source is nil")
+	}
 
-	files, err := filecatalog.FindYAMLFiles(ctx, r.dir)
+	files, err := r.source.findYAMLFiles(ctx)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read prompt definition directory: %w", err)
 	}
@@ -94,33 +114,24 @@ func (r *filesystemRepository) GetPromptDefinition(ctx context.Context, id strin
 		default:
 		}
 
-		relPath := filecatalog.RelativePath(r.dir, fullPath)
-		fileMatch := filecatalog.Stem(filepath.Base(fullPath)) == id
-
-		raw, err := loadPromptDefinitionFile(fullPath)
+		relPath := r.source.displayPath(fullPath)
+		data, err := r.source.readDefinition(fullPath)
 		if err != nil {
-			if fileMatch || promptDefinitionFileHasID(fullPath, id) {
+			return nil, fmt.Errorf("failed to read prompt definition file %s: %w", relPath, err)
+		}
+		raw, err := decodePromptDefinition(data)
+		if err != nil {
+			if promptDefinitionDataMatches(data, id, version) {
 				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidYAML, relPath, err)
 			}
 			continue
 		}
-
-		def, err := normalizePromptDefinition(raw, fullPath)
-		if err != nil {
-			if fileMatch || strings.TrimSpace(raw.ID) == id {
-				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidPromptDefinition, relPath, err)
-			}
-			continue
-		}
-
-		if def.ID != id {
-			continue
-		}
-		if version != "" && def.Version != version {
+		if !promptDefinitionMatches(raw, id, version) {
 			continue
 		}
 		matches = append(matches, promptDefinitionMatch{
-			def:  def,
+			raw:        raw,
+			sourcePath: fullPath,
 			path:       relPath,
 		})
 	}
@@ -137,132 +148,23 @@ func (r *filesystemRepository) GetPromptDefinition(ctx context.Context, id strin
 	}
 
 	if len(matches) == 1 {
-		return matches[0].def, nil
+		match := matches[0]
+		def, err := normalizePromptDefinition(match.raw, r.source, match.sourcePath)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %s: %v", ErrInvalidPromptDefinition, match.path, err)
+		}
+		return def, nil
 	}
 
 	return nil, ErrPromptDefinitionNotFound
 }
 
-func (r *fsRepository) GetPromptDefinition(ctx context.Context, id string, version string) (*domain.PromptDefinition, error) {
-	return loadPromptDefinition(ctx, r.fsys, r.root, id, version)
-}
-
 type promptDefinitionMatch struct {
-	def  *domain.PromptDefinition
+	raw        *promptDefinitionFile
+	sourcePath string
 	path       string
 }
 
-func loadPromptDefinitionFile(path string) (*promptDefinitionFile, error) {
-	data, err := os.ReadFile(path)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read prompt definition file: %w", err)
-	}
-
-	var raw promptDefinitionFile
-	decoder := yaml.NewDecoder(bytes.NewReader(data))
-	decoder.KnownFields(true)
-	if err := decoder.Decode(&raw); err != nil {
-		return nil, err
-	}
-	return &raw, nil
-}
-
-func promptDefinitionFileHasID(path string, id string) bool {
-	data, err := os.ReadFile(path)
-	if err != nil {
-		return false
-	}
-	var raw struct {
-		ID string `yaml:"id"`
-	}
-	if err := yaml.NewDecoder(bytes.NewReader(data)).Decode(&raw); err != nil {
-		return false
-	}
-	return strings.TrimSpace(raw.ID) == id
-}
-
-func loadPromptDefinition(ctx context.Context, fsys fs.FS, root string, id string, version string) (*domain.PromptDefinition, error) {
-	if strings.TrimSpace(id) == "" {
-		return nil, fmt.Errorf("%w: prompt id is required", ErrInvalidPromptDefinition)
-	}
-	if fsys == nil {
-		return nil, fmt.Errorf("failed to read prompt definition directory: filesystem is nil")
-	}
-
-	files, err := filecatalog.FindFSYAMLFiles(ctx, fsys, root)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read prompt definition directory: %w", err)
-	}
-	cleanRoot := filecatalog.CleanFSRoot(root)
-	rootInfo, err := fs.Stat(fsys, cleanRoot)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read prompt definition directory: %w", err)
-	}
-
-	var matches []promptDefinitionMatch
-	for _, fullPath := range files {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
-		}
-
-		relPath := filecatalog.DisplayPath(root, fullPath)
-		fileMatch := filecatalog.Stem(path.Base(fullPath)) == id
-		data, err := fs.ReadFile(fsys, fullPath)
-		if err != nil {
-			if fileMatch {
-				return nil, fmt.Errorf("%w: %s: failed to read prompt definition file: %v", ErrInvalidYAML, relPath, err)
-			}
-			continue
-		}
-
-		raw, err := decodePromptDefinition(data)
-		if err != nil {
-			if fileMatch || promptDefinitionDataHasID(data, id) {
-				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidYAML, relPath, err)
-			}
-			continue
-		}
-
-		def, err := normalizePromptDefinitionFromFS(raw, fsys, root, fullPath, rootInfo.IsDir())
-		if err != nil {
-			if fileMatch || strings.TrimSpace(raw.ID) == id {
-				return nil, fmt.Errorf("%w: %s: %v", ErrInvalidPromptDefinition, relPath, err)
-			}
-			continue
-		}
-
-		if def.ID != id {
-			continue
-		}
-		if version != "" && def.Version != version {
-			continue
-		}
-		matches = append(matches, promptDefinitionMatch{
-			def:  def,
-			path: relPath,
-		})
-	}
-
-	if len(matches) > 1 {
-		paths := make([]string, 0, len(matches))
-		for _, match := range matches {
-			paths = append(paths, match.path)
-		}
-		if version != "" {
-			return nil, fmt.Errorf("%w: duplicate prompt definition id %q version %q found in: %s", ErrInvalidPromptDefinition, id, version, strings.Join(paths, ", "))
-		}
-		return nil, fmt.Errorf("%w: duplicate prompt definition id %q found in: %s", ErrInvalidPromptDefinition, id, strings.Join(paths, ", "))
-	}
-
-	if len(matches) == 1 {
-		return matches[0].def, nil
-	}
-
-	return nil, ErrPromptDefinitionNotFound
-}
-
 func decodePromptDefinition(data []byte) (*promptDefinitionFile, error) {
 	var raw promptDefinitionFile
 	decoder := yaml.NewDecoder(bytes.NewReader(data))
@@ -270,59 +172,44 @@ func decodePromptDefinition(data []byte) (*promptDefinitionFile, error) {
 	if err := decoder.Decode(&raw); err != nil {
 		return nil, err
 	}
+	var additional yaml.Node
+	if err := decoder.Decode(&additional); err != io.EOF {
+		if err != nil {
+			return nil, err
+		}
+		return nil, errors.New("prompt definition file must contain exactly one YAML document")
+	}
 	return &raw, nil
 }
 
-func promptDefinitionDataHasID(data []byte, id string) bool {
+func promptDefinitionDataMatches(data []byte, id string, version string) bool {
 	var raw struct {
 		ID      string `yaml:"id"`
+		Version string `yaml:"version"`
 	}
 	if err := yaml.NewDecoder(bytes.NewReader(data)).Decode(&raw); err != nil {
 		return false
 	}
-	return strings.TrimSpace(raw.ID) == id
+	return promptSelectorMatches(raw.ID, raw.Version, id, version)
 }
 
-func normalizePromptDefinition(raw *promptDefinitionFile, sourcePath string) (*domain.PromptDefinition, error) {
-	promptDir := filepath.Dir(sourcePath)
-	return normalizePromptDefinitionWithContent(raw, func(contentFile string) (string, string, error) {
-		resolvedPath := strings.TrimSpace(contentFile)
-		if !filepath.IsAbs(resolvedPath) {
-			resolvedPath = filepath.Join(promptDir, resolvedPath)
+func promptDefinitionMatches(raw *promptDefinitionFile, id string, version string) bool {
+	if raw == nil {
+		return false
 	}
-		resolvedPath = filepath.Clean(resolvedPath)
-
-		body, err := os.ReadFile(resolvedPath)
-		if err != nil {
-			return "", "", err
-		}
-		return string(body), resolvedPath, nil
-	})
+	return promptSelectorMatches(raw.ID, raw.Version, id, version)
 }
 
-func normalizePromptDefinitionFromFS(raw *promptDefinitionFile, fsys fs.FS, root string, sourcePath string, rootIsDir bool) (*domain.PromptDefinition, error) {
-	promptDir := path.Dir(sourcePath)
-	return normalizePromptDefinitionWithContent(raw, func(contentFile string) (string, string, error) {
-		var resolvedPath string
-		if rootIsDir {
-			var err error
-			resolvedPath, _, err = filecatalog.ResolveFSPath(root, promptDir, contentFile)
-			if err != nil {
-				return "", "", err
-			}
-		} else {
-			resolvedPath = strings.TrimSpace(contentFile)
-			if !path.IsAbs(resolvedPath) {
-				resolvedPath = path.Join(promptDir, resolvedPath)
-			}
-			resolvedPath = strings.TrimPrefix(path.Clean(resolvedPath), "/")
+func promptSelectorMatches(rawID string, rawVersion string, id string, version string) bool {
+	if strings.TrimSpace(rawID) != id {
+		return false
 	}
+	return version == "" || strings.TrimSpace(rawVersion) == version
+}
 
-		body, err := fs.ReadFile(fsys, resolvedPath)
-		if err != nil {
-			return "", "", err
-		}
-		return string(body), resolvedPath, nil
+func normalizePromptDefinition(raw *promptDefinitionFile, sourceRoot contentSourceRoot, sourcePath string) (*domain.PromptDefinition, error) {
+	return normalizePromptDefinitionWithContent(raw, func(contentFile string) (string, string, error) {
+		return sourceRoot.readContentFile(sourcePath, contentFile)
 	})
 }
 
@@ -402,17 +289,14 @@ func normalizePromptDefinitionWithContent(raw *promptDefinitionFile, readContent
 		})
 	}
 
-	if !isValidOutputFormat(raw.Output.Format) {
-		return nil, fmt.Errorf("invalid output format: %q", raw.Output.Format)
+	outputContract := domain.OutputContract{
+		Format:         raw.Output.Format,
+		ValidationMode: raw.Output.ValidationMode,
+		SchemaPath:     strings.TrimSpace(raw.Output.SchemaPath),
+		RepairAttempts: raw.Output.RepairAttempts,
 	}
-	if !isValidValidationMode(raw.Output.ValidationMode) {
-		return nil, fmt.Errorf("invalid validation mode: %q", raw.Output.ValidationMode)
-	}
-	if raw.Output.ValidationMode == domain.ValidationJSONSchema && strings.TrimSpace(raw.Output.SchemaPath) == "" {
-		return nil, errors.New("output.schema_path is required when output.validation_mode is json_schema")
-	}
-	if raw.Output.RepairAttempts < 0 {
-		return nil, errors.New("output.repair_attempts must be greater than or equal to 0")
+	if err := domain.ValidateOutputContract(outputContract); err != nil {
+		return nil, fmt.Errorf("output: %w", err)
 	}
 
 	defaultProfile := ""
@@ -432,12 +316,7 @@ func normalizePromptDefinitionWithContent(raw *promptDefinitionFile, readContent
 		Inputs:         inputs,
 		Templates:      templates,
 		OutputFormat:   raw.Output.Format,
-		Validation: domain.OutputContract{
-			Format:         raw.Output.Format,
-			ValidationMode: raw.Output.ValidationMode,
-			SchemaPath:     strings.TrimSpace(raw.Output.SchemaPath),
-			RepairAttempts: raw.Output.RepairAttempts,
-		},
+		Validation:     outputContract,
 	}, nil
 }
 
@@ -464,21 +343,3 @@ func normalizeCacheControl(raw *cacheControlFile) (*domain.CacheControl, error)
 		TTL:  ttl,
 	}, nil
 }
-
-func isValidOutputFormat(f domain.OutputFormat) bool {
-	switch f {
-	case domain.FormatText, domain.FormatMarkdown, domain.FormatJSON:
-		return true
-	default:
-		return false
-	}
-}
-
-func isValidValidationMode(m domain.ValidationMode) bool {
-	switch m {
-	case domain.ValidationNone, domain.ValidationBasic, domain.ValidationJSON, domain.ValidationJSONSchema:
-		return true
-	default:
-		return false
-	}
-}

internal/promptdef/repository_test.go

@@ -3,23 +3,51 @@ package promptdef
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"testing"
 	"testing/fstest"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
 )
 
-func TestFilesystemRepository_GetPromptDefinition(t *testing.T) {
+func TestPromptRepositoryDefinitionFixtures(t *testing.T) {
+	sources := []struct {
+		name                string
+		newRepository       func(string) Repository
+		contentPathsAreFull bool
+	}{
+		{
+			name:                "operating system",
+			newRepository:       NewFilesystemRepository,
+			contentPathsAreFull: true,
+		},
+		{
+			name: "filesystem",
+			newRepository: func(root string) Repository {
+				return NewFSRepository(os.DirFS(root), ".")
+			},
+		},
+	}
+
+	for _, source := range sources {
+		t.Run(source.name, func(t *testing.T) {
+			testPromptRepositoryDefinitionFixtures(t, source.newRepository, source.contentPathsAreFull)
+		})
+	}
+}
+
+func testPromptRepositoryDefinitionFixtures(t *testing.T, newRepository func(string) Repository, contentPathsAreFull bool) {
 	tmpDir := t.TempDir()
 	if err := copyTree("testdata", tmpDir); err != nil {
 		t.Fatalf("failed to copy testdata: %v", err)
 	}
 
-	repo := NewFilesystemRepository(tmpDir)
+	repo := newRepository(tmpDir)
 	ctx := context.Background()
 
 	t.Run("valid inline prompt", func(t *testing.T) {
@@ -64,8 +92,8 @@ func TestFilesystemRepository_GetPromptDefinition(t *testing.T) {
 		if p.Templates[1].ContentFile == "" {
 			t.Fatal("expected ContentFile source metadata to be preserved")
 		}
-		if !filepath.IsAbs(p.Templates[1].ContentFile) {
-			t.Fatalf("expected resolved content_file path to be absolute, got %q", p.Templates[1].ContentFile)
+		if filepath.IsAbs(p.Templates[1].ContentFile) != contentPathsAreFull {
+			t.Fatalf("unexpected content_file path representation: %q", p.Templates[1].ContentFile)
 		}
 	})
 
@@ -287,20 +315,20 @@ output:
 		targetErr  error
 		errSubstrs []string
 	}{
-		{name: "invalid YAML", id: "invalid_yaml", targetErr: ErrInvalidYAML},
-		{name: "missing id", id: "missing_id", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"id is required"}},
-		{name: "no messages", id: "no_messages", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"at least one message is required"}},
-		{name: "both content and content_file", id: "both_content_and_content_file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"exactly one"}},
-		{name: "neither content nor content_file", id: "neither_content_nor_content_file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"exactly one"}},
-		{name: "missing content_file", id: "missing_content_file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"failed to read content_file"}},
-		{name: "duplicate input names", id: "duplicate_input_names", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"duplicate input name"}},
-		{name: "invalid validation mode", id: "invalid_validation_mode", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"invalid validation mode"}},
-		{name: "json_schema without schema_path", id: "json_schema_without_schema_path", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"schema_path"}},
-		{name: "unknown input field", id: "unknown_input_field", targetErr: ErrInvalidYAML, errSubstrs: []string{"field unknown_input_setting not found"}},
-		{name: "empty cache control type", id: "empty_cache_control_type", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "type is required"}},
-		{name: "unsupported cache control type", id: "unsupported_cache_control_type", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "unsupported type"}},
-		{name: "unsupported cache control ttl", id: "unsupported_cache_control_ttl", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "unsupported ttl"}},
-		{name: "unknown cache control field", id: "unknown_cache_control_field", targetErr: ErrInvalidYAML, errSubstrs: []string{"field unexpected not found"}},
+		{name: "unidentifiable invalid YAML is unrelated", id: "invalid-yaml", targetErr: ErrPromptDefinitionNotFound},
+		{name: "missing id is not selected by filename", id: "missing_id", targetErr: ErrPromptDefinitionNotFound},
+		{name: "no messages", id: "no-messages", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"at least one message is required"}},
+		{name: "both content and content_file", id: "both-content-and-content-file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"exactly one"}},
+		{name: "neither content nor content_file", id: "neither-content-nor-content-file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"exactly one"}},
+		{name: "missing content_file", id: "missing-content-file", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"failed to read content_file"}},
+		{name: "duplicate input names", id: "duplicate-input-names", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"duplicate input name"}},
+		{name: "invalid validation mode", id: "invalid-validation-mode", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"invalid validation mode"}},
+		{name: "json_schema without schema_path", id: "json-schema-without-schema-path", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"schema_path"}},
+		{name: "unknown input field", id: "unknown-input-field", targetErr: ErrInvalidYAML, errSubstrs: []string{"field unknown_input_setting not found"}},
+		{name: "empty cache control type", id: "empty-cache-control-type", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "type is required"}},
+		{name: "unsupported cache control type", id: "unsupported-cache-control-type", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "unsupported type"}},
+		{name: "unsupported cache control ttl", id: "unsupported-cache-control-ttl", targetErr: ErrInvalidPromptDefinition, errSubstrs: []string{"cache_control", "unsupported ttl"}},
+		{name: "unknown cache control field", id: "unknown-cache-control-field", targetErr: ErrInvalidYAML, errSubstrs: []string{"field unexpected not found"}},
 	}
 
 	for _, tc := range cases {
@@ -396,7 +424,7 @@ output:
 
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
-			repo := NewFSRepository(fstest.MapFS{
+			fsys := &recordingFS{FS: fstest.MapFS{
 				"prompts/prompt.yaml": &fstest.MapFile{Data: []byte(`
 id: fs-escaped-prompt
 version: "1.0.0"
@@ -409,7 +437,8 @@ output:
   repair_attempts: 0
 `)},
 				"outside.tmpl": &fstest.MapFile{Data: []byte(`Outside root.`)},
-			}, "prompts")
+			}}
+			repo := NewFSRepository(fsys, "prompts")
 
 			_, err := repo.GetPromptDefinition(context.Background(), "fs-escaped-prompt", "")
 			if !errors.Is(err, ErrInvalidPromptDefinition) {
@@ -418,65 +447,612 @@ output:
 			if !strings.Contains(err.Error(), tc.wantErr) {
 				t.Fatalf("expected error to contain %q, got %v", tc.wantErr, err)
 			}
+			if fsys.wasOpened("outside.tmpl") {
+				t.Fatal("rejected content path opened the outside file")
+			}
 		})
 	}
 }
 
-func TestFSRepositoryRejectsDuplicatePromptIDs(t *testing.T) {
-	repo := NewFSRepository(fstest.MapFS{
-		"one.yaml": &fstest.MapFile{Data: []byte(`
-id: duplicate-fs-prompt
-version: "1.0.0"
-messages:
-  - role: user
-    content: First.
-output:
-  format: text
-  validation_mode: none
-  repair_attempts: 0
-`)},
-		"nested/two.yaml": &fstest.MapFile{Data: []byte(`
-id: duplicate-fs-prompt
-version: "1.0.0"
-messages:
-  - role: user
-    content: Second.
-output:
-  format: text
-  validation_mode: none
-  repair_attempts: 0
-`)},
-	}, ".")
+type recordingFS struct {
+	fs.FS
+	mu     sync.Mutex
+	opened []string
+}
 
-	_, err := repo.GetPromptDefinition(context.Background(), "duplicate-fs-prompt", "")
-	if !errors.Is(err, ErrInvalidPromptDefinition) {
-		t.Fatalf("expected ErrInvalidPromptDefinition, got %v", err)
+func TestPromptRepositoryReturnsDefinitionReadFailures(t *testing.T) {
+	readErr := errors.New("definition read failed")
+	fsys := &definitionReadFailureFS{
+		FS: fstest.MapFS{
+			"prompts/target.yaml": &fstest.MapFile{Data: []byte("unread")},
+		},
+		target: "prompts/target.yaml",
+		err:    readErr,
 	}
-	if !strings.Contains(err.Error(), "one.yaml") || !strings.Contains(err.Error(), "nested/two.yaml") {
-		t.Fatalf("expected duplicate paths in error, got %v", err)
+	repo := NewFSRepository(fsys, "prompts")
+
+	definition, err := repo.GetPromptDefinition(context.Background(), "target", "1")
+	if definition != nil || !errors.Is(err, readErr) {
+		t.Fatalf("GetPromptDefinition() = (%#v, %v), want nil and definition read error", definition, err)
+	}
+	if errors.Is(err, ErrPromptDefinitionNotFound) {
+		t.Fatalf("definition read error was classified as absence: %v", err)
+	}
+	if !strings.Contains(err.Error(), "target.yaml") {
+		t.Fatalf("definition read error lacks source context: %v", err)
 	}
 }
 
-func TestFSRepositoryRejectsUnknownYAMLFields(t *testing.T) {
-	repo := NewFSRepository(fstest.MapFS{
-		"not_named_like_id.yaml": &fstest.MapFile{Data: []byte(`
-id: strict-fs-prompt
-version: "1.0.0"
-unknown: true
+type definitionReadFailureFS struct {
+	fs.FS
+	target string
+	err    error
+}
+
+func (f *definitionReadFailureFS) Open(name string) (fs.File, error) {
+	if name == f.target {
+		return nil, f.err
+	}
+	return f.FS.Open(name)
+}
+
+func (f *recordingFS) Open(name string) (fs.File, error) {
+	f.mu.Lock()
+	f.opened = append(f.opened, name)
+	f.mu.Unlock()
+	return f.FS.Open(name)
+}
+
+func (f *recordingFS) wasOpened(name string) bool {
+	return f.openCount(name) > 0
+}
+
+func (f *recordingFS) openCount(name string) int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	count := 0
+	for _, opened := range f.opened {
+		if opened == name {
+			count++
+		}
+	}
+	return count
+}
+
+func TestPromptRepositorySelectionUsesYAMLMetadata(t *testing.T) {
+	const validDefinition = `
+id: selected-prompt
+version: "1"
 messages:
   - role: user
-    content: Invalid.
+    content: selected
 output:
   format: text
   validation_mode: none
-  repair_attempts: 0
-`)},
-	}, ".")
+`
+	tests := []struct {
+		name        string
+		files       map[string]string
+		wantErr     error
+		diagnostics []string
+		wantContent string
+	}{
+		{
+			name: "same-stem strict error with different YAML ID is unrelated",
+			files: map[string]string{
+				"selected-prompt.yaml": `
+id: another-prompt
+version: "1"
+unknown: true
+`,
+				"valid.yaml": validDefinition,
+			},
+		},
+		{
+			name: "unidentifiable same-stem YAML is unrelated",
+			files: map[string]string{
+				"selected-prompt.yaml": "id: [",
+				"valid.yaml":           validDefinition,
+			},
+		},
+		{
+			name: "same ID invalid different version is unrelated",
+			files: map[string]string{
+				"invalid-version.yaml": `
+id: selected-prompt
+version: "2"
+output:
+  format: text
+  validation_mode: none
+`,
+				"valid.yaml": validDefinition,
+			},
+		},
+		{
+			name: "selected content is resolved relative to its definition",
+			files: map[string]string{
+				"nested/selected.yaml": `
+id: selected-prompt
+version: "1"
+messages:
+  - role: user
+    content_file: ./content/selected.tmpl
+output:
+  format: text
+  validation_mode: none
+`,
+				"nested/content/selected.tmpl": "selected from file",
+			},
+			wantContent: "selected from file",
+		},
+		{
+			name: "duplicate selected definitions are ambiguous",
+			files: map[string]string{
+				"selected-a.yaml": validDefinition,
+				"nested/selected-b.yaml": `
+id: selected-prompt
+version: "1"
+messages:
+  - role: user
+    content: duplicate
+output:
+  format: text
+  validation_mode: none
+`,
+			},
+			wantErr:     ErrInvalidPromptDefinition,
+			diagnostics: []string{"duplicate prompt definition id", "selected-a.yaml", "nested/selected-b.yaml"},
+		},
+		{
+			name: "selected strict error is authoritative",
+			files: map[string]string{
+				"selected-strict.yaml": `
+id: selected-prompt
+version: "1"
+unknown: true
+`,
+			},
+			wantErr:     ErrInvalidYAML,
+			diagnostics: []string{"selected-strict.yaml"},
+		},
+		{
+			name: "selected semantic error is authoritative",
+			files: map[string]string{
+				"selected-invalid.yaml": `
+id: selected-prompt
+version: "1"
+output:
+  format: text
+  validation_mode: none
+`,
+			},
+			wantErr:     ErrInvalidPromptDefinition,
+			diagnostics: []string{"selected-invalid.yaml", "at least one message"},
+		},
+		{
+			name: "selected content error includes definition context",
+			files: map[string]string{
+				"selected-missing-content.yaml": `
+id: selected-prompt
+version: "1"
+messages:
+  - role: user
+    content_file: missing.tmpl
+output:
+  format: text
+  validation_mode: none
+`,
+			},
+			wantErr:     ErrInvalidPromptDefinition,
+			diagnostics: []string{"selected-missing-content.yaml", "failed to read content_file", "missing.tmpl"},
+		},
+	}
 
-	_, err := repo.GetPromptDefinition(context.Background(), "strict-fs-prompt", "")
+	for _, source := range promptRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				repo := source.newRepository(t, tc.files)
+				got, err := repo.GetPromptDefinition(context.Background(), "selected-prompt", "1")
+				if tc.wantErr != nil {
+					if !errors.Is(err, tc.wantErr) {
+						t.Fatalf("expected %v, got %v", tc.wantErr, err)
+					}
+					for _, diagnostic := range tc.diagnostics {
+						if !strings.Contains(err.Error(), diagnostic) {
+							t.Fatalf("expected error to contain %q, got %v", diagnostic, err)
+						}
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load selected prompt: %v", err)
+				}
+				wantContent := tc.wantContent
+				if wantContent == "" {
+					wantContent = "selected"
+				}
+				if got.ID != "selected-prompt" || got.Version != "1" || got.Templates[0].Content != wantContent {
+					t.Fatalf("unexpected selected definition: %+v", got)
+				}
+			})
+		}
+	}
+}
+
+func TestPromptRepositoryHonorsCancellation(t *testing.T) {
+	for _, source := range promptRepositorySources() {
+		t.Run(source.name, func(t *testing.T) {
+			repo := source.newRepository(t, map[string]string{
+				"definition.yaml": `
+id: cancelled-prompt
+version: "1"
+messages:
+  - role: user
+    content: selected
+output:
+  format: text
+  validation_mode: none
+`,
+			})
+			ctx, cancel := context.WithCancel(context.Background())
+			cancel()
+
+			_, err := repo.GetPromptDefinition(ctx, "cancelled-prompt", "1")
+			if !errors.Is(err, context.Canceled) {
+				t.Fatalf("expected context cancellation, got %v", err)
+			}
+		})
+	}
+}
+
+func TestPromptRepositoryRequiresOneYAMLDocument(t *testing.T) {
+	const definition = `
+id: one-document
+version: "1"
+messages:
+  - role: user
+    content: selected
+output:
+  format: text
+  validation_mode: none
+`
+	tests := []struct {
+		name    string
+		suffix  string
+		wantErr bool
+	}{
+		{name: "comments and trailing whitespace", suffix: "\n# trailing comment\n\n"},
+		{name: "second populated document", suffix: "\n---\nid: another\n", wantErr: true},
+		{name: "second empty document", suffix: "\n---\n", wantErr: true},
+		{name: "malformed trailing YAML", suffix: "\n---\n[", wantErr: true},
+	}
+
+	for _, source := range promptRepositorySources() {
+		for _, tc := range tests {
+			t.Run(source.name+"/"+tc.name, func(t *testing.T) {
+				repo := source.newRepository(t, map[string]string{"definition.yaml": definition + tc.suffix})
+				_, err := repo.GetPromptDefinition(context.Background(), "one-document", "1")
+				if tc.wantErr {
 					if !errors.Is(err, ErrInvalidYAML) {
 						t.Fatalf("expected ErrInvalidYAML, got %v", err)
 					}
+					if !strings.Contains(err.Error(), "definition.yaml") {
+						t.Fatalf("expected source path in error, got %v", err)
+					}
+					return
+				}
+				if err != nil {
+					t.Fatalf("load one document: %v", err)
+				}
+			})
+		}
+	}
+}
+
+func TestPromptRepositoryReadsOnlySelectedContent(t *testing.T) {
+	fsys := &recordingFS{FS: fstest.MapFS{
+		"target.yaml": &fstest.MapFile{Data: []byte(`
+id: target
+version: "1"
+messages:
+  - role: user
+    content_file: target.tmpl
+output:
+  format: text
+  validation_mode: none
+`)},
+		"target.tmpl": &fstest.MapFile{Data: []byte("selected")},
+		"unrelated.yaml": &fstest.MapFile{Data: []byte(`
+id: unrelated
+version: "1"
+messages:
+  - role: user
+    content_file: unrelated.tmpl
+output:
+  format: text
+  validation_mode: none
+`)},
+		"unrelated.tmpl": &fstest.MapFile{Data: []byte("unrelated")},
+		"other-version.yaml": &fstest.MapFile{Data: []byte(`
+id: target
+version: "2"
+messages:
+  - role: user
+    content_file: other-version.tmpl
+output:
+  format: text
+  validation_mode: none
+`)},
+		"other-version.tmpl": &fstest.MapFile{Data: []byte("other version")},
+	}}
+	repo := NewFSRepository(fsys, ".")
+
+	for lookup := 1; lookup <= 2; lookup++ {
+		got, err := repo.GetPromptDefinition(context.Background(), "target", "1")
+		if err != nil {
+			t.Fatalf("lookup %d: %v", lookup, err)
+		}
+		if got.Templates[0].Content != "selected" {
+			t.Fatalf("lookup %d content = %q", lookup, got.Templates[0].Content)
+		}
+		if count := fsys.openCount("target.tmpl"); count != lookup {
+			t.Fatalf("selected content opens after lookup %d = %d, want %d", lookup, count, lookup)
+		}
+		for _, name := range []string{"unrelated.tmpl", "other-version.tmpl"} {
+			if count := fsys.openCount(name); count != 0 {
+				t.Fatalf("unselected content %q opened %d times", name, count)
+			}
+		}
+		for _, name := range []string{"target.yaml", "unrelated.yaml", "other-version.yaml"} {
+			if count := fsys.openCount(name); count != lookup {
+				t.Fatalf("metadata %q opens after lookup %d = %d, want %d", name, lookup, count, lookup)
+			}
+		}
+	}
+}
+
+func TestPromptDefinitionNormalizationRules(t *testing.T) {
+	tests := []struct {
+		name           string
+		definition     string
+		wantErr        bool
+		wantDiagnostic string
+		wantSchemaPath string
+	}{
+		{
+			name: "missing version",
+			definition: `
+id: normalization-rule
+messages:
+  - role: user
+    content: test
+output:
+  format: text
+  validation_mode: none
+`,
+			wantErr:        true,
+			wantDiagnostic: "version",
+		},
+		{
+			name: "blank input name",
+			definition: `
+id: normalization-rule
+version: "1"
+inputs:
+  - name: "  "
+messages:
+  - role: user
+    content: test
+output:
+  format: text
+  validation_mode: none
+`,
+			wantErr:        true,
+			wantDiagnostic: "input 0",
+		},
+		{
+			name: "blank message role",
+			definition: `
+id: normalization-rule
+version: "1"
+messages:
+  - role: "  "
+    content: test
+output:
+  format: text
+  validation_mode: none
+`,
+			wantErr:        true,
+			wantDiagnostic: "role",
+		},
+		{
+			name: "invalid output format",
+			definition: `
+id: normalization-rule
+version: "1"
+messages:
+  - role: user
+    content: test
+output:
+  format: binary
+  validation_mode: none
+`,
+			wantErr:        true,
+			wantDiagnostic: "format",
+		},
+		{
+			name: "negative repair attempts",
+			definition: `
+id: normalization-rule
+version: "1"
+messages:
+  - role: user
+    content: test
+output:
+  format: text
+  validation_mode: none
+  repair_attempts: -1
+`,
+			wantErr:        true,
+			wantDiagnostic: "repair_attempts",
+		},
+		{
+			name: "explicit blank default profile",
+			definition: `
+id: normalization-rule
+version: "1"
+default_profile: "  "
+messages:
+  - role: user
+    content: test
+output:
+  format: text
+  validation_mode: none
+`,
+			wantErr:        true,
+			wantDiagnostic: "default_profile",
+		},
+		{
+			name: "schema path normalization",
+			definition: `
+id: normalization-rule
+version: "1"
+messages:
+  - role: user
+    content: test
+output:
+  format: json
+  validation_mode: json_schema
+  schema_path: ' schema.json '
+`,
+			wantSchemaPath: "schema.json",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			repo := NewFSRepository(fstest.MapFS{
+				"definition.yaml": &fstest.MapFile{Data: []byte(tt.definition)},
+			}, ".")
+
+			got, err := repo.GetPromptDefinition(context.Background(), "normalization-rule", "")
+			if tt.wantErr {
+				if !errors.Is(err, ErrInvalidPromptDefinition) {
+					t.Fatalf("expected ErrInvalidPromptDefinition, got %v", err)
+				}
+				if !strings.Contains(err.Error(), tt.wantDiagnostic) {
+					t.Fatalf("expected error containing %q, got %v", tt.wantDiagnostic, err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("load prompt definition: %v", err)
+			}
+			if got.Validation.SchemaPath != tt.wantSchemaPath {
+				t.Fatalf("schema path = %q, want %q", got.Validation.SchemaPath, tt.wantSchemaPath)
+			}
+		})
+	}
+}
+
+type promptRepositorySource struct {
+	name          string
+	newRepository func(t *testing.T, files map[string]string) Repository
+}
+
+func promptRepositorySources() []promptRepositorySource {
+	return []promptRepositorySource{
+		{
+			name: "operating system",
+			newRepository: func(t *testing.T, files map[string]string) Repository {
+				t.Helper()
+				root := t.TempDir()
+				for name, content := range files {
+					filePath := filepath.Join(root, filepath.FromSlash(name))
+					if err := os.MkdirAll(filepath.Dir(filePath), 0o755); err != nil {
+						t.Fatalf("create prompt directory: %v", err)
+					}
+					writePromptTestFile(t, filePath, content)
+				}
+				return NewFilesystemRepository(root)
+			},
+		},
+		{
+			name: "filesystem",
+			newRepository: func(t *testing.T, files map[string]string) Repository {
+				t.Helper()
+				fsys := make(fstest.MapFS, len(files))
+				for name, content := range files {
+					fsys[name] = &fstest.MapFile{Data: []byte(strings.TrimLeft(content, "\n"))}
+				}
+				return NewFSRepository(fsys, ".")
+			},
+		},
+	}
+}
+
+func BenchmarkPromptRepositoryLookup(b *testing.B) {
+	for _, size := range []int{10, 1000} {
+		b.Run(fmt.Sprintf("catalog-%d", size), func(b *testing.B) {
+			files := fstest.MapFS{
+				"target.yaml": &fstest.MapFile{Data: []byte(`
+id: target
+version: "1"
+messages:
+  - role: user
+    content_file: target.tmpl
+output:
+  format: text
+  validation_mode: none
+`)},
+				"target.tmpl": &fstest.MapFile{Data: []byte("selected")},
+			}
+			metadataNames := []string{"target.yaml"}
+			contentNames := make([]string, 0, size-1)
+			for i := 1; i < size; i++ {
+				definitionName := fmt.Sprintf("prompt-%04d.yaml", i)
+				contentName := fmt.Sprintf("prompt-%04d.tmpl", i)
+				files[definitionName] = &fstest.MapFile{Data: []byte(fmt.Sprintf(`
+id: prompt-%04d
+version: "1"
+messages:
+  - role: user
+    content_file: %s
+output:
+  format: text
+  validation_mode: none
+`, i, contentName))}
+				files[contentName] = &fstest.MapFile{Data: []byte("unrelated")}
+				metadataNames = append(metadataNames, definitionName)
+				contentNames = append(contentNames, contentName)
+			}
+
+			fsys := &recordingFS{FS: files}
+			repo := NewFSRepository(fsys, ".")
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				if _, err := repo.GetPromptDefinition(context.Background(), "target", "1"); err != nil {
+					b.Fatal(err)
+				}
+			}
+			b.StopTimer()
+
+			if got := fsys.openCount("target.tmpl"); got != b.N {
+				b.Fatalf("selected content opens = %d, want %d", got, b.N)
+			}
+			for _, name := range contentNames {
+				if got := fsys.openCount(name); got != 0 {
+					b.Fatalf("unrelated content %q opened %d times", name, got)
+				}
+			}
+			for _, name := range metadataNames {
+				if got := fsys.openCount(name); got != b.N {
+					b.Fatalf("metadata %q opens = %d, want %d", name, got, b.N)
+				}
+			}
+		})
+	}
 }
 
 func assertCacheControl(t *testing.T, got *domain.CacheControl, wantType domain.CacheControlType, wantTTL string) {

internal/promptdef/source.go

@@ -0,0 +1,63 @@
+package promptdef
+
+import (
+	"context"
+	"errors"
+	"io/fs"
+	"os"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/filecatalog"
+)
+
+type promptDefinitionSource interface {
+	contentSourceRoot
+	findYAMLFiles(context.Context) ([]string, error)
+	readDefinition(string) ([]byte, error)
+	displayPath(string) string
+}
+
+type osPromptSource struct {
+	root        string
+	contentRoot osContentSourceRoot
+}
+
+func (s osPromptSource) findYAMLFiles(ctx context.Context) ([]string, error) {
+	return filecatalog.FindYAMLFiles(ctx, s.root)
+}
+
+func (s osPromptSource) readDefinition(name string) ([]byte, error) {
+	return os.ReadFile(name)
+}
+
+func (s osPromptSource) displayPath(name string) string {
+	return filecatalog.RelativePath(s.root, name)
+}
+
+func (s osPromptSource) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	return s.contentRoot.readContentFile(sourcePath, contentFile)
+}
+
+type fsPromptSource struct {
+	fsys        fs.FS
+	root        string
+	contentRoot contentSourceRoot
+}
+
+func (s fsPromptSource) findYAMLFiles(ctx context.Context) ([]string, error) {
+	if s.fsys == nil {
+		return nil, errors.New("filesystem is nil")
+	}
+	return filecatalog.FindFSYAMLFiles(ctx, s.fsys, s.root)
+}
+
+func (s fsPromptSource) readDefinition(name string) ([]byte, error) {
+	return fs.ReadFile(s.fsys, name)
+}
+
+func (s fsPromptSource) displayPath(name string) string {
+	return filecatalog.DisplayPath(s.root, name)
+}
+
+func (s fsPromptSource) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	return s.contentRoot.readContentFile(sourcePath, contentFile)
+}

internal/usecase/capacity_error.go

@@ -0,0 +1,24 @@
+package usecase
+
+import (
+	"fmt"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
+)
+
+// CapacityError identifies bounded admission rejected for one selected backend.
+type CapacityError struct {
+	BackendID string
+}
+
+func (e *CapacityError) Error() string {
+	if e == nil || strings.TrimSpace(e.BackendID) == "" {
+		return capacity.ErrCapacityExceeded.Error()
+	}
+	return fmt.Sprintf("backend %q admission: %v", e.BackendID, capacity.ErrCapacityExceeded)
+}
+
+func (e *CapacityError) Unwrap() error {
+	return capacity.ErrCapacityExceeded
+}

internal/usecase/execution_settings_test.go

@@ -0,0 +1,83 @@
+package usecase
+
+import (
+	"context"
+	"errors"
+	"math"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+func TestRunnerPrepareExecutionRejectsInvalidExecutionSettings(t *testing.T) {
+	runner := NewRunner(
+		&fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)},
+		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+		nil,
+		defaultArtifactReader(),
+		defaultRenderer(),
+		&fakeLLM{forbid: true},
+		nil,
+		nil,
+	)
+
+	_, err := runner.PrepareExecution(context.Background(), domain.RunRequest{
+		PromptID:  "p",
+		ProfileID: "exec",
+		Inputs:    singleInputRef(),
+		Execution: &domain.ExecutionTargetOverride{TopP: float64Ptr(math.Inf(-1))},
+	})
+	if !errors.Is(err, ErrInvalidRequest) {
+		t.Fatalf("expected ErrInvalidRequest, got %v", err)
+	}
+}
+
+func TestRunnerPrepareExecutionValidatesAndNormalizesRequestEndpoints(t *testing.T) {
+	newRunner := func() *Runner {
+		return NewRunner(
+			&fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)},
+			&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+			nil,
+			defaultArtifactReader(),
+			defaultRenderer(),
+			&fakeLLM{forbid: true},
+			nil,
+			nil,
+		)
+	}
+
+	invalidEndpoints := []string{
+		"/v1",
+		"https:///v1",
+		"ftp://provider.example/v1",
+		"https://user@provider.example/v1",
+		"https://provider.example/v1?mode=chat",
+		"https://provider.example/v1#chat",
+	}
+	for _, endpoint := range invalidEndpoints {
+		t.Run(endpoint, func(t *testing.T) {
+			_, err := newRunner().PrepareExecution(context.Background(), domain.RunRequest{
+				PromptID:  "p",
+				ProfileID: "exec",
+				Inputs:    singleInputRef(),
+				Execution: &domain.ExecutionTargetOverride{Endpoint: endpoint},
+			})
+			if !errors.Is(err, ErrInvalidRequest) {
+				t.Fatalf("expected ErrInvalidRequest, got %v", err)
+			}
+		})
+	}
+
+	prepared, err := newRunner().PrepareExecution(context.Background(), domain.RunRequest{
+		PromptID:  "p",
+		ProfileID: "exec",
+		Inputs:    singleInputRef(),
+		Execution: &domain.ExecutionTargetOverride{Endpoint: "  https://provider.example/nested/v1  "},
+	})
+	if err != nil {
+		t.Fatalf("prepare normalized endpoint: %v", err)
+	}
+	if got := prepared.Details().EffectiveModelParams.Endpoint; got != "https://provider.example/nested/v1" {
+		t.Fatalf("effective endpoint = %q", got)
+	}
+}

internal/usecase/generation_request.go

@@ -0,0 +1,19 @@
+package usecase
+
+import "gitea.maximumdirect.net/eric/promptkit/internal/domain"
+
+func newGenerationRequest(
+	prompt domain.RenderedPrompt,
+	sessionID string,
+	target domain.ExecutionTarget,
+	targetPresence domain.ExecutionTargetPresence,
+	structuredOutput *domain.StructuredOutputSpec,
+) domain.GenerateRequest {
+	prompt.SessionID = sessionID
+	return domain.GenerateRequest{
+		Prompt:           prompt,
+		Target:           target,
+		TargetPresence:   targetPresence,
+		StructuredOutput: structuredOutput,
+	}
+}

internal/usecase/output_contract_test.go

@@ -0,0 +1,185 @@
+package usecase
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+type outputContractTestCollaborators struct {
+	artifacts *fakeArtifactReader
+	renderer  *fakeRenderer
+	llm       *fakeLLM
+	validator *recordingValidationPreparer
+	admitter  *fakeRunAdmitter
+}
+
+func newOutputContractTestRunner() (*Runner, outputContractTestCollaborators) {
+	collaborators := outputContractTestCollaborators{
+		artifacts: defaultArtifactReader(),
+		renderer:  defaultRenderer(),
+		llm:       &fakeLLM{forbid: true},
+		validator: &recordingValidationPreparer{plan: &recordingPreparedValidation{}},
+		admitter:  &fakeRunAdmitter{},
+	}
+	return NewRunner(
+		&fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)},
+		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+		nil,
+		collaborators.artifacts,
+		collaborators.renderer,
+		collaborators.llm,
+		collaborators.validator,
+		collaborators.admitter,
+	), collaborators
+}
+
+func TestRunnerPreparationNormalizesOutputContractConsistently(t *testing.T) {
+	tests := []struct {
+		name     string
+		override domain.OutputContract
+		want     domain.OutputContract
+	}{
+		{
+			name:     "empty replacement format defaults to text",
+			override: domain.OutputContract{ValidationMode: domain.ValidationNone},
+			want:     domain.OutputContract{Format: domain.FormatText, ValidationMode: domain.ValidationNone},
+		},
+		{
+			name:     "markdown basic replacement",
+			override: domain.OutputContract{Format: domain.FormatMarkdown, ValidationMode: domain.ValidationBasic},
+			want:     domain.OutputContract{Format: domain.FormatMarkdown, ValidationMode: domain.ValidationBasic},
+		},
+		{
+			name: "json replacement preserves non-schema fields",
+			override: domain.OutputContract{
+				Format:         domain.FormatJSON,
+				ValidationMode: domain.ValidationJSON,
+				SchemaPath:     "ignored.json",
+				RepairAttempts: 2,
+			},
+			want: domain.OutputContract{
+				Format:         domain.FormatJSON,
+				ValidationMode: domain.ValidationJSON,
+				SchemaPath:     "ignored.json",
+				RepairAttempts: 2,
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			runner, _ := newOutputContractTestRunner()
+			req := domain.RunRequest{
+				PromptID:   "p",
+				ProfileID:  "exec",
+				Inputs:     singleInputRef(),
+				Validation: &tt.override,
+			}
+
+			prepared, err := runner.Prepare(context.Background(), req)
+			if err != nil {
+				t.Fatalf("prepare: %v", err)
+			}
+			preparedExecution, err := runner.PrepareExecution(context.Background(), req)
+			if err != nil {
+				t.Fatalf("prepare execution: %v", err)
+			}
+			details := preparedExecution.Details()
+			if details == nil {
+				t.Fatal("prepared execution returned nil details")
+			}
+			if prepared.OutputContract != tt.want || details.OutputContract != tt.want {
+				t.Fatalf("output contracts = (%+v, %+v), want %+v", prepared.OutputContract, details.OutputContract, tt.want)
+			}
+		})
+	}
+}
+
+func TestRunnerPreparationRejectsInvalidOutputContractsBeforeCompletion(t *testing.T) {
+	tests := []struct {
+		name     string
+		override domain.OutputContract
+	}{
+		{name: "unsupported format", override: domain.OutputContract{Format: "binary", ValidationMode: domain.ValidationNone}},
+		{name: "empty validation mode", override: domain.OutputContract{Format: domain.FormatText}},
+		{name: "negative repair attempts", override: domain.OutputContract{Format: domain.FormatText, ValidationMode: domain.ValidationNone, RepairAttempts: -1}},
+		{name: "json schema without path", override: domain.OutputContract{Format: domain.FormatJSON, ValidationMode: domain.ValidationJSONSchema}},
+	}
+
+	for _, tt := range tests {
+		for _, operation := range []string{"Prepare", "PrepareExecution"} {
+			t.Run(tt.name+"/"+operation, func(t *testing.T) {
+				runner, collaborators := newOutputContractTestRunner()
+				req := domain.RunRequest{
+					PromptID:   "p",
+					ProfileID:  "exec",
+					Inputs:     singleInputRef(),
+					Validation: &tt.override,
+				}
+
+				var err error
+				switch operation {
+				case "Prepare":
+					var prepared *domain.PreparedRun
+					prepared, err = runner.Prepare(context.Background(), req)
+					if prepared != nil {
+						t.Fatalf("expected no partial prepared run, got %+v", prepared)
+					}
+				case "PrepareExecution":
+					var prepared *PreparedExecution
+					prepared, err = runner.PrepareExecution(context.Background(), req)
+					if prepared != nil {
+						t.Fatalf("expected no partial prepared execution, got %+v", prepared)
+					}
+				default:
+					t.Fatalf("unknown operation %q", operation)
+				}
+
+				if !errors.Is(err, ErrInvalidRequest) {
+					t.Fatalf("expected ErrInvalidRequest, got %v", err)
+				}
+				assertOutputContractCompletionSkipped(t, collaborators)
+			})
+		}
+	}
+}
+
+func TestRunnerRunRejectsInvalidOutputContractBeforeAdmission(t *testing.T) {
+	runner, collaborators := newOutputContractTestRunner()
+	result, err := runner.Run(context.Background(), domain.RunRequest{
+		PromptID:  "p",
+		ProfileID: "exec",
+		Inputs:    singleInputRef(),
+		Validation: &domain.OutputContract{
+			Format:         domain.OutputFormat("binary"),
+			ValidationMode: domain.ValidationNone,
+		},
+	})
+	if result != nil {
+		t.Fatalf("expected no partial result, got %+v", result)
+	}
+	if !errors.Is(err, ErrInvalidRequest) {
+		t.Fatalf("expected ErrInvalidRequest, got %v", err)
+	}
+	assertOutputContractCompletionSkipped(t, collaborators)
+}
+
+func assertOutputContractCompletionSkipped(t *testing.T, collaborators outputContractTestCollaborators) {
+	t.Helper()
+	if collaborators.artifacts.calls != 0 || collaborators.renderer.calls != 0 ||
+		collaborators.validator.prepareCalls != 0 || collaborators.validator.directValidateCalls != 0 ||
+		len(collaborators.admitter.backendIDs) != 0 || collaborators.llm.calls != 0 {
+		t.Fatalf(
+			"invalid output contract reached downstream work: artifacts=%d renderer=%d prepare_validation=%d validation=%d admissions=%d generation=%d",
+			collaborators.artifacts.calls,
+			collaborators.renderer.calls,
+			collaborators.validator.prepareCalls,
+			collaborators.validator.directValidateCalls,
+			len(collaborators.admitter.backendIDs),
+			collaborators.llm.calls,
+		)
+	}
+}

internal/usecase/prepared_execution.go

@@ -42,25 +42,12 @@ func (r *Runner) PrepareExecution(ctx context.Context, req domain.RunRequest) (*
 		return nil, err
 	}
 
-	validationPlan, err := r.prepareValidation(ctx, state.effectiveContract)
+	operation, err := r.completePreparation(ctx, req, state)
 	if err != nil {
 		return nil, err
 	}
 
-	structuredOutput, err := r.structuredOutputFromValidationPlan(
-		state.definition,
-		state.effectiveContract,
-		validationPlan,
-	)
-	if err != nil {
-		return nil, err
-	}
-	prepared, err := r.completePreparationWithStructuredOutput(ctx, req, state, structuredOutput)
-	if err != nil {
-		return nil, err
-	}
-
-	executionSnapshot, err := clonePreparedRun(prepared)
+	executionSnapshot, err := clonePreparedRun(operation.run)
 	if err != nil {
 		return nil, fmt.Errorf("%w: failed to copy prepared execution: %v", ErrInvalidRequest, err)
 	}
@@ -76,52 +63,12 @@ func (r *Runner) PrepareExecution(ctx context.Context, req domain.RunRequest) (*
 		details: details,
 		payload: &preparedExecutionPayload{
 			prepared:   executionSnapshot,
-			validation: validationPlan,
+			validation: operation.validation,
 			directKey:  state.effectiveModel.APIKey,
 		},
 	}, nil
 }
 
-func (r *Runner) prepareValidation(
-	ctx context.Context,
-	contract domain.OutputContract,
-) (validate.PreparedValidation, error) {
-	if r.validator == nil {
-		return noOpPreparedValidation{contract: contract}, nil
-	}
-	preparer, ok := r.validator.(validate.ValidationPreparer)
-	if !ok {
-		return nil, fmt.Errorf("%w: validator does not support prepared validation", ErrValidation)
-	}
-	plan, err := preparer.PrepareValidation(ctx, contract)
-	if err != nil {
-		return nil, fmt.Errorf("%w: %w", ErrValidation, err)
-	}
-	if plan == nil {
-		return nil, fmt.Errorf("%w: validator returned nil prepared validation", ErrValidation)
-	}
-	return plan, nil
-}
-
-func (r *Runner) structuredOutputFromValidationPlan(
-	def *domain.PromptDefinition,
-	contract domain.OutputContract,
-	plan validate.PreparedValidation,
-) (*domain.StructuredOutputSpec, error) {
-	if contract.ValidationMode != domain.ValidationJSONSchema {
-		return nil, nil
-	}
-
-	schemaDocument := plan.SchemaDocument()
-	if schemaDocument == nil {
-		if r.validator == nil {
-			return nil, nil
-		}
-		return nil, fmt.Errorf("%w: prepared json_schema validation has no schema document", ErrValidation)
-	}
-	return structuredOutputSpec(def, schemaDocument), nil
-}
-
 // Details returns a fresh credential-redacted copy of the prepared run.
 func (p *PreparedExecution) Details() *domain.PreparedRun {
 	if p == nil {

internal/usecase/prepared_execution_test.go

@@ -52,6 +52,12 @@ type recordingValidationPreparer struct {
 	directValidateCalls int
 }
 
+type validationOnly struct{}
+
+func (validationOnly) Validate(context.Context, *domain.Artifact, domain.OutputContract) (domain.ValidationResult, error) {
+	return domain.ValidationResult{}, nil
+}
+
 func (v *recordingValidationPreparer) Validate(
 	context.Context,
 	*domain.Artifact,
@@ -164,6 +170,77 @@ func TestRunnerPrepareExecutionCompletesWithoutAdmissionOrGeneration(t *testing.
 	}
 }
 
+func TestRunnerPreparationRejectsExcessivelyDeepPreparedSchema(t *testing.T) {
+	operations := []struct {
+		name string
+		run  func(*Runner, domain.RunRequest) error
+	}{
+		{
+			name: "Prepare",
+			run: func(runner *Runner, request domain.RunRequest) error {
+				_, err := runner.Prepare(context.Background(), request)
+				return err
+			},
+		},
+		{
+			name: "Run",
+			run: func(runner *Runner, request domain.RunRequest) error {
+				_, err := runner.Run(context.Background(), request)
+				return err
+			},
+		},
+		{
+			name: "PrepareExecution",
+			run: func(runner *Runner, request domain.RunRequest) error {
+				_, err := runner.PrepareExecution(context.Background(), request)
+				return err
+			},
+		},
+	}
+
+	for _, operation := range operations {
+		t.Run(operation.name, func(t *testing.T) {
+			def := promptDef(domain.FormatJSON, domain.ValidationJSONSchema, 0)
+			def.Validation.SchemaPath = "schema.json"
+			llmClient := &fakeLLM{forbid: true}
+			validator := &recordingValidationPreparer{
+				plan: &recordingPreparedValidation{schemaDocument: excessivelyDeepPreparedJSONValue()},
+			}
+			runner := NewRunner(
+				&fakePromptRepo{def: def},
+				&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+				nil,
+				defaultArtifactReader(),
+				defaultRenderer(),
+				llmClient,
+				validator,
+				nil,
+			)
+
+			err := operation.run(runner, domain.RunRequest{
+				PromptID:  "p",
+				ProfileID: "exec",
+				Inputs:    singleInputRef(),
+			})
+			if !errors.Is(err, ErrValidation) {
+				t.Fatalf("expected ErrValidation, got %v", err)
+			}
+			if llmClient.calls != 0 {
+				t.Fatalf("invalid prepared schema reached generation: %d calls", llmClient.calls)
+			}
+		})
+	}
+}
+
+func excessivelyDeepPreparedJSONValue() any {
+	const clearlyUnsafeContainerDepth = 1_000
+	var value any = true
+	for level := 0; level < clearlyUnsafeContainerDepth; level++ {
+		value = map[string]any{"child": value}
+	}
+	return value
+}
+
 func TestRunnerRunPreparedRechecksEnvironmentCredentialBeforeAdmission(t *testing.T) {
 	const environmentName = "PROMPTKIT_PREPARED_EXECUTION_TEST_KEY"
 	t.Setenv(environmentName, "available-during-preparation")
@@ -271,7 +348,13 @@ func TestRunnerRunPreparedUsesFrozenValidationForInitialAndRepairOutputs(t *test
 		},
 	}
 	repairer := &fakeRepairer{
-		responses: []*domain.GenerateResponse{{Content: `{"repaired":true}`}},
+		responses: []*domain.GenerateResponse{{
+			Content: `{"repaired":true}`,
+			Usage: domain.TokenUsage{
+				PromptTokens: 2, CompletionTokens: 3, TotalTokens: 5,
+				CachedTokens: 7, CacheWriteTokens: 11,
+			},
+		}},
 	}
 	admitter := &fakeRunAdmitter{}
 	reader := defaultArtifactReader()
@@ -282,7 +365,13 @@ func TestRunnerRunPreparedUsesFrozenValidationForInitialAndRepairOutputs(t *test
 		nil,
 		reader,
 		renderer,
-		&fakeLLM{resp: &domain.GenerateResponse{Content: `{"broken":true}`}},
+		&fakeLLM{resp: &domain.GenerateResponse{
+			Content: `{"broken":true}`,
+			Usage: domain.TokenUsage{
+				PromptTokens: 13, CompletionTokens: 17, TotalTokens: 19,
+				CachedTokens: 23, CacheWriteTokens: 29,
+			},
+		}},
 		validator,
 		repairer,
 		admitter,
@@ -309,6 +398,13 @@ func TestRunnerRunPreparedUsesFrozenValidationForInitialAndRepairOutputs(t *test
 	if result.Validation.Status != domain.ValidationPassed || result.Validation.RepairAttempts != 1 {
 		t.Fatalf("unexpected repaired validation result: %+v", result.Validation)
 	}
+	wantUsage := domain.TokenUsage{
+		PromptTokens: 15, CompletionTokens: 20, TotalTokens: 24,
+		CachedTokens: 30, CacheWriteTokens: 40,
+	}
+	if result.Usage != wantUsage {
+		t.Fatalf("prepared cumulative usage = %+v, want %+v", result.Usage, wantUsage)
+	}
 	if admitter.releaseCalls != 1 {
 		t.Fatalf("admission releases=%d, want 1", admitter.releaseCalls)
 	}
@@ -492,7 +588,7 @@ func TestRunnerPrepareExecutionRequiresValidationPreparer(t *testing.T) {
 		reader,
 		defaultRenderer(),
 		&fakeLLM{forbid: true},
-		&fakeValidator{},
+		validationOnly{},
 		nil,
 	)
 

internal/usecase/profile_inspection.go

@@ -0,0 +1,106 @@
+package usecase
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+type resolvedProfileSelection struct {
+	id      string
+	profile *domain.ExecutionProfile
+	backend *domain.Backend
+}
+
+func (r *Runner) resolveProfileSelection(
+	ctx context.Context,
+	profileID string,
+) (*resolvedProfileSelection, error) {
+	normalizedID := strings.TrimSpace(profileID)
+	if normalizedID == "" {
+		return nil, fmt.Errorf("%w: profile id is required", ErrInvalidRequest)
+	}
+	if r == nil || r.profiles == nil {
+		return nil, fmt.Errorf("%w: profile repository is not configured", ErrProfileLoad)
+	}
+
+	selectedProfile, err := r.profiles.GetProfile(ctx, normalizedID)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrProfileLoad, err)
+	}
+	if selectedProfile == nil {
+		return nil, fmt.Errorf("%w: profile repository returned nil profile", ErrProfileLoad)
+	}
+
+	profileValue := *selectedProfile
+	profileValue.BackendID = strings.TrimSpace(profileValue.BackendID)
+
+	var selectedBackend *domain.Backend
+	if profileValue.BackendID != "" {
+		if r.backends == nil {
+			return nil, fmt.Errorf("%w: backend %q cannot be resolved", ErrProfileLoad, profileValue.BackendID)
+		}
+		backendValue, err := r.backends.GetBackend(profileValue.BackendID)
+		if err != nil {
+			return nil, fmt.Errorf("%w: backend %q: %w", ErrProfileLoad, profileValue.BackendID, err)
+		}
+		selectedBackend = &backendValue
+	}
+
+	return &resolvedProfileSelection{
+		id:      normalizedID,
+		profile: &profileValue,
+		backend: selectedBackend,
+	}, nil
+}
+
+func normalizeResolvedExecutionTarget(target domain.ExecutionTarget) (domain.ExecutionTarget, error) {
+	endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(target.Endpoint)
+	if err != nil {
+		return domain.ExecutionTarget{}, fmt.Errorf("execution endpoint: %w", err)
+	}
+	target.Endpoint = endpoint
+	if strings.TrimSpace(target.Model) == "" {
+		return domain.ExecutionTarget{}, errors.New("execution model is required")
+	}
+	if err := domain.ValidateExecutionTargetSettings(target); err != nil {
+		return domain.ExecutionTarget{}, err
+	}
+	return target, nil
+}
+
+// InspectProfile resolves one explicit profile without prompt or execution work.
+func (r *Runner) InspectProfile(
+	ctx context.Context,
+	profileID string,
+) (*domain.ProfileInspection, error) {
+	normalizedID := strings.TrimSpace(profileID)
+	if normalizedID == "" {
+		return nil, fmt.Errorf("%w: profile id is required", ErrInvalidRequest)
+	}
+	select {
+	case <-ctx.Done():
+		return nil, fmt.Errorf("%w: %w", ErrProfileLoad, ctx.Err())
+	default:
+	}
+
+	selection, err := r.resolveProfileSelection(ctx, normalizedID)
+	if err != nil {
+		return nil, err
+	}
+	target, _ := resolveExecutionTarget(selection.backend, selection.profile, nil)
+	target, err = normalizeResolvedExecutionTarget(target)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrProfileLoad, err)
+	}
+	target.APIKey = ""
+
+	return &domain.ProfileInspection{
+		ProfileID:            selection.id,
+		EffectiveModelParams: target,
+		APIKeyRequired:       target.APIKeyRequired,
+	}, nil
+}

internal/usecase/profile_inspection_test.go

@@ -0,0 +1,213 @@
+package usecase
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
+)
+
+type inspectionProfileRepository struct {
+	profile *domain.ExecutionProfile
+	err     error
+	calls   int
+	id      string
+}
+
+func (r *inspectionProfileRepository) GetProfile(
+	_ context.Context,
+	id string,
+) (*domain.ExecutionProfile, error) {
+	r.calls++
+	r.id = id
+	if r.err != nil {
+		return nil, r.err
+	}
+	return r.profile, nil
+}
+
+type inspectionBackendResolver struct {
+	backend domain.Backend
+	err     error
+	calls   int
+	id      string
+}
+
+func (r *inspectionBackendResolver) GetBackend(id string) (domain.Backend, error) {
+	r.calls++
+	r.id = id
+	if r.err != nil {
+		return domain.Backend{}, r.err
+	}
+	return r.backend, nil
+}
+
+func TestRunnerInspectProfileResolvesProfileAndBackendOnce(t *testing.T) {
+	profiles := &inspectionProfileRepository{profile: &domain.ExecutionProfile{
+		ID:              "profile",
+		BackendID:       "  backend  ",
+		Model:           "profile-model",
+		Temperature:     0.4,
+		MaxTokens:       32,
+		TimeoutSeconds:  45,
+		ServiceTier:     "priority",
+		ReasoningEffort: "high",
+		ExtraParams: map[string]any{
+			"profile": "value",
+		},
+	}}
+	backends := &inspectionBackendResolver{backend: domain.Backend{
+		ID:        "backend",
+		Endpoint:  "https://backend.example/v1",
+		APIKeyEnv: "BACKEND_KEY",
+		ExtraParams: map[string]any{
+			"backend": "value",
+		},
+	}}
+	runner := &Runner{profiles: profiles, backends: backends}
+
+	inspection, err := runner.InspectProfile(context.Background(), " profile ")
+	if err != nil {
+		t.Fatalf("inspect profile: %v", err)
+	}
+	if profiles.calls != 1 || profiles.id != "profile" {
+		t.Fatalf("profile lookup=(calls=%d id=%q), want one exact lookup", profiles.calls, profiles.id)
+	}
+	if backends.calls != 1 || backends.id != "backend" {
+		t.Fatalf("backend lookup=(calls=%d id=%q), want one exact lookup", backends.calls, backends.id)
+	}
+	if profiles.profile.BackendID != "  backend  " {
+		t.Fatalf("inspection mutated repository profile backend: %q", profiles.profile.BackendID)
+	}
+
+	wantTarget := domain.ExecutionTarget{
+		BackendID:       "backend",
+		Endpoint:        "https://backend.example/v1",
+		Model:           "profile-model",
+		Temperature:     0.4,
+		MaxTokens:       32,
+		TopP:            defaults.ExecutionTargetDefault().TopP,
+		TimeoutSeconds:  45,
+		ServiceTier:     "priority",
+		ReasoningEffort: "high",
+		APIKeyEnv:       "BACKEND_KEY",
+		ExtraParams: map[string]any{
+			"profile": "value",
+		},
+	}
+	if inspection.ProfileID != "profile" || inspection.APIKeyRequired ||
+		!reflect.DeepEqual(inspection.EffectiveModelParams, wantTarget) {
+		t.Fatalf("inspection=%#v, want profile=%q target=%#v", inspection, "profile", wantTarget)
+	}
+}
+
+func TestRunnerInspectProfileDoesNotNeedExecutionCollaboratorsOrCredentials(t *testing.T) {
+	t.Setenv("PROMPTKIT_INSPECTION_TEST_KEY", "")
+	profiles := &inspectionProfileRepository{profile: &domain.ExecutionProfile{
+		ID:        "endpoint-only",
+		Endpoint:  "https://profile.example/v1",
+		Model:     "profile-model",
+		APIKeyEnv: "PROMPTKIT_INSPECTION_TEST_KEY",
+	}}
+	runner := &Runner{profiles: profiles}
+
+	inspection, err := runner.InspectProfile(context.Background(), "endpoint-only")
+	if err != nil {
+		t.Fatalf("inspect endpoint-only profile: %v", err)
+	}
+	if inspection.EffectiveModelParams.BackendID != "" ||
+		inspection.EffectiveModelParams.APIKeyEnv != "PROMPTKIT_INSPECTION_TEST_KEY" ||
+		inspection.APIKeyRequired {
+		t.Fatalf("unexpected endpoint-only inspection: %#v", inspection)
+	}
+}
+
+func TestRunnerInspectProfileDirectCredentialRequirementClearsBackendEnvironment(t *testing.T) {
+	profiles := &inspectionProfileRepository{profile: &domain.ExecutionProfile{
+		ID:             "direct-key",
+		BackendID:      "backend",
+		Model:          "profile-model",
+		APIKeyRequired: true,
+	}}
+	backends := &inspectionBackendResolver{backend: domain.Backend{
+		ID:        "backend",
+		Endpoint:  "https://backend.example/v1",
+		APIKeyEnv: "BACKEND_KEY",
+	}}
+
+	inspection, err := (&Runner{profiles: profiles, backends: backends}).InspectProfile(
+		context.Background(),
+		"direct-key",
+	)
+	if err != nil {
+		t.Fatalf("inspect direct-key profile: %v", err)
+	}
+	if !inspection.APIKeyRequired || inspection.EffectiveModelParams.APIKeyEnv != "" {
+		t.Fatalf("credential requirement was not resolved exclusively: %#v", inspection)
+	}
+}
+
+func TestRunnerInspectProfileClassifiesFailuresWithoutRepositoryWorkAfterCancellation(t *testing.T) {
+	t.Run("blank ID", func(t *testing.T) {
+		profiles := &inspectionProfileRepository{}
+		_, err := (&Runner{profiles: profiles}).InspectProfile(context.Background(), " \t ")
+		if !errors.Is(err, ErrInvalidRequest) || profiles.calls != 0 {
+			t.Fatalf("blank inspection=(%v, calls=%d), want invalid request without lookup", err, profiles.calls)
+		}
+	})
+
+	t.Run("canceled context", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+		profiles := &inspectionProfileRepository{}
+		_, err := (&Runner{profiles: profiles}).InspectProfile(ctx, "profile")
+		if !errors.Is(err, ErrProfileLoad) || !errors.Is(err, context.Canceled) || profiles.calls != 0 {
+			t.Fatalf("canceled inspection=(%v, calls=%d), want profile load and context identities without lookup", err, profiles.calls)
+		}
+	})
+
+	t.Run("missing profile", func(t *testing.T) {
+		profiles := &inspectionProfileRepository{err: profile.ErrProfileNotFound}
+		_, err := (&Runner{profiles: profiles}).InspectProfile(context.Background(), "missing")
+		if !errors.Is(err, ErrProfileLoad) || !errors.Is(err, profile.ErrProfileNotFound) {
+			t.Fatalf("missing profile error=%v, want profile load and not-found identities", err)
+		}
+	})
+
+	t.Run("unknown backend", func(t *testing.T) {
+		backendErr := errors.New("unknown backend")
+		profiles := &inspectionProfileRepository{profile: &domain.ExecutionProfile{
+			ID: "profile", BackendID: "backend", Model: "profile-model",
+		}}
+		backends := &inspectionBackendResolver{err: backendErr}
+		_, err := (&Runner{profiles: profiles, backends: backends}).InspectProfile(context.Background(), "profile")
+		if !errors.Is(err, ErrProfileLoad) || !errors.Is(err, backendErr) {
+			t.Fatalf("unknown backend error=%v, want profile load and backend identities", err)
+		}
+	})
+
+	t.Run("defensive invalid dependencies", func(t *testing.T) {
+		cases := []struct {
+			name   string
+			runner *Runner
+		}{
+			{name: "nil repository", runner: &Runner{}},
+			{name: "nil profile", runner: &Runner{profiles: &inspectionProfileRepository{}}},
+			{name: "invalid target", runner: &Runner{profiles: &inspectionProfileRepository{
+				profile: &domain.ExecutionProfile{ID: "profile", Endpoint: "https://profile.example/v1"},
+			}}},
+		}
+		for _, tc := range cases {
+			t.Run(tc.name, func(t *testing.T) {
+				_, err := tc.runner.InspectProfile(context.Background(), "profile")
+				if !errors.Is(err, ErrProfileLoad) {
+					t.Fatalf("inspection error=%v, want profile load", err)
+				}
+			})
+		}
+	})
+}

internal/usecase/prompt_inspection.go

@@ -0,0 +1,73 @@
+package usecase
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+type resolvedPromptDefinition struct {
+	definition *domain.PromptDefinition
+	hash       string
+}
+
+func (r *Runner) resolvePromptDefinition(
+	ctx context.Context,
+	promptID string,
+	promptVersion string,
+) (*resolvedPromptDefinition, error) {
+	if strings.TrimSpace(promptID) == "" {
+		return nil, fmt.Errorf("%w: prompt id is required", ErrInvalidRequest)
+	}
+	if r == nil || r.promptDefs == nil {
+		return nil, fmt.Errorf("%w: prompt repository is not configured", ErrPromptLoad)
+	}
+
+	definition, err := r.promptDefs.GetPromptDefinition(ctx, promptID, promptVersion)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrPromptLoad, err)
+	}
+	if definition == nil {
+		return nil, fmt.Errorf("%w: prompt repository returned nil definition", ErrPromptLoad)
+	}
+
+	hash, err := hashPromptDefinition(definition)
+	if err != nil {
+		return nil, fmt.Errorf("%w: failed to hash prompt definition: %v", ErrPromptLoad, err)
+	}
+	return &resolvedPromptDefinition{definition: definition, hash: hash}, nil
+}
+
+// InspectPrompt resolves one explicit prompt without execution work.
+func (r *Runner) InspectPrompt(
+	ctx context.Context,
+	promptID string,
+	promptVersion string,
+) (*domain.PromptInspection, error) {
+	if strings.TrimSpace(promptID) == "" {
+		return nil, fmt.Errorf("%w: prompt id is required", ErrInvalidRequest)
+	}
+	select {
+	case <-ctx.Done():
+		return nil, fmt.Errorf("%w: %w", ErrPromptLoad, ctx.Err())
+	default:
+	}
+
+	selection, err := r.resolvePromptDefinition(ctx, promptID, promptVersion)
+	if err != nil {
+		return nil, err
+	}
+	inputs := make([]domain.PromptInput, len(selection.definition.Inputs))
+	copy(inputs, selection.definition.Inputs)
+
+	return &domain.PromptInspection{
+		PromptID:         selection.definition.ID,
+		PromptVersion:    selection.definition.Version,
+		PromptHash:       selection.hash,
+		DefaultProfileID: selection.definition.DefaultProfile,
+		Inputs:           inputs,
+		OutputContract:   selection.definition.Validation,
+	}, nil
+}

internal/usecase/prompt_inspection_test.go

@@ -0,0 +1,157 @@
+package usecase
+
+import (
+	"context"
+	"errors"
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/promptdef"
+)
+
+type inspectionPromptRepository struct {
+	definition *domain.PromptDefinition
+	err        error
+	calls      int
+	id         string
+	version    string
+}
+
+func (r *inspectionPromptRepository) GetPromptDefinition(
+	_ context.Context,
+	id string,
+	version string,
+) (*domain.PromptDefinition, error) {
+	r.calls++
+	r.id = id
+	r.version = version
+	if r.err != nil {
+		return nil, r.err
+	}
+	return r.definition, nil
+}
+
+func TestRunnerInspectPromptResolvesOneDefinitionWithoutExecutionCollaborators(t *testing.T) {
+	definition := &domain.PromptDefinition{
+		ID:             "normalized.prompt",
+		Version:        "1.2.3",
+		DefaultProfile: "not-resolved",
+		Inputs: []domain.PromptInput{
+			{Name: "document", Required: true, ContentType: "text/plain", Description: "Source document."},
+			{Name: "audience", ContentType: "text/plain", Description: "Intended reader."},
+		},
+		Validation: domain.OutputContract{
+			Format:         domain.FormatJSON,
+			ValidationMode: domain.ValidationJSONSchema,
+			SchemaPath:     "schemas/result.json",
+			RepairAttempts: 2,
+		},
+	}
+	repository := &inspectionPromptRepository{definition: definition}
+	runner := &Runner{promptDefs: repository}
+
+	inspection, err := runner.InspectPrompt(context.Background(), " prompt-id ", " version ")
+	if err != nil {
+		t.Fatalf("inspect prompt: %v", err)
+	}
+	wantHash, err := hashPromptDefinition(definition)
+	if err != nil {
+		t.Fatalf("hash prompt definition: %v", err)
+	}
+	if repository.calls != 1 || repository.id != " prompt-id " || repository.version != " version " {
+		t.Fatalf("prompt lookup=(calls=%d id=%q version=%q), want one unchanged lookup", repository.calls, repository.id, repository.version)
+	}
+	if inspection.PromptID != definition.ID ||
+		inspection.PromptVersion != definition.Version ||
+		inspection.PromptHash != wantHash ||
+		inspection.DefaultProfileID != definition.DefaultProfile ||
+		!reflect.DeepEqual(inspection.Inputs, definition.Inputs) ||
+		inspection.OutputContract != definition.Validation {
+		t.Fatalf("inspection=%#v, want definition metadata", inspection)
+	}
+
+	inspection.Inputs[0].Name = "changed"
+	second, err := runner.InspectPrompt(context.Background(), " prompt-id ", " version ")
+	if err != nil {
+		t.Fatalf("inspect prompt again: %v", err)
+	}
+	if definition.Inputs[0].Name != "document" || second.Inputs[0].Name != "document" {
+		t.Fatalf("inspection input mutation escaped caller result: definition=%#v next=%#v", definition.Inputs, second.Inputs)
+	}
+}
+
+func TestRunnerInspectPromptClassifiesFailuresWithoutRepositoryWorkAfterCancellation(t *testing.T) {
+	t.Run("blank ID", func(t *testing.T) {
+		repository := &inspectionPromptRepository{}
+		_, err := (&Runner{promptDefs: repository}).InspectPrompt(context.Background(), " \t ", "version")
+		if !errors.Is(err, ErrInvalidRequest) || repository.calls != 0 {
+			t.Fatalf("blank inspection=(%v, calls=%d), want invalid request without lookup", err, repository.calls)
+		}
+	})
+
+	t.Run("canceled context", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+		repository := &inspectionPromptRepository{}
+		_, err := (&Runner{promptDefs: repository}).InspectPrompt(ctx, "prompt", "version")
+		if !errors.Is(err, ErrPromptLoad) || !errors.Is(err, context.Canceled) || repository.calls != 0 {
+			t.Fatalf("canceled inspection=(%v, calls=%d), want prompt load and context identities without lookup", err, repository.calls)
+		}
+	})
+
+	t.Run("missing prompt", func(t *testing.T) {
+		repository := &inspectionPromptRepository{err: promptdef.ErrPromptDefinitionNotFound}
+		_, err := (&Runner{promptDefs: repository}).InspectPrompt(context.Background(), "missing", "version")
+		if !errors.Is(err, ErrPromptLoad) || !errors.Is(err, promptdef.ErrPromptDefinitionNotFound) {
+			t.Fatalf("missing prompt error=%v, want prompt load and not-found identities", err)
+		}
+	})
+
+	t.Run("defensive prompt dependencies", func(t *testing.T) {
+		var nilRunner *Runner
+		cases := []struct {
+			name   string
+			runner *Runner
+		}{
+			{name: "nil runner", runner: nilRunner},
+			{name: "nil repository", runner: &Runner{}},
+			{name: "nil definition", runner: &Runner{promptDefs: &inspectionPromptRepository{}}},
+		}
+		for _, tc := range cases {
+			t.Run(tc.name, func(t *testing.T) {
+				_, err := tc.runner.InspectPrompt(context.Background(), "prompt", "version")
+				if !errors.Is(err, ErrPromptLoad) {
+					t.Fatalf("inspection error=%v, want prompt load", err)
+				}
+			})
+		}
+	})
+}
+
+func TestRunnerPrepareUsesThePromptInspectionSelectionAndHash(t *testing.T) {
+	definition := promptDef(domain.FormatMarkdown, domain.ValidationBasic, 0)
+	repository := &fakePromptRepo{def: definition}
+	runner := NewRunner(
+		repository,
+		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+		nil,
+		&fakeArtifactReader{},
+		&fakeRenderer{rendered: &domain.RenderedPrompt{Messages: []domain.RenderedMessage{{Role: "user", Content: "hello"}}}},
+		nil,
+		nil,
+		nil,
+	)
+
+	inspection, err := runner.InspectPrompt(context.Background(), definition.ID, definition.Version)
+	if err != nil {
+		t.Fatalf("inspect prompt: %v", err)
+	}
+	prepared, err := runner.Prepare(context.Background(), domain.RunRequest{PromptID: definition.ID, PromptVersion: definition.Version, ProfileID: "exec"})
+	if err != nil {
+		t.Fatalf("prepare prompt: %v", err)
+	}
+	if inspection.PromptHash != prepared.PromptHash {
+		t.Fatalf("inspection hash=%q, preparation hash=%q", inspection.PromptHash, prepared.PromptHash)
+	}
+}

internal/usecase/repairer.go

@@ -19,6 +19,7 @@ type RepairRequest struct {
 	ValidationErrors []string
 	SessionID        string
 	Target           domain.ExecutionTarget
+	TargetPresence   domain.ExecutionTargetPresence
 	StructuredOutput *domain.StructuredOutputSpec
 	Attempt          int
 	MaxAttempts      int
@@ -44,7 +45,6 @@ func (r *defaultOutputRepairer) Repair(ctx context.Context, req RepairRequest) (
 	}
 
 	prompt := domain.RenderedPrompt{
-		SessionID: req.SessionID,
 		Messages: []domain.RenderedMessage{
 			{
 				Role:    "system",
@@ -64,11 +64,13 @@ func (r *defaultOutputRepairer) Repair(ctx context.Context, req RepairRequest) (
 		},
 	}
 
-	resp, err := r.llm.Generate(ctx, domain.GenerateRequest{
-		Prompt:           prompt,
-		Target:           req.Target,
-		StructuredOutput: req.StructuredOutput,
-	})
+	resp, err := r.llm.Generate(ctx, newGenerationRequest(
+		prompt,
+		req.SessionID,
+		req.Target,
+		req.TargetPresence,
+		req.StructuredOutput,
+	))
 	if err != nil {
 		return nil, err
 	}

internal/usecase/runner.go

@@ -17,6 +17,7 @@ import (
 	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
 	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
 	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
 	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
 	"gitea.maximumdirect.net/eric/promptkit/internal/prompt"
@@ -71,6 +72,11 @@ type preparationState struct {
 	start                time.Time
 }
 
+type preparedOperation struct {
+	run        *domain.PreparedRun
+	validation validate.PreparedValidation
+}
+
 func NewRunner(
 	promptDefs promptdef.Repository,
 	profiles profile.Repository,
@@ -137,18 +143,20 @@ func (r *Runner) Run(ctx context.Context, req domain.RunRequest) (*domain.RunRes
 	}
 	defer release()
 
-	prepared, err := r.completePreparation(ctx, req, state)
+	operation, err := r.completePreparation(ctx, req, state)
 	if err != nil {
 		return nil, err
 	}
 	directAPIKey := state.effectiveModel.APIKey
 
-	return r.executePreparedRun(ctx, prepared, directAPIKey, runID, start, func(
+	return r.executePreparedRun(ctx, operation.run, directAPIKey, runID, start, func(
 		ctx context.Context,
 		artifact *domain.Artifact,
 		attemptsUsed int,
 	) (domain.ValidationResult, error) {
-		return r.validateOutput(ctx, artifact, prepared.OutputContract, attemptsUsed)
+		result, err := operation.validation.Validate(ctx, artifact)
+		result.RepairAttempts = attemptsUsed
+		return result, err
 	})
 }
 
@@ -168,18 +176,20 @@ func (r *Runner) executePreparedRun(
 ) (*domain.RunResult, error) {
 	executionTarget := prepared.EffectiveModelParams
 	executionTarget.APIKey = directAPIKey
-	genResp, err := r.llm.Generate(ctx, domain.GenerateRequest{
-		Prompt:           domain.RenderedPrompt{SessionID: prepared.SessionID, Messages: prepared.Messages},
-		Target:           executionTarget,
-		TargetPresence:   prepared.TargetPresence,
-		StructuredOutput: prepared.StructuredOutput,
-	})
+	genResp, err := r.llm.Generate(ctx, newGenerationRequest(
+		domain.RenderedPrompt{Messages: prepared.Messages},
+		prepared.SessionID,
+		executionTarget,
+		prepared.TargetPresence,
+		prepared.StructuredOutput,
+	))
 	if err != nil {
 		if errors.Is(err, llm.ErrInvalidRequest) {
 			return nil, fmt.Errorf("%w: %w", ErrInvalidRequest, err)
 		}
 		return nil, fmt.Errorf("%w: %w", ErrLLMGenerate, err)
 	}
+	usage := genResp.Usage
 
 	outputArtifact := buildOutputArtifact(genResp.Content, prepared.OutputContract.Format)
 	validationResult, err := validateArtifact(ctx, &outputArtifact, 0)
@@ -197,6 +207,7 @@ func (r *Runner) executePreparedRun(
 				ValidationErrors: validationResult.Errors,
 				SessionID:        prepared.SessionID,
 				Target:           executionTarget,
+				TargetPresence:   prepared.TargetPresence,
 				StructuredOutput: prepared.StructuredOutput,
 				Attempt:          attemptsUsed,
 				MaxAttempts:      prepared.OutputContract.RepairAttempts,
@@ -210,6 +221,7 @@ func (r *Runner) executePreparedRun(
 			}
 
 			genResp = repairResp
+			usage = addTokenUsage(usage, repairResp.Usage)
 			outputArtifact = buildOutputArtifact(genResp.Content, prepared.OutputContract.Format)
 
 			validationResult, err = validateArtifact(ctx, &outputArtifact, attemptsUsed)
@@ -238,19 +250,33 @@ func (r *Runner) executePreparedRun(
 		Endpoint:             prepared.EffectiveModelParams.Endpoint,
 		EffectiveModelParams: executionTarget,
 		InputHashes:          prepared.InputHashes,
-		Usage:                genResp.Usage,
+		Usage:                usage,
 		StartTime:            start,
 		EndTime:              end,
 		Duration:             end.Sub(start),
 	}, nil
 }
 
+func addTokenUsage(total, next domain.TokenUsage) domain.TokenUsage {
+	return domain.TokenUsage{
+		PromptTokens:     total.PromptTokens + next.PromptTokens,
+		CompletionTokens: total.CompletionTokens + next.CompletionTokens,
+		TotalTokens:      total.TotalTokens + next.TotalTokens,
+		CachedTokens:     total.CachedTokens + next.CachedTokens,
+		CacheWriteTokens: total.CacheWriteTokens + next.CacheWriteTokens,
+	}
+}
+
 func (r *Runner) Prepare(ctx context.Context, req domain.RunRequest) (*domain.PreparedRun, error) {
 	state, err := r.resolvePreparation(ctx, req, time.Now().UTC())
 	if err != nil {
 		return nil, err
 	}
-	return r.completePreparation(ctx, req, state)
+	operation, err := r.completePreparation(ctx, req, state)
+	if err != nil {
+		return nil, err
+	}
+	return operation.run, nil
 }
 
 func (r *Runner) resolvePreparation(
@@ -266,13 +292,15 @@ func (r *Runner) resolvePreparation(
 		return nil, fmt.Errorf("%w: session_id: %v", ErrInvalidRequest, err)
 	}
 
-	def, err := r.promptDefs.GetPromptDefinition(ctx, req.PromptID, req.PromptVersion)
+	promptSelection, err := r.resolvePromptDefinition(ctx, req.PromptID, req.PromptVersion)
 	if err != nil {
-		return nil, fmt.Errorf("%w: %w", ErrPromptLoad, err)
+		return nil, err
 	}
-	promptDefinitionHash, err := hashPromptDefinition(def)
+	def := promptSelection.definition
+	promptDefinitionHash := promptSelection.hash
+	effectiveContract, err := resolveOutputContract(def, req.Validation)
 	if err != nil {
-		return nil, fmt.Errorf("%w: failed to hash prompt definition: %v", ErrPromptLoad, err)
+		return nil, fmt.Errorf("%w: output contract: %v", ErrInvalidRequest, err)
 	}
 
 	selectedProfileID := strings.TrimSpace(req.ProfileID)
@@ -283,45 +311,26 @@ func (r *Runner) resolvePreparation(
 		return nil, fmt.Errorf("%w: %w: profile id is required either in request or prompt default_profile", ErrInvalidRequest, ErrProfileRequired)
 	}
 
-	execProfile, err := r.profiles.GetProfile(ctx, selectedProfileID)
+	selection, err := r.resolveProfileSelection(ctx, selectedProfileID)
 	if err != nil {
-		return nil, fmt.Errorf("%w: %w", ErrProfileLoad, err)
+		return nil, err
 	}
 
-	var selectedBackend *domain.Backend
-	if backendID := strings.TrimSpace(execProfile.BackendID); backendID != "" {
-		execProfile.BackendID = backendID
-		if r.backends == nil {
-			return nil, fmt.Errorf("%w: backend %q cannot be resolved", ErrProfileLoad, backendID)
-		}
-		resolvedBackend, resolveErr := r.backends.GetBackend(backendID)
-		if resolveErr != nil {
-			return nil, fmt.Errorf("%w: backend %q: %w", ErrProfileLoad, backendID, resolveErr)
-		}
-		selectedBackend = &resolvedBackend
-	}
-
-	effectiveModel, targetPresence, err := resolveExecutionTarget(selectedBackend, execProfile, req.Execution)
+	effectiveModel, targetPresence := resolveExecutionTarget(selection.backend, selection.profile, req.Execution)
+	effectiveModel.APIKey = req.APIKey
+	effectiveModel, err = normalizeResolvedExecutionTarget(effectiveModel)
 	if err != nil {
 		return nil, fmt.Errorf("%w: %w", ErrInvalidRequest, err)
 	}
-	effectiveModel.APIKey = req.APIKey
-	if strings.TrimSpace(effectiveModel.Endpoint) == "" {
-		return nil, fmt.Errorf("%w: execution endpoint is required", ErrInvalidRequest)
-	}
-	if strings.TrimSpace(effectiveModel.Model) == "" {
-		return nil, fmt.Errorf("%w: execution model is required", ErrInvalidRequest)
-	}
 	if err := validateAPIKey(effectiveModel.APIKeyEnv, effectiveModel.APIKey, effectiveModel.APIKeyRequired); err != nil {
 		return nil, fmt.Errorf("%w: %w", ErrInvalidRequest, err)
 	}
 
-	effectiveContract := resolveOutputContract(def, req.Validation)
 	return &preparationState{
 		definition:           def,
 		directSessionID:      directSessionID,
 		promptDefinitionHash: promptDefinitionHash,
-		selectedProfileID:    selectedProfileID,
+		selectedProfileID:    selection.id,
 		effectiveModel:       effectiveModel,
 		targetPresence:       targetPresence,
 		effectiveContract:    effectiveContract,
@@ -333,16 +342,68 @@ func (r *Runner) completePreparation(
 	ctx context.Context,
 	req domain.RunRequest,
 	state *preparationState,
-) (*domain.PreparedRun, error) {
-	structuredOutput, err := r.resolveStructuredOutput(
-		ctx,
+) (*preparedOperation, error) {
+	validationPlan, err := r.prepareValidation(ctx, state.effectiveContract)
+	if err != nil {
+		return nil, err
+	}
+	structuredOutput, err := r.structuredOutputFromValidationPlan(
 		state.definition,
 		state.effectiveContract,
+		validationPlan,
 	)
 	if err != nil {
 		return nil, err
 	}
-	return r.completePreparationWithStructuredOutput(ctx, req, state, structuredOutput)
+	prepared, err := r.completePreparationWithStructuredOutput(ctx, req, state, structuredOutput)
+	if err != nil {
+		return nil, err
+	}
+	return &preparedOperation{run: prepared, validation: validationPlan}, nil
+}
+
+func (r *Runner) prepareValidation(
+	ctx context.Context,
+	contract domain.OutputContract,
+) (validate.PreparedValidation, error) {
+	if r.validator == nil {
+		return noOpPreparedValidation{contract: contract}, nil
+	}
+	preparer, ok := r.validator.(validate.ValidationPreparer)
+	if !ok {
+		return nil, fmt.Errorf("%w: validator does not support prepared validation", ErrValidation)
+	}
+	plan, err := preparer.PrepareValidation(ctx, contract)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrValidation, err)
+	}
+	if plan == nil {
+		return nil, fmt.Errorf("%w: validator returned nil prepared validation", ErrValidation)
+	}
+	return plan, nil
+}
+
+func (r *Runner) structuredOutputFromValidationPlan(
+	def *domain.PromptDefinition,
+	contract domain.OutputContract,
+	plan validate.PreparedValidation,
+) (*domain.StructuredOutputSpec, error) {
+	if contract.ValidationMode != domain.ValidationJSONSchema {
+		return nil, nil
+	}
+
+	schemaDocument := plan.SchemaDocument()
+	if schemaDocument == nil {
+		if r.validator == nil {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("%w: prepared json_schema validation has no schema document", ErrValidation)
+	}
+	schemaDocument, err := jsonvalue.Copy(schemaDocument)
+	if err != nil {
+		return nil, fmt.Errorf("%w: invalid prepared json_schema schema document: %v", ErrValidation, err)
+	}
+	return structuredOutputSpec(def, schemaDocument), nil
 }
 
 func (r *Runner) completePreparationWithStructuredOutput(
@@ -408,32 +469,14 @@ func (r *Runner) admitRun(ctx context.Context, backendID string) (func(), error)
 	}
 	release, err := r.admitter.Admit(ctx, backendID)
 	if err != nil {
-		if errors.Is(err, capacity.ErrCapacityExceeded) {
-			return nil, fmt.Errorf("backend %q admission: %w", backendID, err)
+		if errors.Is(err, capacity.ErrCapacityExceeded) && strings.TrimSpace(backendID) != "" {
+			return nil, &CapacityError{BackendID: backendID}
 		}
 		return nil, err
 	}
 	return release, nil
 }
 
-func (r *Runner) resolveStructuredOutput(ctx context.Context, def *domain.PromptDefinition, contract domain.OutputContract) (*domain.StructuredOutputSpec, error) {
-	if contract.ValidationMode != domain.ValidationJSONSchema {
-		return nil, nil
-	}
-
-	loader, ok := r.validator.(validate.SchemaDocumentLoader)
-	if !ok || loader == nil {
-		return nil, fmt.Errorf("%w: json_schema output requires schema document loader", ErrValidation)
-	}
-
-	schemaDoc, err := loader.LoadSchemaDocument(ctx, contract.SchemaPath)
-	if err != nil {
-		return nil, fmt.Errorf("%w: failed to load json schema for structured output: %v", ErrValidation, err)
-	}
-
-	return structuredOutputSpec(def, schemaDoc), nil
-}
-
 func structuredOutputSpec(def *domain.PromptDefinition, schemaDocument any) *domain.StructuredOutputSpec {
 	return &domain.StructuredOutputSpec{
 		Type: domain.StructuredOutputJSONSchema,
@@ -471,25 +514,6 @@ func deriveStructuredSchemaName(promptID string, promptVersion string) string {
 	return name
 }
 
-func (r *Runner) validateOutput(ctx context.Context, artifact *domain.Artifact, contract domain.OutputContract, attemptsUsed int) (domain.ValidationResult, error) {
-	if r.validator == nil || contract.ValidationMode == domain.ValidationNone {
-		return domain.ValidationResult{
-			Status:         domain.ValidationSkipped,
-			Mode:           contract.ValidationMode,
-			SchemaPath:     contract.SchemaPath,
-			RepairAttempts: attemptsUsed,
-			IsValid:        true,
-		}, nil
-	}
-
-	res, err := r.validator.Validate(ctx, artifact, contract)
-	if err != nil {
-		return domain.ValidationResult{}, err
-	}
-	res.RepairAttempts = attemptsUsed
-	return res, nil
-}
-
 func (r *Runner) shouldAttemptRepair(contract domain.OutputContract, validationResult domain.ValidationResult) bool {
 	if r.repairer == nil {
 		return false
@@ -545,7 +569,7 @@ func mergeExecutionTarget(base domain.ExecutionTarget, override domain.Execution
 	return out
 }
 
-func mergeExecutionTargetOverride(base domain.ExecutionTarget, override domain.ExecutionTargetOverride) (domain.ExecutionTarget, domain.ExecutionTargetPresence, error) {
+func mergeExecutionTargetOverride(base domain.ExecutionTarget, override domain.ExecutionTargetOverride) (domain.ExecutionTarget, domain.ExecutionTargetPresence) {
 	out := base
 	var presence domain.ExecutionTargetPresence
 	if override.Endpoint != "" {
@@ -555,30 +579,18 @@ func mergeExecutionTargetOverride(base domain.ExecutionTarget, override domain.E
 		out.Model = override.Model
 	}
 	if override.Temperature != nil {
-		if *override.Temperature < 0 || *override.Temperature > 2 {
-			return domain.ExecutionTarget{}, domain.ExecutionTargetPresence{}, errors.New("temperature must be between 0 and 2")
-		}
 		out.Temperature = *override.Temperature
 		presence.Temperature = true
 	}
 	if override.MaxTokens != nil {
-		if *override.MaxTokens < 0 {
-			return domain.ExecutionTarget{}, domain.ExecutionTargetPresence{}, errors.New("max_tokens must be greater than or equal to 0")
-		}
 		out.MaxTokens = *override.MaxTokens
 		presence.MaxTokens = true
 	}
 	if override.TopP != nil {
-		if *override.TopP < 0 || *override.TopP > 1 {
-			return domain.ExecutionTarget{}, domain.ExecutionTargetPresence{}, errors.New("top_p must be between 0 and 1")
-		}
 		out.TopP = *override.TopP
 		presence.TopP = true
 	}
 	if override.TimeoutSeconds != nil {
-		if *override.TimeoutSeconds < 0 {
-			return domain.ExecutionTarget{}, domain.ExecutionTargetPresence{}, errors.New("timeout_seconds must be greater than or equal to 0")
-		}
 		out.TimeoutSeconds = *override.TimeoutSeconds
 		presence.TimeoutSeconds = true
 	}
@@ -594,22 +606,18 @@ func mergeExecutionTargetOverride(base domain.ExecutionTarget, override domain.E
 	if len(override.ExtraParams) > 0 {
 		out.ExtraParams = copyExtraParams(override.ExtraParams)
 	}
-	return out, presence, nil
+	return out, presence
 }
 
-func resolveExecutionTarget(backendValue *domain.Backend, profileValue *domain.ExecutionProfile, override *domain.ExecutionTargetOverride) (domain.ExecutionTarget, domain.ExecutionTargetPresence, error) {
+func resolveExecutionTarget(backendValue *domain.Backend, profileValue *domain.ExecutionProfile, override *domain.ExecutionTargetOverride) (domain.ExecutionTarget, domain.ExecutionTargetPresence) {
 	out := defaults.ExecutionTargetDefault()
 	out = mergeExecutionTarget(out, backendToTarget(backendValue))
 	out = mergeExecutionTarget(out, executionProfileToTarget(profileValue))
 	var presence domain.ExecutionTargetPresence
 	if override != nil {
-		var err error
-		out, presence, err = mergeExecutionTargetOverride(out, *override)
-		if err != nil {
-			return domain.ExecutionTarget{}, domain.ExecutionTargetPresence{}, err
+		out, presence = mergeExecutionTargetOverride(out, *override)
 	}
-	}
-	return out, presence, nil
+	return out, presence
 }
 
 func validateAPIKey(apiKeyEnv string, apiKey string, apiKeyRequired bool) error {
@@ -676,18 +684,21 @@ func copyExtraParams(src map[string]any) map[string]any {
 	return cp
 }
 
-func resolveOutputContract(def *domain.PromptDefinition, override *domain.OutputContract) domain.OutputContract {
+func resolveOutputContract(def *domain.PromptDefinition, override *domain.OutputContract) (domain.OutputContract, error) {
 	contract := def.Validation
 	if contract.Format == "" {
 		contract.Format = def.OutputFormat
 	}
 	if override != nil {
 		contract = *override
-	}
 		if contract.Format == "" {
 			contract.Format = domain.FormatText
 		}
-	return contract
+	}
+	if err := domain.ValidateOutputContract(contract); err != nil {
+		return domain.OutputContract{}, err
+	}
+	return contract, nil
 }
 
 func hashRenderedPrompt(p domain.RenderedPrompt) string {

internal/usecase/runner_test.go

@@ -6,9 +6,11 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"math"
 	"path/filepath"
 	"reflect"
 	"regexp"
+	"strconv"
 	"strings"
 	"sync"
 	"testing"
@@ -189,16 +191,34 @@ func (f *fakeValidator) Validate(ctx context.Context, artifact *domain.Artifact,
 	return f.result, nil
 }
 
-func (f *fakeValidator) LoadSchemaDocument(ctx context.Context, schemaPath string) (any, error) {
+func (f *fakeValidator) PrepareValidation(_ context.Context, contract domain.OutputContract) (validate.PreparedValidation, error) {
+	var schemaDocument any
+	if contract.ValidationMode == domain.ValidationJSONSchema {
 		f.schemaLoads++
-	f.schemaLoadPath = schemaPath
+		f.schemaLoadPath = contract.SchemaPath
 		if f.schemaErr != nil {
 			return nil, f.schemaErr
 		}
-	if f.schemaDoc != nil {
-		return f.schemaDoc, nil
+		schemaDocument = f.schemaDoc
+		if schemaDocument == nil {
+			schemaDocument = map[string]any{"type": "object"}
 		}
-	return map[string]any{"type": "object"}, nil
+	}
+	return &fakePreparedValidator{validator: f, contract: contract, schemaDocument: schemaDocument}, nil
+}
+
+type fakePreparedValidator struct {
+	validator      *fakeValidator
+	contract       domain.OutputContract
+	schemaDocument any
+}
+
+func (p *fakePreparedValidator) Validate(ctx context.Context, artifact *domain.Artifact) (domain.ValidationResult, error) {
+	return p.validator.Validate(ctx, artifact, p.contract)
+}
+
+func (p *fakePreparedValidator) SchemaDocument() any {
+	return p.schemaDocument
 }
 
 type fakeRepairer struct {
@@ -208,6 +228,30 @@ type fakeRepairer struct {
 	reqs      []RepairRequest
 }
 
+type sequenceLLM struct {
+	responses []*domain.GenerateResponse
+	requests  []domain.GenerateRequest
+}
+
+func (c *sequenceLLM) Generate(_ context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error) {
+	c.requests = append(c.requests, req)
+	index := len(c.requests) - 1
+	if index >= len(c.responses) {
+		return nil, errors.New("no generation response configured")
+	}
+	return c.responses[index], nil
+}
+
+type recordingRepairer struct {
+	next OutputRepairer
+	reqs []RepairRequest
+}
+
+func (r *recordingRepairer) Repair(ctx context.Context, req RepairRequest) (*domain.GenerateResponse, error) {
+	r.reqs = append(r.reqs, req)
+	return r.next.Repair(ctx, req)
+}
+
 type fakeRunAdmitter struct {
 	backendIDs   []string
 	err          error
@@ -502,6 +546,35 @@ func TestRunnerDirectSessionResolution(t *testing.T) {
 			t.Fatalf("invalid direct session invoked generation %d times", llmClient.calls)
 		}
 	})
+
+	t.Run("malformed direct value fails before loading or generation", func(t *testing.T) {
+		promptRepo := &fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)}
+		llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: "unexpected"}}
+		runner := NewRunner(
+			promptRepo,
+			&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}},
+			nil,
+			defaultArtifactReader(),
+			defaultRenderer(),
+			llmClient,
+			nil, nil)
+
+		_, err := runner.Run(context.Background(), domain.RunRequest{
+			PromptID:  "p",
+			ProfileID: "exec",
+			SessionID: "session" + string([]byte{0xff}),
+			Inputs:    singleInputRef(),
+		})
+		if !errors.Is(err, ErrInvalidRequest) {
+			t.Fatalf("expected ErrInvalidRequest, got %v", err)
+		}
+		if promptRepo.lastID != "" {
+			t.Fatalf("invalid direct session loaded prompt %q", promptRepo.lastID)
+		}
+		if llmClient.calls != 0 {
+			t.Fatalf("invalid direct session invoked generation %d times", llmClient.calls)
+		}
+	})
 }
 
 func TestRunnerPrepareUsesPromptDefaultProfileWhenNoExplicitProfileID(t *testing.T) {
@@ -704,16 +777,23 @@ func TestRunnerPrepareRequestNumericOverridePresence(t *testing.T) {
 }
 
 func TestRunnerPrepareInvalidRequestNumericOverridesFail(t *testing.T) {
-	tests := []struct {
+	type testCase struct {
 		name     string
 		override *domain.ExecutionTargetOverride
-	}{
+	}
+	tests := []testCase{
 		{name: "temperature below range", override: &domain.ExecutionTargetOverride{Temperature: float64Ptr(-0.1)}},
 		{name: "temperature above range", override: &domain.ExecutionTargetOverride{Temperature: float64Ptr(2.1)}},
 		{name: "max tokens below range", override: &domain.ExecutionTargetOverride{MaxTokens: intPtr(-1)}},
 		{name: "top p below range", override: &domain.ExecutionTargetOverride{TopP: float64Ptr(-0.1)}},
 		{name: "top p above range", override: &domain.ExecutionTargetOverride{TopP: float64Ptr(1.1)}},
 		{name: "timeout below range", override: &domain.ExecutionTargetOverride{TimeoutSeconds: intPtr(-1)}},
+		{name: "temperature is not finite", override: &domain.ExecutionTargetOverride{Temperature: float64Ptr(math.NaN())}},
+		{name: "top p is not finite", override: &domain.ExecutionTargetOverride{TopP: float64Ptr(math.Inf(1))}},
+	}
+	if strconv.IntSize == 64 {
+		durationLimit := int64(math.MaxInt64 / int64(time.Second))
+		tests = append(tests, testCase{name: "timeout cannot be represented as a duration", override: &domain.ExecutionTargetOverride{TimeoutSeconds: intPtr(int(durationLimit) + 1)}})
 	}
 
 	for _, tc := range tests {
@@ -1359,12 +1439,12 @@ func TestRunnerAdmissionFailureSkipsCompletionCollaborators(t *testing.T) {
 	tests := []struct {
 		name             string
 		admissionError   error
-		wantBackendContext bool
+		wantCapacityType bool
 	}{
 		{
 			name:             "capacity exhausted",
 			admissionError:   capacity.ErrCapacityExceeded,
-			wantBackendContext: true,
+			wantCapacityType: true,
 		},
 		{
 			name:           "context canceled",
@@ -1414,8 +1494,16 @@ func TestRunnerAdmissionFailureSkipsCompletionCollaborators(t *testing.T) {
 			if errors.Is(err, ErrInvalidRequest) || errors.Is(err, ErrLLMGenerate) {
 				t.Fatalf("admission error was recategorized: %v", err)
 			}
-			if tc.wantBackendContext && !strings.Contains(err.Error(), "custom") {
-				t.Fatalf("capacity error lacks backend context: %v", err)
+			var capacityErr *CapacityError
+			if tc.wantCapacityType {
+				if !errors.As(err, &capacityErr) {
+					t.Fatalf("capacity error=%v, want internal typed identity", err)
+				}
+				if capacityErr.BackendID != "custom" {
+					t.Fatalf("capacity backend ID=%q, want custom", capacityErr.BackendID)
+				}
+			} else if errors.As(err, &capacityErr) {
+				t.Fatalf("non-capacity admission error exposed typed capacity identity: %v", err)
 			}
 			if !reflect.DeepEqual(admitter.backendIDs, []string{"custom"}) {
 				t.Fatalf("admitted backend IDs=%#v, want custom", admitter.backendIDs)
@@ -1682,36 +1770,6 @@ func TestRunnerRunSelectedProfileBeatsBuiltInDefault(t *testing.T) {
 	}
 }
 
-func TestRunnerRunBuiltInDefaultsUsedWhenProfileOmitsOptionalFields(t *testing.T) {
-	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)}
-	execRepo := &fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{
-		"exec": {ID: "exec", Endpoint: "http://profile/v1", Model: "profile-model"},
-	}}
-	llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: "ok"}}
-	runner := NewRunner(promptRepo, execRepo, nil, defaultArtifactReader(), defaultRenderer(), llmClient, nil, nil)
-
-	res, err := runner.Run(context.Background(), domain.RunRequest{
-		PromptID:  "p",
-		ProfileID: "exec",
-		Inputs:    singleInputRef(),
-	})
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	if res.EffectiveModelParams.Temperature != defaults.ExecutionDefaultTemperature {
-		t.Fatalf("expected default temperature %v, got %v", defaults.ExecutionDefaultTemperature, res.EffectiveModelParams.Temperature)
-	}
-	if res.EffectiveModelParams.TopP != defaults.ExecutionDefaultTopP {
-		t.Fatalf("expected default top_p %v, got %v", defaults.ExecutionDefaultTopP, res.EffectiveModelParams.TopP)
-	}
-	if res.EffectiveModelParams.MaxTokens != defaults.ExecutionDefaultMaxTokens {
-		t.Fatalf("expected default max_tokens %d, got %d", defaults.ExecutionDefaultMaxTokens, res.EffectiveModelParams.MaxTokens)
-	}
-	if res.EffectiveModelParams.TimeoutSeconds != defaults.ExecutionDefaultTimeoutSeconds {
-		t.Fatalf("expected default timeout_seconds %d, got %d", defaults.ExecutionDefaultTimeoutSeconds, res.EffectiveModelParams.TimeoutSeconds)
-	}
-}
-
 func TestRunnerRunAPIKeyEnvResolvesFromEnvironment(t *testing.T) {
 	t.Setenv("PROMPTKIT_TEST_API_KEY", "secret")
 	promptRepo := &fakePromptRepo{def: promptDef(domain.FormatText, domain.ValidationNone, 0)}
@@ -2036,50 +2094,255 @@ func TestRunnerRunValidationStillWorks(t *testing.T) {
 	}
 }
 
-func TestRunnerRunStructuredRepairRemainsBoundedAndUsesEffectiveModelSettings(t *testing.T) {
-	repairer := &fakeRepairer{responses: []*domain.GenerateResponse{{Content: `{"broken":`}, {Content: `{"still":`}}}
-	llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: `{"initial":`}}
+func TestRunnerRepairStateMachine(t *testing.T) {
+	failed := func(mode domain.ValidationMode, diagnostic string) domain.ValidationResult {
+		return domain.ValidationResult{
+			Status:  domain.ValidationFailed,
+			Mode:    mode,
+			Errors:  []string{diagnostic},
+			IsValid: false,
+		}
+	}
+	passed := func(mode domain.ValidationMode) domain.ValidationResult {
+		return domain.ValidationResult{
+			Status:  domain.ValidationPassed,
+			Mode:    mode,
+			IsValid: true,
+		}
+	}
+	responses := func(count int) []*domain.GenerateResponse {
+		values := make([]*domain.GenerateResponse, count)
+		for index := range values {
+			unit := index + 1
+			values[index] = &domain.GenerateResponse{
+				Content: fmt.Sprintf(`{"candidate":%d}`, index),
+				Usage: domain.TokenUsage{
+					PromptTokens:     unit,
+					CompletionTokens: unit * 10,
+					TotalTokens:      unit * 100,
+					CachedTokens:     unit * 1000,
+					CacheWriteTokens: unit * 10000,
+				},
+			}
+		}
+		return values
+	}
+	zeroOverrides := &domain.ExecutionTargetOverride{
+		Temperature:    float64Ptr(0),
+		MaxTokens:      intPtr(0),
+		TopP:           float64Ptr(0),
+		TimeoutSeconds: intPtr(0),
+	}
+	allPresent := domain.ExecutionTargetPresence{
+		Temperature:    true,
+		MaxTokens:      true,
+		TopP:           true,
+		TimeoutSeconds: true,
+	}
 
+	tests := []struct {
+		name              string
+		mode              domain.ValidationMode
+		budget            int
+		validationResults []domain.ValidationResult
+		responses         []*domain.GenerateResponse
+		execution         *domain.ExecutionTargetOverride
+		wantPresence      domain.ExecutionTargetPresence
+		wantRepairs       int
+		wantStatus        domain.ValidationStatus
+		structured        bool
+	}{
+		{
+			name:              "initial success does not repair",
+			mode:              domain.ValidationJSON,
+			budget:            3,
+			validationResults: []domain.ValidationResult{passed(domain.ValidationJSON)},
+			responses:         responses(1),
+			wantStatus:        domain.ValidationPassed,
+		},
+		{
+			name:              "basic failure is ineligible despite budget",
+			mode:              domain.ValidationBasic,
+			budget:            3,
+			validationResults: []domain.ValidationResult{failed(domain.ValidationBasic, "empty output")},
+			responses:         responses(1),
+			wantStatus:        domain.ValidationFailed,
+		},
+		{
+			name:   "inherited numeric values remain absent",
+			mode:   domain.ValidationJSON,
+			budget: 1,
+			validationResults: []domain.ValidationResult{
+				failed(domain.ValidationJSON, "initial syntax"),
+				passed(domain.ValidationJSON),
+			},
+			responses:   responses(2),
+			wantRepairs: 1,
+			wantStatus:  domain.ValidationPassed,
+		},
+		{
+			name:       "explicit numeric zeros remain present",
+			mode:       domain.ValidationJSONSchema,
+			budget:     1,
+			execution:  zeroOverrides,
+			structured: true,
+			validationResults: []domain.ValidationResult{
+				failed(domain.ValidationJSONSchema, "initial schema mismatch"),
+				passed(domain.ValidationJSONSchema),
+			},
+			responses:    responses(2),
+			wantPresence: allPresent,
+			wantRepairs:  1,
+			wantStatus:   domain.ValidationPassed,
+		},
+		{
+			name:   "successful repair stops below larger budget",
+			mode:   domain.ValidationJSON,
+			budget: 4,
+			validationResults: []domain.ValidationResult{
+				failed(domain.ValidationJSON, "candidate zero"),
+				failed(domain.ValidationJSON, "candidate one"),
+				passed(domain.ValidationJSON),
+			},
+			responses:   responses(3),
+			wantRepairs: 2,
+			wantStatus:  domain.ValidationPassed,
+		},
+		{
+			name:   "failed repairs exhaust exact larger budget",
+			mode:   domain.ValidationJSON,
+			budget: 3,
+			validationResults: []domain.ValidationResult{
+				failed(domain.ValidationJSON, "candidate zero"),
+				failed(domain.ValidationJSON, "candidate one"),
+				failed(domain.ValidationJSON, "candidate two"),
+				failed(domain.ValidationJSON, "candidate three"),
+			},
+			responses:   responses(4),
+			wantRepairs: 3,
+			wantStatus:  domain.ValidationFailed,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			definition := promptDef(domain.FormatJSON, tc.mode, tc.budget)
+			plan := &recordingPreparedValidation{results: tc.validationResults}
+			if tc.structured {
+				definition.Validation.SchemaPath = "schema.json"
+				plan.schemaDocument = map[string]any{"type": "object"}
+			}
+			validator := &recordingValidationPreparer{plan: plan}
+			client := &sequenceLLM{responses: tc.responses}
+			repairer := &recordingRepairer{next: NewDefaultOutputRepairer(client)}
 			runner := NewRunnerWithRepairer(
-		&fakePromptRepo{def: promptDef(domain.FormatJSON, domain.ValidationJSON, 1)},
+				&fakePromptRepo{def: definition},
 				&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{
-			"exec": {ID: "exec", BackendID: "custom", Model: "profile-model", TimeoutSeconds: 55},
-		}}, fakeBackendResolver{backends: map[string]domain.Backend{
-			"custom": {ID: "custom", Endpoint: "http://backend/v1"},
+					"exec": {ID: "exec", BackendID: "custom", Model: "profile-model"},
+				}},
+				fakeBackendResolver{backends: map[string]domain.Backend{
+					"custom": {ID: "custom", Endpoint: "http://backend.example/v1"},
 				}},
-
 				defaultArtifactReader(),
 				defaultRenderer(),
-		llmClient,
-		validate.NewStandardValidator("."),
-		repairer, nil)
+				client,
+				validator,
+				repairer,
+				nil,
+			)
 
-	res, err := runner.Run(context.Background(), domain.RunRequest{
+			result, err := runner.Run(context.Background(), domain.RunRequest{
 				PromptID:  "p",
 				ProfileID: "exec",
+				SessionID: " repair-session ",
+				APIKey:    "direct-secret",
 				Inputs:    singleInputRef(),
-		Execution: &domain.ExecutionTargetOverride{Endpoint: "http://override/v1", Model: "override-model", TimeoutSeconds: intPtr(22)},
+				Execution: tc.execution,
 			})
 			if err != nil {
-		t.Fatalf("expected no error, got %v", err)
+				t.Fatalf("run: %v", err)
 			}
-	if repairer.calls != 1 || res.Validation.RepairAttempts != 1 {
-		t.Fatalf("expected one bounded repair, calls=%d attempts=%d", repairer.calls, res.Validation.RepairAttempts)
+			if len(client.requests) != tc.wantRepairs+1 || len(repairer.reqs) != tc.wantRepairs {
+				t.Fatalf(
+					"generation/repair calls = (%d, %d), want (%d, %d)",
+					len(client.requests), len(repairer.reqs), tc.wantRepairs+1, tc.wantRepairs,
+				)
 			}
-	if len(repairer.reqs) != 1 {
-		t.Fatalf("expected one repair request, got %d", len(repairer.reqs))
+			if len(plan.artifacts) != tc.wantRepairs+1 {
+				t.Fatalf("validation calls = %d, want %d", len(plan.artifacts), tc.wantRepairs+1)
 			}
-	if repairer.reqs[0].Target.Endpoint != "http://override/v1" || repairer.reqs[0].Target.Model != "override-model" {
-		t.Fatalf("expected repair to use effective target, got %+v", repairer.reqs[0].Target)
+
+			initialRequest := client.requests[0]
+			if initialRequest.TargetPresence != tc.wantPresence {
+				t.Fatalf("initial target presence = %+v, want %+v", initialRequest.TargetPresence, tc.wantPresence)
 			}
-	if repairer.reqs[0].Target.TimeoutSeconds != 22 {
-		t.Fatalf("expected repair to use effective timeout, got %d", repairer.reqs[0].Target.TimeoutSeconds)
+			if initialRequest.Target.APIKey != "direct-secret" || initialRequest.Target.BackendID != "custom" ||
+				initialRequest.Prompt.SessionID != "repair-session" {
+				t.Fatalf("initial common request fields = %+v", initialRequest)
 			}
-	if llmClient.lastReq.Target.BackendID != "custom" ||
-		repairer.reqs[0].Target.BackendID != "custom" ||
-		res.SelectedBackendID != "custom" {
-		t.Fatalf("expected backend identity in generation, repair, and result: generate=%q repair=%q result=%q",
-			llmClient.lastReq.Target.BackendID, repairer.reqs[0].Target.BackendID, res.SelectedBackendID)
+			if initialRequest.Target.Endpoint != "http://backend.example/v1" ||
+				initialRequest.Target.Model != "profile-model" ||
+				initialRequest.Target.Temperature != 0 || initialRequest.Target.MaxTokens != 0 || initialRequest.Target.TopP != 0 {
+				t.Fatalf("initial effective target = %+v", initialRequest.Target)
+			}
+			if tc.structured != (initialRequest.StructuredOutput != nil) {
+				t.Fatalf("initial structured output = %+v, want present %v", initialRequest.StructuredOutput, tc.structured)
+			}
+			if tc.structured && (initialRequest.StructuredOutput.JSONSchema == nil ||
+				initialRequest.StructuredOutput.JSONSchema.Name != "p_1") {
+				t.Fatalf("initial JSON Schema metadata = %+v, want derived schema name p_1", initialRequest.StructuredOutput)
+			}
+
+			for index, req := range repairer.reqs {
+				if req.Attempt != index+1 || req.MaxAttempts != tc.budget || req.Mode != tc.mode {
+					t.Fatalf("repair request %d progression = %+v", index, req)
+				}
+				if req.PreviousOutput != tc.responses[index].Content ||
+					!reflect.DeepEqual(req.ValidationErrors, tc.validationResults[index].Errors) {
+					t.Fatalf("repair request %d prior state = %+v", index, req)
+				}
+				if req.TargetPresence != tc.wantPresence || !reflect.DeepEqual(req.Target, initialRequest.Target) ||
+					req.SessionID != initialRequest.Prompt.SessionID ||
+					!reflect.DeepEqual(req.StructuredOutput, initialRequest.StructuredOutput) {
+					t.Fatalf("repair request %d common fields drifted: %+v", index, req)
+				}
+
+				generated := client.requests[index+1]
+				if generated.TargetPresence != initialRequest.TargetPresence ||
+					!reflect.DeepEqual(generated.Target, initialRequest.Target) ||
+					generated.Prompt.SessionID != initialRequest.Prompt.SessionID ||
+					!reflect.DeepEqual(generated.StructuredOutput, initialRequest.StructuredOutput) {
+					t.Fatalf("repair generation request %d common fields drifted: %+v", index, generated)
+				}
+				if reflect.DeepEqual(generated.Prompt.Messages, initialRequest.Prompt.Messages) {
+					t.Fatalf("repair generation request %d reused the initial prompt", index)
+				}
+			}
+
+			lastResponse := tc.responses[tc.wantRepairs]
+			if result.RawOutput != lastResponse.Content || string(result.Artifact.Body) != lastResponse.Content {
+				t.Fatalf("final output = (%q, %q), want %q", result.RawOutput, result.Artifact.Body, lastResponse.Content)
+			}
+			if result.Validation.Status != tc.wantStatus || result.Validation.RepairAttempts != tc.wantRepairs {
+				t.Fatalf("final validation = %+v, want status %q and %d repairs", result.Validation, tc.wantStatus, tc.wantRepairs)
+			}
+			if result.SelectedBackendID != "custom" || result.SessionID != "repair-session" ||
+				result.EffectiveModelParams.APIKey != "" {
+				t.Fatalf("result execution metadata = %+v", result)
+			}
+
+			var wantUsage domain.TokenUsage
+			for _, response := range tc.responses[:tc.wantRepairs+1] {
+				wantUsage.PromptTokens += response.Usage.PromptTokens
+				wantUsage.CompletionTokens += response.Usage.CompletionTokens
+				wantUsage.TotalTokens += response.Usage.TotalTokens
+				wantUsage.CachedTokens += response.Usage.CachedTokens
+				wantUsage.CacheWriteTokens += response.Usage.CacheWriteTokens
+			}
+			if result.Usage != wantUsage {
+				t.Fatalf("cumulative usage = %+v, want %+v", result.Usage, wantUsage)
+			}
+		})
 	}
 }
 
@@ -2174,96 +2437,6 @@ func TestRunnerSchedulesInitialAndRepairGenerationThroughOneBackendPool(t *testi
 	}
 }
 
-func TestRunnerRunRepairCarriesEffectiveSessionID(t *testing.T) {
-	llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: `{"broken":`}}
-	runner := NewRunnerWithRepairer(
-		&fakePromptRepo{def: promptDef(domain.FormatJSON, domain.ValidationJSON, 1)},
-		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{
-			"exec": {ID: "exec", Endpoint: "http://example.test/v1", Model: "model"},
-		}},
-		nil,
-		defaultArtifactReader(),
-		defaultRenderer(),
-		llmClient,
-		validate.NewStandardValidator("."),
-		NewDefaultOutputRepairer(llmClient), nil)
-
-	result, err := runner.Run(context.Background(), domain.RunRequest{
-		PromptID:  "p",
-		ProfileID: "exec",
-		SessionID: " repair-session ",
-		Inputs:    singleInputRef(),
-	})
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	if llmClient.calls != 2 {
-		t.Fatalf("expected initial generation and one repair, got %d calls", llmClient.calls)
-	}
-	if llmClient.lastReq.Prompt.SessionID != "repair-session" {
-		t.Fatalf("expected repair generation to retain effective session, got %q", llmClient.lastReq.Prompt.SessionID)
-	}
-	if result.SessionID != "repair-session" {
-		t.Fatalf("expected result to retain effective session, got %q", result.SessionID)
-	}
-}
-
-func TestRunnerRunJSONSchemaRepairCarriesStructuredOutputSpec(t *testing.T) {
-	def := promptDef(domain.FormatJSON, domain.ValidationJSONSchema, 1)
-	def.Validation.SchemaPath = "events.schema.json"
-
-	validator := &fakeValidator{
-		result: domain.ValidationResult{
-			Status:  domain.ValidationFailed,
-			Mode:    domain.ValidationJSONSchema,
-			Errors:  []string{"schema mismatch"},
-			IsValid: false,
-		},
-		schemaDoc: map[string]any{
-			"type": "object",
-			"properties": map[string]any{
-				"events": map[string]any{"type": "array"},
-			},
-		},
-	}
-	repairer := &fakeRepairer{
-		responses: []*domain.GenerateResponse{
-			{Content: `{"events":[]}`},
-		},
-	}
-	llmClient := &fakeLLM{resp: &domain.GenerateResponse{Content: `{"events":[1]}`}}
-	runner := NewRunnerWithRepairer(
-		&fakePromptRepo{def: def},
-		&fakeExecutionProfileRepo{profiles: map[string]*domain.ExecutionProfile{"exec": defaultExecutionProfile()}}, nil,
-
-		defaultArtifactReader(),
-		defaultRenderer(),
-		llmClient,
-		validator,
-		repairer, nil)
-
-	_, err := runner.Run(context.Background(), domain.RunRequest{
-		PromptID:  "p",
-		ProfileID: "exec",
-		Inputs:    singleInputRef(),
-	})
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	if llmClient.lastReq.StructuredOutput == nil || llmClient.lastReq.StructuredOutput.JSONSchema == nil {
-		t.Fatalf("expected initial llm request to include structured output, got %+v", llmClient.lastReq.StructuredOutput)
-	}
-	if len(repairer.reqs) != 1 {
-		t.Fatalf("expected one repair request, got %d", len(repairer.reqs))
-	}
-	if repairer.reqs[0].StructuredOutput == nil || repairer.reqs[0].StructuredOutput.JSONSchema == nil {
-		t.Fatalf("expected repair request structured output, got %+v", repairer.reqs[0].StructuredOutput)
-	}
-	if repairer.reqs[0].StructuredOutput.JSONSchema.Name != "p_1" {
-		t.Fatalf("expected derived schema name p_1, got %q", repairer.reqs[0].StructuredOutput.JSONSchema.Name)
-	}
-}
-
 func TestExecutionProfileToTargetPopulatesAllFieldsAndCopiesExtraParams(t *testing.T) {
 	src := &domain.ExecutionProfile{
 		ID:              "exec",
@@ -2322,10 +2495,7 @@ func TestResolveExecutionTargetProfileValuesPopulateAllSupportedFields(t *testin
 		},
 	}
 
-	target, presence, err := resolveExecutionTarget(nil, profileValue, nil)
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
+	target, presence := resolveExecutionTarget(nil, profileValue, nil)
 	if presence != (domain.ExecutionTargetPresence{}) {
 		t.Fatalf("expected no request override presence, got %+v", presence)
 	}
@@ -2377,10 +2547,7 @@ func TestResolveExecutionTargetRuntimeOverridesBeatProfileForAllOverrideableFiel
 		},
 	}
 
-	target, presence, err := resolveExecutionTarget(nil, profileValue, override)
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
+	target, presence := resolveExecutionTarget(nil, profileValue, override)
 	if presence != (domain.ExecutionTargetPresence{Temperature: true, MaxTokens: true, TopP: true, TimeoutSeconds: true}) {
 		t.Fatalf("unexpected override presence: %+v", presence)
 	}
@@ -2427,12 +2594,9 @@ func TestResolveExecutionTargetReasoningOverrideStates(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			target, _, err := resolveExecutionTarget(nil, profileValue, &domain.ExecutionTargetOverride{
+			target, _ := resolveExecutionTarget(nil, profileValue, &domain.ExecutionTargetOverride{
 				ReasoningEffort: tt.override,
 			})
-			if err != nil {
-				t.Fatalf("resolve execution target: %v", err)
-			}
 			if target.ReasoningEffort != tt.want {
 				t.Fatalf("reasoning effort = %q, want %q", target.ReasoningEffort, tt.want)
 			}
@@ -2561,10 +2725,7 @@ func TestResolveExecutionTargetUsesBackendProfileAndRequestPrecedence(t *testing
 		ExtraParams: map[string]any{"request": true},
 	}
 
-	target, _, err := resolveExecutionTarget(backendValue, profileValue, override)
-	if err != nil {
-		t.Fatalf("resolve target: %v", err)
-	}
+	target, _ := resolveExecutionTarget(backendValue, profileValue, override)
 	if target.BackendID != "custom" {
 		t.Fatalf("endpoint override changed backend identity: %+v", target)
 	}
@@ -2575,12 +2736,9 @@ func TestResolveExecutionTargetUsesBackendProfileAndRequestPrecedence(t *testing
 		t.Fatalf("expected whole-map request replacement, got %#v", target.ExtraParams)
 	}
 
-	target, _, err = resolveExecutionTarget(backendValue, &domain.ExecutionProfile{
+	target, _ = resolveExecutionTarget(backendValue, &domain.ExecutionProfile{
 		ID: "exec", BackendID: "custom", Model: "profile-model",
 	}, nil)
-	if err != nil {
-		t.Fatalf("resolve backend defaults: %v", err)
-	}
 	if target.Endpoint != backendValue.Endpoint ||
 		target.APIKeyEnv != backendValue.APIKeyEnv ||
 		!reflect.DeepEqual(target.ExtraParams, backendValue.ExtraParams) {

internal/validate/cancellation_test.go

@@ -0,0 +1,311 @@
+package validate
+
+import (
+	"context"
+	"errors"
+	"io/fs"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"testing/fstest"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"github.com/santhosh-tekuri/jsonschema/v6"
+)
+
+func TestValidationCancellationBeforeWorkDoesNotOpenSchemaSource(t *testing.T) {
+	source := &countingSchemaFS{FS: fstest.MapFS{
+		"schema.json": {Data: []byte(`{"type":"object"}`)},
+	}}
+	validator := NewFSValidator(source, ".").(ValidationPreparer)
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	plan, err := validator.PrepareValidation(ctx, domain.OutputContract{
+		ValidationMode: domain.ValidationJSONSchema,
+		SchemaPath:     "schema.json",
+	})
+	if plan != nil || !errors.Is(err, context.Canceled) {
+		t.Fatalf("PrepareValidation() = (%v, %v), want nil plan and context cancellation", plan, err)
+	}
+	if opens := source.opens.Load(); opens != 0 {
+		t.Fatalf("schema source opens = %d, want 0", opens)
+	}
+}
+
+func TestValidationCancellationBetweenReferencedSchemaReadChunks(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	source := &controlledSchemaFS{
+		FS: fstest.MapFS{
+			"root.json":  {Data: []byte(`{"$ref":"child.json"}`)},
+			"child.json": {Data: []byte(`{"type":"string"}` + strings.Repeat(" ", schemaReadChunkSize*2))},
+		},
+		target: "child.json",
+		cancel: cancel,
+	}
+	validator := NewFSValidator(source, ".").(ValidationPreparer)
+
+	plan, err := validator.PrepareValidation(ctx, domain.OutputContract{
+		ValidationMode: domain.ValidationJSONSchema,
+		SchemaPath:     "root.json",
+	})
+	if plan != nil || !errors.Is(err, context.Canceled) {
+		t.Fatalf("PrepareValidation() = (%v, %v), want nil plan and context cancellation", plan, err)
+	}
+	if reads := source.reads.Load(); reads != 1 {
+		t.Fatalf("controlled child reads = %d, want 1", reads)
+	}
+	if closes := source.closes.Load(); closes != 1 {
+		t.Fatalf("controlled child closes = %d, want 1", closes)
+	}
+}
+
+func TestDecodeCancellationAfterSynchronousCallWins(t *testing.T) {
+	ctx := newCheckpointContext(2)
+	value, err := decodeJSONValue(ctx, []byte(`{"value":1}`))
+	if value != nil || !errors.Is(err, context.Canceled) {
+		t.Fatalf("decodeJSONValue() = (%v, %v), want nil value and context cancellation", value, err)
+	}
+}
+
+func TestCompileCancellationAfterSynchronousCallWins(t *testing.T) {
+	for _, dependencyErr := range []error{nil, errors.New("compile failed")} {
+		ctx, cancel := context.WithCancel(context.Background())
+		compiled := &jsonschema.Schema{}
+		schema, err := compileJSONSchema(ctx, "promptkit-schema:/root.json", func(string) (*jsonschema.Schema, error) {
+			cancel()
+			return compiled, dependencyErr
+		})
+		if schema != nil || !errors.Is(err, context.Canceled) {
+			t.Fatalf("compileJSONSchema() = (%v, %v), want authoritative context cancellation", schema, err)
+		}
+		if dependencyErr != nil && errors.Is(err, dependencyErr) {
+			t.Fatalf("compileJSONSchema() error = %v, dependency error should not win", err)
+		}
+	}
+}
+
+func TestExecutionCancellationAfterSynchronousCallWins(t *testing.T) {
+	for _, dependencyErr := range []error{nil, errors.New("schema mismatch")} {
+		ctx, cancel := context.WithCancel(context.Background())
+		executor := &controlledSchemaExecutor{cancel: cancel, err: dependencyErr}
+		validationErrors, err := executeJSONSchema(ctx, executor, map[string]any{"ok": true})
+		if validationErrors != nil || !errors.Is(err, context.Canceled) {
+			t.Fatalf("executeJSONSchema() = (%v, %v), want no result and context cancellation", validationErrors, err)
+		}
+		if calls := executor.calls.Load(); calls != 1 {
+			t.Fatalf("schema execution calls = %d, want 1", calls)
+		}
+	}
+}
+
+func TestCancellationDoesNotDetachBlockedSchemaRead(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	started := make(chan struct{})
+	release := make(chan struct{})
+	source := &controlledSchemaFS{
+		FS: fstest.MapFS{
+			"schema.json": {Data: []byte(`{"type":"object"}`)},
+		},
+		target:  "schema.json",
+		started: started,
+		release: release,
+	}
+	validator := NewFSValidator(source, ".").(ValidationPreparer)
+	type outcome struct {
+		plan PreparedValidation
+		err  error
+	}
+	result := make(chan outcome, 1)
+	go func() {
+		plan, err := validator.PrepareValidation(ctx, domain.OutputContract{
+			ValidationMode: domain.ValidationJSONSchema,
+			SchemaPath:     "schema.json",
+		})
+		result <- outcome{plan: plan, err: err}
+	}()
+
+	waitForSignal(t, started, "schema read to start")
+	cancel()
+	select {
+	case got := <-result:
+		t.Fatalf("blocked dependency returned before release: (%v, %v)", got.plan, got.err)
+	default:
+	}
+	close(release)
+	got := waitForOutcome(t, result)
+	if got.plan != nil || !errors.Is(got.err, context.Canceled) {
+		t.Fatalf("PrepareValidation() after release = (%v, %v), want nil plan and context cancellation", got.plan, got.err)
+	}
+	if reads := source.reads.Load(); reads != 1 {
+		t.Fatalf("blocked reads = %d, want 1 completed read", reads)
+	}
+}
+
+func TestCancellationDoesNotDetachBlockedSchemaExecution(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	started := make(chan struct{})
+	release := make(chan struct{})
+	executor := &controlledSchemaExecutor{started: started, release: release}
+	result := make(chan error, 1)
+	go func() {
+		_, err := executeJSONSchema(ctx, executor, map[string]any{"ok": true})
+		result <- err
+	}()
+
+	waitForSignal(t, started, "schema execution to start")
+	cancel()
+	select {
+	case err := <-result:
+		t.Fatalf("blocked dependency returned before release: %v", err)
+	default:
+	}
+	close(release)
+	select {
+	case err := <-result:
+		if !errors.Is(err, context.Canceled) {
+			t.Fatalf("executeJSONSchema() after release = %v, want context cancellation", err)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for released schema execution")
+	}
+	if calls := executor.calls.Load(); calls != 1 {
+		t.Fatalf("schema execution calls = %d, want 1 completed call", calls)
+	}
+}
+
+type countingSchemaFS struct {
+	fs.FS
+	opens atomic.Int32
+}
+
+func (f *countingSchemaFS) Open(name string) (fs.File, error) {
+	f.opens.Add(1)
+	return f.FS.Open(name)
+}
+
+type controlledSchemaFS struct {
+	fs.FS
+	target  string
+	cancel  context.CancelFunc
+	started chan struct{}
+	release chan struct{}
+	once    sync.Once
+	reads   atomic.Int32
+	closes  atomic.Int32
+}
+
+func (f *controlledSchemaFS) Open(name string) (fs.File, error) {
+	file, err := f.FS.Open(name)
+	if err != nil || name != f.target {
+		return file, err
+	}
+	return &controlledSchemaFile{File: file, owner: f}, nil
+}
+
+type controlledSchemaFile struct {
+	fs.File
+	owner *controlledSchemaFS
+}
+
+func (f *controlledSchemaFile) Read(buffer []byte) (int, error) {
+	f.owner.once.Do(func() {
+		if f.owner.started != nil {
+			close(f.owner.started)
+		}
+		if f.owner.release != nil {
+			<-f.owner.release
+		}
+	})
+	n, err := f.File.Read(buffer)
+	f.owner.reads.Add(1)
+	if f.owner.cancel != nil {
+		f.owner.cancel()
+	}
+	return n, err
+}
+
+func (f *controlledSchemaFile) Close() error {
+	f.owner.closes.Add(1)
+	return f.File.Close()
+}
+
+type controlledSchemaExecutor struct {
+	cancel  context.CancelFunc
+	err     error
+	started chan struct{}
+	release chan struct{}
+	calls   atomic.Int32
+}
+
+func (e *controlledSchemaExecutor) Validate(any) error {
+	e.calls.Add(1)
+	if e.started != nil {
+		close(e.started)
+	}
+	if e.release != nil {
+		<-e.release
+	}
+	if e.cancel != nil {
+		e.cancel()
+	}
+	return e.err
+}
+
+type checkpointContext struct {
+	context.Context
+	mu        sync.Mutex
+	remaining int
+	canceled  bool
+	done      chan struct{}
+}
+
+func newCheckpointContext(checksUntilCancel int) *checkpointContext {
+	return &checkpointContext{
+		Context:   context.Background(),
+		remaining: checksUntilCancel,
+		done:      make(chan struct{}),
+	}
+}
+
+func (c *checkpointContext) Done() <-chan struct{} {
+	return c.done
+}
+
+func (c *checkpointContext) Err() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.canceled {
+		return context.Canceled
+	}
+	c.remaining--
+	if c.remaining == 0 {
+		c.canceled = true
+		close(c.done)
+		return context.Canceled
+	}
+	return nil
+}
+
+func waitForSignal(t *testing.T, signal <-chan struct{}, description string) {
+	t.Helper()
+	select {
+	case <-signal:
+	case <-time.After(2 * time.Second):
+		t.Fatalf("timed out waiting for %s", description)
+	}
+}
+
+func waitForOutcome[T any](t *testing.T, result <-chan T) T {
+	t.Helper()
+	select {
+	case value := <-result:
+		return value
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for released dependency")
+		var zero T
+		return zero
+	}
+}

internal/validate/standard_validator.go

@@ -1,15 +1,18 @@
 package validate
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"net/url"
 	"os"
 	"path"
 	"path/filepath"
+	"runtime"
 	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
@@ -19,6 +22,8 @@ import (
 
 const jsonSchemaDraft2020 = "https://json-schema.org/draft/2020-12/schema"
 
+const schemaReadChunkSize = 64 * 1024
+
 // StandardValidator provides basic, JSON, and JSON Schema output validation.
 type StandardValidator struct {
 	schemaBaseDir string
@@ -48,7 +53,7 @@ func (v *FSValidator) Validate(ctx context.Context, artifact *domain.Artifact, c
 type preparedValidation struct {
 	contract       domain.OutputContract
 	schemaDocument any
-	schema         *jsonschema.Schema
+	schema         schemaExecutor
 }
 
 func (p *preparedValidation) Validate(ctx context.Context, artifact *domain.Artifact) (domain.ValidationResult, error) {
@@ -59,14 +64,11 @@ func (p *preparedValidation) SchemaDocument() any {
 	return p.schemaDocument
 }
 
-func (p *preparedValidation) validateJSONSchema(instance any, _ string) ([]string, error) {
+func (p *preparedValidation) validateJSONSchema(ctx context.Context, instance any, _ string) ([]string, error) {
 	if p.schema == nil {
 		return nil, errors.New("prepared JSON schema is unavailable")
 	}
-	if err := p.schema.Validate(instance); err != nil {
-		return []string{fmt.Sprintf("json schema validation failed: %v", err)}, nil
-	}
-	return nil, nil
+	return executeJSONSchema(ctx, p.schema, instance)
 }
 
 func (v *StandardValidator) PrepareValidation(ctx context.Context, contract domain.OutputContract) (PreparedValidation, error) {
@@ -79,11 +81,11 @@ func (v *StandardValidator) PrepareValidation(ctx context.Context, contract doma
 		return prepared, nil
 	}
 
-	resolvedSchemaPath, err := v.resolveSchemaPath(contract.SchemaPath)
+	resolvedSchemaPath, err := v.resolveSchemaPath(ctx, contract.SchemaPath)
 	if err != nil {
 		return nil, err
 	}
-	schemaDocument, err := loadJSONSchemaFile(resolvedSchemaPath)
+	schemaDocument, err := loadJSONSchemaFile(ctx, resolvedSchemaPath)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", resolvedSchemaPath, err)
 	}
@@ -91,11 +93,24 @@ func (v *StandardValidator) PrepareValidation(ctx context.Context, contract doma
 	if err != nil {
 		return nil, err
 	}
-	compiler := newSchemaCompiler(standardSchemaLoader{root: schemaRoot})
-	if err := compiler.AddResource(resolvedSchemaPath, schemaDocument); err != nil {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	compiler := newSchemaCompiler(standardSchemaLoader{ctx: ctx, root: schemaRoot})
+	resourceURL := fileSchemaResourceURL(resolvedSchemaPath)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if err := compiler.AddResource(resourceURL.String(), schemaDocument); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
 		return nil, fmt.Errorf("failed to register JSON schema %q: %w", resolvedSchemaPath, err)
 	}
-	schema, err := compiler.Compile(resolvedSchemaPath)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	schema, err := compileJSONSchema(ctx, resourceURL.String(), compiler.Compile)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", resolvedSchemaPath, err)
 	}
@@ -118,16 +133,25 @@ func (v *FSValidator) PrepareValidation(ctx context.Context, contract domain.Out
 		return prepared, nil
 	}
 
-	schemaName, schemaDocument, err := v.loadSchemaDocument(contract.SchemaPath)
+	schemaName, schemaDocument, err := v.loadSchemaDocument(ctx, contract.SchemaPath)
 	if err != nil {
 		return nil, err
 	}
 	resourceURL := fsSchemaResourceURL(schemaName)
-	compiler := newSchemaCompiler(fsSchemaLoader{fsys: v.fsys, root: filecatalog.CleanFSRoot(v.root)})
-	if err := compiler.AddResource(resourceURL, schemaDocument); err != nil {
+	compiler := newSchemaCompiler(fsSchemaLoader{ctx: ctx, fsys: v.fsys, root: filecatalog.CleanFSRoot(v.root)})
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if err := compiler.AddResource(resourceURL.String(), schemaDocument); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
 		return nil, fmt.Errorf("failed to register JSON schema %q: %w", schemaName, err)
 	}
-	schema, err := compiler.Compile(resourceURL)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	schema, err := compileJSONSchema(ctx, resourceURL.String(), compiler.Compile)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", schemaName, err)
 	}
@@ -140,7 +164,7 @@ func (v *FSValidator) PrepareValidation(ctx context.Context, contract domain.Out
 	return prepared, nil
 }
 
-type schemaValidatorFunc func(instance any, schemaPath string) ([]string, error)
+type schemaValidatorFunc func(ctx context.Context, instance any, schemaPath string) ([]string, error)
 
 func validateArtifact(ctx context.Context, artifact *domain.Artifact, contract domain.OutputContract, validateSchema schemaValidatorFunc) (domain.ValidationResult, error) {
 	select {
@@ -165,7 +189,11 @@ func validateArtifact(ctx context.Context, artifact *domain.Artifact, contract d
 		res.IsValid = true
 		return res, nil
 	case domain.ValidationBasic:
-		if strings.TrimSpace(string(artifact.Body)) == "" {
+		empty := strings.TrimSpace(string(artifact.Body)) == ""
+		if err := ctx.Err(); err != nil {
+			return domain.ValidationResult{}, err
+		}
+		if empty {
 			res.Status = domain.ValidationFailed
 			res.IsValid = false
 			res.Errors = []string{"output is empty"}
@@ -175,26 +203,32 @@ func validateArtifact(ctx context.Context, artifact *domain.Artifact, contract d
 		res.IsValid = true
 		return res, nil
 	case domain.ValidationJSON:
-		_, jsonErr := parseJSON(artifact.Body)
-		if jsonErr != nil {
+		valid := json.Valid(artifact.Body)
+		if err := ctx.Err(); err != nil {
+			return domain.ValidationResult{}, err
+		}
+		if !valid {
 			res.Status = domain.ValidationFailed
 			res.IsValid = false
-			res.Errors = []string{fmt.Sprintf("invalid JSON: %v", jsonErr)}
+			res.Errors = []string{"invalid JSON"}
 			return res, nil
 		}
 		res.Status = domain.ValidationPassed
 		res.IsValid = true
 		return res, nil
 	case domain.ValidationJSONSchema:
-		instance, jsonErr := parseJSON(artifact.Body)
+		instance, jsonErr := decodeJSONValue(ctx, artifact.Body)
 		if jsonErr != nil {
+			if contextErr := ctx.Err(); contextErr != nil {
+				return domain.ValidationResult{}, contextErr
+			}
 			res.Status = domain.ValidationFailed
 			res.IsValid = false
 			res.Errors = []string{fmt.Sprintf("invalid JSON: %v", jsonErr)}
 			return res, nil
 		}
 
-		validationErrors, err := validateSchema(instance, contract.SchemaPath)
+		validationErrors, err := validateSchema(ctx, instance, contract.SchemaPath)
 		if err != nil {
 			return domain.ValidationResult{}, err
 		}
@@ -213,8 +247,8 @@ func validateArtifact(ctx context.Context, artifact *domain.Artifact, contract d
 	}
 }
 
-func (v *StandardValidator) validateJSONSchema(instance any, schemaPath string) ([]string, error) {
-	resolvedSchemaPath, err := v.resolveSchemaPath(schemaPath)
+func (v *StandardValidator) validateJSONSchema(ctx context.Context, instance any, schemaPath string) ([]string, error) {
+	resolvedSchemaPath, err := v.resolveSchemaPath(ctx, schemaPath)
 	if err != nil {
 		return nil, err
 	}
@@ -223,20 +257,21 @@ func (v *StandardValidator) validateJSONSchema(instance any, schemaPath string)
 	if err != nil {
 		return nil, err
 	}
-	compiler := newSchemaCompiler(standardSchemaLoader{root: schemaRoot})
-	schema, err := compiler.Compile(resolvedSchemaPath)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	compiler := newSchemaCompiler(standardSchemaLoader{ctx: ctx, root: schemaRoot})
+	resourceURL := fileSchemaResourceURL(resolvedSchemaPath)
+	schema, err := compileJSONSchema(ctx, resourceURL.String(), compiler.Compile)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", resolvedSchemaPath, err)
 	}
 
-	if err := schema.Validate(instance); err != nil {
-		return []string{fmt.Sprintf("json schema validation failed: %v", err)}, nil
-	}
-	return nil, nil
+	return executeJSONSchema(ctx, schema, instance)
 }
 
-func (v *FSValidator) validateJSONSchema(instance any, schemaPath string) ([]string, error) {
-	schemaName, schemaDoc, err := v.loadSchemaDocument(schemaPath)
+func (v *FSValidator) validateJSONSchema(ctx context.Context, instance any, schemaPath string) ([]string, error) {
+	schemaName, schemaDoc, err := v.loadSchemaDocument(ctx, schemaPath)
 	if err != nil {
 		return nil, err
 	}
@@ -245,71 +280,60 @@ func (v *FSValidator) validateJSONSchema(instance any, schemaPath string) ([]str
 	if err := validateSchemaDialect(schemaDoc); err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", schemaName, err)
 	}
-	compiler := newSchemaCompiler(fsSchemaLoader{fsys: v.fsys, root: filecatalog.CleanFSRoot(v.root)})
-	if err := compiler.AddResource(resourceURL, schemaDoc); err != nil {
+	compiler := newSchemaCompiler(fsSchemaLoader{ctx: ctx, fsys: v.fsys, root: filecatalog.CleanFSRoot(v.root)})
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if err := compiler.AddResource(resourceURL.String(), schemaDoc); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
 		return nil, fmt.Errorf("failed to register JSON schema %q: %w", schemaName, err)
 	}
-	schema, err := compiler.Compile(resourceURL)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	schema, err := compileJSONSchema(ctx, resourceURL.String(), compiler.Compile)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile JSON schema %q: %w", schemaName, err)
 	}
 
-	if err := schema.Validate(instance); err != nil {
-		return []string{fmt.Sprintf("json schema validation failed: %v", err)}, nil
-	}
-	return nil, nil
+	return executeJSONSchema(ctx, schema, instance)
 }
 
-func parseJSON(body []byte) (any, error) {
-	var v any
-	if err := json.Unmarshal(body, &v); err != nil {
+func decodeJSONValue(ctx context.Context, body []byte) (any, error) {
+	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
-	return v, nil
-}
+	decoder := json.NewDecoder(bytes.NewReader(body))
+	decoder.UseNumber()
 
-func (v *StandardValidator) LoadSchemaDocument(ctx context.Context, schemaPath string) (any, error) {
-	select {
-	case <-ctx.Done():
-		return nil, ctx.Err()
-	default:
-	}
-
-	resolved, err := v.resolveSchemaPath(schemaPath)
-	if err != nil {
+	var value any
+	decodeErr := decoder.Decode(&value)
+	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
-
-	raw, err := os.ReadFile(resolved)
-	if err != nil {
-		return nil, fmt.Errorf("failed to read schema file %q: %w", resolved, err)
+	if decodeErr != nil {
+		return nil, decodeErr
 	}
 
-	var doc any
-	if err := json.Unmarshal(raw, &doc); err != nil {
-		return nil, fmt.Errorf("failed to decode JSON schema %q: %w", resolved, err)
-	}
-	if err := validateSchemaDialect(doc); err != nil {
-		return nil, fmt.Errorf("failed to decode JSON schema %q: %w", resolved, err)
-	}
-	return doc, nil
-}
-
-func (v *FSValidator) LoadSchemaDocument(ctx context.Context, schemaPath string) (any, error) {
-	select {
-	case <-ctx.Done():
-		return nil, ctx.Err()
-	default:
-	}
-
-	_, doc, err := v.loadSchemaDocument(schemaPath)
-	if err != nil {
+	var trailing any
+	trailingErr := decoder.Decode(&trailing)
+	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
-	return doc, nil
+	if errors.Is(trailingErr, io.EOF) {
+		return value, nil
+	} else if trailingErr != nil {
+		return nil, trailingErr
+	}
+	return nil, errors.New("multiple JSON values")
 }
 
-func (v *StandardValidator) resolveSchemaPath(schemaPath string) (string, error) {
+func (v *StandardValidator) resolveSchemaPath(ctx context.Context, schemaPath string) (string, error) {
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	if strings.TrimSpace(schemaPath) == "" {
 		return "", errors.New("schema path is required for json_schema validation")
 	}
@@ -318,13 +342,25 @@ func (v *StandardValidator) resolveSchemaPath(schemaPath string) (string, error)
 	if err != nil {
 		return "", err
 	}
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	resolved, err := containedFilesystemPath(root, schemaPath)
 	if err != nil {
 		return "", err
 	}
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	if _, err := os.Stat(resolved); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return "", contextErr
+		}
 		return "", fmt.Errorf("failed to access schema file %q: %w", resolved, err)
 	}
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 
 	return resolved, nil
 }
@@ -345,28 +381,39 @@ func (v *StandardValidator) schemaRoot() (string, error) {
 	return resolved, nil
 }
 
-func (v *FSValidator) loadSchemaDocument(schemaPath string) (string, any, error) {
-	resolved, err := v.resolveSchemaPath(schemaPath)
+func (v *FSValidator) loadSchemaDocument(ctx context.Context, schemaPath string) (string, any, error) {
+	resolved, err := v.resolveSchemaPath(ctx, schemaPath)
 	if err != nil {
 		return "", nil, err
 	}
 
-	raw, err := fs.ReadFile(v.fsys, resolved)
+	raw, err := readSchemaFile(ctx, func() (fs.File, error) {
+		return v.fsys.Open(resolved)
+	})
 	if err != nil {
 		return "", nil, fmt.Errorf("failed to read schema file %q: %w", resolved, err)
 	}
 
-	var doc any
-	if err := json.Unmarshal(raw, &doc); err != nil {
+	doc, err := decodeJSONValue(ctx, raw)
+	if err != nil {
 		return "", nil, fmt.Errorf("failed to decode JSON schema %q: %w", resolved, err)
 	}
 	if err := validateSchemaDialect(doc); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return "", nil, contextErr
+		}
 		return "", nil, fmt.Errorf("failed to decode JSON schema %q: %w", resolved, err)
 	}
+	if err := ctx.Err(); err != nil {
+		return "", nil, err
+	}
 	return resolved, doc, nil
 }
 
-func (v *FSValidator) resolveSchemaPath(schemaPath string) (string, error) {
+func (v *FSValidator) resolveSchemaPath(ctx context.Context, schemaPath string) (string, error) {
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	if strings.TrimSpace(schemaPath) == "" {
 		return "", errors.New("schema path is required for json_schema validation")
 	}
@@ -377,8 +424,14 @@ func (v *FSValidator) resolveSchemaPath(schemaPath string) (string, error) {
 	cleanRoot := filecatalog.CleanFSRoot(v.root)
 	rootInfo, err := fs.Stat(v.fsys, cleanRoot)
 	if err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return "", contextErr
+		}
 		return "", fmt.Errorf("failed to access schema source %q: %w", cleanRoot, err)
 	}
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 
 	var resolved string
 	if rootInfo.IsDir() {
@@ -392,15 +445,21 @@ func (v *FSValidator) resolveSchemaPath(schemaPath string) (string, error) {
 		if err != nil {
 			return "", err
 		}
-		if cleanSchemaPath != path.Base(cleanRoot) {
+		if cleanSchemaPath != strings.TrimSpace(path.Base(cleanRoot)) {
 			return "", fmt.Errorf("schema path %q does not match schema file %q", cleanSchemaPath, path.Base(cleanRoot))
 		}
 		resolved = cleanRoot
 	}
 
 	if _, err := fs.Stat(v.fsys, resolved); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return "", contextErr
+		}
 		return "", fmt.Errorf("failed to access schema file %q: %w", resolved, err)
 	}
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
 	return resolved, nil
 }
 
@@ -416,8 +475,19 @@ func cleanSchemaFSPath(schemaPath string) (string, error) {
 	return cleaned, nil
 }
 
-func fsSchemaResourceURL(schemaName string) string {
-	return "promptkit-schema:///" + strings.TrimPrefix(path.Clean(schemaName), "/")
+func fileSchemaResourceURL(schemaName string) *url.URL {
+	filePath := filepath.ToSlash(schemaName)
+	if runtime.GOOS == "windows" && !strings.HasPrefix(filePath, "/") {
+		filePath = "/" + filePath
+	}
+	return &url.URL{Scheme: "file", Path: filePath}
+}
+
+func fsSchemaResourceURL(schemaName string) *url.URL {
+	return &url.URL{
+		Scheme: "promptkit-schema",
+		Path:   "/" + strings.TrimPrefix(path.Clean(schemaName), "/"),
+	}
 }
 
 func newSchemaCompiler(loader jsonschema.URLLoader) *jsonschema.Compiler {
@@ -427,6 +497,35 @@ func newSchemaCompiler(loader jsonschema.URLLoader) *jsonschema.Compiler {
 	return compiler
 }
 
+type schemaExecutor interface {
+	Validate(instance any) error
+}
+
+func compileJSONSchema(ctx context.Context, resourceURL string, compile func(string) (*jsonschema.Schema, error)) (*jsonschema.Schema, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	schema, compileErr := compile(resourceURL)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	return schema, compileErr
+}
+
+func executeJSONSchema(ctx context.Context, schema schemaExecutor, instance any) ([]string, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	validationErr := schema.Validate(instance)
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if validationErr != nil {
+		return []string{fmt.Sprintf("json schema validation failed: %v", validationErr)}, nil
+	}
+	return nil, nil
+}
+
 func validateSchemaDialect(doc any) error {
 	object, ok := doc.(map[string]any)
 	if !ok {
@@ -447,19 +546,33 @@ func validateSchemaDialect(doc any) error {
 }
 
 type standardSchemaLoader struct {
+	ctx  context.Context
 	root string
 }
 
 func (l standardSchemaLoader) Load(resourceURL string) (any, error) {
+	if err := l.ctx.Err(); err != nil {
+		return nil, err
+	}
+	parsed, err := url.Parse(resourceURL)
+	if err != nil || parsed.Scheme != "file" || parsed.Host != "" || parsed.RawQuery != "" || parsed.Opaque != "" {
+		return nil, fmt.Errorf("schema reference %q is not a contained file reference", resourceURL)
+	}
 	fileName, err := (jsonschema.FileLoader{}).ToFile(resourceURL)
 	if err != nil {
 		return nil, fmt.Errorf("schema reference %q is not a contained file reference: %w", resourceURL, err)
 	}
 	resolved, err := containedFilesystemPath(l.root, fileName)
 	if err != nil {
+		if contextErr := l.ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
 		return nil, err
 	}
-	return loadJSONSchemaFile(resolved)
+	if err := l.ctx.Err(); err != nil {
+		return nil, err
+	}
+	return loadJSONSchemaFile(l.ctx, resolved)
 }
 
 func containedFilesystemPath(root, name string) (string, error) {
@@ -485,38 +598,94 @@ func containedFilesystemPath(root, name string) (string, error) {
 	return candidate, nil
 }
 
-func loadJSONSchemaFile(name string) (any, error) {
-	raw, err := os.ReadFile(name)
+func loadJSONSchemaFile(ctx context.Context, name string) (any, error) {
+	raw, err := readSchemaFile(ctx, func() (fs.File, error) {
+		return os.Open(name)
+	})
 	if err != nil {
 		return nil, err
 	}
-	var doc any
-	if err := json.Unmarshal(raw, &doc); err != nil {
+	doc, err := decodeJSONValue(ctx, raw)
+	if err != nil {
 		return nil, err
 	}
 	if err := validateSchemaDialect(doc); err != nil {
+		if contextErr := ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
+		return nil, err
+	}
+	if err := ctx.Err(); err != nil {
 		return nil, err
 	}
 	return doc, nil
 }
 
+func readSchemaFile(ctx context.Context, open func() (fs.File, error)) ([]byte, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	file, openErr := open()
+	if err := ctx.Err(); err != nil {
+		if file != nil {
+			_ = file.Close()
+		}
+		return nil, err
+	}
+	if openErr != nil {
+		if file != nil {
+			_ = file.Close()
+		}
+		return nil, openErr
+	}
+	if file == nil {
+		return nil, errors.New("schema source returned a nil file")
+	}
+	defer file.Close()
+
+	var contents []byte
+	chunk := make([]byte, schemaReadChunkSize)
+	for {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		n, readErr := file.Read(chunk)
+		if n > 0 {
+			contents = append(contents, chunk[:n]...)
+		}
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		if errors.Is(readErr, io.EOF) {
+			return contents, nil
+		}
+		if readErr != nil {
+			return nil, readErr
+		}
+		if n == 0 {
+			return nil, io.ErrNoProgress
+		}
+	}
+}
+
 type fsSchemaLoader struct {
+	ctx  context.Context
 	fsys fs.FS
 	root string
 }
 
 func (l fsSchemaLoader) Load(resourceURL string) (any, error) {
+	if err := l.ctx.Err(); err != nil {
+		return nil, err
+	}
 	parsed, err := url.Parse(resourceURL)
 	if err != nil {
 		return nil, fmt.Errorf("invalid schema reference %q: %w", resourceURL, err)
 	}
-	if parsed.Scheme != "promptkit-schema" || parsed.Host != "" {
+	if parsed.Scheme != "promptkit-schema" || parsed.Host != "" || parsed.RawQuery != "" || parsed.Opaque != "" {
 		return nil, fmt.Errorf("schema reference %q is not allowed", resourceURL)
 	}
-	name, err := url.PathUnescape(strings.TrimPrefix(parsed.Path, "/"))
-	if err != nil {
-		return nil, fmt.Errorf("invalid schema reference %q: %w", resourceURL, err)
-	}
+	name := strings.TrimPrefix(parsed.Path, "/")
 	name = path.Clean(name)
 	if l.root == "." {
 		if strings.HasPrefix(name, "../") || name == ".." {
@@ -528,21 +697,35 @@ func (l fsSchemaLoader) Load(resourceURL string) (any, error) {
 
 	rootInfo, err := fs.Stat(l.fsys, l.root)
 	if err != nil {
+		if contextErr := l.ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
+		return nil, err
+	}
+	if err := l.ctx.Err(); err != nil {
 		return nil, err
 	}
 	if !rootInfo.IsDir() && name != l.root {
 		return nil, fmt.Errorf("schema reference %q is outside the configured schema file", resourceURL)
 	}
 
-	raw, err := fs.ReadFile(l.fsys, name)
+	raw, err := readSchemaFile(l.ctx, func() (fs.File, error) {
+		return l.fsys.Open(name)
+	})
 	if err != nil {
 		return nil, err
 	}
-	var doc any
-	if err := json.Unmarshal(raw, &doc); err != nil {
+	doc, err := decodeJSONValue(l.ctx, raw)
+	if err != nil {
 		return nil, err
 	}
 	if err := validateSchemaDialect(doc); err != nil {
+		if contextErr := l.ctx.Err(); contextErr != nil {
+			return nil, contextErr
+		}
+		return nil, err
+	}
+	if err := l.ctx.Err(); err != nil {
 		return nil, err
 	}
 	return doc, nil

internal/validate/standard_validator_test.go

@@ -3,9 +3,11 @@ package validate
 import (
 	"context"
 	"encoding/json"
+	"net/url"
 	"os"
 	"path/filepath"
 	"reflect"
+	"runtime"
 	"strconv"
 	"strings"
 	"testing"
@@ -93,6 +95,51 @@ func TestStandardValidatorJSONFailure(t *testing.T) {
 	}
 }
 
+func TestJSONValidationChecksCompleteSyntaxWithoutChangingArtifact(t *testing.T) {
+	tests := []struct {
+		name      string
+		body      string
+		wantValid bool
+	}{
+		{name: "ordinary object", body: `{"count":2,"ok":true}`, wantValid: true},
+		{name: "integer at exact float boundary", body: `9007199254740992`, wantValid: true},
+		{name: "integer beyond exact float boundary", body: `9007199254740993`, wantValid: true},
+		{name: "large exponent", body: `1e400`, wantValid: true},
+		{name: "precise decimal", body: `0.123456789012345678901234567890`, wantValid: true},
+		{name: "surrounding whitespace", body: " \n [1,2,3] \t", wantValid: true},
+		{name: "malformed document", body: `{"count":`, wantValid: false},
+		{name: "trailing value", body: `1 2`, wantValid: false},
+	}
+
+	validator := NewStandardValidator("")
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			body := []byte(tc.body)
+			before := append([]byte(nil), body...)
+			artifact := &domain.Artifact{Body: body}
+
+			result, err := validator.Validate(context.Background(), artifact, domain.OutputContract{
+				ValidationMode: domain.ValidationJSON,
+			})
+			if err != nil {
+				t.Fatalf("validate JSON: %v", err)
+			}
+			if result.IsValid != tc.wantValid {
+				t.Fatalf("valid = %v, want %v; result=%+v", result.IsValid, tc.wantValid, result)
+			}
+			if tc.wantValid && result.Status != domain.ValidationPassed {
+				t.Fatalf("status = %q, want %q", result.Status, domain.ValidationPassed)
+			}
+			if !tc.wantValid && result.Status != domain.ValidationFailed {
+				t.Fatalf("status = %q, want %q", result.Status, domain.ValidationFailed)
+			}
+			if !reflect.DeepEqual(artifact.Body, before) {
+				t.Fatalf("artifact body changed: got %q, want %q", artifact.Body, before)
+			}
+		})
+	}
+}
+
 func TestStandardValidatorJSONSchemaSuccess(t *testing.T) {
 	tmp := t.TempDir()
 	schemaPath := filepath.Join(tmp, "schema.json")
@@ -285,55 +332,6 @@ func TestStandardValidatorJSONSchemaCompilationError(t *testing.T) {
 	}
 }
 
-func TestStandardValidatorLoadSchemaDocumentSuccess(t *testing.T) {
-	tmp := t.TempDir()
-	if err := os.WriteFile(filepath.Join(tmp, "schema.json"), []byte(`{
-  "type": "object",
-  "properties": {
-    "name": {"type": "string"}
-  }
-}`), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	v := NewStandardValidator(tmp)
-	loader, ok := v.(SchemaDocumentLoader)
-	if !ok {
-		t.Fatal("standard validator must implement SchemaDocumentLoader")
-	}
-
-	doc, err := loader.LoadSchemaDocument(context.Background(), "schema.json")
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-
-	obj, ok := doc.(map[string]any)
-	if !ok {
-		t.Fatalf("expected object document, got %#v", doc)
-	}
-	if obj["type"] != "object" {
-		t.Fatalf("expected schema type=object, got %#v", obj["type"])
-	}
-}
-
-func TestStandardValidatorLoadSchemaDocumentInvalidJSON(t *testing.T) {
-	tmp := t.TempDir()
-	if err := os.WriteFile(filepath.Join(tmp, "schema.json"), []byte(`{`), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	v := NewStandardValidator(tmp)
-	loader, ok := v.(SchemaDocumentLoader)
-	if !ok {
-		t.Fatal("standard validator must implement SchemaDocumentLoader")
-	}
-
-	_, err := loader.LoadSchemaDocument(context.Background(), "schema.json")
-	if err == nil {
-		t.Fatal("expected decode error")
-	}
-}
-
 func TestFSValidatorJSONSchemaSuccess(t *testing.T) {
 	v := NewFSValidator(fstest.MapFS{
 		"schemas/events.schema.json": &fstest.MapFile{Data: []byte(`{
@@ -416,17 +414,70 @@ func TestFSValidatorPreparedSchemaSurvivesSourceMutation(t *testing.T) {
 	}
 }
 
-func TestFSValidatorJSONSchemaRegistrationError(t *testing.T) {
+func TestFSValidatorEscapesSchemaResourcePath(t *testing.T) {
+	for _, schemaName := range []string{"%zz.json", "space name.json", "hash#.json", "query?.json", "rún.json"} {
+		t.Run(schemaName, func(t *testing.T) {
 			v := NewFSValidator(fstest.MapFS{
-		"schemas/%zz.json": &fstest.MapFile{Data: []byte(`{"type":"object"}`)},
+				"schemas/" + schemaName: &fstest.MapFile{Data: []byte(`{"type":"object"}`)},
 			}, "schemas")
 
 			res, err := v.Validate(context.Background(), &domain.Artifact{Body: []byte(`{}`)}, domain.OutputContract{
 				ValidationMode: domain.ValidationJSONSchema,
-		SchemaPath:     "%zz.json",
+				SchemaPath:     schemaName,
 			})
-	if err == nil || !strings.Contains(err.Error(), "failed to register JSON schema") {
-		t.Fatalf("expected schema registration error, got result=%#v error=%v", res, err)
+			if err != nil || !res.IsValid {
+				t.Fatalf("validate schema %q: result=%#v error=%v", schemaName, res, err)
+			}
+		})
+	}
+}
+
+func TestSchemaReferencesPreserveEscapedFilenames(t *testing.T) {
+	for _, name := range []string{"%2F.json", "space name.json", "hash#.json", "query?.json", "rún.json"} {
+		t.Run(name, func(t *testing.T) {
+			rootName := "root-" + name
+			childName := "child-" + name
+			childPath := "nested/" + childName
+			reference := (&url.URL{Path: childPath}).EscapedPath()
+			rootSchema := []byte(`{"$ref":` + strconv.Quote(reference) + `}`)
+			childSchema := []byte(`{"type":"integer","minimum":2}`)
+
+			t.Run("fs.FS", func(t *testing.T) {
+				validator := NewFSValidator(fstest.MapFS{
+					"schemas/" + rootName:  &fstest.MapFile{Data: rootSchema},
+					"schemas/" + childPath: &fstest.MapFile{Data: childSchema},
+				}, "schemas")
+				assertSchemaValidation(t, validator, rootName)
+			})
+
+			t.Run("operating system files", func(t *testing.T) {
+				if runtime.GOOS == "windows" && strings.ContainsAny(rootName+childName, `<>:"/\|?*`) {
+					t.Skip("filename is not legal on Windows")
+				}
+				root := t.TempDir()
+				if err := os.Mkdir(filepath.Join(root, "nested"), 0o755); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(filepath.Join(root, rootName), rootSchema, 0o644); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(filepath.Join(root, filepath.FromSlash(childPath)), childSchema, 0o644); err != nil {
+					t.Fatal(err)
+				}
+				assertSchemaValidation(t, NewStandardValidator(root), rootName)
+			})
+		})
+	}
+}
+
+func assertSchemaValidation(t *testing.T, validator Validator, schemaPath string) {
+	t.Helper()
+	result, err := validator.Validate(context.Background(), &domain.Artifact{Body: []byte(`2`)}, domain.OutputContract{
+		ValidationMode: domain.ValidationJSONSchema,
+		SchemaPath:     schemaPath,
+	})
+	if err != nil || !result.IsValid {
+		t.Fatalf("validate schema %q: result=%#v error=%v", schemaPath, result, err)
 	}
 }
 
@@ -516,25 +567,6 @@ func TestFSValidatorSingleSchemaFileUsesBaseName(t *testing.T) {
 	}
 }
 
-func TestFSValidatorLoadSchemaDocument(t *testing.T) {
-	v := NewFSValidator(fstest.MapFS{
-		"schemas/schema.json": &fstest.MapFile{Data: []byte(`{"type":"object"}`)},
-	}, "schemas")
-	loader, ok := v.(SchemaDocumentLoader)
-	if !ok {
-		t.Fatal("fs validator must implement SchemaDocumentLoader")
-	}
-
-	doc, err := loader.LoadSchemaDocument(context.Background(), "schema.json")
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	obj, ok := doc.(map[string]any)
-	if !ok || obj["type"] != "object" {
-		t.Fatalf("unexpected schema document: %#v", doc)
-	}
-}
-
 func TestStandardValidatorJSONSchemaReferenceBoundaries(t *testing.T) {
 	root := t.TempDir()
 	if err := os.WriteFile(filepath.Join(root, "child.json"), []byte(`{
@@ -629,6 +661,225 @@ func TestFSValidatorJSONSchemaReferenceBoundaries(t *testing.T) {
 	}
 }
 
+func TestJSONSchemaNumericConstraintsRetainJSONPrecision(t *testing.T) {
+	tests := []struct {
+		name      string
+		schema    string
+		instance  string
+		wantValid bool
+	}{
+		{
+			name:      "const distinguishes adjacent large integers",
+			schema:    `{"const":9007199254740993}`,
+			instance:  `9007199254740993`,
+			wantValid: true,
+		},
+		{
+			name:      "const rejects adjacent large integer",
+			schema:    `{"const":9007199254740993}`,
+			instance:  `9007199254740992`,
+			wantValid: false,
+		},
+		{
+			name:      "const accepts exponent beyond float range",
+			schema:    `{"const":1e400}`,
+			instance:  `1e400`,
+			wantValid: true,
+		},
+		{
+			name:      "minimum accepts precise decimal boundary",
+			schema:    `{"type":"number","minimum":0.123456789012345678901234567890}`,
+			instance:  `0.123456789012345678901234567890`,
+			wantValid: true,
+		},
+		{
+			name:      "minimum rejects lower precise decimal",
+			schema:    `{"type":"number","minimum":0.123456789012345678901234567890}`,
+			instance:  `0.123456789012345678901234567889`,
+			wantValid: false,
+		},
+		{
+			name:      "maximum distinguishes adjacent large integers",
+			schema:    `{"type":"number","maximum":9007199254740992}`,
+			instance:  `9007199254740993`,
+			wantValid: false,
+		},
+		{
+			name:      "multiple of accepts exact decimal multiple",
+			schema:    `{"type":"number","multipleOf":0.0000000000000000001}`,
+			instance:  `0.0000000000000000003`,
+			wantValid: true,
+		},
+		{
+			name:      "multiple of rejects inexact decimal multiple",
+			schema:    `{"type":"number","multipleOf":0.0000000000000000001}`,
+			instance:  `0.00000000000000000031`,
+			wantValid: false,
+		},
+		{
+			name:      "ordinary number remains supported",
+			schema:    `{"type":"number","minimum":1,"maximum":3}`,
+			instance:  `2`,
+			wantValid: true,
+		},
+	}
+
+	for _, source := range jsonSchemaValidatorSources() {
+		t.Run(source.name, func(t *testing.T) {
+			for _, tc := range tests {
+				t.Run(tc.name, func(t *testing.T) {
+					validator := source.new(t, []byte(tc.schema))
+					result, err := validator.Validate(context.Background(), &domain.Artifact{Body: []byte(tc.instance)}, domain.OutputContract{
+						ValidationMode: domain.ValidationJSONSchema,
+						SchemaPath:     "schema.json",
+					})
+					if err != nil {
+						t.Fatalf("validate JSON Schema instance: %v", err)
+					}
+					if result.IsValid != tc.wantValid {
+						t.Fatalf("valid = %v, want %v; result=%+v", result.IsValid, tc.wantValid, result)
+					}
+				})
+			}
+		})
+	}
+}
+
+func TestJSONSchemaDecodingRequiresOneCompleteDocument(t *testing.T) {
+	for _, source := range jsonSchemaValidatorSources() {
+		t.Run(source.name, func(t *testing.T) {
+			for _, schema := range []string{`{"type":`, `{} {}`} {
+				validator := source.new(t, []byte(schema))
+				_, err := validator.Validate(context.Background(), &domain.Artifact{Body: []byte(`1`)}, domain.OutputContract{
+					ValidationMode: domain.ValidationJSONSchema,
+					SchemaPath:     "schema.json",
+				})
+				if err == nil {
+					t.Fatalf("schema %q: expected decoding error", schema)
+				}
+			}
+
+			validator := source.new(t, []byte(`{}`))
+			for _, instance := range []string{`{"value":`, `1 2`} {
+				result, err := validator.Validate(context.Background(), &domain.Artifact{Body: []byte(instance)}, domain.OutputContract{
+					ValidationMode: domain.ValidationJSONSchema,
+					SchemaPath:     "schema.json",
+				})
+				if err != nil {
+					t.Fatalf("instance %q: expected completed validation, got %v", instance, err)
+				}
+				if result.Status != domain.ValidationFailed || result.IsValid || len(result.Errors) == 0 {
+					t.Fatalf("instance %q: expected failed validation, got %+v", instance, result)
+				}
+			}
+		})
+	}
+}
+
+func TestPreparedSchemaDocumentsRetainExactNumbers(t *testing.T) {
+	const schema = `{
+  "const": 9007199254740993,
+  "minimum": 0.123456789012345678901234567890,
+  "maximum": 1e400,
+  "multipleOf": 0.0000000000000000001
+}`
+	want := map[string]string{
+		"const":      "9007199254740993",
+		"minimum":    "0.123456789012345678901234567890",
+		"maximum":    "1e400",
+		"multipleOf": "0.0000000000000000001",
+	}
+
+	for _, source := range jsonSchemaValidatorSources() {
+		t.Run(source.name, func(t *testing.T) {
+			validator := source.new(t, []byte(schema))
+			preparer, ok := validator.(ValidationPreparer)
+			if !ok {
+				t.Fatal("validator does not support validation preparation")
+			}
+			prepared, err := preparer.PrepareValidation(context.Background(), domain.OutputContract{
+				ValidationMode: domain.ValidationJSONSchema,
+				SchemaPath:     "schema.json",
+			})
+			if err != nil {
+				t.Fatalf("prepare validation: %v", err)
+			}
+			document, ok := prepared.SchemaDocument().(map[string]any)
+			if !ok {
+				t.Fatalf("schema document = %#v, want object", prepared.SchemaDocument())
+			}
+			for name, wantNumber := range want {
+				got, ok := document[name].(json.Number)
+				if !ok {
+					t.Fatalf("schema field %q = %#v, want json.Number", name, document[name])
+				}
+				if got.String() != wantNumber {
+					t.Fatalf("schema field %q = %q, want %q", name, got, wantNumber)
+				}
+			}
+		})
+	}
+}
+
+type jsonSchemaValidatorSource struct {
+	name string
+	new  func(*testing.T, []byte) Validator
+}
+
+func jsonSchemaValidatorSources() []jsonSchemaValidatorSource {
+	return []jsonSchemaValidatorSource{
+		{
+			name: "operating system files",
+			new: func(t *testing.T, schema []byte) Validator {
+				t.Helper()
+				root := t.TempDir()
+				if err := os.WriteFile(filepath.Join(root, "schema.json"), schema, 0o644); err != nil {
+					t.Fatalf("write schema: %v", err)
+				}
+				return NewStandardValidator(root)
+			},
+		},
+		{
+			name: "fs.FS",
+			new: func(t *testing.T, schema []byte) Validator {
+				t.Helper()
+				return NewFSValidator(fstest.MapFS{
+					"schema.json": &fstest.MapFile{Data: schema},
+				}, ".")
+			},
+		},
+	}
+}
+
+func BenchmarkJSONValidation(b *testing.B) {
+	largeArray := []byte(`[` + strings.Repeat(`12345678901234567890,`, 32*1024) + `0]`)
+	benchmarks := []struct {
+		name string
+		body []byte
+	}{
+		{name: "scalar", body: []byte(`1e400`)},
+		{name: "object", body: []byte(`{"name":"eris","count":9007199254740993,"enabled":true}`)},
+		{name: "large array", body: largeArray},
+	}
+	validator := NewStandardValidator("")
+	contract := domain.OutputContract{ValidationMode: domain.ValidationJSON}
+
+	for _, benchmark := range benchmarks {
+		b.Run(benchmark.name, func(b *testing.B) {
+			artifact := &domain.Artifact{Body: benchmark.body}
+			b.ReportAllocs()
+			b.SetBytes(int64(len(benchmark.body)))
+			b.ResetTimer()
+			for range b.N {
+				result, err := validator.Validate(context.Background(), artifact, contract)
+				if err != nil || !result.IsValid {
+					b.Fatalf("validate JSON: result=%+v error=%v", result, err)
+				}
+			}
+		})
+	}
+}
+
 func TestJSONSchemaDialectIsDraft2020(t *testing.T) {
 	tests := []struct {
 		name      string
@@ -673,8 +924,8 @@ func TestJSONSchemaDialectIsDraft2020(t *testing.T) {
 func assertSchemaDocument(t *testing.T, got any, expectedJSON []byte) {
 	t.Helper()
 
-	var expected any
-	if err := json.Unmarshal(expectedJSON, &expected); err != nil {
+	expected, err := decodeJSONValue(context.Background(), expectedJSON)
+	if err != nil {
 		t.Fatalf("decode expected schema document: %v", err)
 	}
 	if !reflect.DeepEqual(got, expected) {

internal/validate/validator.go

@@ -7,11 +7,16 @@ import (
 )
 
 // Validator validates the generated artifact based on the output contract.
+// Validation checks ctx around Promptkit-controlled work and synchronous
+// dependency calls. A dependency call already in progress cannot be preempted;
+// after it returns, cancellation takes precedence over its result.
 type Validator interface {
 	Validate(ctx context.Context, artifact *domain.Artifact, contract domain.OutputContract) (domain.ValidationResult, error)
 }
 
 // PreparedValidation validates artifacts against one frozen output contract.
+// Its cancellation boundary is synchronous: Validate does not detach schema
+// execution, and an observed context error prevents publication of a result.
 type PreparedValidation interface {
 	Validate(ctx context.Context, artifact *domain.Artifact) (domain.ValidationResult, error)
 	// SchemaDocument returns the root JSON Schema document used for provider
@@ -21,11 +26,9 @@ type PreparedValidation interface {
 }
 
 // ValidationPreparer freezes validation resources for one output contract.
+// Preparation reads schemas in context-checked chunks and checks ctx around
+// decoding and compilation. Filesystem and compiler calls remain synchronous,
+// so cancellation becomes authoritative when an in-progress call returns.
 type ValidationPreparer interface {
 	PrepareValidation(ctx context.Context, contract domain.OutputContract) (PreparedValidation, error)
 }
-
-// SchemaDocumentLoader loads JSON schema documents using validator path semantics.
-type SchemaDocumentLoader interface {
-	LoadSchemaDocument(ctx context.Context, schemaPath string) (any, error)
-}

json.go

@@ -2,9 +2,16 @@ package promptkit
 
 import (
 	"encoding/json"
+	"fmt"
+	"math"
 	"time"
 )
 
+const (
+	minDurationMilliseconds = int64(time.Duration(math.MinInt64) / time.Millisecond)
+	maxDurationMilliseconds = int64(time.Duration(math.MaxInt64) / time.Millisecond)
+)
+
 // MarshalJSON implements json.Marshaler for PreparedRun. It uses RFC 3339
 // timestamps, integer duration_ms, and omits zero timing values.
 func (r PreparedRun) MarshalJSON() ([]byte, error) {
@@ -21,35 +28,8 @@ func (r PreparedRun) MarshalJSON() ([]byte, error) {
 		durationMS = &r.DurationMS
 	}
 
-	return json.Marshal(struct {
-		PromptID             string                `json:"prompt_id"`
-		PromptVersion        string                `json:"prompt_version,omitempty"`
-		PromptHash           string                `json:"prompt_hash,omitempty"`
-		SelectedProfileID    string                `json:"selected_profile_id"`
-		SelectedBackendID    string                `json:"selected_backend_id,omitempty"`
-		EffectiveModelParams ExecutionTarget       `json:"effective_model_params"`
-		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:             r.PromptID,
-		PromptVersion:        r.PromptVersion,
-		PromptHash:           r.PromptHash,
-		SelectedProfileID:    r.SelectedProfileID,
-		SelectedBackendID:    r.SelectedBackendID,
-		EffectiveModelParams: r.EffectiveModelParams,
-		OutputContract:       r.OutputContract,
-		StructuredOutput:     r.StructuredOutput,
-		InputHashes:          r.InputHashes,
-		SessionID:            r.SessionID,
-		RenderedPromptHash:   r.RenderedPromptHash,
-		Messages:             r.Messages,
+	return json.Marshal(preparedRunJSON{
+		preparedRunJSONFields: preparedRunJSONFields(r),
 		StartTime:             startTime,
 		EndTime:               endTime,
 		DurationMS:            durationMS,
@@ -74,22 +54,7 @@ func (r RunResult) MarshalJSON() ([]byte, error) {
 	}
 
 	return json.Marshal(runResultJSON{
-		RunID:                r.RunID,
-		Artifact:             r.Artifact,
-		RawOutput:            r.RawOutput,
-		Validation:           r.Validation,
-		PromptID:             r.PromptID,
-		PromptVersion:        r.PromptVersion,
-		PromptHash:           r.PromptHash,
-		SessionID:            r.SessionID,
-		RenderedPromptHash:   r.RenderedPromptHash,
-		SelectedProfileID:    r.SelectedProfileID,
-		SelectedBackendID:    r.SelectedBackendID,
-		ModelName:            r.ModelName,
-		Endpoint:             r.Endpoint,
-		EffectiveModelParams: r.EffectiveModelParams,
-		InputHashes:          r.InputHashes,
-		Usage:                r.Usage,
+		runResultJSONFields: runResultJSONFields(r),
 		StartTime:           startTime,
 		EndTime:             endTime,
 		DurationMS:          durationMS,
@@ -97,66 +62,49 @@ func (r RunResult) MarshalJSON() ([]byte, error) {
 }
 
 // UnmarshalJSON implements json.Unmarshaler for RunResult. It decodes
-// duration_ms into Duration with millisecond precision.
+// duration_ms into Duration with millisecond precision. A duration_ms outside
+// the range representable by time.Duration returns an error without changing
+// the receiver.
 func (r *RunResult) UnmarshalJSON(data []byte) error {
 	var wire runResultJSON
 	if err := json.Unmarshal(data, &wire); err != nil {
 		return err
 	}
 
-	*r = RunResult{
-		RunID:                wire.RunID,
-		Artifact:             wire.Artifact,
-		RawOutput:            wire.RawOutput,
-		Validation:           wire.Validation,
-		PromptID:             wire.PromptID,
-		PromptVersion:        wire.PromptVersion,
-		PromptHash:           wire.PromptHash,
-		SessionID:            wire.SessionID,
-		RenderedPromptHash:   wire.RenderedPromptHash,
-		SelectedProfileID:    wire.SelectedProfileID,
-		SelectedBackendID:    wire.SelectedBackendID,
-		ModelName:            wire.ModelName,
-		Endpoint:             wire.Endpoint,
-		EffectiveModelParams: wire.EffectiveModelParams,
-		InputHashes:          wire.InputHashes,
-		Usage:                wire.Usage,
-		Duration:             time.Duration(valueOrZero(wire.DurationMS)) * time.Millisecond,
+	result := RunResult(wire.runResultJSONFields)
+	if wire.DurationMS != nil {
+		if *wire.DurationMS < minDurationMilliseconds || *wire.DurationMS > maxDurationMilliseconds {
+			return fmt.Errorf(
+				"decode RunResult duration_ms: %d cannot be represented as time.Duration",
+				*wire.DurationMS,
+			)
+		}
+		result.Duration = time.Duration(*wire.DurationMS) * time.Millisecond
 	}
 	if wire.StartTime != nil {
-		r.StartTime = *wire.StartTime
+		result.StartTime = *wire.StartTime
 	}
 	if wire.EndTime != nil {
-		r.EndTime = *wire.EndTime
+		result.EndTime = *wire.EndTime
 	}
+	*r = result
 	return nil
 }
 
-type runResultJSON struct {
-	RunID                string            `json:"run_id"`
-	Artifact             Artifact          `json:"artifact"`
-	RawOutput            string            `json:"raw_output"`
-	Validation           ValidationResult  `json:"validation"`
-	PromptID             string            `json:"prompt_id"`
-	PromptVersion        string            `json:"prompt_version,omitempty"`
-	PromptHash           string            `json:"prompt_hash,omitempty"`
-	SessionID            string            `json:"session_id,omitempty"`
-	RenderedPromptHash   string            `json:"rendered_prompt_hash"`
-	SelectedProfileID    string            `json:"selected_profile_id"`
-	SelectedBackendID    string            `json:"selected_backend_id,omitempty"`
-	ModelName            string            `json:"model_name"`
-	Endpoint             string            `json:"endpoint"`
-	EffectiveModelParams ExecutionTarget   `json:"effective_model_params"`
-	InputHashes          map[string]string `json:"input_hashes,omitempty"`
-	Usage                TokenUsage        `json:"usage"`
+type preparedRunJSONFields PreparedRun
+
+type preparedRunJSON struct {
+	preparedRunJSONFields
 	StartTime  *time.Time `json:"start_time,omitempty"`
 	EndTime    *time.Time `json:"end_time,omitempty"`
 	DurationMS *int64     `json:"duration_ms,omitempty"`
 }
 
-func valueOrZero(value *int64) int64 {
-	if value == nil {
-		return 0
-	}
-	return *value
+type runResultJSONFields RunResult
+
+type runResultJSON struct {
+	runResultJSONFields
+	StartTime  *time.Time `json:"start_time,omitempty"`
+	EndTime    *time.Time `json:"end_time,omitempty"`
+	DurationMS *int64     `json:"duration_ms,omitempty"`
 }

json_contract_test.go

@@ -0,0 +1,328 @@
+package promptkit_test
+
+import (
+	"encoding/json"
+	"math"
+	"reflect"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+func TestPreparedRunJSONContractRoundTripsAllFields(t *testing.T) {
+	value := fullyPopulatedPreparedRun()
+	payload, err := json.Marshal(value)
+	if err != nil {
+		t.Fatalf("marshal PreparedRun: %v", err)
+	}
+
+	object := decodeJSONObject(t, payload)
+	assertJSONFields(t, object,
+		"prompt_id",
+		"prompt_version",
+		"prompt_hash",
+		"selected_profile_id",
+		"selected_backend_id",
+		"effective_model_params",
+		"output_contract",
+		"structured_output",
+		"input_hashes",
+		"session_id",
+		"rendered_prompt_hash",
+		"messages",
+		"start_time",
+		"end_time",
+		"duration_ms",
+	)
+
+	var messages []map[string]json.RawMessage
+	if err := json.Unmarshal(object["messages"], &messages); err != nil {
+		t.Fatalf("decode PreparedRun messages: %v", err)
+	}
+	if len(messages) != 2 {
+		t.Fatalf("message count = %d, want 2", len(messages))
+	}
+	if _, ok := messages[0]["cache_control"]; !ok {
+		t.Fatalf("first message omitted cache_control: %s", object["messages"])
+	}
+	if _, ok := messages[1]["cache_control"]; ok {
+		t.Fatalf("second message included empty cache_control: %s", object["messages"])
+	}
+
+	var decoded promptkit.PreparedRun
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("unmarshal PreparedRun: %v", err)
+	}
+	if !reflect.DeepEqual(decoded, value) {
+		t.Fatalf("PreparedRun did not round trip:\ngot  %#v\nwant %#v", decoded, value)
+	}
+
+	zeroPayload, err := json.Marshal(promptkit.PreparedRun{})
+	if err != nil {
+		t.Fatalf("marshal zero PreparedRun: %v", err)
+	}
+	zeroObject := decodeJSONObject(t, zeroPayload)
+	for _, field := range []string{
+		"prompt_version",
+		"prompt_hash",
+		"selected_backend_id",
+		"structured_output",
+		"input_hashes",
+		"session_id",
+		"start_time",
+		"end_time",
+		"duration_ms",
+	} {
+		if _, ok := zeroObject[field]; ok {
+			t.Fatalf("zero PreparedRun included %q: %s", field, zeroPayload)
+		}
+	}
+}
+
+func TestRunResultJSONContractRoundTripsAllFields(t *testing.T) {
+	value := fullyPopulatedRunResult()
+	payload, err := json.Marshal(value)
+	if err != nil {
+		t.Fatalf("marshal RunResult: %v", err)
+	}
+
+	object := decodeJSONObject(t, payload)
+	assertJSONFields(t, object,
+		"run_id",
+		"artifact",
+		"raw_output",
+		"validation",
+		"prompt_id",
+		"prompt_version",
+		"prompt_hash",
+		"session_id",
+		"rendered_prompt_hash",
+		"selected_profile_id",
+		"selected_backend_id",
+		"model_name",
+		"endpoint",
+		"effective_model_params",
+		"input_hashes",
+		"usage",
+		"start_time",
+		"end_time",
+		"duration_ms",
+	)
+	if _, ok := object["duration"]; ok {
+		t.Fatalf("RunResult included nanosecond duration field: %s", payload)
+	}
+
+	var decoded promptkit.RunResult
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("unmarshal RunResult: %v", err)
+	}
+	if !reflect.DeepEqual(decoded, value) {
+		t.Fatalf("RunResult did not round trip:\ngot  %#v\nwant %#v", decoded, value)
+	}
+
+	zeroPayload, err := json.Marshal(promptkit.RunResult{})
+	if err != nil {
+		t.Fatalf("marshal zero RunResult: %v", err)
+	}
+	zeroObject := decodeJSONObject(t, zeroPayload)
+	for _, field := range []string{
+		"prompt_version",
+		"prompt_hash",
+		"session_id",
+		"selected_backend_id",
+		"input_hashes",
+		"start_time",
+		"end_time",
+		"duration_ms",
+		"duration",
+	} {
+		if _, ok := zeroObject[field]; ok {
+			t.Fatalf("zero RunResult included %q: %s", field, zeroPayload)
+		}
+	}
+}
+
+func TestRunResultJSONDurationMillisecondBoundaries(t *testing.T) {
+	maxMilliseconds := int64(time.Duration(math.MaxInt64) / time.Millisecond)
+	minMilliseconds := int64(time.Duration(math.MinInt64) / time.Millisecond)
+
+	for _, milliseconds := range []int64{minMilliseconds, maxMilliseconds} {
+		t.Run(strconv.FormatInt(milliseconds, 10), func(t *testing.T) {
+			var decoded promptkit.RunResult
+			if err := json.Unmarshal(durationPayload(milliseconds), &decoded); err != nil {
+				t.Fatalf("decode representable duration_ms: %v", err)
+			}
+			want := time.Duration(milliseconds) * time.Millisecond
+			if decoded.Duration != want {
+				t.Fatalf("Duration = %v, want %v", decoded.Duration, want)
+			}
+		})
+	}
+
+	for _, milliseconds := range []int64{
+		minMilliseconds - 1,
+		maxMilliseconds + 1,
+		math.MinInt64,
+		math.MaxInt64,
+	} {
+		t.Run(strconv.FormatInt(milliseconds, 10), func(t *testing.T) {
+			original := fullyPopulatedRunResult()
+			decoded := original
+			err := json.Unmarshal(durationPayload(milliseconds), &decoded)
+			if err == nil || !strings.Contains(err.Error(), "duration_ms") || !strings.Contains(err.Error(), "time.Duration") {
+				t.Fatalf("overflow error = %v", err)
+			}
+			if !reflect.DeepEqual(decoded, original) {
+				t.Fatalf("failed decode partially updated receiver:\ngot  %#v\nwant %#v", decoded, original)
+			}
+		})
+	}
+}
+
+func fullyPopulatedPreparedRun() promptkit.PreparedRun {
+	start := time.Date(2026, time.August, 11, 12, 13, 14, 150_000_000, time.UTC)
+	return promptkit.PreparedRun{
+		PromptID:             "prompt.prepared",
+		PromptVersion:        "2.1.0",
+		PromptHash:           "prompt-hash",
+		SelectedProfileID:    "profile-prepared",
+		SelectedBackendID:    "backend-prepared",
+		EffectiveModelParams: jsonContractExecutionTarget(),
+		OutputContract: promptkit.OutputContract{
+			Format:         promptkit.FormatJSON,
+			ValidationMode: promptkit.ValidationJSONSchema,
+			SchemaPath:     "schemas/prepared.json",
+			RepairAttempts: 2,
+		},
+		StructuredOutput: &promptkit.StructuredOutputSpec{
+			Type: promptkit.StructuredOutputJSONSchema,
+			JSONSchema: &promptkit.StructuredOutputJSONSpec{
+				Name:   "prepared_schema",
+				Strict: true,
+				Schema: map[string]any{
+					"type":     "object",
+					"required": []any{"value"},
+					"properties": map[string]any{
+						"value": map[string]any{"minimum": float64(1)},
+					},
+				},
+			},
+		},
+		InputHashes:        map[string]string{"first": "hash-1", "second": "hash-2"},
+		SessionID:          "session-prepared",
+		RenderedPromptHash: "rendered-hash",
+		Messages: []promptkit.RenderedMessage{
+			{
+				Role:    "system",
+				Content: "System message",
+				CacheControl: &promptkit.CacheControl{
+					Type: promptkit.CacheControlEphemeral,
+					TTL:  "1h",
+				},
+			},
+			{Role: "user", Content: "User message"},
+		},
+		StartTime:  start,
+		EndTime:    start.Add(1501 * time.Millisecond),
+		DurationMS: 1501,
+	}
+}
+
+func fullyPopulatedRunResult() promptkit.RunResult {
+	start := time.Date(2026, time.August, 11, 15, 16, 17, 250_000_000, time.UTC)
+	return promptkit.RunResult{
+		RunID: "run-id",
+		Artifact: promptkit.Artifact{
+			Name:        "result.json",
+			ContentType: "application/json",
+			Body:        []byte(`{"value":2}`),
+			URI:         "memory://result.json",
+			Size:        11,
+			Hash:        "artifact-hash",
+		},
+		RawOutput: `{"value":2}`,
+		Validation: promptkit.ValidationResult{
+			Status:         promptkit.ValidationFailed,
+			Mode:           promptkit.ValidationJSONSchema,
+			Errors:         []string{"first error", "second error"},
+			SchemaPath:     "schemas/result.json",
+			RepairAttempts: 2,
+			IsValid:        false,
+		},
+		PromptID:             "prompt.result",
+		PromptVersion:        "3.2.1",
+		PromptHash:           "result-prompt-hash",
+		SessionID:            "session-result",
+		RenderedPromptHash:   "result-rendered-hash",
+		SelectedProfileID:    "profile-result",
+		SelectedBackendID:    "backend-result",
+		ModelName:            "model-result",
+		Endpoint:             "https://result.example/v1",
+		EffectiveModelParams: jsonContractExecutionTarget(),
+		InputHashes:          map[string]string{"input": "input-hash"},
+		Usage: promptkit.TokenUsage{
+			PromptTokens:     101,
+			CompletionTokens: 202,
+			TotalTokens:      303,
+			CachedTokens:     44,
+			CacheWriteTokens: 55,
+		},
+		StartTime: start,
+		EndTime:   start.Add(1750 * time.Millisecond),
+		Duration:  1750 * time.Millisecond,
+	}
+}
+
+func jsonContractExecutionTarget() promptkit.ExecutionTarget {
+	return promptkit.ExecutionTarget{
+		BackendID:       "backend-target",
+		Endpoint:        "https://target.example/v1",
+		Model:           "model-target",
+		Temperature:     0.75,
+		MaxTokens:       321,
+		TopP:            0.875,
+		TimeoutSeconds:  43,
+		ServiceTier:     "priority",
+		ReasoningEffort: "high",
+		APIKeyEnv:       "PROMPTKIT_JSON_CONTRACT_KEY",
+		ExtraParams: map[string]any{
+			"enabled": true,
+			"weight":  float64(1.25),
+			"nested":  map[string]any{"name": "value"},
+		},
+	}
+}
+
+func durationPayload(milliseconds int64) []byte {
+	return []byte(`{"duration_ms":` + strconv.FormatInt(milliseconds, 10) + `}`)
+}
+
+func decodeJSONObject(t *testing.T, payload []byte) map[string]json.RawMessage {
+	t.Helper()
+	var object map[string]json.RawMessage
+	if err := json.Unmarshal(payload, &object); err != nil {
+		t.Fatalf("decode JSON object: %v", err)
+	}
+	return object
+}
+
+func assertJSONFields(t *testing.T, object map[string]json.RawMessage, fields ...string) {
+	t.Helper()
+	want := make(map[string]struct{}, len(fields))
+	for _, field := range fields {
+		want[field] = struct{}{}
+	}
+	for field := range object {
+		if _, ok := want[field]; !ok {
+			t.Errorf("unexpected JSON field %q", field)
+		}
+	}
+	for field := range want {
+		if _, ok := object[field]; !ok {
+			t.Errorf("missing JSON field %q", field)
+		}
+	}
+}

llm_adapter_internal_test.go

@@ -0,0 +1,96 @@
+package promptkit
+
+import (
+	"context"
+	"reflect"
+	"strconv"
+	"sync"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+func TestPublicLLMClientAdapterGivesClientOwnedNestedValues(t *testing.T) {
+	source := adapterOwnershipRequest()
+	want := adapterOwnershipRequest()
+	client := &retainingMutatingLLMClient{}
+	adapter := publicLLMClientAdapter{client: client}
+
+	if _, err := adapter.Generate(context.Background(), source); err != nil {
+		t.Fatalf("generate: %v", err)
+	}
+	if !reflect.DeepEqual(source, want) {
+		t.Fatalf("client mutation changed prepared source:\ngot  %#v\nwant %#v", source, want)
+	}
+
+	var mutations sync.WaitGroup
+	mutations.Add(1)
+	go func() {
+		defer mutations.Done()
+		for i := 0; i < 10_000; i++ {
+			mutateGenerateRequest(&client.retained, strconv.Itoa(i))
+		}
+	}()
+	for i := 0; i < 10_000; i++ {
+		laterRequest := fromDomainGenerateRequest(source)
+		if laterRequest.Prompt.Messages[0].Content != "source-message" ||
+			laterRequest.Prompt.Messages[0].CacheControl.TTL != "source-ttl" ||
+			laterRequest.Target.ExtraParams["nested"].([]any)[0] != "source-extra" ||
+			laterRequest.StructuredOutput.JSONSchema.Schema.(map[string]any)["enum"].([]any)[0] != "source-schema" {
+			t.Fatal("retained client mutation reached a later execution request")
+		}
+	}
+	mutations.Wait()
+
+	if !reflect.DeepEqual(source, want) {
+		t.Fatalf("retained client mutation changed prepared source:\ngot  %#v\nwant %#v", source, want)
+	}
+}
+
+type retainingMutatingLLMClient struct {
+	retained GenerateRequest
+}
+
+func (c *retainingMutatingLLMClient) Generate(_ context.Context, request GenerateRequest) (*GenerateResponse, error) {
+	c.retained = request
+	mutateGenerateRequest(&c.retained, "client-mutation")
+	return &GenerateResponse{Content: "generated"}, nil
+}
+
+func adapterOwnershipRequest() domain.GenerateRequest {
+	return domain.GenerateRequest{
+		Prompt: domain.RenderedPrompt{
+			SessionID: "source-session",
+			Messages: []domain.RenderedMessage{{
+				Role:    "user",
+				Content: "source-message",
+				CacheControl: &domain.CacheControl{
+					Type: domain.CacheControlEphemeral,
+					TTL:  "source-ttl",
+				},
+			}},
+		},
+		Target: domain.ExecutionTarget{
+			Model:  "source-model",
+			APIKey: "source-api-key",
+			ExtraParams: map[string]any{
+				"nested": []any{"source-extra"},
+			},
+		},
+		StructuredOutput: &domain.StructuredOutputSpec{
+			Type: domain.StructuredOutputJSONSchema,
+			JSONSchema: &domain.StructuredOutputJSONSpec{
+				Name:   "source-schema-name",
+				Strict: true,
+				Schema: map[string]any{"enum": []any{"source-schema"}},
+			},
+		},
+	}
+}
+
+func mutateGenerateRequest(request *GenerateRequest, value string) {
+	request.Prompt.Messages[0].Content = value
+	request.Prompt.Messages[0].CacheControl.TTL = value
+	request.Target.ExtraParams["nested"].([]any)[0] = value
+	request.StructuredOutput.JSONSchema.Schema.(map[string]any)["enum"].([]any)[0] = value
+}

output_contract_contract_test.go

@@ -0,0 +1,48 @@
+package promptkit_test
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/promptkit"
+)
+
+func TestPreparationRejectsInvalidOutputContractWithPublicError(t *testing.T) {
+	engine, err := promptkit.NewEngine(
+		promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "message"), "."),
+		promptkit.WithProfiles(promptkit.Profile{
+			ID:       "profile",
+			Endpoint: "http://example.test/v1",
+			Model:    "model",
+		}),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+
+	req := promptkit.RunRequest{
+		PromptID: "prompt",
+		Validation: &promptkit.OutputContract{
+			Format:         promptkit.OutputFormat("binary"),
+			ValidationMode: promptkit.ValidationNone,
+		},
+	}
+
+	prepared, err := engine.Prepare(context.Background(), req)
+	if prepared != nil {
+		t.Fatalf("expected no partial prepared run, got %+v", prepared)
+	}
+	if !errors.Is(err, promptkit.ErrInvalidRequest) {
+		t.Fatalf("prepare error = %v, want ErrInvalidRequest", err)
+	}
+
+	preparedExecution, err := engine.PrepareExecution(context.Background(), req)
+	if preparedExecution != nil {
+		t.Fatalf("expected no partial prepared execution, got %+v", preparedExecution)
+	}
+	if !errors.Is(err, promptkit.ErrInvalidRequest) {
+		t.Fatalf("prepare execution error = %v, want ErrInvalidRequest", err)
+	}
+}

prepared_execution.go

@@ -44,12 +44,12 @@ func (p *PreparedExecution) Discard() {
 
 // String returns a constant representation that exposes no retained request,
 // rendered content, or credential data.
-func (p *PreparedExecution) String() string {
+func (p PreparedExecution) String() string {
 	return preparedExecutionString
 }
 
 // GoString returns a constant Go-syntax representation that exposes no
 // retained request, rendered content, or credential data.
-func (p *PreparedExecution) GoString() string {
+func (p PreparedExecution) GoString() string {
 	return preparedExecutionString
 }

prepared_execution_contract_test.go

@@ -409,14 +409,35 @@ func TestPreparedExecutionDiscardAndFormattingDoNotExposePrivateState(t *testing
 		t.Fatalf("prepare execution: %v", err)
 	}
 
-	formattedValues := []string{
-		fmt.Sprint(prepared),
-		fmt.Sprintf("%+v", prepared),
-		fmt.Sprintf("%#v", prepared),
-	}
-	for _, formatted := range formattedValues {
+	copied := *prepared
+	zeroValue := promptkit.PreparedExecution{}
+	var nilHandle *promptkit.PreparedExecution
+	for name, value := range map[string]any{
+		"original pointer": prepared,
+		"copied value":     copied,
+		"zero value":       zeroValue,
+		"zero pointer":     &zeroValue,
+	} {
+		for format, formatted := range map[string]string{
+			"String":   fmt.Sprintf("%s", value),
+			"GoString": fmt.Sprintf("%#v", value),
+			"v":        fmt.Sprintf("%v", value),
+			"+v":       fmt.Sprintf("%+v", value),
+		} {
 			if formatted != "promptkit.PreparedExecution{opaque}" {
-			t.Fatalf("unexpected opaque formatting: %q", formatted)
+				t.Fatalf("%s %s formatting = %q, want opaque representation", name, format, formatted)
+			}
+			assertPreparedPrivateValuesAbsent(t, formatted, directCredential, renderedContent)
+		}
+	}
+	for format, formatted := range map[string]string{
+		"String":   fmt.Sprintf("%s", nilHandle),
+		"GoString": fmt.Sprintf("%#v", nilHandle),
+		"v":        fmt.Sprintf("%v", nilHandle),
+		"+v":       fmt.Sprintf("%+v", nilHandle),
+	} {
+		if formatted != "<nil>" {
+			t.Fatalf("nil pointer %s formatting = %q, want <nil>", format, formatted)
 		}
 		assertPreparedPrivateValuesAbsent(t, formatted, directCredential, renderedContent)
 	}
@@ -433,27 +454,9 @@ func TestPreparedExecutionDiscardAndFormattingDoNotExposePrivateState(t *testing
 	}
 	assertPreparedPrivateValuesAbsent(t, string(detailsJSON), directCredential)
 
-	prepared.Discard()
-	prepared.Discard()
-	result, lifecycleErr := engine.RunPrepared(context.Background(), prepared)
-	if result != nil || !errors.Is(lifecycleErr, promptkit.ErrInvalidRequest) {
-		t.Fatalf("discarded execution result=(%+v, %v), want ErrInvalidRequest", result, lifecycleErr)
-	}
-	assertPreparedPrivateValuesAbsent(t, lifecycleErr.Error(), directCredential, renderedContent)
-	if !reflect.DeepEqual(prepared.Details(), detailsBefore) {
-		t.Fatal("details changed after discard")
-	}
-
-	executed, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{
-		PromptID: "prepared",
-		APIKey:   directCredential,
-	})
+	executionResult, err := engine.RunPrepared(context.Background(), &copied)
 	if err != nil {
-		t.Fatalf("prepare execution for request inspection: %v", err)
-	}
-	executionResult, err := engine.RunPrepared(context.Background(), executed)
-	if err != nil {
-		t.Fatalf("run execution for request inspection: %v", err)
+		t.Fatalf("run copied execution after formatting: %v", err)
 	}
 	requests := client.snapshot()
 	if len(requests) != 1 || requests[0].APIKey != directCredential {
@@ -478,16 +481,34 @@ func TestPreparedExecutionDiscardAndFormattingDoNotExposePrivateState(t *testing
 	}
 	assertPreparedPrivateValuesAbsent(t, string(resultJSON), directCredential)
 
-	var nilHandle *promptkit.PreparedExecution
 	nilHandle.Discard()
 	if !reflect.DeepEqual(nilHandle.Details(), promptkit.PreparedRun{}) {
 		t.Fatalf("nil handle details=%+v, want zero value", nilHandle.Details())
 	}
-	zeroHandle := &promptkit.PreparedExecution{}
+	zeroHandle := &zeroValue
 	zeroHandle.Discard()
 	if !reflect.DeepEqual(zeroHandle.Details(), promptkit.PreparedRun{}) {
 		t.Fatalf("zero handle details=%+v, want zero value", zeroHandle.Details())
 	}
+
+	discarded, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{
+		PromptID: "prepared",
+		APIKey:   directCredential,
+	})
+	if err != nil {
+		t.Fatalf("prepare execution for discard: %v", err)
+	}
+	discardedDetails := discarded.Details()
+	discarded.Discard()
+	discarded.Discard()
+	result, lifecycleErr := engine.RunPrepared(context.Background(), discarded)
+	if result != nil || !errors.Is(lifecycleErr, promptkit.ErrInvalidRequest) {
+		t.Fatalf("discarded execution result=(%+v, %v), want ErrInvalidRequest", result, lifecycleErr)
+	}
+	assertPreparedPrivateValuesAbsent(t, lifecycleErr.Error(), directCredential, renderedContent)
+	if !reflect.DeepEqual(discarded.Details(), discardedDetails) {
+		t.Fatal("details changed after discard")
+	}
 }
 
 func TestPreparedExecutionCredentialCapacityAndTimingBoundaries(t *testing.T) {
@@ -560,6 +581,11 @@ func TestPreparedExecutionCredentialCapacityAndTimingBoundaries(t *testing.T) {
 		if result, err := engine.RunPrepared(context.Background(), prepared); result != nil ||
 			!errors.Is(err, promptkit.ErrCapacityExceeded) {
 			t.Fatalf("capacity execution=(%+v, %v), want ErrCapacityExceeded", result, err)
+		} else {
+			var capacityErr *promptkit.CapacityError
+			if !errors.As(err, &capacityErr) || capacityErr == nil || capacityErr.BackendID != "limited" {
+				t.Fatalf("capacity execution=%v, want limited CapacityError", err)
+			}
 		}
 		if result, err := engine.RunPrepared(context.Background(), prepared); result != nil ||
 			!errors.Is(err, promptkit.ErrInvalidRequest) {

profiles.go

@@ -100,33 +100,34 @@ func toDomainProfile(publicProfile Profile) (domain.ExecutionProfile, error) {
 		APIKeyRequired:  publicProfile.APIKeyRequired,
 		ExtraParams:     extraParams,
 	}
-	if err := validatePublicProfile(prof); err != nil {
+	if err := normalizeAndValidatePublicProfile(&prof); err != nil {
 		return domain.ExecutionProfile{}, err
 	}
 	return prof, nil
 }
 
-func validatePublicProfile(prof domain.ExecutionProfile) error {
+func normalizeAndValidatePublicProfile(prof *domain.ExecutionProfile) error {
 	if strings.TrimSpace(prof.ID) == "" {
 		return errors.New("id is required")
 	}
-	if strings.TrimSpace(prof.BackendID) == "" && strings.TrimSpace(prof.Endpoint) == "" {
+	prof.Endpoint = strings.TrimSpace(prof.Endpoint)
+	if strings.TrimSpace(prof.BackendID) == "" && prof.Endpoint == "" {
 		return errors.New("backend or endpoint is required")
 	}
+	if prof.Endpoint != "" {
+		endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(prof.Endpoint)
+		if err != nil {
+			return err
+		}
+		prof.Endpoint = endpoint
+	}
 	if strings.TrimSpace(prof.Model) == "" {
 		return errors.New("model is required")
 	}
-	if prof.Temperature < 0 || prof.Temperature > 2 {
-		return errors.New("temperature must be between 0 and 2")
-	}
-	if prof.MaxTokens < 0 {
-		return errors.New("max_tokens must be greater than or equal to 0")
-	}
-	if prof.TopP < 0 || prof.TopP > 1 {
-		return errors.New("top_p must be between 0 and 1")
-	}
-	if prof.TimeoutSeconds < 0 {
-		return errors.New("timeout_seconds must be greater than or equal to 0")
-	}
-	return nil
+	return domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{
+		Temperature:    prof.Temperature,
+		MaxTokens:      prof.MaxTokens,
+		TopP:           prof.TopP,
+		TimeoutSeconds: prof.TimeoutSeconds,
+	})
 }

public_contract_test.go

@@ -5,26 +5,423 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io/fs"
 	"reflect"
 	"strings"
 	"sync"
 	"sync/atomic"
 	"testing"
 	"testing/fstest"
-	"time"
 
 	"gitea.maximumdirect.net/eric/promptkit"
 )
 
-func TestPreparedRunJSONOmitsZeroTimingValues(t *testing.T) {
-	payload, err := json.Marshal(promptkit.PreparedRun{})
+type inspectionCountingFS struct {
+	opens atomic.Int64
+}
+
+func (f *inspectionCountingFS) Open(string) (fs.File, error) {
+	f.opens.Add(1)
+	return nil, fs.ErrNotExist
+}
+
+func TestInspectProfileResolvesCredentialStatesWithoutPromptOrGeneration(t *testing.T) {
+	const environmentName = "PROMPTKIT_INSPECTION_ABSENT_KEY"
+	t.Setenv(environmentName, "")
+	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "unexpected"}}
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(fstest.MapFS{}, "."),
+		promptkit.WithProfileFS(fstest.MapFS{
+			"environment.yaml": &fstest.MapFile{Data: []byte(`id: environment
+endpoint: http://environment.example/v1
+model: environment-model
+api_key_env: PROMPTKIT_INSPECTION_ABSENT_KEY
+`)},
+		}, "."),
+		promptkit.WithProfiles(
+			promptkit.Profile{ID: "direct", Endpoint: "http://direct.example/v1", Model: "direct-model", APIKeyRequired: true},
+			promptkit.Profile{ID: "none", Endpoint: "http://none.example/v1", Model: "none-model"},
+		),
+		promptkit.WithLLMClient(client),
+	)
 	if err != nil {
-		t.Fatalf("marshal prepared run: %v", err)
+		t.Fatalf("construct inspection engine: %v", err)
 	}
-	for _, field := range []string{"start_time", "end_time", "duration_ms"} {
-		if strings.Contains(string(payload), `"`+field+`"`) {
-			t.Fatalf("expected zero %s to be omitted, got %s", field, payload)
+
+	for _, tc := range []struct {
+		profileID     string
+		wantEnv       string
+		wantDirectKey bool
+		wantEndpoint  string
+	}{
+		{profileID: " environment ", wantEnv: environmentName, wantEndpoint: "http://environment.example/v1"},
+		{profileID: "direct", wantDirectKey: true, wantEndpoint: "http://direct.example/v1"},
+		{profileID: "none", wantEndpoint: "http://none.example/v1"},
+	} {
+		t.Run(tc.profileID, func(t *testing.T) {
+			inspection, err := engine.InspectProfile(context.Background(), tc.profileID)
+			if err != nil {
+				t.Fatalf("inspect profile: %v", err)
 			}
+			if inspection.ProfileID != strings.TrimSpace(tc.profileID) ||
+				inspection.EffectiveModelParams.Endpoint != tc.wantEndpoint ||
+				inspection.EffectiveModelParams.BackendID != "" ||
+				inspection.EffectiveModelParams.APIKeyEnv != tc.wantEnv ||
+				inspection.APIKeyRequired != tc.wantDirectKey {
+				t.Fatalf("unexpected inspection: %#v", inspection)
+			}
+		})
+	}
+	if len(client.requests) != 0 {
+		t.Fatalf("inspection invoked the model client %d times", len(client.requests))
+	}
+}
+
+func TestFileProfileNormalizedIDMatchesInspectionAndPreparation(t *testing.T) {
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", "normalized-profile", "message"), "."),
+		promptkit.WithProfileFS(fstest.MapFS{
+			"profile.yaml": &fstest.MapFile{Data: []byte(`
+id: "  normalized-profile  "
+endpoint: http://profile.example/v1
+model: normalized-model
+`)},
+		}, "."),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+
+	inspection, err := engine.InspectProfile(context.Background(), " normalized-profile ")
+	if err != nil {
+		t.Fatalf("inspect normalized profile: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{
+		PromptID:  "prompt",
+		ProfileID: " normalized-profile ",
+	})
+	if err != nil {
+		t.Fatalf("prepare with normalized profile: %v", err)
+	}
+
+	if inspection.ProfileID != "normalized-profile" ||
+		prepared.SelectedProfileID != inspection.ProfileID ||
+		inspection.EffectiveModelParams.Model != "normalized-model" ||
+		prepared.EffectiveModelParams.Model != inspection.EffectiveModelParams.Model {
+		t.Fatalf("inspection=%#v prepared=%#v", inspection, prepared)
+	}
+}
+
+func TestInspectProfilePreservesPublicErrorIdentities(t *testing.T) {
+	newEngine := func(t *testing.T, options ...promptkit.Option) *promptkit.Engine {
+		t.Helper()
+		engine, err := promptkit.NewEngine(
+			promptkit.Config{},
+			append([]promptkit.Option{promptkit.WithPromptFS(fstest.MapFS{}, ".")}, options...)...,
+		)
+		if err != nil {
+			t.Fatalf("construct inspection engine: %v", err)
+		}
+		return engine
+	}
+
+	var nilEngine *promptkit.Engine
+	if result, err := nilEngine.InspectProfile(context.Background(), "profile"); result != nil ||
+		!errors.Is(err, promptkit.ErrInvalidConfig) {
+		t.Fatalf("nil engine result=(%#v, %v), want ErrInvalidConfig", result, err)
+	}
+
+	valid := newEngine(t, promptkit.WithProfiles(promptkit.Profile{
+		ID: "profile", Endpoint: "http://profile.example/v1", Model: "model",
+	}))
+	if result, err := valid.InspectProfile(context.Background(), " \t "); result != nil ||
+		!errors.Is(err, promptkit.ErrInvalidRequest) {
+		t.Fatalf("blank profile result=(%#v, %v), want ErrInvalidRequest", result, err)
+	}
+	if result, err := valid.InspectProfile(context.Background(), "missing"); result != nil ||
+		!errors.Is(err, promptkit.ErrProfileNotFound) || errors.Is(err, promptkit.ErrProfileLoad) {
+		t.Fatalf("missing profile result=(%#v, %v), want only ErrProfileNotFound", result, err)
+	}
+
+	malformed := newEngine(t, promptkit.WithProfileFS(fstest.MapFS{
+		"broken.yaml": &fstest.MapFile{Data: []byte("id: broken\nendpoint: http://broken.example/v1\nmodel: model\nextra_params:\n  invalid: .nan\n")},
+	}, "."))
+	if result, err := malformed.InspectProfile(context.Background(), "broken"); result != nil ||
+		!errors.Is(err, promptkit.ErrProfileLoad) {
+		t.Fatalf("malformed profile result=(%#v, %v), want ErrProfileLoad", result, err)
+	}
+
+	unknownBackend := newEngine(t, promptkit.WithProfiles(promptkit.Profile{
+		ID: "unknown-backend", BackendID: "unknown", Model: "model",
+	}))
+	if result, err := unknownBackend.InspectProfile(context.Background(), "unknown-backend"); result != nil ||
+		!errors.Is(err, promptkit.ErrProfileLoad) {
+		t.Fatalf("unknown backend result=(%#v, %v), want ErrProfileLoad", result, err)
+	}
+
+	countingFS := &inspectionCountingFS{}
+	canceled := newEngine(t, promptkit.WithProfileFS(countingFS, "."))
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if result, err := canceled.InspectProfile(ctx, "profile"); result != nil ||
+		!errors.Is(err, promptkit.ErrProfileLoad) || !errors.Is(err, context.Canceled) || countingFS.opens.Load() != 0 {
+		t.Fatalf("canceled inspection result=(%#v, %v), opens=%d", result, err, countingFS.opens.Load())
+	}
+}
+
+func TestInspectProfileReturnsIndependentTargetMatchingPreparation(t *testing.T) {
+	extraParams := map[string]any{
+		"nested": map[string]any{"value": "original"},
+	}
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "message"), "."),
+		promptkit.WithProfiles(promptkit.Profile{
+			ID: "profile", Endpoint: "http://profile.example/v1", Model: "model", ExtraParams: extraParams,
+		}),
+	)
+	if err != nil {
+		t.Fatalf("construct inspection engine: %v", err)
+	}
+
+	first, err := engine.InspectProfile(context.Background(), "profile")
+	if err != nil {
+		t.Fatalf("first inspection: %v", err)
+	}
+	first.EffectiveModelParams.ExtraParams["nested"].(map[string]any)["value"] = "changed"
+	first.EffectiveModelParams.ExtraParams["later"] = true
+
+	second, err := engine.InspectProfile(context.Background(), "profile")
+	if err != nil {
+		t.Fatalf("second inspection: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("prepare after inspection mutation: %v", err)
+	}
+	for _, target := range []promptkit.ExecutionTarget{second.EffectiveModelParams, prepared.EffectiveModelParams} {
+		if target.ExtraParams["nested"].(map[string]any)["value"] != "original" || target.ExtraParams["later"] != nil {
+			t.Fatalf("inspection mutation reached engine-owned target: %#v", target.ExtraParams)
+		}
+	}
+	if !reflect.DeepEqual(second.EffectiveModelParams, prepared.EffectiveModelParams) {
+		t.Fatalf("inspection target=%#v, preparation target=%#v", second.EffectiveModelParams, prepared.EffectiveModelParams)
+	}
+}
+
+func TestInspectPromptReturnsDeclaredMetadataWithoutExecutionWork(t *testing.T) {
+	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "unexpected"}}
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(fstest.MapFS{
+			"report-v1.yaml": &fstest.MapFile{Data: []byte(`id: report
+version: "1.0.0"
+messages:
+  - role: user
+    content: old report
+output:
+  format: text
+  validation_mode: none
+`)},
+			"report-v2.yaml": &fstest.MapFile{Data: []byte(`id: report
+version: "2.0.0"
+default_profile: missing-profile
+inputs:
+  - name: location
+    required: true
+    content_type: text/plain
+    description: Forecast location.
+  - name: units
+    content_type: text/plain
+    description: Unit preference.
+messages:
+  - role: user
+    content_file: messages/report.md
+output:
+  format: json
+  validation_mode: json_schema
+  schema_path: schemas/report.json
+`)},
+			"messages/report.md": &fstest.MapFile{Data: []byte("rendered report body is not returned")},
+		}, "."),
+		promptkit.WithLLMClient(client),
+	)
+	if err != nil {
+		t.Fatalf("construct prompt-inspection engine: %v", err)
+	}
+
+	inspection, err := engine.InspectPrompt(context.Background(), "report", "2.0.0")
+	if err != nil {
+		t.Fatalf("inspect prompt: %v", err)
+	}
+	if inspection.PromptID != "report" ||
+		inspection.PromptVersion != "2.0.0" ||
+		inspection.PromptHash == "" ||
+		inspection.DefaultProfileID != "missing-profile" ||
+		inspection.OutputContract != (promptkit.OutputContract{
+			Format:         promptkit.FormatJSON,
+			ValidationMode: promptkit.ValidationJSONSchema,
+			SchemaPath:     "schemas/report.json",
+		}) {
+		t.Fatalf("unexpected inspection metadata: %#v", inspection)
+	}
+	wantInputs := []promptkit.PromptInputDefinition{
+		{Name: "location", Required: true, ContentType: "text/plain", Description: "Forecast location."},
+		{Name: "units", ContentType: "text/plain", Description: "Unit preference."},
+	}
+	if !reflect.DeepEqual(inspection.Inputs, wantInputs) {
+		t.Fatalf("inspection inputs=%#v, want %#v", inspection.Inputs, wantInputs)
+	}
+	if len(client.requests) != 0 {
+		t.Fatalf("inspection invoked the model client %d times", len(client.requests))
+	}
+}
+
+func TestInspectPromptPreservesPublicErrorIdentities(t *testing.T) {
+	newEngine := func(t *testing.T, source fstest.MapFS) *promptkit.Engine {
+		t.Helper()
+		engine, err := promptkit.NewEngine(promptkit.Config{}, promptkit.WithPromptFS(source, "."))
+		if err != nil {
+			t.Fatalf("construct prompt-inspection engine: %v", err)
+		}
+		return engine
+	}
+	validSource := fstest.MapFS{
+		"prompt.yaml": &fstest.MapFile{Data: []byte(`id: prompt
+version: "1"
+messages:
+  - role: user
+    content: body
+output:
+  format: text
+  validation_mode: none
+`)},
+	}
+
+	var nilEngine *promptkit.Engine
+	if result, err := nilEngine.InspectPrompt(context.Background(), "prompt", "1"); result != nil ||
+		!errors.Is(err, promptkit.ErrInvalidConfig) {
+		t.Fatalf("nil engine result=(%#v, %v), want ErrInvalidConfig", result, err)
+	}
+
+	valid := newEngine(t, validSource)
+	if result, err := valid.InspectPrompt(context.Background(), " \t ", "1"); result != nil ||
+		!errors.Is(err, promptkit.ErrInvalidRequest) {
+		t.Fatalf("blank prompt result=(%#v, %v), want ErrInvalidRequest", result, err)
+	}
+	if result, err := valid.InspectPrompt(context.Background(), "missing", "1"); result != nil ||
+		!errors.Is(err, promptkit.ErrPromptNotFound) || errors.Is(err, promptkit.ErrPromptLoad) {
+		t.Fatalf("missing prompt result=(%#v, %v), want only ErrPromptNotFound", result, err)
+	}
+	if result, err := valid.InspectPrompt(context.Background(), "prompt", "missing"); result != nil ||
+		!errors.Is(err, promptkit.ErrPromptNotFound) || errors.Is(err, promptkit.ErrPromptLoad) {
+		t.Fatalf("missing version result=(%#v, %v), want only ErrPromptNotFound", result, err)
+	}
+
+	ambiguous := newEngine(t, fstest.MapFS{
+		"one.yaml": &fstest.MapFile{Data: []byte(`id: prompt
+version: "1"
+messages:
+  - role: user
+    content: first
+output:
+  format: text
+  validation_mode: none
+`)},
+		"two.yaml": &fstest.MapFile{Data: []byte(`id: prompt
+version: "2"
+messages:
+  - role: user
+    content: second
+output:
+  format: text
+  validation_mode: none
+`)},
+	})
+	if result, err := ambiguous.InspectPrompt(context.Background(), "prompt", ""); result != nil ||
+		!errors.Is(err, promptkit.ErrPromptLoad) {
+		t.Fatalf("ambiguous prompt result=(%#v, %v), want ErrPromptLoad", result, err)
+	}
+
+	for name, source := range map[string]fstest.MapFS{
+		"malformed definition": {
+			"broken.yaml": &fstest.MapFile{Data: []byte("id: broken\nversion: \"1\"\nunknown: value\n")},
+		},
+		"missing content file": {
+			"broken.yaml": &fstest.MapFile{Data: []byte(`id: broken
+version: "1"
+messages:
+  - role: user
+    content_file: missing.md
+output:
+  format: text
+  validation_mode: none
+`)},
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if result, err := newEngine(t, source).InspectPrompt(context.Background(), "broken", "1"); result != nil ||
+				!errors.Is(err, promptkit.ErrPromptLoad) {
+				t.Fatalf("broken prompt result=(%#v, %v), want ErrPromptLoad", result, err)
+			}
+		})
+	}
+
+	countingFS := &inspectionCountingFS{}
+	canceled, err := promptkit.NewEngine(promptkit.Config{}, promptkit.WithPromptFS(countingFS, "."))
+	if err != nil {
+		t.Fatalf("construct canceled prompt-inspection engine: %v", err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	if result, err := canceled.InspectPrompt(ctx, "prompt", "1"); result != nil ||
+		!errors.Is(err, promptkit.ErrPromptLoad) || !errors.Is(err, context.Canceled) || countingFS.opens.Load() != 0 {
+		t.Fatalf("canceled inspection result=(%#v, %v), opens=%d", result, err, countingFS.opens.Load())
+	}
+}
+
+func TestInspectPromptReturnsIndependentMetadataMatchingPreparation(t *testing.T) {
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(fstest.MapFS{
+			"prompt.yaml": &fstest.MapFile{Data: []byte(`id: prompt
+version: "1"
+default_profile: profile
+inputs:
+  - name: subject
+    content_type: text/plain
+    description: Summary subject.
+messages:
+  - role: user
+    content: summarize
+output:
+  format: markdown
+  validation_mode: basic
+`)},
+		}, "."),
+		promptkit.WithProfiles(promptkit.Profile{
+			ID: "profile", Endpoint: "http://profile.example/v1", Model: "model",
+		}),
+	)
+	if err != nil {
+		t.Fatalf("construct prompt-inspection engine: %v", err)
+	}
+
+	first, err := engine.InspectPrompt(context.Background(), "prompt", "1")
+	if err != nil {
+		t.Fatalf("first inspection: %v", err)
+	}
+	first.Inputs[0].Name = "changed"
+	first.OutputContract.SchemaPath = "changed.json"
+
+	second, err := engine.InspectPrompt(context.Background(), "prompt", "1")
+	if err != nil {
+		t.Fatalf("second inspection: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt", PromptVersion: "1"})
+	if err != nil {
+		t.Fatalf("prepare after inspection mutation: %v", err)
+	}
+	if second.Inputs[0].Name != "subject" || second.OutputContract.SchemaPath != "" ||
+		prepared.OutputContract.SchemaPath != "" || second.PromptHash != prepared.PromptHash {
+		t.Fatalf("inspection mutation reached engine-owned prompt metadata: inspection=%#v prepared=%#v", second, prepared)
 	}
 }
 
@@ -382,6 +779,7 @@ func TestBackendRegistrationRejectsInvalidAndDuplicateDefinitions(t *testing.T)
 		{name: "reserved extra parameter", backends: []promptkit.Backend{{ID: "custom", Endpoint: "http://example.test/v1", ExtraParams: map[string]any{"model": "override"}}}},
 		{name: "cyclic extra parameter", backends: []promptkit.Backend{{ID: "custom", Endpoint: "http://example.test/v1", ExtraParams: cycle}}},
 		{name: "malformed JSON number", backends: []promptkit.Backend{{ID: "custom", Endpoint: "http://example.test/v1", ExtraParams: map[string]any{"value": json.Number("01")}}}},
+		{name: "excessively deep extra parameter", backends: []promptkit.Backend{{ID: "custom", Endpoint: "http://example.test/v1", ExtraParams: map[string]any{"value": excessivelyDeepJSONValue()}}}},
 		{name: "duplicate consumer id", backends: []promptkit.Backend{
 			{ID: " custom ", Endpoint: "http://one.example/v1"},
 			{ID: "custom", Endpoint: "http://two.example/v1"},
@@ -443,92 +841,6 @@ func TestBackendExtraParamsAreDeeplyCopiedAtConstructionAndLookup(t *testing.T)
 	}
 }
 
-func TestPreparedRunJSONTimingRoundTrips(t *testing.T) {
-	start := time.Date(2026, time.July, 29, 12, 0, 0, 0, time.UTC)
-	prepared := promptkit.PreparedRun{
-		PromptID:   "prompt",
-		StartTime:  start,
-		EndTime:    start.Add(1250 * time.Millisecond),
-		DurationMS: 1250,
-	}
-
-	payload, err := json.Marshal(prepared)
-	if err != nil {
-		t.Fatalf("marshal prepared run: %v", err)
-	}
-	var decoded promptkit.PreparedRun
-	if err := json.Unmarshal(payload, &decoded); err != nil {
-		t.Fatalf("unmarshal prepared run: %v", err)
-	}
-	if decoded.DurationMS != prepared.DurationMS ||
-		!decoded.StartTime.Equal(prepared.StartTime) ||
-		!decoded.EndTime.Equal(prepared.EndTime) {
-		t.Fatalf("timing values did not round trip: got %#v, want %#v", decoded, prepared)
-	}
-}
-
-func TestRunResultJSONUsesMillisecondsAndRoundTrips(t *testing.T) {
-	start := time.Date(2026, time.July, 29, 12, 0, 0, 0, time.UTC)
-	result := promptkit.RunResult{
-		RunID:     "opaque-run-id",
-		Artifact:  promptkit.Artifact{Name: "output", ContentType: "text/plain", Body: []byte("ok")},
-		SessionID: "session-123",
-		StartTime: start,
-		EndTime:   start.Add(1500 * time.Millisecond),
-		Duration:  1500 * time.Millisecond,
-	}
-
-	payload, err := json.Marshal(result)
-	if err != nil {
-		t.Fatalf("marshal run result: %v", err)
-	}
-	var object map[string]any
-	if err := json.Unmarshal(payload, &object); err != nil {
-		t.Fatalf("decode run result JSON: %v", err)
-	}
-	if got := object["duration_ms"]; got != float64(1500) {
-		t.Fatalf("expected duration_ms=1500, got %#v in %s", got, payload)
-	}
-	if _, exists := object["duration"]; exists {
-		t.Fatalf("unexpected nanosecond duration field in %s", payload)
-	}
-	if got := object["session_id"]; got != result.SessionID {
-		t.Fatalf("expected session_id=%q, got %#v in %s", result.SessionID, got, payload)
-	}
-	artifact, ok := object["artifact"].(map[string]any)
-	if !ok || artifact["content_type"] != "text/plain" {
-		t.Fatalf("expected stable artifact JSON fields, got %#v", object["artifact"])
-	}
-
-	var decoded promptkit.RunResult
-	if err := json.Unmarshal(payload, &decoded); err != nil {
-		t.Fatalf("unmarshal run result: %v", err)
-	}
-	if decoded.SessionID != result.SessionID ||
-		decoded.Duration != result.Duration ||
-		!decoded.StartTime.Equal(result.StartTime) ||
-		!decoded.EndTime.Equal(result.EndTime) {
-		t.Fatalf("timing values did not round trip: got %#v, want %#v", decoded, result)
-	}
-
-	payload, err = json.Marshal(promptkit.RunResult{})
-	if err != nil {
-		t.Fatalf("marshal zero run result: %v", err)
-	}
-	for _, field := range []string{"session_id", "start_time", "end_time", "duration_ms"} {
-		if strings.Contains(string(payload), `"`+field+`"`) {
-			t.Fatalf("expected zero %s to be omitted, got %s", field, payload)
-		}
-	}
-	var decodedEmpty promptkit.RunResult
-	if err := json.Unmarshal(payload, &decodedEmpty); err != nil {
-		t.Fatalf("unmarshal run result without session_id: %v", err)
-	}
-	if decodedEmpty.SessionID != "" {
-		t.Fatalf("expected absent session_id to decode empty, got %q", decodedEmpty.SessionID)
-	}
-}
-
 func TestEngineValidationIsSinglePass(t *testing.T) {
 	client := &fakeLLMClient{
 		response: &promptkit.GenerateResponse{Content: "not-json"},
@@ -598,6 +910,24 @@ func TestRepeatedOptionsUseLastValueInEachCategory(t *testing.T) {
 		}
 	})
 
+	t.Run("fallback profile source", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "message"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS("profile", "first-model"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS("profile", "second-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+		if err != nil {
+			t.Fatalf("prepare from last fallback profile source: %v", err)
+		}
+		if prepared.EffectiveModelParams.Model != "second-model" {
+			t.Fatalf("expected last fallback profile source, got %q", prepared.EffectiveModelParams.Model)
+		}
+	})
+
 	t.Run("in-memory profiles", func(t *testing.T) {
 		first := profile
 		first.Model = "first-model"
@@ -682,6 +1012,227 @@ func TestRepeatedOptionsUseLastValueInEachCategory(t *testing.T) {
 	})
 }
 
+func TestFallbackProfileSourcePrecedence(t *testing.T) {
+	const profileID = "application-profile"
+
+	prepareModel := func(t *testing.T, engine *promptkit.Engine, promptID string) string {
+		t.Helper()
+		prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: promptID})
+		if err != nil {
+			t.Fatalf("prepare: %v", err)
+		}
+		return prepared.EffectiveModelParams.Model
+	}
+
+	t.Run("in-memory profiles override ordinary and fallback profiles", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithProfiles(promptkit.Profile{ID: profileID, Endpoint: "http://example.test/v1", Model: "memory-model"}),
+			promptkit.WithProfileFS(contractProfileFS(profileID, "ordinary-model"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != "memory-model" {
+			t.Fatalf("expected in-memory profile, got %q", model)
+		}
+	})
+
+	t.Run("ordinary filesystem source overrides fallback profile", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithProfileFS(contractProfileFS(profileID, "ordinary-model"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != "ordinary-model" {
+			t.Fatalf("expected ordinary profile, got %q", model)
+		}
+	})
+
+	t.Run("ordinary option replaces configured directory", func(t *testing.T) {
+		profileDir := t.TempDir()
+		writePublicProfileFile(t, profileDir, profileID, "http://example.test/v1", "directory-model")
+		engine, err := promptkit.NewEngine(promptkit.Config{ProfileDir: profileDir},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithProfileFS(contractProfileFS(profileID, "option-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != "option-model" {
+			t.Fatalf("expected ordinary option profile, got %q", model)
+		}
+	})
+
+	t.Run("configured directory overrides fallback profile", func(t *testing.T) {
+		profileDir := t.TempDir()
+		writePublicProfileFile(t, profileDir, profileID, "http://example.test/v1", "directory-model")
+		engine, err := promptkit.NewEngine(promptkit.Config{ProfileDir: profileDir},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != "directory-model" {
+			t.Fatalf("expected configured directory profile, got %q", model)
+		}
+	})
+
+	t.Run("fallback profile overrides built-in profile", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", "mistral-small-3", "message"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS("mistral-small-3", "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != "fallback-model" {
+			t.Fatalf("expected fallback profile, got %q", model)
+		}
+	})
+
+	t.Run("missing fallback profile uses built-in profile", func(t *testing.T) {
+		t.Setenv("OPENROUTER_API_KEY", "test-key")
+		baseline, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", "mistral-small-3", "message"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct baseline engine: %v", err)
+		}
+		want := prepareModel(t, baseline, "prompt")
+
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", "mistral-small-3", "message"), "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if model := prepareModel(t, engine, "prompt"); model != want {
+			t.Fatalf("expected built-in profile model %q, got %q", want, model)
+		}
+	})
+}
+
+func TestFallbackProfileSourcePreservesLazyLoadingAndErrors(t *testing.T) {
+	const profileID = "application-profile"
+
+	t.Run("construction defers malformed fallback profiles", func(t *testing.T) {
+		_, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(fstest.MapFS{}, "."),
+			promptkit.WithFallbackProfileFS(fstest.MapFS{
+				"broken.yaml": &fstest.MapFile{Data: []byte("id: broken\nunknown: value\n")},
+			}, "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine with malformed fallback profile: %v", err)
+		}
+	})
+
+	t.Run("unrelated malformed fallback profile does not block matching definition", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithFallbackProfileFS(fstest.MapFS{
+				"broken.yaml": &fstest.MapFile{Data: []byte("id: unrelated\nunknown: value\n")},
+				"valid.yaml":  &fstest.MapFile{Data: []byte("id: application-profile\nendpoint: http://example.test/v1\nmodel: fallback-model\n")},
+			}, "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+		if err != nil {
+			t.Fatalf("prepare from valid fallback profile: %v", err)
+		}
+		if prepared.EffectiveModelParams.Model != "fallback-model" {
+			t.Fatalf("unexpected fallback profile model: %q", prepared.EffectiveModelParams.Model)
+		}
+	})
+
+	t.Run("matching malformed fallback profile does not reach built-in profile", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", "mistral-small-3", "message"), "."),
+			promptkit.WithFallbackProfileFS(fstest.MapFS{
+				"mistral-small-3.yaml": &fstest.MapFile{Data: []byte("id: mistral-small-3\nendpoint: http://example.test/v1\nmodel: fallback-model\nunknown: value\n")},
+			}, "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if _, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"}); !errors.Is(err, promptkit.ErrProfileLoad) {
+			t.Fatalf("expected ErrProfileLoad, got %v", err)
+		}
+	})
+
+	t.Run("matching malformed ordinary profile does not reach fallback profile", func(t *testing.T) {
+		engine, err := promptkit.NewEngine(promptkit.Config{},
+			promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+			promptkit.WithProfileFS(fstest.MapFS{
+				"application-profile.yaml": &fstest.MapFile{Data: []byte("id: application-profile\nendpoint: http://example.test/v1\nmodel: ordinary-model\nunknown: value\n")},
+			}, "."),
+			promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		)
+		if err != nil {
+			t.Fatalf("construct engine: %v", err)
+		}
+		if _, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"}); !errors.Is(err, promptkit.ErrProfileLoad) {
+			t.Fatalf("expected ErrProfileLoad, got %v", err)
+		}
+	})
+}
+
+func TestFallbackProfileSourceWorksAcrossWorkflows(t *testing.T) {
+	const profileID = "application-profile"
+	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "ok"}}
+	engine, err := promptkit.NewEngine(promptkit.Config{},
+		promptkit.WithPromptFS(contractPromptFS("prompt", profileID, "message"), "."),
+		promptkit.WithFallbackProfileFS(contractProfileFS(profileID, "fallback-model"), "."),
+		promptkit.WithLLMClient(client),
+	)
+	if err != nil {
+		t.Fatalf("construct engine: %v", err)
+	}
+
+	inspection, err := engine.InspectProfile(context.Background(), profileID)
+	if err != nil {
+		t.Fatalf("inspect fallback profile: %v", err)
+	}
+	prepared, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("prepare fallback profile: %v", err)
+	}
+	preparedExecution, err := engine.PrepareExecution(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("prepare execution with fallback profile: %v", err)
+	}
+	preparedDetails := preparedExecution.Details()
+	preparedResult, err := engine.RunPrepared(context.Background(), preparedExecution)
+	if err != nil {
+		t.Fatalf("run prepared fallback profile: %v", err)
+	}
+	runResult, err := engine.Run(context.Background(), promptkit.RunRequest{PromptID: "prompt"})
+	if err != nil {
+		t.Fatalf("run fallback profile: %v", err)
+	}
+
+	for name, model := range map[string]string{
+		"inspection":         inspection.EffectiveModelParams.Model,
+		"preparation":        prepared.EffectiveModelParams.Model,
+		"prepared execution": preparedDetails.EffectiveModelParams.Model,
+		"prepared result":    preparedResult.EffectiveModelParams.Model,
+		"run result":         runResult.EffectiveModelParams.Model,
+	} {
+		if model != "fallback-model" {
+			t.Fatalf("%s model=%q, want fallback-model", name, model)
+		}
+	}
+}
+
 func TestEngineSupportsConcurrentPrepareAndRun(t *testing.T) {
 	engine, err := promptkit.NewEngine(promptkit.Config{},
 		promptkit.WithPromptFS(contractPromptFS("prompt", "profile", "message"), "."),

types.go

@@ -82,7 +82,8 @@ const (
 // Prepare, PrepareExecution, and Run copy the request's maps, pointers, and
 // nested JSON-compatible values before using them. The caller may mutate the
 // request after any method returns. A successful PrepareExecution retains its
-// own private execution snapshot for RunPrepared.
+// own private execution snapshot for RunPrepared. Excessively deep or large
+// JSON-shaped values are rejected for safety.
 type RunRequest struct {
 	// PromptID is the required non-empty prompt identifier.
 	PromptID string
@@ -116,7 +117,8 @@ type RunRequest struct {
 	// empty maps are equivalent.
 	Vars map[string]string
 	// Execution optionally overrides individual execution settings. Nil uses
-	// the selected profile over its backend, when any, and framework defaults.
+	// the selected profile over its backend, when any, and the framework
+	// baseline.
 	Execution *ExecutionTargetOverride
 	// Validation optionally replaces the prompt's complete output contract. It
 	// does not merge individual fields. Nil uses the prompt contract.
@@ -144,9 +146,10 @@ type PreparedRun struct {
 	// SelectedBackendID equals EffectiveModelParams.BackendID. It is empty for
 	// an endpoint-only profile.
 	SelectedBackendID string `json:"selected_backend_id,omitempty"`
-	// EffectiveModelParams contains framework defaults overlaid by the selected
-	// backend, profile, and then request overrides. It excludes resolved API-key
-	// values.
+	// EffectiveModelParams contains settings resolved from the framework timeout
+	// baseline, selected backend, profile, and then request overrides. Unset
+	// optional provider controls remain zero rather than reporting a provider
+	// default. It excludes resolved API-key values.
 	EffectiveModelParams ExecutionTarget `json:"effective_model_params"`
 	// OutputContract is the complete effective output contract.
 	OutputContract OutputContract `json:"output_contract"`
@@ -240,8 +243,8 @@ type ArtifactRef struct {
 	// URI is the file path for ArtifactRefFile and optional provenance metadata
 	// for ArtifactRefInline.
 	URI string
-	// Body is the content for ArtifactRefInline and is ignored for
-	// ArtifactRefFile.
+	// Body is the content for ArtifactRefInline, where an empty value is valid,
+	// and is ignored for ArtifactRefFile.
 	Body string
 }
 
@@ -294,17 +297,22 @@ type ExecutionTarget struct {
 	// empty for endpoint-only profiles. It is supplied to injected LLMClient
 	// implementations as part of the effective target.
 	BackendID string `json:"backend_id,omitempty"`
-	// Endpoint is the model-provider base URL.
+	// Endpoint is the normalized absolute HTTP or HTTPS model-provider base URL.
+	// It has a host and no user information, query, or fragment.
 	Endpoint string `json:"endpoint"`
 	// Model is the provider model identifier.
 	Model string `json:"model"`
-	// Temperature is the effective sampling temperature from 0 through 2.
+	// Temperature is the resolved sampling temperature from 0 through 2. Zero
+	// leaves the field unspecified to compatible providers unless the
+	// corresponding ExecutionTargetPresence bit is true.
 	Temperature float64 `json:"temperature"`
-	// MaxTokens is the non-negative effective output-token limit. Zero leaves
-	// the limit unspecified to compatible providers unless it was an explicit
-	// request override.
+	// MaxTokens is the non-negative resolved output-token limit. Zero leaves
+	// the limit unspecified to compatible providers unless the corresponding
+	// ExecutionTargetPresence bit is true.
 	MaxTokens int `json:"max_tokens"`
-	// TopP is the effective nucleus-sampling value from 0 through 1.
+	// TopP is the resolved nucleus-sampling value from 0 through 1. Zero leaves
+	// the field unspecified to compatible providers unless the corresponding
+	// ExecutionTargetPresence bit is true.
 	TopP float64 `json:"top_p"`
 	// TimeoutSeconds is the non-negative per-generation deadline. Zero disables
 	// this deadline without disabling caller cancellation or the transport cap.
@@ -320,6 +328,63 @@ type ExecutionTarget struct {
 	ExtraParams map[string]any `json:"extra_params"`
 }
 
+// ProfileInspection is the caller-owned result of [Engine.InspectProfile].
+// It has no stable JSON representation.
+//
+// EffectiveModelParams contains a copied effective target. APIKeyRequired is
+// separate from that target to preserve ExecutionTarget's general execution
+// and stable JSON contracts.
+type ProfileInspection struct {
+	// ProfileID is the trimmed, exact profile ID inspected by the engine.
+	ProfileID string
+	// EffectiveModelParams contains settings resolved from the framework timeout
+	// baseline, selected backend, and then profile, without a request override.
+	// Unset optional provider controls remain zero rather than reporting a
+	// provider default. APIKeyEnv is an environment-variable name, never its
+	// credential value.
+	EffectiveModelParams ExecutionTarget
+	// APIKeyRequired reports that a later execution must supply a direct API
+	// key or an explicit request environment override. It is mutually exclusive
+	// with a nonblank EffectiveModelParams.APIKeyEnv.
+	APIKeyRequired bool
+}
+
+// PromptInputDefinition describes one declared prompt input.
+// It has no stable JSON representation.
+type PromptInputDefinition struct {
+	// Name is the normalized prompt input name.
+	Name string
+	// Required is the prompt definition's declared required flag. When true,
+	// preparation fails if the input is omitted. A false value does not account
+	// for input references in message or session-ID templates.
+	Required bool
+	// ContentType is the declared input media-type metadata.
+	ContentType string
+	// Description is the declared human-readable input description.
+	Description string
+}
+
+// PromptInspection is the caller-owned result of [Engine.InspectPrompt].
+// It has no stable JSON representation.
+//
+// Inputs contains copied declared input metadata in definition order.
+// OutputContract is the normalized contract declared by the prompt definition,
+// rather than a request-level effective override. PromptHash is opaque.
+type PromptInspection struct {
+	// PromptID is the normalized ID of the selected prompt definition.
+	PromptID string
+	// PromptVersion is the normalized version of the selected prompt definition.
+	PromptVersion string
+	// PromptHash is the opaque equality value for the selected definition.
+	PromptHash string
+	// DefaultProfileID is declared metadata and is not resolved by inspection.
+	DefaultProfileID string
+	// Inputs contains caller-owned declared input metadata in definition order.
+	Inputs []PromptInputDefinition
+	// OutputContract is the normalized contract declared by the definition.
+	OutputContract OutputContract
+}
+
 // ExecutionTargetOverride represents per-request runtime setting overrides and
 // has no stable JSON representation.
 //
@@ -327,19 +392,28 @@ type ExecutionTarget struct {
 // fields replace profile values and preserve explicit zero or empty values. A
 // non-empty ExtraParams map replaces the complete profile or backend map
 // rather than merging keys. Empty string fields, nil pointers, and a nil or
-// empty ExtraParams map inherit the selected profile over its backend, when
-// any, and framework defaults.
+// empty ExtraParams map inherit lower-precedence values. An optional provider
+// control that remains zero is unspecified; TimeoutSeconds retains its
+// framework deadline when no higher-precedence value is present.
 type ExecutionTargetOverride struct {
 	// Endpoint replaces the profile or backend endpoint when non-empty without
-	// changing the effective BackendID.
+	// changing the effective BackendID. Preparation trims it and requires an
+	// absolute HTTP or HTTPS URL with a host and no user information, query, or
+	// fragment.
 	Endpoint string
 	// Model replaces the profile model when non-empty.
 	Model string
-	// Temperature, when non-nil, must point to a value from 0 through 2.
+	// Temperature, when non-nil, must point to a value from 0 through 2. A
+	// pointed-to zero is explicitly present; nil inherits a lower-precedence
+	// value and otherwise leaves the provider control unspecified.
 	Temperature *float64
-	// MaxTokens, when non-nil, must point to a non-negative value.
+	// MaxTokens, when non-nil, must point to a non-negative value. A pointed-to
+	// zero is explicitly present; nil inherits a lower-precedence value and
+	// otherwise leaves the provider control unspecified.
 	MaxTokens *int
-	// TopP, when non-nil, must point to a value from 0 through 1.
+	// TopP, when non-nil, must point to a value from 0 through 1. A pointed-to
+	// zero is explicitly present; nil inherits a lower-precedence value and
+	// otherwise leaves the provider control unspecified.
 	TopP *float64
 	// TimeoutSeconds, when non-nil, must point to a non-negative value. A
 	// pointed-to zero disables the per-generation deadline.
@@ -358,7 +432,8 @@ type ExecutionTargetOverride struct {
 	APIKeyEnv string
 	// ExtraParams, when non-empty, replaces the complete profile or backend map.
 	// Values must be JSON-compatible: nil, booleans, finite numbers, strings,
-	// arrays or slices, and maps with non-empty string keys. Cycles are invalid.
+	// arrays or slices, and maps with non-empty string keys. Cycles and
+	// excessively deep or large values are invalid.
 	ExtraParams map[string]any
 }
 
@@ -370,9 +445,12 @@ type ExecutionTargetOverride struct {
 // use profile YAML api_key_env with file and FS profile sources. Profile has no
 // stable JSON representation.
 //
-// WithProfiles validates and copies Profile values during NewEngine. Numeric
-// zero, blank strings, and an empty ExtraParams map inherit framework defaults;
-// use ExecutionTargetOverride pointer fields to request explicit numeric zero.
+// WithProfiles validates and copies Profile values during NewEngine. Zero
+// Temperature, MaxTokens, and TopP values and blank ServiceTier and
+// ReasoningEffort values leave those provider controls unspecified. A zero
+// TimeoutSeconds retains the framework deadline, while an empty ExtraParams map
+// inherits backend request defaults. Use ExecutionTargetOverride pointer fields
+// to request an explicit numeric zero.
 type Profile struct {
 	// ID is the required non-blank profile identifier. WithProfiles trims it.
 	ID string
@@ -382,23 +460,24 @@ type Profile struct {
 	BackendID string
 	// Endpoint is the model-provider base URL. It is required only when
 	// BackendID is blank and otherwise overrides the backend endpoint when
-	// non-blank.
+	// non-blank. WithProfiles trims it and requires an absolute HTTP or HTTPS URL
+	// with a host and no user information, query, or fragment.
 	Endpoint string
 	// Model is the required non-blank provider model identifier.
 	Model string
-	// Temperature is from 0 through 2. Zero inherits the framework default.
+	// Temperature is from 0 through 2. Zero leaves the provider control
+	// unspecified.
 	Temperature float64
-	// MaxTokens is non-negative. Zero inherits the framework default.
+	// MaxTokens is non-negative. Zero leaves the provider control unspecified.
 	MaxTokens int
-	// TopP is from 0 through 1. Zero inherits the framework default rather than
-	// selecting an explicit zero.
+	// TopP is from 0 through 1. Zero leaves the provider control unspecified
+	// rather than selecting an explicit zero.
 	TopP float64
-	// TimeoutSeconds is non-negative. Zero inherits the framework default.
+	// TimeoutSeconds is non-negative. Zero retains the framework deadline.
 	TimeoutSeconds int
-	// ServiceTier is optional; a blank value inherits the framework default.
+	// ServiceTier is optional; a blank value leaves it unspecified.
 	ServiceTier string
-	// ReasoningEffort is optional; a blank value inherits the framework
-	// default.
+	// ReasoningEffort is optional; a blank value leaves it unspecified.
 	ReasoningEffort string
 	// APIKeyRequired clears a backend's inherited API-key environment name and
 	// requires a non-blank RunRequest.APIKey unless the request explicitly
@@ -406,7 +485,8 @@ type Profile struct {
 	APIKeyRequired bool
 	// ExtraParams contains provider-specific JSON-compatible values. An empty
 	// map inherits backend request defaults, when any. WithProfiles validates
-	// and deeply copies it during NewEngine.
+	// and deeply copies it during NewEngine. Excessively deep or large values
+	// are rejected for safety.
 	ExtraParams map[string]any
 }
 
@@ -468,8 +548,8 @@ type ExecutionTargetPresence struct {
 // does not merge fields. The public Engine validates generated output once and
 // does not install an output repairer.
 type OutputContract struct {
-	// Format selects generated artifact metadata. An empty effective value
-	// defaults to FormatText.
+	// Format selects generated artifact metadata. An empty value in a non-nil
+	// request replacement defaults to FormatText.
 	Format OutputFormat `json:"format"`
 	// ValidationMode selects the content check. Use one of the declared
 	// ValidationMode constants.
@@ -477,8 +557,8 @@ type OutputContract struct {
 	// SchemaPath is required when ValidationMode is ValidationJSONSchema and is
 	// ignored by other modes.
 	SchemaPath string `json:"schema_path"`
-	// RepairAttempts is a requested repair limit. A non-positive value requests
-	// no repairs. The public Engine performs no repairs even when this value is
+	// RepairAttempts is a non-negative requested repair limit. Zero requests no
+	// repairs. The public Engine performs no repairs even when this value is
 	// positive, so its runs report zero attempts used.
 	RepairAttempts int `json:"repair_attempts"`
 }
@@ -624,8 +704,12 @@ type GenerateResponse struct {
 
 // File returns a file-backed artifact reference whose URI is path.
 //
-// The default artifact reader opens path as a caller-selected operating-system
-// path without restricting it to an application root or imposing a size limit.
+// The default artifact reader accepts path only when it resolves to a regular
+// operating-system file, checking that condition before and after opening it.
+// It reads synchronously in bounded chunks and checks context cancellation
+// before opening, before and after each read, and before returning the
+// artifact; it cannot interrupt a filesystem operation already in progress.
+// It does not restrict path to an application root or impose a size limit.
 // Applications accepting untrusted paths must validate them before calling
 // Promptkit or use [WithArtifactReader] to enforce application policy.
 func File(path string) ArtifactRef {
@@ -633,13 +717,13 @@ func File(path string) ArtifactRef {
 }
 
 // Inline returns an inline artifact reference whose Body is body and whose URI
-// is empty.
+// is empty. An empty body is a valid, explicitly supplied input.
 func Inline(body string) ArtifactRef {
 	return ArtifactRef{Type: ArtifactRefInline, Body: body}
 }
 
 // InlineWithURI returns an inline artifact reference with body content and uri
-// provenance metadata.
+// provenance metadata. An empty body is a valid, explicitly supplied input.
 func InlineWithURI(uri string, body string) ArtifactRef {
 	return ArtifactRef{Type: ArtifactRefInline, URI: uri, Body: body}
 }