Add ConfigKit typed configuration loading core

2026-09-30 02:08:20 +00:00
parent 5f7b19403f
commit 2b847ac2ae
8 changed files with 497 additions and 1 deletions
--- a/docs/internal/overview.md
+++ b/docs/internal/overview.md
@@ -17,6 +17,7 @@ contributor workflow and validation.
 | `examples/go-library/observe` | Demonstrates offline built-in HTTP retry and synchronous metadata observation across structured proposal and assessment runs using embedded sources, two profiles on one finite backend, and an application decision. It is not a public library package. | [Example program](../../examples/go-library/observe/main.go) |
 | `internal/backend` | Constructs each engine's immutable registry from maintained definitions and consumer additions, validates and defensively copies definitions through the shared JSON-value package, and consumes the LLM-owned OpenAI-compatible reserved request-field rule. | [Backend registry](../../internal/backend/registry.go) |
 | `internal/catalog` | Strictly validates imported immutable maintained backend and profile catalog assets before engine assembly uses them. | [Catalog adapter](../../internal/catalog/catalog.go), [internal sources](sources.md#profiles-and-built-ins) |
+| `internal/configuration` | Loads keyed backend, profile, and prompt configuration through ConfigKit, recording effective field presence and validating final backend/profile values. It is not yet connected to engine assembly. | [Typed loader](../../internal/configuration/load.go), [internal sources](sources.md#typed-configuration-loading) |
 | `internal/capacity` | Owns engine-local bounded execution admission and FIFO model-generation permits for limited backend IDs, including cancellation-safe waiter removal and client wrapping. | [Internal capacity management](capacity.md) |
 | `internal/domain` | Defines internal framework values for requests, artifacts, prompt definitions, profiles, execution targets, rendering, generation, and validation, and owns source-neutral invariants for shared execution settings, OpenAI-compatible base endpoints, session identifiers, and output contracts. Source parsing, required fields, other source-specific normalization, defaulting, and boundary-specific error classification remain with their callers. | [Domain declarations](../../internal/domain/domain.go), [endpoint invariant](../../internal/domain/endpoint.go) |
 | `internal/engine` | Assembles external catalogs, Promptkit-owned profiles, repositories, registry, capacity, collaborators, repairer, and the one use-case runner for each engine instance. | [Engine assembly](../../internal/engine/engine.go), [internal sources](sources.md#profiles-and-built-ins), [internal runner](runner.md) |
--- a/docs/internal/sources.md
+++ b/docs/internal/sources.md
@@ -10,6 +10,19 @@ and the internal engine assembles them behind the public facade's source options
 The [framework format reference](../formats.md) owns the exact file fields,
 validation modes, built-in catalog, and source precedence.

+## Typed Configuration Loading
+
+`internal/configuration` now contains a private ConfigKit adapter for keyed
+backend, profile, and prompt mappings. It performs one layered load, records
+effective field presence (including explicit null), normalizes backend and
+profile fields through ConfigKit resolution, and validates final backend and
+profile domain values. A lower-layer domain value replaced before the handoff
+is not separately validated. Its focused tests exercise real ConfigKit loading.
+
+This loader is not yet wired into engine assembly. The public engine continues
+to use the source and repository behavior described below; prompt resource
+capture and full prompt validation are subsequent implementation work.
+
 ## Prompt Definitions

 `internal/promptdef` uses one source-neutral flow for prompt selection and
--- a/docs/oss/attribution.md
+++ b/docs/oss/attribution.md
@@ -16,6 +16,20 @@ License and notices: [CC BY-SA 4.0](licenses/CC-BY-SA-4.0.txt) |

 [Source](https://gitea.maximumdirect.net/eric/policy/src/commit/d84a38ebab26f048cafbe59a2246700c35d29843).

+## ConfigKit
+
+Selected module: `gitea.maximumdirect.net/eric/ConfigKit` at `v0.5.0`.
+
+Copyright (C) 2026 Eric Rakestraw
+
+SPDX-License-Identifier: LGPL-3.0-or-later
+
+License and notices: [LGPL 3.0](../../LICENSE) |
+[COPYRIGHT](https://gitea.maximumdirect.net/eric/ConfigKit/src/commit/dc09959cca4e105f49ec316c6d4ba585bd2340bd/COPYRIGHT) |
+[LICENSE](https://gitea.maximumdirect.net/eric/ConfigKit/src/commit/dc09959cca4e105f49ec316c6d4ba585bd2340bd/LICENSE).
+
+[Source](https://gitea.maximumdirect.net/eric/ConfigKit/src/commit/dc09959cca4e105f49ec316c6d4ba585bd2340bd).
+
 ## Promptkit OpenRouter Catalog

 Selected module: `gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2`
@@ -91,3 +105,22 @@ License and notices: [MIT](licenses/MIT.txt) |
 [NOTICE](https://github.com/go-yaml/yaml/blob/f6f7691b1fdeb513f56608cd2c32c51f8194bf51/NOTICE).

 [Source](https://github.com/go-yaml/yaml/tree/f6f7691b1fdeb513f56608cd2c32c51f8194bf51).
+
+## Go YAML v4
+
+Selected module: `go.yaml.in/yaml/v4` at `v4.0.0-rc.6` (transitive dependency).
+
+Copyright 2006-2010 Kirill Simonov
+
+Copyright 2011-2019 Canonical Ltd
+
+Copyright 2025 The go-yaml Project Contributors
+
+SPDX-License-Identifier: MIT AND Apache-2.0
+
+License and notices: [MIT](licenses/MIT.txt) |
+[Apache 2.0](licenses/Apache-2.0.txt) |
+[LICENSE](https://github.com/yaml/go-yaml/blob/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125/LICENSE) |
+[NOTICE](https://github.com/yaml/go-yaml/blob/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125/NOTICE).
+
+[Source](https://github.com/yaml/go-yaml/tree/1c17b9cee72bf81ae73a8be50fbd7dd3a9985125).
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -305,6 +305,8 @@ and cancellation remain at their established runtime boundaries.

 ## Stage 1 — Add The Dependency And Typed Loading Core

+**Completed:** 2026-09-30.
+
 Scope: module metadata, `internal/configuration` DTOs, real ConfigKit loading,
 and its focused tests. Leave engine assembly on the old path for this stage.

--- a/go.mod
+++ b/go.mod
@@ -3,10 +3,14 @@ module gitea.maximumdirect.net/eric/promptkit
 go 1.25.5

 require (
+	gitea.maximumdirect.net/eric/ConfigKit v0.5.0
 	gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0
 	gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2 v2.20260926.0
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.2
 	gopkg.in/yaml.v3 v3.0.1
 )

-require golang.org/x/text v0.14.0 // indirect
+require (
+	go.yaml.in/yaml/v4 v4.0.0-rc.6 // indirect
+	golang.org/x/text v0.14.0 // indirect
+)
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,5 @@
+gitea.maximumdirect.net/eric/ConfigKit v0.5.0 h1:2KwG10+kApWM3avOoYA+p768xcbHUp7tQ2rqizBNpyg=
+gitea.maximumdirect.net/eric/ConfigKit v0.5.0/go.mod h1:tYWpsrbLyu05r8+1MapWp5fN6ZrX9I8hU2xEPedYmYk=
 gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0 h1:wdab+R+lgMZxzYwhbAuCrW7zdSQ1cW9ovBR6UzLmZR4=
 gitea.maximumdirect.net/eric/promptkit-backend-openrouter/v2 v2.20260926.0/go.mod h1:a3VBbh9oaGXD6ruxhtwHj+AWW6DY/SSyby1QtMmYSUo=
 gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome/v2 v2.20260926.0 h1:baCCIB6Ee5t0S4Zc++NTBIPcJEv5UPS6DlSrpZfykwg=
@@ -6,6 +8,8 @@ github.com/dlclark/regexp2 v1.11.0 h1:G/nrcoOa7ZXlpoa/91N3X7mM3r8eIlMBBJZvsz/mxK
 github.com/dlclark/regexp2 v1.11.0/go.mod h1:DHkYz0B9wPfa6wondMfaivmHpzrQ3v9q8cnmRbL6yW8=
 github.com/santhosh-tekuri/jsonschema/v6 v6.0.2 h1:KRzFb2m7YtdldCEkzs6KqmJw4nqEVZGK7IN2kJkjTuQ=
 github.com/santhosh-tekuri/jsonschema/v6 v6.0.2/go.mod h1:JXeL+ps8p7/KNMjDQk3TCwPpBy0wYklyWTfbkIzdIFU=
+go.yaml.in/yaml/v4 v4.0.0-rc.6 h1:1h7H1ohdUh93/FyE4YaDa1Zh64K6VVbjF4K6WUxMtH4=
+go.yaml.in/yaml/v4 v4.0.0-rc.6/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=
 golang.org/x/text v0.14.0 h1:ScX5w1eTa3QqT8oi6+ziP7dTV1S2+ALU0bI+0zXKWiQ=
 golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
--- a/internal/configuration/load.go
+++ b/internal/configuration/load.go
@@ -0,0 +1,301 @@
+// Package configuration adapts ConfigKit's effective configuration to
+// Promptkit's definition and execution boundaries.
+package configuration
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/ConfigKit"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+	"gitea.maximumdirect.net/eric/promptkit/internal/jsonvalue"
+	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
+)
+
+type document struct {
+	Backends map[string]backendConfig           `yaml:"backends"`
+	Profiles map[string]profileConfig           `yaml:"profiles"`
+	Prompts  map[string]map[string]promptConfig `yaml:"prompts"`
+}
+
+type backendConfig struct {
+	Endpoint         *string        `yaml:"endpoint"`
+	APIKeyEnv        *string        `yaml:"api_key_env"`
+	ConcurrencyLimit *int           `yaml:"concurrency_limit"`
+	QueueCapacity    *int           `yaml:"queue_capacity"`
+	ExtraParams      map[string]any `yaml:"extra_params"`
+}
+
+type profileConfig struct {
+	Backend         *string        `yaml:"backend"`
+	Endpoint        *string        `yaml:"endpoint"`
+	Model           *string        `yaml:"model"`
+	Temperature     *float64       `yaml:"temperature"`
+	TopP            *float64       `yaml:"top_p"`
+	MaxTokens       *int           `yaml:"max_tokens"`
+	TimeoutSeconds  *int           `yaml:"timeout_seconds"`
+	ServiceTier     *string        `yaml:"service_tier"`
+	ReasoningEffort *string        `yaml:"reasoning_effort"`
+	APIKeyEnv       *string        `yaml:"api_key_env"`
+	APIKeyRequired  *bool          `yaml:"api_key_required"`
+	ExtraParams     map[string]any `yaml:"extra_params"`
+}
+
+type promptConfig struct {
+	DefaultProfile *string               `yaml:"default_profile"`
+	Description    *string               `yaml:"description"`
+	SessionID      *string               `yaml:"session_id"`
+	Inputs         []promptInputConfig   `yaml:"inputs"`
+	Messages       []promptMessageConfig `yaml:"messages"`
+	Output         *promptOutputConfig   `yaml:"output"`
+}
+
+type promptInputConfig struct {
+	Name        string `yaml:"name"`
+	Required    bool   `yaml:"required"`
+	ContentType string `yaml:"content_type"`
+	Description string `yaml:"description"`
+}
+
+type promptMessageConfig struct {
+	Role         *string             `yaml:"role"`
+	Content      *string             `yaml:"content"`
+	ContentFile  *string             `yaml:"content_file"`
+	CacheControl *cacheControlConfig `yaml:"cache_control"`
+}
+
+type cacheControlConfig struct {
+	Type *string `yaml:"type"`
+	TTL  *string `yaml:"ttl"`
+}
+
+type promptOutputConfig struct {
+	Format         *string `yaml:"format"`
+	ValidationMode *string `yaml:"validation_mode"`
+	SchemaPath     *string `yaml:"schema_path"`
+	RepairAttempts int     `yaml:"repair_attempts"`
+}
+
+// fieldState distinguishes omission, an explicit value, and an explicit null.
+// Inherited values are explicit because ConfigKit has already expanded them.
+type fieldState uint8
+
+const (
+	fieldAbsent fieldState = iota
+	fieldValue
+	fieldNull
+)
+
+type loaded struct {
+	result   *configkit.Result[document]
+	backends map[string]map[string]fieldState
+	profiles map[string]map[string]fieldState
+}
+
+var envName = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)
+
+var backendFields = []string{"endpoint", "api_key_env", "concurrency_limit", "queue_capacity", "extra_params"}
+var profileFields = []string{"backend", "endpoint", "model", "temperature", "top_p", "max_tokens", "timeout_seconds", "service_tier", "reasoning_effort", "api_key_env", "api_key_required", "extra_params"}
+
+// load performs one ConfigKit lifecycle over the selected source tiers. Engine
+// assembly is intentionally not connected to this adapter yet.
+func load(main configkit.Input, underlays []configkit.Underlay) (*loaded, error) {
+	state := &loaded{
+		backends: make(map[string]map[string]fieldState),
+		profiles: make(map[string]map[string]fieldState),
+	}
+	result, err := configkit.LoadLayered(main, configkit.LayeredOptions[document]{
+		Underlays: underlays,
+		Definition: configkit.Definition[document]{
+			Resolve: func(config *document, resolution *configkit.Resolution) error {
+				captureFields(config.Backends, "backends", backendFields, resolution, state.backends)
+				captureFields(config.Profiles, "profiles", profileFields, resolution, state.profiles)
+				resolveBackends(config.Backends, resolution)
+				resolveProfiles(config.Profiles, resolution)
+				return nil
+			},
+			Validate: validateEffective,
+		},
+	})
+	if err != nil {
+		return nil, fmt.Errorf("load configuration: %w", err)
+	}
+	state.result = result
+	return state, nil
+}
+
+func captureFields[T any](entries map[string]T, collection string, fields []string, resolution *configkit.Resolution, destination map[string]map[string]fieldState) {
+	for id := range entries {
+		states := make(map[string]fieldState, len(fields))
+		for _, field := range fields {
+			info, exists := resolution.InputInfo(configkit.Keys(collection, id, field))
+			switch {
+			case !exists || !info.Explicit:
+				states[field] = fieldAbsent
+			case info.Null:
+				states[field] = fieldNull
+			default:
+				states[field] = fieldValue
+			}
+		}
+		destination[id] = states
+	}
+}
+
+func sortedKeys[T any](entries map[string]T) []string {
+	keys := make([]string, 0, len(entries))
+	for key := range entries {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+func normalizeString(value **string, path configkit.Path, resolution *configkit.Resolution, normalized string) {
+	if value != nil && *value != nil && **value != normalized {
+		configkit.Normalize(resolution, path, value, &normalized, "normalize configuration value")
+	}
+}
+
+func resolveBackends(backends map[string]backendConfig, resolution *configkit.Resolution) {
+	for _, id := range sortedKeys(backends) {
+		backend := backends[id]
+		base := configkit.Keys("backends", id)
+		if backend.Endpoint != nil {
+			endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(*backend.Endpoint)
+			if err != nil {
+				resolution.Error(base.Key("endpoint"), err.Error())
+			} else {
+				normalizeString(&backend.Endpoint, base.Key("endpoint"), resolution, endpoint)
+			}
+		}
+		if backend.APIKeyEnv != nil {
+			normalizeString(&backend.APIKeyEnv, base.Key("api_key_env"), resolution, strings.TrimSpace(*backend.APIKeyEnv))
+		}
+		if backend.ConcurrencyLimit != nil && *backend.ConcurrencyLimit > 0 && backend.QueueCapacity == nil {
+			capacity := 1024
+			if resolution.IsExplicit(base.Key("queue_capacity")) {
+				configkit.Normalize(resolution, base.Key("queue_capacity"), &backend.QueueCapacity, &capacity, "select default queue capacity")
+			} else {
+				configkit.Default(resolution, base.Key("queue_capacity"), &backend.QueueCapacity, &capacity, "select default queue capacity")
+			}
+		}
+		backends[id] = backend
+	}
+}
+
+func resolveProfiles(profiles map[string]profileConfig, resolution *configkit.Resolution) {
+	for _, id := range sortedKeys(profiles) {
+		profile := profiles[id]
+		base := configkit.Keys("profiles", id)
+		if profile.Endpoint != nil && *profile.Endpoint != "" {
+			endpoint, err := domain.NormalizeOpenAICompatibleBaseEndpoint(*profile.Endpoint)
+			if err != nil {
+				resolution.Error(base.Key("endpoint"), err.Error())
+			} else {
+				normalizeString(&profile.Endpoint, base.Key("endpoint"), resolution, endpoint)
+			}
+		}
+		for _, field := range []struct {
+			name  string
+			value **string
+		}{
+			{"service_tier", &profile.ServiceTier},
+			{"reasoning_effort", &profile.ReasoningEffort},
+			{"api_key_env", &profile.APIKeyEnv},
+		} {
+			if *field.value != nil {
+				normalizeString(field.value, base.Key(field.name), resolution, strings.TrimSpace(**field.value))
+			}
+		}
+		profiles[id] = profile
+	}
+}
+
+func validateEffective(config *document, validation *configkit.Validation) {
+	for _, id := range sortedKeys(config.Backends) {
+		backend := config.Backends[id]
+		base := configkit.Keys("backends", id)
+		if strings.TrimSpace(id) == "" {
+			validation.Error(base, "backend ID must not be blank")
+		}
+		if backend.Endpoint == nil || *backend.Endpoint == "" {
+			validation.Error(base.Key("endpoint"), "endpoint is required")
+		}
+		if backend.APIKeyEnv != nil && *backend.APIKeyEnv != "" && !envName.MatchString(*backend.APIKeyEnv) {
+			validation.Error(base.Key("api_key_env"), "environment variable name is invalid")
+		}
+		if backend.ConcurrencyLimit != nil && *backend.ConcurrencyLimit < 0 {
+			validation.Error(base.Key("concurrency_limit"), "concurrency limit must not be negative")
+		}
+		if backend.QueueCapacity != nil {
+			if *backend.QueueCapacity < 0 {
+				validation.Error(base.Key("queue_capacity"), "queue capacity must not be negative")
+			}
+			if backend.ConcurrencyLimit == nil || *backend.ConcurrencyLimit <= 0 {
+				validation.Error(base.Key("queue_capacity"), "queue capacity requires a positive concurrency limit")
+			} else if *backend.QueueCapacity > int(^uint(0)>>1)-*backend.ConcurrencyLimit {
+				validation.Error(base.Key("queue_capacity"), "total capacity overflows int")
+			}
+		}
+		validateExtraParams(backend.ExtraParams, base.Key("extra_params"), true, validation)
+	}
+	for _, id := range sortedKeys(config.Profiles) {
+		profile := config.Profiles[id]
+		base := configkit.Keys("profiles", id)
+		if strings.TrimSpace(id) == "" {
+			validation.Error(base, "profile ID must not be blank")
+		}
+		if profile.Backend != nil && *profile.Backend != "" {
+			if _, exists := config.Backends[*profile.Backend]; !exists {
+				validation.Error(base.Key("backend"), "backend is not defined")
+			}
+		}
+		if profile.Model != nil && *profile.Model != "" && strings.TrimSpace(*profile.Model) == "" {
+			validation.Error(base.Key("model"), "model must not be blank")
+		}
+		if profile.APIKeyEnv != nil && *profile.APIKeyEnv != "" && !envName.MatchString(*profile.APIKeyEnv) {
+			validation.Error(base.Key("api_key_env"), "environment variable name is invalid")
+		}
+		if profile.Temperature != nil {
+			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{Temperature: *profile.Temperature}); err != nil {
+				validation.Error(base.Key("temperature"), err.Error())
+			}
+		}
+		if profile.TopP != nil {
+			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TopP: *profile.TopP}); err != nil {
+				validation.Error(base.Key("top_p"), err.Error())
+			}
+		}
+		if profile.MaxTokens != nil {
+			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{MaxTokens: *profile.MaxTokens}); err != nil {
+				validation.Error(base.Key("max_tokens"), err.Error())
+			}
+		}
+		if profile.TimeoutSeconds != nil {
+			if err := domain.ValidateExecutionTargetSettings(domain.ExecutionTarget{TimeoutSeconds: *profile.TimeoutSeconds}); err != nil {
+				validation.Error(base.Key("timeout_seconds"), err.Error())
+			}
+		}
+		validateExtraParams(profile.ExtraParams, base.Key("extra_params"), false, validation)
+	}
+}
+
+func validateExtraParams(values map[string]any, path configkit.Path, backend bool, validation *configkit.Validation) {
+	if values == nil {
+		return
+	}
+	if _, err := jsonvalue.CopyMap(values); err != nil {
+		validation.Error(path, "extra parameters must be a JSON-compatible map with nonempty keys")
+		return
+	}
+	if backend {
+		for key := range values {
+			if llm.IsReservedOpenAIChatRequestField(key) {
+				validation.Error(path.Key(key), "extra parameter conflicts with a request field")
+			}
+		}
+	}
+}
--- a/internal/configuration/load_test.go
+++ b/internal/configuration/load_test.go
@@ -0,0 +1,138 @@
+package configuration
+
+import (
+	"errors"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+func mapping(label string, values map[string]any) configkit.Input {
+	return configkit.Input{Source: configkit.Mapping(label, values)}
+}
+
+func TestLoadComposesLiteralKeysAndEffectivePresence(t *testing.T) {
+	base := mapping("defaults", map[string]any{
+		"backends": map[string]any{
+			"local.v1": map[string]any{"endpoint": "http://localhost:8080/v1", "concurrency_limit": 2},
+		},
+		"profiles": map[string]any{
+			"base/one": map[string]any{"backend": "local.v1", "temperature": 0.8, "top_p": 0.9, "api_key_required": true,
+				"extra_params": map[string]any{"provider": map[string]any{"first": 1, "second": 2}}},
+			"child.v1": map[string]any{"extends": "base/one"},
+		},
+		"prompts": map[string]any{"invoice/summary": map[string]any{"v1.0": map[string]any{
+			"messages": []any{map[string]any{"role": "user", "content": "Summarize."}},
+			"output":   map[string]any{"format": "text", "validation_mode": "basic"},
+		}}},
+	})
+	overlay := mapping("operator", map[string]any{
+		"backends": map[string]any{"local.v1": map[string]any{"queue_capacity": 0}},
+		"profiles": map[string]any{"child.v1": map[string]any{
+			"temperature": 0, "top_p": nil, "api_key_required": false,
+			"extra_params": map[string]any{"provider": map[string]any{"second": 3}},
+		}},
+	})
+	loaded, err := load(configkit.Input{Source: configkit.NoSource()}, []configkit.Underlay{
+		{Inputs: []configkit.Input{base}}, {Inputs: []configkit.Input{overlay}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	profile := loaded.result.Config.Profiles["child.v1"]
+	if profile.Temperature == nil || *profile.Temperature != 0 || profile.TopP != nil || profile.APIKeyRequired == nil || *profile.APIKeyRequired {
+		t.Fatalf("effective values were not retained: %+v", profile)
+	}
+	if loaded.profiles["child.v1"]["temperature"] != fieldValue || loaded.profiles["child.v1"]["top_p"] != fieldNull || loaded.profiles["child.v1"]["api_key_required"] != fieldValue {
+		t.Fatalf("effective presence was lost: %+v", loaded.profiles["child.v1"])
+	}
+	provider := profile.ExtraParams["provider"].(map[string]any)
+	if provider["first"] != int64(1) || provider["second"] != int64(3) {
+		t.Fatalf("recursive overlay failed: %+v", provider)
+	}
+	backend := loaded.result.Config.Backends["local.v1"]
+	if backend.QueueCapacity == nil || *backend.QueueCapacity != 0 || loaded.backends["local.v1"]["queue_capacity"] != fieldValue {
+		t.Fatalf("explicit zero queue capacity was lost: %+v", backend)
+	}
+	if loaded.result.Config.Prompts["invoice/summary"]["v1.0"].Messages[0].Content == nil {
+		t.Fatal("literal prompt ID and version were not decoded")
+	}
+}
+
+func TestLoadRecordsBackendNormalizationAndNullDefault(t *testing.T) {
+	loaded, err := load(mapping("backend", map[string]any{"backends": map[string]any{
+		"local": map[string]any{"endpoint": " HTTP://localhost:8080/v1 ", "api_key_env": " TOKEN_NAME ",
+			"concurrency_limit": 2, "queue_capacity": nil},
+	}}), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	backend := loaded.result.Config.Backends["local"]
+	if backend.Endpoint == nil || *backend.Endpoint != "http://localhost:8080/v1" ||
+		backend.APIKeyEnv == nil || *backend.APIKeyEnv != "TOKEN_NAME" ||
+		backend.QueueCapacity == nil || *backend.QueueCapacity != 1024 {
+		t.Fatalf("backend normalization/default was not applied: %+v", backend)
+	}
+	if loaded.backends["local"]["queue_capacity"] != fieldNull {
+		t.Fatalf("explicit null was not retained: %+v", loaded.backends["local"])
+	}
+}
+
+func TestLoadDefaultsAbsentQueueCapacity(t *testing.T) {
+	loaded, err := load(mapping("backend", map[string]any{"backends": map[string]any{
+		"local": map[string]any{"endpoint": "http://localhost:8080/v1", "concurrency_limit": 1},
+	}}), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	backend := loaded.result.Config.Backends["local"]
+	if backend.QueueCapacity == nil || *backend.QueueCapacity != 1024 || loaded.backends["local"]["queue_capacity"] != fieldAbsent {
+		t.Fatalf("absent queue capacity did not receive its default: %+v", backend)
+	}
+}
+
+func TestLoadRejectsStrictGroupConflict(t *testing.T) {
+	_, err := load(configkit.Input{Source: configkit.NoSource()}, []configkit.Underlay{{Inputs: []configkit.Input{
+		mapping("first", map[string]any{"profiles": map[string]any{"shared": map[string]any{"model": "one"}}}),
+		mapping("second", map[string]any{"profiles": map[string]any{"shared": map[string]any{"model": "one"}}}),
+	}}})
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) {
+		t.Fatalf("expected ConfigKit load error, got %v", err)
+	}
+}
+
+func TestLoadValidatesOnlyFinalDomainValues(t *testing.T) {
+	underlay := mapping("defaults", map[string]any{
+		"backends": map[string]any{"local": map[string]any{"endpoint": "not a URL"}},
+		"profiles": map[string]any{"partial": map[string]any{"backend": "local"}},
+	})
+	main := mapping("operator", map[string]any{"backends": map[string]any{"local": map[string]any{"endpoint": "http://localhost:8080/v1"}}})
+	loaded, err := load(main, []configkit.Underlay{{Inputs: []configkit.Input{underlay}}})
+	if err != nil {
+		t.Fatalf("replaced lower-layer domain value should not fail: %v", err)
+	}
+	if loaded.result.Config.Profiles["partial"].Model != nil {
+		t.Fatal("unused partial profile unexpectedly gained a model")
+	}
+
+	_, err = load(configkit.Input{Source: configkit.NoSource()}, []configkit.Underlay{{Inputs: []configkit.Input{
+		mapping("invalid", map[string]any{"backends": map[string]any{"unused": map[string]any{"endpoint": "not a URL"}}}),
+	}}})
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) {
+		t.Fatalf("expected path-aware effective backend failure, got %v", err)
+	}
+	if diagnostics := loadError.Diagnostics(); len(diagnostics) != 1 || diagnostics[0].Path.String() != "/backends/unused/endpoint" {
+		t.Fatalf("expected endpoint diagnostic, got %+v", diagnostics)
+	}
+}
+
+func TestLoadKeepsSyntaxErrorsFromLowerTiers(t *testing.T) {
+	_, err := load(mapping("operator", map[string]any{"backends": map[string]any{"local": map[string]any{"endpoint": "http://localhost:8080"}}}),
+		[]configkit.Underlay{{Inputs: []configkit.Input{{Source: configkit.Bytes("broken", []byte("backends: ["))}}}})
+	var loadError *configkit.LoadError
+	if !errors.As(err, &loadError) {
+		t.Fatalf("expected lower-tier parsing error, got %v", err)
+	}
+}