Document ConfigKit sibling inheritance

docs/config.md

@@ -4,6 +4,8 @@ This reference describes the version-2 configuration loader in `internal/core/co
 Use the maintained [local](../examples/minimal-config.yml) and
 [service](../examples/production-config.yml) examples with their PromptKit
 [profiles](../examples/profiles/) and optional [testing overlay](../examples/overlays/testing.yml).
+The [ConfigKit inheritance example](../examples/configkit-inheritance.yml)
+shows a local child backend reusing and overriding sibling settings.
 Choose real models for your endpoint; a testing profile makes no cost or quality
 guarantee. See the [migration guide](migrations/v2.md) for retired inputs.
 
@@ -20,6 +22,33 @@ and secret-directory bootstrap are disabled. Unknown fields and missing, null,
 or non-integer `version: 2` are errors. Version-1 files require migration; no
 compatibility loader or implicit environment configuration remains.
 
+After overlay and explicit CLI override precedence is applied, ConfigKit resolves
+native sibling inheritance before typed decoding. Any input mapping may use
+`extends: <sibling-name>`; the child keeps its key, inherits parent settings, and
+overrides them with its own settings. Selected overlay and CLI values therefore
+participate in inheritance at their normal precedence. The generic syntax and
+resolution rules are defined by ConfigKit v0.5.0's
+[sibling inheritance contract](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.5.0/docs/config.md#sibling-inheritance).
+
+`extends` is reserved structural input in base files, imports, overlays, and
+other application input mappings, including mapping values supplied by explicit
+CLI setting overrides. ConfigKit consumes it before typed decoding. A previously
+valid backend whose ID is literally `extends` cannot be represented under this
+rule. Rename that backend to a non-conflicting ID and update every PromptKit
+profile that selects it. This compatibility impact means the upgrade does not
+promise that every previously valid configuration remains valid. PromptKit
+profile documents keep their existing syntax and do not gain ConfigKit
+inheritance.
+
+Inherited values count as explicit input, including zero, false, empty, and
+null. Existing field rules still apply: for example, inherited backend
+concurrency must be positive, while an inherited queue capacity of zero is
+valid. Parent backends undergo the same decoding and application validation as
+other backends, whether or not a selected profile uses them. A child
+`credential: null` removes the child's inherited credential; it does not remove
+the parent's credential reference, which remains subject to ordinary secret
+resolution.
+
 Validation runs after overlays, explicit overrides, and derived settings have
 resolved. An override can therefore repair an invalid lower-precedence setting
 when that setting can be decoded. ConfigKit retains field origins and derivations

docs/internal/cli-config.md

@@ -35,9 +35,11 @@ From the repository root, validate the maintained configuration examples:
 
 ```sh
 go run ./cmd/audita config validate --config examples/minimal-config.yml
+go run ./cmd/audita config validate --config examples/configkit-inheritance.yml
 AUDITA_SERVICE_KEY=synthetic-example go run ./cmd/audita config validate --config examples/production-config.yml
 AUDITA_SERVICE_KEY=synthetic-example go run ./cmd/audita config validate --config examples/production-config.yml --overlay testing
 go run ./cmd/audita config print-effective --config examples/minimal-config.yml --view profiles
+go run ./cmd/audita config print-effective --config examples/configkit-inheritance.yml --view explain
 ```
 
 Only referenced credentials read environment values; use a controlled synthetic

docs/roadmap/configkit.md

@@ -2,10 +2,11 @@
 
 **Last updated:** 2026-10-03
 
-**Status:** Planned; implementation has not begun. The dependency-only review
-passed Audita's existing offline test suite in a disposable checkout. That is
-baseline compatibility evidence, not completion of the feature. The
-[implementation plan](implementation.md) owns the ordered work and verification.
+**Status:** Complete. The implementation and tests are committed through
+`8175ed8`. Final documentation and example changes were included in the full
+build, test, example-validation, and local-link checks before the documentation
+completion commit. The [implementation plan](implementation.md) records the
+ordered work and verification.
 
 ## Purpose and Baseline
 

docs/roadmap/implementation.md

@@ -1,7 +1,7 @@
 # Implementation Plan: ConfigKit v0.5.0 Adoption
 
 **Last updated:** 2026-10-03
-**Status:** Ready for implementation.
+**Status:** Complete.
 **Audience:** Luna coding agent.
 
 ## Scope and Execution
@@ -195,6 +195,8 @@ risk, then commit the runtime/CLI verification unit.
 
 ## Stage 5 — Document Native Inheritance and Close the Adoption Unit
 
+**Completion:** Complete.
+
 **Primary files:** `docs/config.md`, `examples/configkit-inheritance.yml`,
 `docs/internal/cli-config.md`, and `docs/roadmap/configkit.md`. Update another
 canonical document only where an implemented statement actually changes.

examples/configkit-inheritance.yml

@@ -0,0 +1,14 @@
+version: 2
+backends:
+  local-base:
+    endpoint: http://127.0.0.1:11434/v1
+    concurrency: 4
+    queue_capacity: 0
+  local:
+    extends: local-base
+    concurrency: 2
+llm:
+  proposal_profile: local-proposal
+  validation_profile: local-validation
+pipeline:
+  modules: [grammar]