Record shared source version policy

docs/adr/0013-shared-source-version-checks.md

@@ -0,0 +1,89 @@
+# ADR 0013: Check Source Versions with One Shared Policy
+
+## Status
+
+Accepted. The [shared source-version roadmap](../roadmap/source-version-checks.md)
+owns target behavior, and its [implementation plan](../roadmap/implementation.md)
+owns delivery status and sequencing.
+
+## Date
+
+2026-10-15
+
+## Context
+
+Applications that assemble one configuration from independently authored
+documents need a way to require that each contributing document declares a
+version accepted by the application's existing `Definition.Version` checker.
+Checking only the eventual composed value lets another source hide a rejected
+declaration, while separate consumer-side parsing duplicates ConfigKit's source
+handling and diagnostics.
+
+The extension must preserve one application-owned acceptance policy and the
+existing loading lifecycle. Source declarations are compatibility evidence, not
+independent fragment schemas or values to compare for equality. Existing
+composition, placement, precedence, source identity, diagnostics, and
+sensitivity rules remain authoritative.
+
+## Decision
+
+Provide a load-wide source-version mode for ordinary and layered loading. The
+zero-value mode preserves current behavior. The enabled modes check declarations
+when present or require them, using the existing `Definition.Version` path and
+checker. Interpret the configured path relative to each participating source
+before placement or composition. Different declarations may be accepted by the
+same checker; ConfigKit adds no equality, SemVer, or expected-version rule.
+
+Apply the selected policy to the actual main document, direct underlays,
+imports, and selected overlays. Missing non-main declarations are skipped in
+if-present mode and rejected in required mode. Existing main absence behavior
+remains, with required mode additionally rejecting an absent declaration on an
+actual main document. `NoSource`, unmatched optional inputs, synthetic field
+operations, and empty groups do not become documents that need declarations.
+
+Reuse the existing version vocabulary and validation boundary: absence, null,
+exact strings, and strict decimal integers retain their established meanings;
+unsupported present values fail version-type validation. Warnings remain
+nonfatal, and source declarations do not replace final application decoding or
+domain validation.
+
+After an accepted non-main declaration is checked, consume exactly that node
+before its remaining application content is composed or overlaid. Preserve the
+main declaration and its value semantics. Keep the declaration, source-local
+path, physical location, and checked absence as detached source evidence,
+separate from effective application values and history. Apply established
+sensitivity rules to that evidence, including original mounted paths and
+ancestors; retain existing safe failure disclosure.
+
+In enabled modes, the main declaration remains source-local while its protected
+application path is derived from the main input's destination. This distinction
+does not change default-mode path interpretation or weaken protection of
+remaining payload and synthetic operations.
+
+Public option-field additions and the enabled-mode interpretation for mounted
+main inputs are compatibility considerations for separately authorized minor-
+release preparation. This decision does not select a release version or
+authorize release notes or publication.
+
+## Alternatives Considered
+
+- **Check only the final composed value.** Later sources can hide an earlier
+  rejected declaration, so this does not validate every contributing document.
+- **Let consumers parse and check each source.** This duplicates acquisition,
+  source attribution, safe diagnostics, and lifecycle coordination in every
+  application.
+- **Require declarations to be equal or impose a universal version grammar.**
+  Consumers already own the acceptance policy; ConfigKit need not invent an
+  expected value or a domain-specific compatibility rule.
+- **Keep accepted non-main declarations in application payload.** A selected
+  source-local declaration is metadata for this policy and cannot also remain
+  an ordinary field at the same path without ambiguity.
+
+## Consequences
+
+Consumers can apply one existing version policy across contributing documents
+and select gradual or required adoption per load. Accepted non-main headers no
+longer participate in application composition; their inspectable evidence is
+kept separate and subject to sensitivity classification. Default callers retain
+current behavior. The implementation plan records the concrete API names,
+integration order, and validation evidence.

docs/development.md

@@ -50,6 +50,7 @@ public behavior.
 Accepted decisions:
 
 - [Separate composition and overlay](adr/0001-separate-composition-and-overlay.md)
+- [Check source versions with one shared policy](adr/0013-shared-source-version-checks.md)
 - [Own YAML semantics behind a private parser boundary](adr/0002-own-yaml-semantics.md)
 - [Preserve presence and record application resolution](adr/0003-preserve-presence-and-resolution-history.md)
 - [Secret references and explicit bootstrap](adr/0004-secret-references-and-explicit-bootstrap.md)

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implement shared source version checks
 
-Status: planned; no implementation stages are complete.
+Status: Stage 1 complete; runtime implementation has not started.
 
 Audience: a Luna coding agent implementing one numbered stage per prompt, in
 order. The [feature roadmap](source-version-checks.md) owns target behavior and
@@ -219,6 +219,15 @@ git diff --check
 Validate: local-link test and whitespace. Done: baseline and accepted decision
 recorded, with no runtime changes.
 
+Completion evidence: reviewed baseline `d9f08ff7198ad5a8fb5c49a43e7ccdad2ad0e707`
+and the clean implementation worktree at `70c95bf660794809e58182d736c67c9085238705`;
+confirmed ADR 0013 was unused. The everyday check passed with Go
+`go1.26.8 linux/amd64` using
+`GOTOOLCHAIN=local GOPROXY=off ./scripts/check.sh`. Documentation links and
+whitespace are validated for this unit. No environmental limitation affected
+these checks; validation was performed on Linux/amd64 only. No runtime changes
+were made.
+
 ## Stage 2 — Share version interpretation without changing defaults
 
 1. Separate reusable value interpretation and callback reporting from checkVersion,

docs/roadmap/source-version-checks.md

@@ -1,6 +1,7 @@
 # Shared Source Version Checks Roadmap
 
-Status: design decisions settled; implementation has not started. The
+Status: design decisions are recorded in [ADR 0013](../adr/0013-shared-source-version-checks.md);
+implementation has not started. The
 [implementation plan](implementation.md) owns execution order, concrete API and
 integration decisions, and completion evidence. This roadmap develops the
 partially accepted source-version request in