Check source versions in direct underlays

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implement shared source version checks
 
-Status: Stages 1–5 complete; direct underlay integration has not started.
+Status: Stages 1–6 complete; selected overlay integration 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
@@ -379,6 +379,26 @@ No environmental limitation affected validation; checks ran on Linux/amd64.
 Validate: grouped/underlay/destination/version tests and everyday check. Done:
 direct and imported underlays follow the same checking policy.
 
+Completion evidence: threaded the per-load version state through direct underlay
+group acquisition and invoked the shared processor with contribution semantics
+for each acquired underlay root. Its own processed payload/import declarations
+now drive placement and recursive imports, while remaining placed payload is
+still checked against the effective main-owned path before strict composition.
+Warnings are accumulated through underlay groups; source records retain their
+layer and group index, and the existing accounting, context, and reusable-source
+paths remain in place. Added coverage for distinct declarations within one
+strict group, warning retention across groups, rejected declarations beneath a
+later main value, required omissions, empty groups and NoSource, mounted nested
+headers/imports, and protected remaining payload. Existing default underlay
+version-protection coverage remains passing. These checks passed with Go
+`go1.26.8 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test ./internal/engine -run 'SourceVersion|Version|Import|Underlay|Overlay|Destination' -count=1`
+- `GOTOOLCHAIN=local ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 7 — Integrate selected overlays and final ownership checks
 
 1. Process overlay headers after parse/structural validation, before remaining