Unify layered provenance history

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 ## Status and ownership
 
-Status: implementation in progress; Stages 1–13 are complete and later stages are
+Status: implementation in progress; Stages 1–14 are complete and later stages are
 pending.
 
 Audience: a `gpt-5.6-terra` coding agent implementing one stage per prompt, in
@@ -1038,7 +1038,31 @@ Acceptance:
 
 ## Stage 14 — Verify layered provenance and final snapshot agreement
 
-Status: pending.
+Status: complete.
+
+Completion evidence (2026-09-06):
+
+- Unified default, composed base, profile displacement, and resolution records in
+  the metadata history index. Container resolution now appends its operation to each
+  changed, added, or removed descendant while preserving the ancestor operation path
+  and path-specific previous origin; effective metadata still contains only the final
+  projected paths.
+- Added a representative public `Load` workflow spanning a fresh default, selected
+  source, depth-first import, profile, derived default, mapping deletion, and
+  whole-sequence normalization. It verifies source order, equal-to-default
+  explicitness, null state, composite empty-mapping origins, chronological parent
+  replacement history, deduplicated reasons/dependencies, typed/final snapshot
+  agreement, and unchanged siblings.
+- Verified nested metadata, source import locations, diagnostics, caller-owned
+  configuration, and private snapshots are detached. Repeated concurrent selected-
+  profile loads retain independent typed values, metadata, sources, and histories;
+  the race baseline passes.
+- Promoted layered metadata semantics and concrete composite/synthetic origin cases
+  to the [current metadata contract](../config.md#layered-metadata), updated Go
+  reference comments, and recorded the adapted Narratio ownership/inspection cases.
+  Rendering, redaction, value snapshots, and explanation remain within later stages.
+  Verified `go test ./...`, `go test -race ./...`, `go vet ./...`, `go build ./...`,
+  `go mod tidy -diff`, and `git diff --check` with Go 1.26.7 on linux/amd64.
 
 Read: feature [presence](initial.md#paths-and-presence),
 [history](initial.md#provenance-diagnostics-and-redaction), metadata API.