Clarify collection contracts and migration docs

docs/roadmap/implementation.md

@@ -782,6 +782,16 @@ Validation: review changed Markdown links and example references, check GoDoc
 against declarations, and run `git diff --check`. Release notes and version/tag
 selection belong to the later requested release preparation, not this stage.
 
+Completion: canonical format, consumer, README, internal, and public GoDoc
+contracts now describe collection identity, source headers and origins,
+namespace-scoped selection, global inventories, descriptive labels, and
+caller-supplied provider configuration. Reviewed architecture, release policy
+and procedure, development guidance, and attribution; no additional local
+changes were needed, and historical release notes and immutable ADRs remain
+unchanged. Validation passed: local Markdown link targets and example references
+were reviewed, affected GoDoc was checked against declarations, and
+`git diff --check`.
+
 ## Stage 18: Verify Cross-Boundary Behavior And Close The Sprint
 
 Scope: focused integration gaps and final regression validation, not new features.