Record underlay group scheduling completion

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Import Discovery and Dependency-Ready Ordering
 
-Status: Stages 1–6 complete; 13 implementation stages remain.
+Status: Stages 1–7 complete; 12 implementation stages remain.
 
 ## Authority, baseline, and execution
 
@@ -367,6 +367,13 @@ uses the expected schedule; separate tiers still replace sequences wholesale.
 Test same-label distinct native namespaces and copies of one namespace. NoSource
 still contributes no source or explicit empty root.
 
+Completion: implemented in commit `014b995` (`Schedule underlay groups as
+dependency forests`). Verified with `go test ./internal/engine -count=1`,
+`go test . -count=1`, `go test -race ./internal/engine`, `go vet ./...`,
+`go build ./...`, the local documentation-link test, and `git diff --check`.
+`./scripts/check.sh` still reaches only the two prompt-catalog ordering
+expectations assigned to Stage 18. Stage 8 onward remains.
+
 ## Stage 8 — Define private defaults and the final declaration parser
 
 Add the private defaults snapshot/validation and resolved-policy helpers. Add