Apply sequence policy across loading tiers

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Sequence Placement and Composition
 
-Status: implementation in progress; stages 1–8 completed.
+Status: implementation in progress; stages 1–9 completed.
 
 ## Purpose and authority
 
@@ -543,6 +543,21 @@ Validation: load/grouped/overlay/override/resolution/default tests and
 `./scripts/check.sh`. Completion: private engine policy is applied at strict
 composition boundaries only, including the one-source case.
 
+Completion evidence: compiled sequence policy now reaches ordinary input
+composition, imported scopes, and each underlay group. Registered sequences
+are checked even for one-source loads and before tier replacement; identity
+state resets at tier boundaries, while replacement overlays, CLI values, and
+recorded resolver results retain their existing behavior. Lifecycle tests cover
+grouped composition, empty-list replacement, unregistered conflicts, malformed
+lower tiers hidden by main or overlay replacement, duplicate replacements, and
+application validation. These checks passed with Go `go1.26.9 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test ./internal/engine -run 'SequenceRegistration|Import|Grouped|Overlay|Override|Resolution|Default' -count=1`
+- `GOTOOLCHAIN=local ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 10 — Preserve source-version and structural ownership under placement
 
 Scope: version path projection and existing protected-path checks.