Expose sequence placement controls in the public API

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Sequence Placement and Composition
 
-Status: implementation in progress; stages 1–10 completed.
+Status: implementation in progress; stages 1–11 completed.
 
 ## Purpose and authority
 
@@ -658,6 +658,25 @@ Validation: focused facade tests,
 Completion: both public entry points expose the complete feature with the same
 composition rules and independently owned evidence.
 
+Completion evidence: the root facade now exposes sequence registrations,
+ordinary and layered placement controls, and detached placement-mode and
+destination-resolution source evidence. Public integration coverage exercises
+ordinary/layered placement, strict registration with authored and glob-imported
+items, shifted origins and resource contexts, option preflight, early and
+post-placement failure snapshots, nested fallback containers, registration and
+snapshot ownership, and zero-value mapping behavior. The existing resolver
+callback runs after item projection, so its source snapshots are exact; the
+unresolved helper fallback is observable on early failure. No acquisition-time
+callback exposes `SourceInfo`, and no additional callback lifecycle was added.
+These checks passed with Go `go1.26.9 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test . -run 'TestPublicFacadeBoundary|TestDependencyImportBoundary' -count=1`
+- `GOTOOLCHAIN=local GOPROXY=off go test -race ./...`
+- `GOTOOLCHAIN=local GOPROXY=off ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 12 — Close cross-cutting regression and limit gaps
 
 Scope: risks that require the assembled feature, not duplicate mechanism tests.