Retain ordered acquisition scopes

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Sequence Placement and Composition
 
-Status: implementation in progress; stages 1–5 completed.
+Status: implementation in progress; stages 1–6 completed.
 
 ## Purpose and authority
 
@@ -414,6 +414,20 @@ Scope: `imports.go`, `load_input.go`, `load_request.go`, and their handoffs.
 Validation: import/destination/grouped/source-version/resource-context tests and
 `./scripts/check.sh`. Completion: this is a behavior-preserving private refactor.
 
+Completion evidence: acquisition now retains ordered ordinary-mapping scopes
+with source-local payloads, placed contributions, destinations, source records,
+and source-version processing results. Underlay groups compose those acquired
+contributions at their boundary instead of treating retained history values as
+complete roots. Existing filesystem contexts, import traversal/repetition
+state, load-wide accounting, hooks, and lifecycle handling remain in their
+existing paths. These checks passed with Go `go1.26.9 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test ./internal/engine -run 'Destination|Import|Grouped|SourceVersion|Resource' -count=1`
+- `GOTOOLCHAIN=local ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 7 — Add the private item-placement operation and accounting
 
 Scope: placement primitives and engine per-input options; not public exposure.