Compose registered sequences by identity

docs/roadmap/implementation.md

@@ -256,6 +256,22 @@ Scope: `internal/engine/compose.go` and focused composition tests.
 Validation: composition tests and `./scripts/check.sh`. Completion: the private
 composer returns the correct tree and range projection without aliasing inputs.
 
+Completion evidence: added a policy-aware private composer while retaining the
+unregistered adapter. Registered sequences validate every actual contribution,
+including singleton and empty lists; distinct records append in source/list
+order, duplicate exact string identities fail, and other overlap kinds retain
+strict-conflict behavior. The result carries per-source sequence ranges for
+later projection. Tests cover malformed identity records, within/across-list
+duplicates including empty IDs and differing bodies, absent/non-sequence paths,
+empty lists, unregistered conflicts, and input/result ownership. These checks
+passed with Go `go1.26.9 linux/amd64`:
+
+- `GOTOOLCHAIN=local GOPROXY=off go test ./internal/engine -run 'Compose' -count=1`
+- `GOTOOLCHAIN=local ./scripts/check.sh`
+- `git diff --check`
+
+No environmental limitation affected validation; checks ran on Linux/amd64.
+
 ## Stage 3 — Project composition origins and claims onto appended indexes
 
 Scope: composition evidence, not import acquisition.