refactor: retain workflow as optional editor

docs/ENGINE_EDITOR_SPLIT.md

@@ -118,3 +118,20 @@ but the canonical baseline remains available.
 The extraction must preserve existing definition IDs, revision IDs, active
 revision selection, instance foreign keys, idempotency keys, API routes, and
 audit references.
+
+## Implemented Boundary
+
+The split is implemented in the `govoplan-workflow-engine` repository. Engine
+owns the unchanged migration chain and `/api/v1/workflow` API, retains the
+existing `workflow:*` permission namespace through an explicit manifest
+compatibility field, and exposes headless runtime and contribution
+capabilities. `govoplan-workflow` now has a hard dependency on runtime module
+ID `workflow_engine`, contributes only its WebUI/navigation/editor contract,
+and keeps one release line of `govoplan_workflow.backend` import facades.
+
+Module manifests can announce versioned workflow baselines. Reconciliation is
+idempotent, records module/schema/hash provenance, keeps a newly supplied
+baseline revision inactive when an older revision is active, and fails closed
+when required capabilities or interfaces are absent. Baselines are immutable;
+editing derives a pinned local override, and reset archives that override
+without removing revision or instance history.