build: integrate workflow engine repository

tools/checks/check_dependency_boundaries.py

@@ -109,9 +109,36 @@ class AllowlistedImport:
     reason: str
 
 
-# Transitional exceptions. This should remain empty; add entries only with a
-# dated removal plan and a capability/API contract issue.
-ALLOWLIST: tuple[AllowlistedImport, ...] = ()
+# Transitional exceptions. This should remain empty outside explicit,
+# time-bounded compatibility facades with a tracked removal issue.
+_WORKFLOW_ENGINE_COMPATIBILITY_FACADES = (
+    "backend/bpmn.py",
+    "backend/bpmn_adapters.py",
+    "backend/bpmn_graph.py",
+    "backend/db/__init__.py",
+    "backend/db/models.py",
+    "backend/governance.py",
+    "backend/instance_service.py",
+    "backend/manifest.py",
+    "backend/node_library.py",
+    "backend/router.py",
+    "backend/runtime.py",
+    "backend/schemas.py",
+    "backend/service.py",
+    "backend/validation.py",
+)
+ALLOWLIST: tuple[AllowlistedImport, ...] = tuple(
+    AllowlistedImport(
+        owner="govoplan-workflow",
+        relative_path=relative_path,
+        imported_owner="govoplan-workflow-engine",
+        reason=(
+            "One-release Engine extraction facade; remove for 0.2 under "
+            "govoplan-workflow#14 and govoplan-core#40."
+        ),
+    )
+    for relative_path in _WORKFLOW_ENGINE_COMPATIBILITY_FACADES
+)
 ALLOWLIST_KEYS = {(item.owner, item.relative_path, item.imported_owner) for item in ALLOWLIST}