test(workflows): guard dead in-memory background machinery stays deleted

src/backend/base/langflow/api/v2/workflow.py

@@ -246,10 +246,10 @@ async def execute_workflow(
             )
 
         if parsed.mode == "background":
-            # Background owns its own adapter construction inside
-            # ``_buffer_background_run`` because the fire-and-forget coroutine
-            # needs its own ``StreamAdapterContext`` (different ``run_id``).
-            # The name-only check above already covered the 422 contract.
+            # Background runs are delegated to BackgroundExecutionService via
+            # ``execute_workflow_background``. The facade creates the durable job
+            # row, persists the request, enqueues the work, and owns ownership /
+            # IDOR. The name-only check above already covered the 422 contract.
             return await execute_workflow_background(
                 parsed=parsed,
                 flow=flow,

src/backend/tests/unit/api/v2/test_workflow_facade.py

@@ -323,3 +323,28 @@ class TestNoBreakingChange:
         assert response.status_code == 200
         event_ids = [line.removeprefix("id:").strip() for line in response.text.splitlines() if line.startswith("id:")]
         assert "0" not in event_ids
+
+
+class TestDeadMachineryRemoved:
+    """The process-local background buffer machinery is gone after the cutover.
+
+    ``execute_workflow_background`` is intentionally kept: it is now a thin
+    facade-delegating wrapper (builds the request dict, threads idempotency_key),
+    not the old in-memory run loop, so it is NOT in this list.
+    """
+
+    def test_in_memory_background_machinery_is_deleted(self):
+        """The old _BackgroundRun buffer and its helpers no longer exist."""
+        from langflow.api.v2 import workflow as wf
+
+        for name in (
+            "_BackgroundRun",
+            "_BACKGROUND_RUNS",
+            "_register_background_run",
+            "_clear_background_run",
+            "_buffer_background_run",
+            "_finalize_job_status",
+            "_MAX_BACKGROUND_RUNS",
+            "_MAX_FRAMES_PER_BACKGROUND_RUN",
+        ):
+            assert not hasattr(wf, name), f"{name} should have been deleted in the facade cutover"