[builder] lock heartbeat -> embedding

faiss_index/build_run_lock.json

@@ -4,7 +4,7 @@
   "stage": "embedding",
   "status": "building",
   "started_at": null,
-  "updated_at": "2026-05-17T16:10:13.824415+00:00",
+  "updated_at": "2026-05-17T16:13:47.687346+00:00",
   "completed_at": null,
   "dataset_repo": "diatribe00/ItalianLawEngine"
 }