[builder] lock heartbeat -> embedding

faiss_index/build_run_lock.json

@@ -4,7 +4,7 @@
   "stage": "embedding",
   "status": "building",
   "started_at": null,
-  "updated_at": "2026-05-17T15:15:20.167449+00:00",
+  "updated_at": "2026-05-17T15:17:29.999908+00:00",
   "completed_at": null,
   "dataset_repo": "diatribe00/ItalianLawEngine"
 }