A bare .stream() over calls/ returned 503 "Query timed out. Please try either limiting the entities scanned", which the Firestore client then re-raised as an AttributeError from its own retry path -- so the real cause was only visible in the chained traceback. The collection has simply outgrown a single scan. Both passes now walk each collection in 500-document pages ordered by document id, which needs no composite index. The counting pass also stops building a list of every document just to count the ones missing org_id. Documents written mid-run may be missed or seen twice; neither matters, since post-tenancy code stamps org_id at write time and the update is idempotent, so a second run cleans up anything the first skipped. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>