fix(backup): fit live reconcile idempotency key

apps/api/tests/test_backup_restore_legacy_backfill_job.py

@@ -576,6 +576,16 @@ async def test_live_reconciler_reserves_only_unowned_incomplete_cards(
     assert "backup-signal:" in sql
 
 
+def test_live_reconciler_idempotency_channel_fits_durable_schema() -> None:
+    # awooop_run_idempotency.channel_type is VARCHAR(32).  This invariant must
+    # be checked without relying on a mock database, which cannot reproduce a
+    # production PostgreSQL 22001 truncation error.
+    assert job.LIVE_RECONCILE_IDEMPOTENCY_CHANNEL == (
+        "backup_restore_live_reconcile"
+    )
+    assert len(job.LIVE_RECONCILE_IDEMPOTENCY_CHANNEL) <= 32
+
+
 @pytest.mark.asyncio
 async def test_live_reconciler_projects_bounded_agent99_receipt(
     monkeypatch: pytest.MonkeyPatch,