fix(test): test_849 expects 3 begin_nested/lot after upsert-reconcile SAVEPOINT (#1921)

197068c (#1921) added a per-lot SAVEPOINT around the listings upsert to catch
IntegrityError on UNIQUE(source,source_id) (migration 133) and reconcile via UPDATE.
That's a legit 3rd begin_nested/lot (upsert + snapshot + hook), so the test's
== 2*len(lots) proxy was stale → red main gate blocking all tradein deploys.
Hook itself still opens no inner SAVEPOINT (base.py:715) — test intent preserved.

tradein-mvp/backend/tests/test_849_matching_savepoint.py

@@ -309,13 +309,16 @@ class TestSingleSavepointBatchIsolation:
 
         save_listings(db, lots)
 
-        # save_listings calls begin_nested once per lot for the snapshot
-        # and once per lot for the hook — so 2 * len(lots) total.
-        # If _link_listing_to_house opens an INNER begin_nested too,
-        # the count would be > 2 * len(lots).
-        # (snapshot SAVEPOINT + hook SAVEPOINT = 2 per lot, no extra inner)
-        assert db.begin_nested.call_count == 2 * len(lots), (
-            f"Expected exactly 2 begin_nested per lot (snapshot + hook outer), "
+        # save_listings calls begin_nested THREE times per lot:
+        #   1) upsert SAVEPOINT — ловит IntegrityError на UNIQUE(source,source_id)
+        #      (migration 133) при dedup_hash-дрейфе → rollback + прямой UPDATE (#1921);
+        #   2) snapshot SAVEPOINT;
+        #   3) hook SAVEPOINT (_link_listing_to_house).
+        # If _link_listing_to_house opened an INNER begin_nested too,
+        # the count would be > 3 * len(lots). The intent of this test (no double-nesting
+        # INSIDE the hook) holds — base.py keeps exactly one SAVEPOINT level in the hook.
+        assert db.begin_nested.call_count == 3 * len(lots), (
+            f"Expected exactly 3 begin_nested per lot (upsert + snapshot + hook outer), "
             f"got {db.begin_nested.call_count} — inner SAVEPOINT may still be present"
         )