diff --git a/tradein-mvp/backend/tests/test_3480_no_open_transaction_over_http.py b/tradein-mvp/backend/tests/test_3480_no_open_transaction_over_http.py
new file mode 100644
index 00000000..8d1e8011
--- /dev/null
+++ b/tradein-mvp/backend/tests/test_3480_no_open_transaction_over_http.py
@@ -0,0 +1,90 @@
+"""Проверка отмены не оставляет транзакцию открытой на сетевую фазу свипа (#3480).
+
+Прод 17.09 07:48 UTC, pg_stat_activity БД tradein: pid 1933154 из tradein-scraper,
+'idle in transaction' 1 ч 35 мин, последний запрос `SELECT status FROM scrape_runs
+WHERE id = $1` (runs.is_cancelled), xact_start через 30 мс после старта
+domclick_city_sweep_moskva 7344. За 14 суток 10 из 12 окон «транзакция > 1 ч»
+совпали со свипами ДомКлика.
+
+Сессия настоящая (SQLAlchemy + SQLite): значение `in_transaction()` — то же, что видит
+Postgres как 'idle in transaction'.
+"""
+
+from __future__ import annotations
+
+import os
+from types import SimpleNamespace
+from typing import Any
+from unittest.mock import MagicMock, patch
+
+os.environ.setdefault("DATABASE_URL", "postgresql+psycopg://test:test@localhost/test_db")
+
+from scraper_kit.orchestration import pipeline as pl
+from scraper_kit.orchestration import runs
+from sqlalchemy import create_engine, text
+from sqlalchemy.orm import Session
+
+
+def _session() -> Session:
+    db = Session(create_engine("sqlite://"))
+    db.execute(text("CREATE TABLE scrape_runs (id INTEGER, status TEXT, counters TEXT)"))
+    db.execute(
+        text(
+            "INSERT INTO scrape_runs VALUES "
+            "(7333, 'done', NULL), (7344, 'running', NULL), (7345, 'cancelled', NULL)"
+        )
+    )
+    db.commit()
+    return db
+
+
+def test_is_cancelled_closes_its_transaction() -> None:
+    db = _session()
+
+    assert runs.is_cancelled(db, 7344) is False
+    assert db.in_transaction() is False
+    assert runs.is_cancelled(db, 7345) is True
+    assert db.in_transaction() is False
+
+
+async def test_domclick_sweep_http_phase_runs_outside_transaction() -> None:
+    db = _session()
+    seen: list[bool] = []
+
+    class _Scraper:
+        blocked = False
+        geo_filtered = fetch_errors = buckets_completed = buckets_total = 0
+        bucket_start_index = 0
+        completed_buckets: list[str] = []  # noqa: RUF012
+
+        def __init__(self, *_a: Any, **_kw: Any) -> None: ...
+
+        async def __aenter__(self) -> _Scraper:
+            return self
+
+        async def __aexit__(self, *_e: Any) -> None:
+            return None
+
+        async def fetch_city(self, **_kw: Any) -> list[Any]:
+            seen.append(db.in_transaction())  # момент сетевого обхода
+            return []
+
+    with (
+        patch.object(pl, "DomClickScraper", _Scraper),
+        patch.object(runs, "update_heartbeat", MagicMock()),
+        patch.object(runs, "mark_done", MagicMock()),
+        patch.object(runs, "mark_failed", MagicMock()),
+        patch.object(runs, "mark_banned", MagicMock()),
+    ):
+        await pl.run_domclick_city_sweep(
+            db,
+            run_id=7344,
+            config=SimpleNamespace(browser_http_endpoint="http://x:9000"),
+            matcher=MagicMock(),
+            city_id=4,
+            pages=1,
+            request_delay_sec=0.0,
+            resume_run_id=7333,  # резюм-SELECT тоже открывает транзакцию
+        )
+
+    assert seen == [False]
diff --git a/tradein-mvp/packages/scraper-kit/src/scraper_kit/orchestration/runs.py b/tradein-mvp/packages/scraper-kit/src/scraper_kit/orchestration/runs.py
index 4b38558a..b2d32d91 100644
--- a/tradein-mvp/packages/scraper-kit/src/scraper_kit/orchestration/runs.py
+++ b/tradein-mvp/packages/scraper-kit/src/scraper_kit/orchestration/runs.py
@@ -815,11 +815,19 @@ def honors_cancel(source: str) -> bool:
 
 
 def is_cancelled(db: Session, run_id: int) -> bool:
-    """Проверить status='cancelled' (cooperative cancel в long-running pipeline)."""
+    """Проверить status='cancelled' (cooperative cancel в long-running pipeline).
+
+    #3480: SELECT открывает транзакцию (autobegin), а вызывающие сразу уходят в сетевую
+    фазу. Без commit сессия висела 'idle in transaction' весь обход и держала горизонт
+    vacuum всей БД: прод 17.09, domclick_city_sweep_moskva 7344 — транзакция 1.6 ч с
+    последним запросом ровно этим SELECT; 10 из 12 окон > 1 ч за 14 суток — свипы
+    ДомКлика. Закрываем здесь: проверку отмены зовут перед каждым долгим await.
+    """
     row = db.execute(
         text("SELECT status FROM scrape_runs WHERE id = :id"),
         {"id": run_id},
     ).fetchone()
+    db.commit()
     return row is not None and row.status == "cancelled"