test(tradein/scraper-kit): assert config= at avito_detail_backfill call sites (#2310)

Code-review follow-up: the Group C regression tests for the fetch_detail
backconnect footgun and AvitoScraper's config requirement proved the KIT
LIBRARY behavior in isolation, but nothing asserted the actual call sites in
avito_detail_backfill.py still pass config=RealScraperConfig() at fetch_detail
and AvitoScraper construction. Mirrors #2306's test_backfill_wave2.py:282-286
pattern -- isinstance-checks the captured call_args instead of a bare
assert_called().

Verified the new assertions actually catch the regression: temporarily
removed both config=RealScraperConfig() call-site args from
avito_detail_backfill.py, confirmed test_backfill_processes_snapshot_to_completion
fails exactly on the new assertion line, then restored (git diff was empty
afterward).

Refs #2310

tradein-mvp/backend/tests/tasks/test_avito_detail_backfill.py

@@ -109,6 +109,8 @@ async def test_backfill_empty_snapshot_marks_done() -> None:
 @pytest.mark.asyncio
 async def test_backfill_processes_snapshot_to_completion() -> None:
     """3 listings -> all fetched and enriched, mark_done called."""
+    from app.services.scraper_adapters import RealScraperConfig
+
     snapshot = _make_snapshot(3)
     db = _mock_db(snapshot)
     runs = MagicMock()
@@ -119,7 +121,7 @@ async def test_backfill_processes_snapshot_to_completion() -> None:
     with (
         patch(_SETTINGS, fake_settings),
         patch(_SESSION, return_value=AsyncMock()),
-        patch(_SCRAPER),
+        patch(_SCRAPER) as mock_scraper_cls,
         patch(_RUNS, runs),
         patch(_FETCH, mock_fetch),
         patch(_SAVE, mock_save),
@@ -136,6 +138,14 @@ async def test_backfill_processes_snapshot_to_completion() -> None:
     assert mock_fetch.call_count == 3
     runs.mark_done.assert_called_once()
     runs.mark_failed.assert_not_called()
+    # #2310 regression guard: kit fetch_detail silently drops the backconnect-
+    # on-403 retry (and kit AvitoScraper can't read avito_proxy_rotate_url at
+    # all) unless config=RealScraperConfig() is passed/injected at the call
+    # site — assert_called()/call_count alone wouldn't catch someone dropping
+    # that kwarg later (mirrors #2306's test_backfill_wave2.py:282-286 pattern).
+    _, fetch_call_kwargs = mock_fetch.call_args
+    assert isinstance(fetch_call_kwargs.get("config"), RealScraperConfig)
+    assert isinstance(mock_scraper_cls.call_args.args[0], RealScraperConfig)
 
 
 @pytest.mark.asyncio