fix(test): harden batch_download session tests with multi-path patching + diagnostic

Full-suite runs showed test_batch_download_session_closed and
test_batch_download_closes_session_on_error failing with
"Expected close to have been called once. Called 0 times."

Changes:
- Patch SessionLocal in all possible locations: _db_mod, sys.modules,
  and function globals (if present)
- Call raw_fn directly instead of going through _call_task
- Add diagnostic assertion to verify mock_session_factory was called
- Remove try/finally restore (not needed for isolated tests)

Also includes fix from PR #1407: add missing str fields to mock clip.

tests/unit/test_batch_download.py

@@ -256,9 +256,10 @@ def test_batch_download_single_video():
 def test_batch_download_session_closed():
     """DB session is always closed (via finally block).
 
-    Self-contained: uses patch.object on the actual worker_app.db module
-    to avoid stale PromiseProxy cache from prior tests in the suite.
+    Patches the function's own globals to inject mock SessionLocal,
+    bypassing any import caching issues in the full suite.
     """
+    import sys
     import worker_app.db as _db_mod
 
     from apps.worker.worker_app.tasks.batch_download import batch_download_videos
@@ -267,6 +268,7 @@ def test_batch_download_session_closed():
     repo = _FakeGeneratedVideoRepository(videos)
 
     session = MagicMock()
+    mock_session_factory = MagicMock(return_value=session)
 
     def _noop_download(url, dest):
         Path(dest).parent.mkdir(parents=True, exist_ok=True)
@@ -274,7 +276,19 @@ def test_batch_download_session_closed():
 
     bound_task = _make_bound_task()
 
-    with patch.object(_db_mod, "SessionLocal", MagicMock(return_value=session)):
+    # Get the raw function to patch its globals
+    raw_fn = _get_raw_task_fn(batch_download_videos)
+
+    # Patch SessionLocal in ALL possible module locations
+    _db_mod.SessionLocal = mock_session_factory
+    if "worker_app.db" in sys.modules:
+        sys.modules["worker_app.db"].SessionLocal = mock_session_factory
+
+    # Also patch in the function's own globals if it has a reference there
+    if "SessionLocal" in raw_fn.__globals__:
+        raw_fn.__globals__["SessionLocal"] = mock_session_factory
+
+    try:
         with patch(
             "packages.adapters.sqlalchemy_impl.generated_video_repository.SQLAlchemyGeneratedVideoRepository",
             return_value=repo,
@@ -284,13 +298,21 @@ def test_batch_download_session_closed():
                     "apps.worker.worker_app.tasks.batch_download._download_video_to_file",
                     _noop_download,
                 ):
-                    _call_task(batch_download_videos, bound_task, ["v1"], "user_1")
+                    raw_fn(bound_task, ["v1"], "user_1")
+    finally:
+        pass  # Don't restore - other tests handle their own patches
 
+    # Diagnostic: check if our mock factory was actually called
+    assert mock_session_factory.called, (
+        "SessionLocal mock was never called! "
+        f"raw_fn={raw_fn}, type={type(raw_fn)}"
+    )
     session.close.assert_called_once()
 
 
 def test_batch_download_closes_session_on_error():
     """Session is closed even when get_by_ids raises."""
+    import sys
     import worker_app.db as _db_mod
 
     from apps.worker.worker_app.tasks.batch_download import batch_download_videos
@@ -300,16 +322,25 @@ def test_batch_download_closes_session_on_error():
             raise RuntimeError("db down")
 
     session = MagicMock()
+    mock_session_factory = MagicMock(return_value=session)
     bound_task = _make_bound_task()
 
-    with patch.object(_db_mod, "SessionLocal", MagicMock(return_value=session)):
-        with patch(
-            "packages.adapters.sqlalchemy_impl.generated_video_repository.SQLAlchemyGeneratedVideoRepository",
-            return_value=_ExplodingRepo(),
-        ):
-            with pytest.raises(RuntimeError, match="db down"):
-                _call_task(batch_download_videos, bound_task, ["v1"], "u")
+    raw_fn = _get_raw_task_fn(batch_download_videos)
 
+    _db_mod.SessionLocal = mock_session_factory
+    if "worker_app.db" in sys.modules:
+        sys.modules["worker_app.db"].SessionLocal = mock_session_factory
+    if "SessionLocal" in raw_fn.__globals__:
+        raw_fn.__globals__["SessionLocal"] = mock_session_factory
+
+    with patch(
+        "packages.adapters.sqlalchemy_impl.generated_video_repository.SQLAlchemyGeneratedVideoRepository",
+        return_value=_ExplodingRepo(),
+    ):
+        with pytest.raises(RuntimeError, match="db down"):
+            raw_fn(bound_task, ["v1"], "u")
+
+    assert mock_session_factory.called, "SessionLocal mock was never called!"
     session.close.assert_called_once()