fix: an unfinished download is never stored as an attachment, and the temp sweep keeps any file a library row points at

The importer refuses a staging file (.part, .partial, .megatmp.*) at both
entry points, the same way it refuses a sidecar .json, and
discard_after_attach never deletes one: the age-gated temp sweep owns them.
The sweep checks its stale candidates against image and attachment rows and
keeps any a row points at.

A Google Drive fetch's half-written file had been stored as <sha>.part; the
sweep then deleted it by name and left the row with no file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_maintenance.py

@@ -26,30 +26,50 @@ def _make_batch(session) -> int:
     return batch.id
 
 
-def test_cleanup_orphaned_temp_files_removes_stale_only(tmp_path, monkeypatch):
+def test_cleanup_orphaned_temp_files_removes_stale_only(db_sync, tmp_path, monkeypatch):
     import os
 
+    from backend.app.models import ImageRecord, PostAttachment
     from backend.app.tasks import maintenance as m
 
     monkeypatch.setattr(m, "IMAGES_ROOT", tmp_path)
-    stale = tmp_path / "artist" / "img.jpg.part"      # killed download → orphan
-    stale.parent.mkdir(parents=True)
-    stale.write_bytes(b"x")
     old = datetime.now(UTC).timestamp() - 8 * 3600     # older than the 6h guard
-    os.utime(stale, (old, old))
-    fresh = tmp_path / "in_progress.jpg.partial"       # active download → keep
-    fresh.write_bytes(b"x")
-    keep = tmp_path / "real.jpg"                        # a real image → keep
+
+    def staged(rel: str, *, aged: bool = True):
+        p = tmp_path / rel
+        p.parent.mkdir(parents=True, exist_ok=True)
+        p.write_bytes(b"x")
+        if aged:
+            os.utime(p, (old, old))
+        return p
+
+    stale = staged("artist/img.jpg.part")                 # killed download → orphan
+    mega = staged("artist/.megatmp.AbCd123")              # abandoned megatools stage
+    fresh = staged("in_progress.jpg.partial", aged=False)  # active download → keep
+    keep = tmp_path / "real.jpg"                          # a real image → keep
     keep.write_bytes(b"x")
-    mega = tmp_path / "artist" / ".megatmp.AbCd123"     # abandoned megatools stage
-    mega.write_bytes(b"x")
-    os.utime(mega, (old, old))
+    # Staging-named files a library row points at are library content.
+    attached = staged("attachments/ab/abc.part")
+    imaged = staged("artist/video.mp4.part")
+    db_sync.add(PostAttachment(
+        post_id=None, artist_id=None, sha256="tempsweep-att".ljust(64, "x"),
+        path=str(attached), original_filename="film.mp4.part", ext=".part",
+        size_bytes=1,
+    ))
+    db_sync.add(ImageRecord(
+        path=str(imaged), sha256="tempsweep-img".ljust(64, "x"), size_bytes=1,
+        mime="video/mp4", width=1, height=1, origin="downloaded",
+        integrity_status="ok",
+    ))
+    db_sync.commit()
 
     assert m.cleanup_orphaned_temp_files() == 2
     assert not stale.exists()
     assert not mega.exists()
     assert fresh.exists()
     assert keep.exists()
+    assert attached.exists()
+    assert imaged.exists()
 
 
 def test_recover_interrupted_only_old(db_sync, monkeypatch):