Verify deletion actually removed the file before reporting success

MeTube's /delete only unlinks the file when it's configured with
DELETE_FILE_ON_TRASHCAN=true; otherwise it just drops the entry from its
own "done" list and returns {"status": "ok"} regardless -- we were trusting
that response and marking the job "deleted" (offering a re-download) while
the file was still sitting on mediaVM's disk the whole time.

Now HEAD-check the media_url right after the delete call. If the file is
still reachable, leave the job's status untouched (still "completed", still
playable) and surface a clear 409 explaining MeTube's own config is why,
rather than lying about local state.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_videos.py

@@ -184,6 +184,7 @@ def test_delete_download_success(client, db_session, monkeypatch):
         "app.services.metube_client.MeTubeClient.delete_download",
         lambda self, metube_job_id: calls.setdefault("id", metube_job_id) or {"status": "ok"},
     )
+    monkeypatch.setattr("app.services.metube_client.MeTubeClient.check_media", lambda self, url: False)
 
     resp = client.delete(f"/api/videos/{video.youtube_video_id}/download")
 
@@ -195,3 +196,32 @@ def test_delete_download_success(client, db_session, monkeypatch):
     db_session.refresh(job)
     assert job.status == "deleted"
     assert job.media_url is None
+
+
+def test_delete_download_file_still_present_returns_409(client, db_session, monkeypatch):
+    """MeTube can accept /delete and still leave the file on disk if its own
+    DELETE_FILE_ON_TRASHCAN config is off -- we must not lie about that."""
+    from app.models.download_job import DownloadJob
+
+    video = _seed_single_video(db_session)
+    job = DownloadJob(
+        video_id=video.id,
+        status="completed",
+        metube_job_id="vid1.vid1",
+        media_url="http://metube.local/download/f.mp4",
+    )
+    db_session.add(job)
+    db_session.commit()
+
+    monkeypatch.setattr(
+        "app.services.metube_client.MeTubeClient.delete_download", lambda self, metube_job_id: {"status": "ok"}
+    )
+    monkeypatch.setattr("app.services.metube_client.MeTubeClient.check_media", lambda self, url: True)
+
+    resp = client.delete(f"/api/videos/{video.youtube_video_id}/download")
+
+    assert resp.status_code == 409
+
+    db_session.refresh(job)
+    assert job.status == "completed"
+    assert job.media_url == "http://metube.local/download/f.mp4"