fix(downloads): a conversion's commit, a stopped upload, the fast join and a clip's copy hold up

- The fast join gives each ffconcat entry its own media-only format whitelist, so a library file
  can no longer be opened as a nested concat list (the list's whitelist was handed down to it).
- A file the guarded probe cannot read is a download-only file, not a guess from yt-dlp's info.
- A conversion's or an ingest's commit that raises is re-read in a fresh session before any file
  is removed: a commit that landed keeps the file its row now names.
- An original that cannot be removed after conversion is logged; the upload stays ready.
- An upload whose conversion is cancelled or deleted midway is freed once nothing holds it; a
  paused one is kept.
- A shared link says "preparing" only while its video's job is queued or running.
- The admin storage view counts every file on disk ("Files on disk"), not only ready ones.
- A clip's failure title, unknown failure and cancel dialog, and a clip's and an upload's delete
  dialog speak of what the job made; an upload's quota refusal explains that the original is kept.
- /watch announces "preparing" as an alert and moves focus to the new Retry after an action.

backend/tests/test_upload.py

@@ -803,10 +803,10 @@ def test_ingest_rejects_over_max_jobs(db, make_user, _root, monkeypatch):
 
 def test_ingest_cleans_up_placed_files_on_commit_failure(db, make_user, _root, monkeypatch):
     """A failure AFTER storage.place_file has moved the file onto disk must roll back AND unlink the
-    placed file + any (even partial) poster — otherwise the orphan is permanent (the per-user delete
-    keys off the rolled-back asset.rel_path, and the GC orphan sweep skips the dot-prefixed .uploads/
-    tree). Exercises the rollback/cleanup branch that IS the leak remediation, incl. the poster case
-    where ensure_poster left a partial file but returned None."""
+    placed file + any (even partial) poster — otherwise nothing names it (the per-user delete keys
+    off the rolled-back asset.rel_path) and it sits on disk until the GC's `.uploads` sweep. Exercises
+    the rollback/cleanup branch, incl. the poster case where ensure_poster left a partial file but
+    returned None."""
     _probe(monkeypatch, ("h264", "aac", 320, 240, 5))  # video → the poster path runs
     u = make_user()
 
@@ -837,6 +837,28 @@ def test_ingest_cleans_up_placed_files_on_commit_failure(db, make_user, _root, m
     assert db.query(MediaAsset).count() == 0  # the flushed asset rolled back — no dangling row
 
 
+def test_ingest_keeps_the_file_when_its_commit_landed_but_raised(db, make_user, _root, monkeypatch):
+    # The commit reached the server and lost its answer: the row names the file now, so removing it
+    # as "rolled back" would leave a ready upload pointing at nothing.
+    _probe(monkeypatch, ("h264", "aac", 320, 240, 5))
+    monkeypatch.setattr(uploadmod.editmod, "ensure_poster", lambda *_a: None)
+    u = make_user()
+    real_commit = db.commit
+
+    def _landed_then_lost():
+        real_commit()
+        raise RuntimeError("connection lost after COMMIT")
+
+    monkeypatch.setattr(db, "commit", _landed_then_lost)
+    src = _root / "clip.mp4"
+    src.write_bytes(b"fake-video-bytes")
+    with pytest.raises(RuntimeError):
+        uploadmod.ingest_upload(db, u.id, filename="clip.mp4", src_path=src, size=16)
+
+    (asset,) = db.query(MediaAsset).all()
+    assert storage.abs_path(str(_root), asset.rel_path).exists()
+
+
 # --- classifier: the REAL probe_media parsing (stubs ffprobe one level down) ------------------
 # The ingest/route tests above stub probe_media wholesale; these exercise its OWN logic — image
 # detection, the cover-art skip, dimension/duration parsing — by faking only run_ffprobe_json, so a
@@ -1022,22 +1044,16 @@ class TestResolveMediaFacts:
         )
         assert v is None and mediakind.derive(v, a) == mediakind.FILE
 
-    def test_info_fills_in_only_when_ffprobe_could_not_read_the_file(self, monkeypatch):
-        # ffprobe failed entirely (None) → fall back to info so we never regress the working path.
+    def test_a_file_the_guarded_probe_cannot_read_is_a_download_only_file(self, monkeypatch):
+        # ffprobe (media demuxers only) failed entirely: the player and the editor cannot open it
+        # either, so info's codecs must not make it an editable 'video'. Dimensions still gap-fill.
         self._ffprobe(monkeypatch, None)
         v, a, w, h, _d = probemod.resolve_media_facts(
-            Path("x"), {"vcodec": "vp9", "acodec": "opus", "width": 1920, "height": 1080}
+            Path("x"),
+            {"vcodec": "avc1.64001f", "acodec": "mp4a.40.2", "width": 1920, "height": 1080},
         )
-        assert (v, a, w, h) == ("vp9", "opus", 1920, 1080)
-
-    def test_info_none_codec_string_is_treated_as_absent(self, monkeypatch):
-        # yt-dlp writes the literal "none" for a missing stream — it must not become a codec name.
-        self._ffprobe(monkeypatch, None)  # probe failed → info path, where the "none" scrub applies
-        v, a, w, h, _d = probemod.resolve_media_facts(
-            Path("x"), {"vcodec": "none", "acodec": "aac"}
-        )
-        assert (v, a) == (None, "aac")
-        assert mediakind.derive(v, a) == mediakind.AUDIO
+        assert (v, a, w, h) == (None, None, 1920, 1080)
+        assert mediakind.derive(v, a) == mediakind.FILE
 
 
 # --- the phone-safe conversion (an iPhone's HEVC, a webm, an mkv) ------------------------------