fix(playlists): a refused push spends none of the push allowance

The cooldown was checked before the list was found pushable and before its sync claim, so Watch later
or a list another sync held used up the push allowance. It now counts only a push that runs. The
docstring that called a YouTube mirror unpushable is corrected: its local edits sync back.

backend/tests/test_abuse_limits.py

@@ -177,6 +177,48 @@ def test_plan_and_push_draw_on_one_allowance(db, as_user, make_user, monkeypatch
     assert r.json()["detail"] == {"code": "playlist", "reason": "push_cooldown"}
 
 
+def test_a_refused_push_spends_no_allowance(db, as_user, make_user, monkeypatch):
+    # The allowance counts pushes that run: Watch later (never pushable) and a list another sync
+    # holds are refused before any YouTube call, so they must not leave the next real press at 429.
+    from contextlib import contextmanager
+
+    from app.reader.models import Playlist
+    from app.routes import playlists as plroutes
+
+    user, pl = _pushable_list(db, make_user, monkeypatch, plroutes)
+    wl = Playlist(user_id=user.id, name="Watch later", kind="watch_later")
+    db.add(wl)
+    db.commit()
+    c = as_user(user)
+    over = plroutes.PUSH_ALLOWANCE + 1
+    assert {c.get(f"/api/playlists/{wl.id}/push-plan").status_code for _ in range(over)} == {400}
+    assert {c.post(f"/api/playlists/{wl.id}/push").status_code for _ in range(over)} == {400}
+
+    @contextmanager
+    def busy(_db, _id):
+        yield False
+
+    with monkeypatch.context() as m:
+        m.setattr(plroutes, "sync_claim", busy)
+        assert {c.post(f"/api/playlists/{pl.id}/push").status_code for _ in range(over)} == {409}
+    assert c.post(f"/api/playlists/{pl.id}/push").status_code == 200
+
+
+def test_a_mirrored_youtube_list_is_pushable(db, as_user, make_user, monkeypatch):
+    # A mirror of the user's own YouTube list takes local edits (`dirty`) and syncs them back; only
+    # Watch later is refused.
+    from app.reader.models import Playlist
+    from app.routes import playlists as plroutes
+
+    user, _ = _pushable_list(db, make_user, monkeypatch, plroutes)
+    mirror = Playlist(
+        user_id=user.id, name="Mine", source="youtube", yt_playlist_id="PLx", dirty=True
+    )
+    db.add(mirror)
+    db.commit()
+    assert as_user(user).get(f"/api/playlists/{mirror.id}/push-plan").status_code == 200
+
+
 def test_the_push_cooldown_is_per_user(db, as_user, make_user, monkeypatch):
     from app.routes import playlists as plroutes