fix(plex): a collection created on Plex keeps its editable row when the refresh read fails

The rollback dropped the new row: the next sync recreated it read-only, out of every 'add to' list, and the duplicate-name check let a retry make a second same-named collection on Plex.

backend/tests/test_plex_collections_filter.py

@@ -15,6 +15,7 @@ from app.db import get_db
 from app.main import app
 from app.models import PlexCollection, PlexItem, PlexLibrary, PlexShow, User
 from app.plex.client import PlexError
+from app.plex.lookups import by_rating_key
 from app.routes.plex import collections as coll_routes
 
 
@@ -355,6 +356,16 @@ def test_create_resync_failure_is_422(db, monkeypatch, override_dep):
     assert r.status_code == 422, r.text
     assert r.json()["detail"] == {"code": "refused", "reason": "collection_pending_sync"}
     assert "create_collection" in stub.calls
+    # It exists on Plex: its row stays, editable, until the next sync fills it in — so it is offered
+    # where collections are added to, and the same name is not made twice.
+    row = by_rating_key(db, PlexCollection, "NEW")
+    assert row is not None and row.editable and row.title == "Fresh Coll"
+    again = client.post(
+        "/api/plex/collections",
+        json={"library": "1", "title": "Fresh Coll", "item_rating_key": "m1"},
+    )
+    assert again.status_code == 409, again.text
+    assert stub.calls.count("create_collection") == 1
 
 
 def test_mutation_failure_returns_422_write_failed(db, monkeypatch, override_dep):