Re-running an export created a new LB playlist every time (LB keys on MBID, not name, and
create always mints a new one). Now remember which LB playlist a mirror was pushed to and
update it in place:
- listenbrainz_client: refactor batched-add into _add_tracks_in_batches; add
get_playlist_track_count, delete_playlist, update_playlist (verify exists -> clear items via
item/delete -> re-add -> edit title; reports gone=True if deleted on LB), and
create_or_update_playlist (update when we have a prior MBID, else create; falls back to
create if the remembered one was deleted). Stable URL/MBID across re-syncs.
- playlist_export_targets table + get/set_playlist_export_target: remember (mirror, target) -> LB MBID.
- export job consults/stores the target so push updates in place.
+6 mocked tests (clear+re-add same mbid, gone-fallback, create-or-update branches, delete). API
endpoints (item/delete, playlist/edit, playlist/delete, GET count) confirmed against LB docs;
live round-trip pending explicit auth.
ab8f82af2e