Fifth cluster: reset_<source>_playlist for the four sources with byte-
identical bodies (Tidal, Deezer, Qobuz, Spotify-Public) ->
core.discovery.endpoints.reset_playlist(states, key, *, label,
not_found_message), wired via _reset_source_playlist. Resets phase/status to
'fresh', clears discovery/sync fields, cancels any discovery_future, and
preserves the original playlist payload.
Left with their own bodies (genuinely divergent):
- YouTube: status -> 'parsed' (not 'fresh'), no download_process_id, logs the
playlist name, "reset to fresh state".
- ListenBrainz: status -> 'cached', logs playlist title, returns
{"success": True, "phase": "fresh"} (different payload), _lb_state_key.
- iTunes-Link: state.update(...), no info log, "iTunes Link reset to fresh
phase".
Tests: +4 (404, full clear + playlist preserved + future cancelled, no-future
path, exception -> 500). Full discovery suite: 179 passed.
web_server.py: -100 lines.