Replace play_history with listening_events — one row per track exit, kind (complete/play/skip) plus raw position/duration — and add skip_count/last_skipped to audio_files beside play_count/last_played. The classifier that writes these lands later (plan 021); this is the schema it records into. Also drop the dead queue.source_playlist_id column and remove the stale references to the squashed migration chain in download_*.sql and tagging_items.sql, declaring the missing download-request indexes inline.