Second M4 sub-plan (Fable #346). Periodic worker pulls track-track and
artist-artist similarity edges from LB's public /explore/* endpoints,
filters to the local library, stores top-20 per source track in two new
tables (track_similarity, artist_similarity). Hourly tick, batch=5,
weekly re-fetch cap per row, passive retry via timer. No auth (public
endpoints). Discovery within library handled by LB's collaborative-
filtering response naturally surfacing unplayed library tracks; spec
notes M4c will add a serendipity floor + lazy fetch + sparse-fallback.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
bvandeusen
86cb8e5cbf