Replaces radio's pure ORDER BY RANDOM() with weighted ranking. Each tier now
fetches a generous random POOL (4x the needed count, floored) and
core/radio/selection ranks it before the collector keeps the best:
score_candidate = play_count(log-damped, w=1.0)
+ lastfm_playcount(log-damped, w=0.5)
- recently_played penalty(w=2.0)
+ stable per-id jitter(w=1.0, hash-derived so runs vary but
tests stay reproducible)
Modest weights so popularity guides without burying lesser-played tracks, and
jitter keeps radio from being identical every run. All intelligence is in pure
functions (rank_candidates / score_candidate) so it's tunable + unit-testable
without SQL.
Defensive: the DB method probes PRAGMA table_info(tracks) and omits
play_count/lastfm_playcount from the SELECT when absent (older DBs predating
the listening-history migration) — the scorer treats missing signals as 0, so
radio degrades to jitter-only instead of crashing on 'no such column'.
Tests (tests/radio/, 43 total):
- score_candidate / rank_candidates: deterministic unit coverage (popularity
ordering, lastfm contribution, recency penalty, garbage→0, stable jitter).
These CANNOT pass against pre-Phase-2 code.
- DB end-to-end: ranking surfaces the heavily-played track first out of a
decoy pool (wiring proof — probabilistic vs old random, documented honestly);
plus a no-rank-columns DB proving the defensive degrade path.
- All Phase-0a behavioral/refactor-equivalence tests still green.
60 radio + adjacent-DB tests pass; ruff clean.
BoulderBadgeDad
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