Milestone #160 Opt 3b. Adds device class as a third context axis on top
of the #1531 time-of-day/weekday affinity: on the radio path, a candidate
is boosted when its artist concentrates in the current (daypart × weekday
× device) cell. Client-sent (client_id is opaque; no UA stored), so it's
captured going forward and applies to radio only (daily mixes are
cron-built with no device → stay device-agnostic).
Server:
- Migration 0048: play_events.device_class text NULL (no CHECK; normalized
in Go — one whitelist entry per new client class, not a migration).
- events.go: eventRequest.device_class + normalizeDeviceClass (whitelist →
mobile/web/…, else "other", empty → NULL); threaded through both
RecordPlayStartedWithSource and RecordOfflinePlay into InsertPlayEvent.
- ListArtistContextPlayCountsForUser gains a current-device param; the cell
FILTER adds AND ($2='' OR device_class=$2) — '' reproduces the #1531
time-only behaviour exactly (used by mixes). SessionVector.DeviceClass
carries it; the radio handler derives the current device from the user's
latest play (GetLatestPlayDeviceClassForUser) — request-free proxy.
- No new tuning knob: device narrows the existing ContextAffinityScore
(reuses context_time_weight).
Clients:
- web: play_started sends device_class 'web'.
- android: play_started + offline replay send 'mobile' (EventsWire +
PlayOfflinePayload + MutationReplayer + PlayEventsReporter).
Test: LoadContextAffinity device-narrowing integration test (mobile vs web
artist separation; device-agnostic parity).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
