ML-169.7: record audit findings

backlog/tasks/ml-169.7 - Fix-Stream-reset-on-every-scrobble-PubSub-update.md

@@ -4,6 +4,7 @@ title: "Fix: Stream reset on every scrobble PubSub update"
 status: To Do
 assignee: []
 created_date: "2026-05-19 11:48"
+updated_date: "2026-05-25 09:50"
 labels:
   - perf
   - fix
@@ -58,3 +59,11 @@ This fires every 5 minutes on ALL connected clients, even idle ones.
 - [ ] #4 Existing stream ordering is preserved after insert
 - [ ] #5 No duplicate tracks appear in streams
 <!-- AC:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+
+Audit findings (2026-05-25): ML-169.7 is valid and still unresolved. Evidence: `ListeningStats.update/1` broadcasts `%{track_count: count}` on `"listening_stats:update"` (`lib/music_library/listening_stats.ex:67`), and prod cron runs `RefreshScrobbles` every 5 minutes (`config/prod.exs:65-66`). `StatsLive.Index` handles non-zero updates by calling `assign_scrobble_activity/1`, which re-runs `ListeningStats.recent_activity/1` and `ListeningStats.scrobble_count/0`, then resets `:recent_tracks` and `:recent_albums` (`lib/music_library_web/live/stats_live/index.ex:316-321`, `654-671`). `ScrobbledTracksLive.Index` handles non-zero updates by calling `load_and_assign_tracks/2`, which re-runs `ListeningStats.list_tracks/1` and resets `:tracks` (`lib/music_library_web/live/scrobbled_tracks_live/index.ex:280-282`, `347-355`). Nuance: both LiveViews no-op for `%{track_count: 0}`, so the exact issue is every non-empty scrobble PubSub update, not literally every cron run. Implementation caveats: PubSub currently contains only count, not inserted track IDs; Stats `recent_albums` is deduped from tracks so naive inserts can duplicate albums; prepending multiple stream items must preserve order; ScrobbledTracks should likely insert only for page 1 + `:scrobbled_at` order + matching filter, otherwise show a refresh/new-scrobbles badge. Test coverage gap: current LiveView tests do not exercise this PubSub stream-reset path. Validation during audit: `mix test test/music_library_web/live/stats_live/index_test.exs test/music_library_web/live/scrobbled_tracks_live/index_test.exs` passed (23 tests).
+
+<!-- SECTION:NOTES:END -->