feat(web/player): self-heal a stale system-playlist / radio queue on total failure

When the whole queue proves unplayable (e.g. a tab left open across the
daily system-playlist rebuild — the exact stale-snapshot case), the player
now re-pulls the fresh snapshot and resumes instead of dead-ending on
"Try again". The seeder hands the store an opaque refetch closure so the
store stays decoupled from the playlist API and the per-artist
(songs_like_artist) identity problem: single-instance variants re-pull via
systemShuffle, per-artist mixes via getPlaylist(id), radio re-seeds from
its track. Bounded to one self-heal per exhaustion (reset on the next
successful play) so a still-broken refresh can't loop; "Try again" stays
the genuine last resort. Wired from PlaylistCard, the playlist detail page,
and playRadio. Issue #968.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/lib/components/PlaylistCard.svelte

@@ -5,6 +5,7 @@
   import { user } from '$lib/auth/store.svelte';
   import { getPlaylist, systemShuffle, refreshSystem } from '$lib/api/playlists';
   import { playlistTrackToRef } from '$lib/playlists/playlistTrackToRef';
+  import { systemPlaylistRefetch } from '$lib/playlists/systemRefetch';
   import { errCode } from '$lib/api/errors';
   import { qk } from '$lib/api/queries';
   import { playQueue } from '$lib/player/store.svelte';
@@ -80,7 +81,14 @@
         const detail = await systemShuffle(variant);
         const refs = toTrackRefs(detail.tracks);
         if (refs.length > 0) {
-          playQueue(refs, 0, { source: variant });
+          playQueue(refs, 0, {
+            source: variant,
+            refetch: systemPlaylistRefetch({
+              variant,
+              playlistId: playlist.id,
+              perArtist: false,
+            }),
+          });
         }
       } else {
         const detail = await getPlaylist(playlist.id);
@@ -93,7 +101,14 @@
           // so source attribution stays absent — the PlaylistCard
           // test pins this contract.
           if (variant != null) {
-            playQueue(refs, 0, { source: variant });
+            playQueue(refs, 0, {
+              source: variant,
+              refetch: systemPlaylistRefetch({
+                variant,
+                playlistId: playlist.id,
+                perArtist: true,
+              }),
+            });
           } else {
             playQueue(refs, 0);
           }

web/src/lib/player/store.svelte.ts

@@ -89,6 +89,17 @@ let _queueSource = $state<string | null>(null);
 // looping forever. Reset on a successful play and on a fresh playQueue.
 let _failureStreak = 0;
 
+// Track B (#968): when a queue is seeded from a refreshable source (a system
+// playlist or radio), the seeder hands us a closure that re-pulls the fresh
+// snapshot. On total failure (whole queue unplayable — likely a stale tab
+// left open across the daily rebuild) we call it once to self-heal before
+// surfacing the dead-end. Kept opaque so the store stays decoupled from the
+// playlist API and the per-artist (songs_like_artist) identity problem.
+let _queueRefetch: (() => Promise<TrackRef[]>) | null = null;
+let _selfHealInFlight = false;
+let _selfHealAttempts = 0;
+const MAX_SELF_HEAL_ATTEMPTS = 1;
+
 let _audioEl: HTMLAudioElement | null = null;
 
 export const player = {
@@ -115,13 +126,20 @@ export function registerAudioEl(el: HTMLAudioElement | null): void {
 export function playQueue(
   tracks: TrackRef[],
   startIndex = 0,
-  opts: { shuffle?: boolean; source?: string | null } = {},
+  opts: {
+    shuffle?: boolean;
+    source?: string | null;
+    refetch?: () => Promise<TrackRef[]>;
+  } = {},
 ): void {
   _radioSeedId = null;  // M4c: non-radio enqueue clears the radio refresh state
   // #415: a fresh queue resets the system-playlist source. Set only
   // when seeded from a system playlist (server already returned the
   // rotation-aware order, so no client shuffle in that path).
   _queueSource = opts.source ?? null;
+  // #968: a fresh play replaces the self-heal closure + resets its budget.
+  _queueRefetch = opts.refetch ?? null;
+  _selfHealAttempts = 0;
   if (opts.shuffle && tracks.length > 1) {
     // Fisher-Yates over the whole list. startIndex is ignored — the
     // caller is asking for "random play from this pool," so the first
@@ -271,6 +289,7 @@ export function reportStateFromAudio(
       _state = 'playing';
       _error = null;
       _failureStreak = 0;
+      _selfHealAttempts = 0;
       return;
     case 'paused':
       _state = 'paused';
@@ -323,10 +342,53 @@ function handleLoadFailure(detail?: string): void {
     _error = null;
     return;
   }
+  // Whole queue is unplayable. If it came from a refreshable source, the
+  // snapshot is probably stale — re-pull it and resume before giving up.
+  if (trySelfHeal()) return;
   _state = 'error';
   _error = detail ?? 'Playback failed.';
 }
 
+// #968: re-pull a stale refreshable queue. Returns true if a self-heal was
+// started (caller must not dead-end). Bounded to one attempt per exhaustion
+// (reset on the next successful play) so a still-broken refresh can't loop.
+function trySelfHeal(): boolean {
+  if (_selfHealInFlight) return true;
+  if (_queueRefetch === null) return false;
+  if (_selfHealAttempts >= MAX_SELF_HEAL_ATTEMPTS) return false;
+  _selfHealAttempts++;
+  _selfHealInFlight = true;
+  _state = 'loading';
+  _error = null;
+  const refetch = _queueRefetch;
+  void refetch()
+    .then((refs) => {
+      if (refs.length > 0) {
+        // Re-seed in place — keep _queueSource / _queueRefetch so the new
+        // snapshot can itself self-heal, and don't reset _selfHealAttempts
+        // (only a successful 'playing' clears the budget).
+        _queue = refs;
+        _index = 0;
+        _position = 0;
+        _duration = 0;
+        _failureStreak = 0;
+        _state = 'loading';
+        _error = null;
+      } else {
+        _state = 'error';
+        _error = 'Nothing playable in this mix right now.';
+      }
+    })
+    .catch(() => {
+      _state = 'error';
+      _error = 'Couldn’t refresh this mix. Try again.';
+    })
+    .finally(() => {
+      _selfHealInFlight = false;
+    });
+  return true;
+}
+
 export function enqueueTrack(t: TrackRef): void {
   _radioSeedId = null;  // M4c
   _queue = [..._queue, t];
@@ -371,12 +433,19 @@ export function playNextMany(ts: TrackRef[]): void {
   _queue = [..._queue.slice(0, next), ...ts, ..._queue.slice(next)];
 }
 
-export async function playRadio(seedTrackId: string): Promise<void> {
+async function fetchRadioTracks(seedTrackId: string): Promise<TrackRef[]> {
   const resp = await api.get<RadioResponse>(
     `/api/radio?seed_track=${encodeURIComponent(seedTrackId)}`
   );
-  if (resp.tracks.length === 0) return;
-  playQueue(resp.tracks, 0);
+  return resp.tracks;
+}
+
+export async function playRadio(seedTrackId: string): Promise<void> {
+  const tracks = await fetchRadioTracks(seedTrackId);
+  if (tracks.length === 0) return;
+  // #968: hand the player a self-heal closure so a fully-stale radio queue
+  // re-seeds from the same track instead of dead-ending.
+  playQueue(tracks, 0, { refetch: () => fetchRadioTracks(seedTrackId) });
   _radioSeedId = seedTrackId;  // M4c: set AFTER playQueue (which clears it)
 }
 

web/src/lib/player/store.test.ts

@@ -306,6 +306,32 @@ describe('player store — shuffle + repeat + audio reports', () => {
     expect(player.state).toBe('error');
     expect(player.error).toBe('boom');
   });
+
+  test('reportStateFromAudio("error") self-heals a refreshable queue on total failure', async () => {
+    const fresh = [track('a'), track('b')];
+    const refetch = vi.fn().mockResolvedValue(fresh);
+    playQueue([track('1')], 0, { source: 'for_you', refetch });
+    reportStateFromAudio('error', 'boom'); // sole track fails → exhausted → self-heal
+    expect(refetch).toHaveBeenCalledOnce();
+    expect(player.state).toBe('loading');
+    await Promise.resolve();
+    await Promise.resolve();
+    await Promise.resolve();
+    expect(player.queue.map((t) => t.id)).toEqual(['a', 'b']);
+    expect(player.index).toBe(0);
+  });
+
+  test('self-heal fires at most once per exhaustion, then dead-ends', async () => {
+    const refetch = vi.fn().mockResolvedValue([track('x')]);
+    playQueue([track('1')], 0, { source: 'for_you', refetch });
+    reportStateFromAudio('error', 'boom'); // exhausted → self-heal #1
+    await Promise.resolve();
+    await Promise.resolve();
+    await Promise.resolve();
+    reportStateFromAudio('error', 'boom'); // re-pulled track also fails; budget spent → error
+    expect(player.state).toBe('error');
+    expect(refetch).toHaveBeenCalledOnce();
+  });
 });
 
 import {

web/src/lib/playlists/systemRefetch.ts

@@ -0,0 +1,33 @@
+import type { TrackRef, PlaylistDetail } from '$lib/api/types';
+import { systemShuffle, getPlaylist } from '$lib/api/playlists';
+import { playlistTrackToRef } from './playlistTrackToRef';
+
+// #968: builds the self-heal closure for a system-playlist queue. On total
+// playback failure (every queued track unplayable — typically a stale tab
+// left open across the daily rebuild) the player calls this to re-pull the
+// current snapshot and resume.
+//
+// Single-instance variants (for_you, discover, deep_cuts, …) re-pull by
+// variant via the rotation-aware shuffle endpoint. Per-artist mixes
+// (songs_like_artist — one playlist per seed artist) can't be addressed by
+// variant alone, so they re-pull by playlist id. Mirrors the play routing
+// in PlaylistCard.
+
+function toRefs(detail: PlaylistDetail): TrackRef[] {
+  return detail.tracks
+    .map((r) => playlistTrackToRef(r))
+    .filter((t): t is TrackRef => t !== null);
+}
+
+export function systemPlaylistRefetch(opts: {
+  variant: string;
+  playlistId: string;
+  perArtist: boolean;
+}): () => Promise<TrackRef[]> {
+  return async () => {
+    const detail = opts.perArtist
+      ? await getPlaylist(opts.playlistId)
+      : await systemShuffle(opts.variant);
+    return toRefs(detail);
+  };
+}

web/src/routes/playlists/[id]/+page.svelte

@@ -18,6 +18,7 @@
   import { user } from '$lib/auth/store.svelte';
   import { errCode, errMessage } from '$lib/api/errors';
   import { playQueue } from '$lib/player/store.svelte';
+  import { systemPlaylistRefetch } from '$lib/playlists/systemRefetch';
   import { pushToast } from '$lib/stores/toast.svelte';
   import type { TrackRef } from '$lib/api/types';
 
@@ -61,16 +62,30 @@
 
   function onPlay(position: number) {
     if (!playlistQuery?.data) return;
+    const data = playlistQuery.data;
     // Skip rows where track_id is null (track was removed from library).
-    const live = playlistQuery.data.tracks
-      .filter((t) => t.track_id !== null)
-      .map(toTrackRef);
+    const live = data.tracks.filter((t) => t.track_id !== null).map(toTrackRef);
     // Find which `live` index corresponds to the clicked position. Some
     // positions in the original list may be unavailable (filtered out),
     // so the index in the playable list != the playlist position.
-    const clickedTrackID = playlistQuery.data.tracks.find((t) => t.position === position)?.track_id;
+    const clickedTrackID = data.tracks.find((t) => t.position === position)?.track_id;
     const startIdx = live.findIndex((t) => t.id === clickedTrackID);
-    playQueue(live, Math.max(0, startIdx));
+    // #968: a system playlist played from its detail page gets the same
+    // self-heal closure as the home tile, so a stale snapshot re-pulls on
+    // total failure. (Source attribution is intentionally left to the home
+    // tile / shuffle path — this only adds the recovery closure.)
+    const variant = data.system_variant;
+    if (variant != null) {
+      playQueue(live, Math.max(0, startIdx), {
+        refetch: systemPlaylistRefetch({
+          variant,
+          playlistId: id,
+          perArtist: data.seed_artist_id != null
+        })
+      });
+    } else {
+      playQueue(live, Math.max(0, startIdx));
+    }
   }
 
   function toTrackRef(t: {