…4275)

## Summary

Track downloads were failing in offline mode — the user-visible symptom
is *"clicks download, sees a track attempt, then a failure icon."* This
affects **both individual track downloads** (favoriting a track with
auto-download on, or any other path that queues a single track) **and
tracks inside an album/collection download**, because every track-job
entry point lands in the same queue and is processed by the same worker.

Two compounding issues in `downloadTrackWorker.ts`, both effectively
introduced by the v1 SDK migration (#13728):

1. **`downloadTrackAudio` skipped the v1 pre-signed stream URL.** It
built the URL via `sdk.tracks.getTrackStreamUrl()`, ignoring
`track.stream.url`. The v1 API returns a pre-signed stream URL (with
mirrors) on the track itself; `AudioPlayer` prefers it for online
streaming and only falls back to manual URL construction when
`stream.url` is missing. The offline worker skipped that working path
entirely, so it relied on the fallback for every track.

2. **`downloadTrackCoverArt` was fatal.** It threw when no artwork URI
returned 200, and because cover art runs in `all([cover, audio, json])`,
a single flaky artwork host failed the entire track download — even
though audio is the only essential payload. The collection cover art
download follows the opposite (best-effort) pattern; this PR brings the
track version in line.

Plus `downloadTrackAsync`'s `catch` block silently swallowed the error —
no logs, no Sentry breadcrumb. That's why this had been hard to
diagnose.

### Why this fixes both individual tracks and collections

Every track-job source — `requestDownloadCollectionSaga`,
`requestDownloadFavoritedCollectionSaga`,
`requestDownloadAllFavoritesSaga`, `watchSaveTrackSaga` (standalone
track favorite), `watchAddTrackToPlaylistSaga`, `syncCollectionWorker` —
dispatches `addOfflineEntries({ items: [..., { type: 'track' }, ...]
})`. The queue processor routes every `type === 'track'` job to a single
`downloadTrackWorker`, which calls the two functions patched here. So
both flows share the same broken code path.

## Changes

- `downloadTrackAudio`: prefer `track.stream.url` (with mirror
substitution), keep `getTrackStreamUrl()` + manual signing as a
last-resort fallback. Mirrors `AudioPlayer.tsx` logic.
- `downloadTrackCoverArt`: best-effort — return silently if all URIs
fail rather than throwing.
- Extract shared `buildMirrorUris(primary, mirrors)` helper used by both
audio and cover art.
- Add a `console.warn` in the catch block of `downloadTrackAsync` so
future failures are diagnosable instead of silent.

## Test plan

- [ ] Offline mode → favorite a single track with "download all
favorites" enabled. Track reaches SUCCESS, plays from local file.
- [ ] Offline mode → download an album you don't own (where you've
favorited it). All tracks reach SUCCESS, audio plays from local file.
- [ ] Offline mode → download an album where the artwork host is
degraded. Audio still downloads successfully; cover art is best-effort.
- [ ] Offline mode → download a single track via the track menu. Still
works (no regression).
- [ ] Offline mode → toggle "Download all favorites." Track downloads
succeed.
- [ ] Offline mode → play a downloaded track while offline. File-system
playback still works.
- [ ] Gated content (USDC / NFT) → confirm the manual-URL fallback path
still signs correctly when `stream.url` is unset.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>