qconnect: allow offline-cache to be cast (one consistent rule)

Three sites disagreed: model blocked OfflineCache, live gate allowed it, TS
sync filter blocked qobuz_download. Decision: ALLOW — an offline copy's queue
id is the real Qobuz track id. Flip the TS sync filter and fix the stale model
doc comment to match the live gate.

Also add Rust lock-in tests (offline_cache_is_castable / offline_cache_is_admitted)
and restore the missing $app/environment vitest mock the config already aliases,
so queuePlaybackService.test.ts can load.

cc

src/lib/services/queuePlaybackService.test.ts

@@ -66,3 +66,24 @@ describe('assessQconnectQueueSync', () => {
     });
   });
 });
+
+const track = (over: Partial<BackendQueueTrack>): BackendQueueTrack =>
+  ({ id: 1, title: 't', artist: 'a', album: 'al', duration_secs: 0, artwork_url: null,
+     hires: false, bit_depth: null, sample_rate: null, is_local: false, album_id: null,
+     artist_id: null, streamable: true, source: 'qobuz', parental_warning: false, ...over }) as BackendQueueTrack;
+
+describe('assessQconnectQueueSync — offline-cache', () => {
+  it('treats qobuz_download as syncable (offline copy carries a Qobuz id)', () => {
+    const r = assessQconnectQueueSync([track({ id: 5, source: 'qobuz_download' })]);
+    expect(r.syncable).toBe(true);
+    expect(r.trackIds).toEqual([5]);
+    expect(r.blockedTrackIds).toEqual([]);
+  });
+  it('still blocks local and plex', () => {
+    const r = assessQconnectQueueSync([
+      track({ id: 1, source: 'qobuz' }), track({ id: 2, source: 'local' }),
+    ]);
+    expect(r.syncable).toBe(false);
+    expect(r.blockedTrackIds).toContain(2);
+  });
+});

src/lib/services/queuePlaybackService.ts

@@ -23,7 +23,8 @@ function isQconnectSyncEligibleTrack(track: BackendQueueTrack): boolean {
   if (track.is_local) return false;
 
   const source = (track.source ?? '').toLowerCase();
-  if (source === 'local' || source === 'plex' || source === 'qobuz_download') {
+  // Offline-cache (qobuz_download) IS eligible: its id is the real Qobuz id.
+  if (source === 'local' || source === 'plex') {
     return false;
   }
 

src/test/mocks/app/environment.ts

@@ -0,0 +1,8 @@
+// Test mock for SvelteKit's `$app/environment`.
+// The vitest config aliases `$app` to this directory, but the module was never
+// created, so any test whose import graph reaches `$app/environment` (e.g. via
+// the i18n module) failed to load. This provides the minimal surface the app uses.
+export const browser = false;
+export const dev = false;
+export const building = false;
+export const version = 'test';