perf(player): rebuild preview buttons only on status changes

lib/widgets/preview_button.dart

@@ -39,8 +39,12 @@ class PreviewButton extends ConsumerWidget {
 
     // When the built-in player is currently on this track, mirror and control
     // it (consistent with the mini player) rather than the preview snippet.
-    final mainItem = ref.watch(currentMediaItemProvider).value;
-    if (_isCurrentMainTrack(mainItem)) {
+    final isCurrentMainTrack = ref.watch(
+      currentMediaItemProvider.select(
+        (item) => _isCurrentMainTrack(item.value),
+      ),
+    );
+    if (isCurrentMainTrack) {
       final isPlaying = ref.watch(playbackPlayingProvider);
       return IconButton(
         iconSize: size,
@@ -62,9 +66,13 @@ class PreviewButton extends ConsumerWidget {
 
     if (!track.hasPreview) return const SizedBox.shrink();
 
-    final previewState = ref.watch(previewPlayerProvider);
-    final isActive = previewState.isActiveUrl(track.previewUrl);
-    final status = isActive ? previewState.status : PreviewStatus.idle;
+    final status = ref.watch(
+      previewPlayerProvider.select(
+        (state) => state.isActiveUrl(track.previewUrl)
+            ? state.status
+            : PreviewStatus.idle,
+      ),
+    );
 
     final Widget icon;
     final String tooltip;

test/preview_button_layout_test.dart

@@ -7,6 +7,7 @@ import 'package:spotiflac_android/models/settings.dart';
 import 'package:spotiflac_android/models/track.dart';
 import 'package:spotiflac_android/providers/library_collections_provider.dart';
 import 'package:spotiflac_android/providers/music_player_provider.dart';
+import 'package:spotiflac_android/providers/preview_player_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/widgets/preview_button.dart';
 import 'package:spotiflac_android/widgets/track_collection_quick_actions.dart';
@@ -79,6 +80,69 @@ void main() {
     expectCenteredHitbox(tester, Icons.play_circle_fill_rounded);
   });
 
+  testWidgets('preview progress does not rebuild track buttons', (
+    tester,
+  ) async {
+    final player = _TestPreviewPlayer();
+    var builds = 0;
+    await tester.pumpWidget(
+      ProviderScope(
+        overrides: [
+          currentMediaItemProvider.overrideWith((ref) => Stream.value(null)),
+          previewPlayerProvider.overrideWith(() => player),
+        ],
+        child: MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: Scaffold(
+            body: _CountingPreviewButton(track: track, onBuild: () => builds++),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    player.emit(
+      PreviewPlayerState(
+        activeUrl: track.previewUrl,
+        status: PreviewStatus.playing,
+      ),
+    );
+    await tester.pump();
+    expect(find.byIcon(Icons.pause_circle_filled_rounded), findsOneWidget);
+    final playingBuilds = builds;
+    for (var second = 1; second <= 3; second++) {
+      player.emit(
+        PreviewPlayerState(
+          activeUrl: track.previewUrl,
+          status: PreviewStatus.playing,
+          position: Duration(seconds: second),
+          duration: const Duration(seconds: 30),
+        ),
+      );
+      await tester.pump();
+    }
+    expect(builds, playingBuilds);
+
+    player.emit(
+      PreviewPlayerState(
+        activeUrl: track.previewUrl,
+        status: PreviewStatus.paused,
+      ),
+    );
+    await tester.pump();
+    expect(find.byIcon(Icons.play_circle_fill_rounded), findsOneWidget);
+    expect(builds, playingBuilds + 1);
+
+    player.emit(
+      const PreviewPlayerState(
+        activeUrl: 'https://example.com/another-preview.mp3',
+        status: PreviewStatus.playing,
+      ),
+    );
+    await tester.pump();
+    expect(find.byIcon(Icons.play_circle_outline_rounded), findsOneWidget);
+  });
+
   testWidgets('overflow menu icon is centered in its adjacent hitbox', (
     tester,
   ) async {
@@ -157,6 +221,25 @@ class _TestSettingsNotifier extends SettingsNotifier {
   AppSettings build() => const AppSettings();
 }
 
+class _TestPreviewPlayer extends PreviewPlayerController {
+  @override
+  PreviewPlayerState build() => const PreviewPlayerState();
+
+  void emit(PreviewPlayerState next) => state = next;
+}
+
+class _CountingPreviewButton extends PreviewButton {
+  const _CountingPreviewButton({required super.track, required this.onBuild});
+
+  final VoidCallback onBuild;
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    onBuild();
+    return super.build(context, ref);
+  }
+}
+
 class _TestLibraryCollectionsNotifier extends LibraryCollectionsNotifier {
   @override
   LibraryCollectionsState build() => LibraryCollectionsState(isLoaded: true);