feat(album): zoom artwork when pulling down the Mornye header

lib/widgets/album_detail_header.dart

@@ -201,10 +201,10 @@ class AlbumDetailHeader extends StatelessWidget {
                         alignment: Alignment.topCenter,
                         child: SizedBox.square(
                           dimension: artworkSize,
-                          child: artwork,
+                          child: _AlbumStretchArtwork(child: artwork),
                         ),
                       )
-                    : artwork,
+                    : _AlbumStretchArtwork(child: artwork),
               ),
               Column(
                 children: [
@@ -458,6 +458,44 @@ class AlbumDetailHeader extends StatelessWidget {
   }
 }
 
+class _AlbumStretchArtwork extends StatelessWidget {
+  const _AlbumStretchArtwork({required this.child});
+
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    if (MediaQuery.disableAnimationsOf(context)) return child;
+    final position = Scrollable.of(context).position;
+    return LayoutBuilder(
+      builder: (context, constraints) => AnimatedBuilder(
+        animation: position,
+        child: RepaintBoundary(child: child),
+        builder: (context, artwork) {
+          final overscroll = position.hasContentDimensions
+              ? (position.minScrollExtent - position.pixels).clamp(
+                  0.0,
+                  double.infinity,
+                )
+              : 0.0;
+          final height = constraints.maxHeight;
+          final scale = height > 0 ? 1 + overscroll / height : 1.0;
+          // The viewport moves the details down during a pull. Keep the image
+          // at the top and enlarge it without changing the scrollable layout.
+          return Transform.translate(
+            offset: Offset(0, -overscroll),
+            child: Transform.scale(
+              scale: scale,
+              alignment: Alignment.topCenter,
+              child: artwork,
+            ),
+          );
+        },
+      ),
+    );
+  }
+}
+
 /// Keeps the pinned toolbar above the artwork without shifting the artwork or
 /// metadata down by the toolbar's safe-area height.
 class _AlbumOverlayToolbar extends SingleChildRenderObjectWidget {

test/mornye_detail_headers_test.dart

@@ -355,6 +355,106 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  for (final squareArtwork in [true, false]) {
+    for (final reduceMotion in [false, true]) {
+      testWidgets(
+        'album pull preserves controls (square: $squareArtwork, reduced motion: $reduceMotion)',
+        (tester) async {
+          tester.view.physicalSize = const Size(390, 844);
+          tester.view.devicePixelRatio = 1;
+          tester.view.padding = FakeViewPadding(top: 59, bottom: 34);
+          addTearDown(tester.view.reset);
+          final controller = ScrollController();
+          addTearDown(controller.dispose);
+          const artworkKey = ValueKey('stretch-album-artwork');
+          var plays = 0;
+          await tester.pumpWidget(
+            ProviderScope(
+              child: MaterialApp(
+                theme: MornyeTheme.build(Brightness.dark),
+                scrollBehavior: const MaterialScrollBehavior().copyWith(
+                  physics: const BouncingScrollPhysics(
+                    parent: AlwaysScrollableScrollPhysics(),
+                  ),
+                ),
+                builder: (context, child) => MediaQuery(
+                  data: MediaQuery.of(
+                    context,
+                  ).copyWith(disableAnimations: reduceMotion),
+                  child: child!,
+                ),
+                home: CollectionScaffold(
+                  scrollController: controller,
+                  isSelectionMode: false,
+                  onExitSelectionMode: () {},
+                  bottomInset: 0,
+                  appBar: AlbumDetailHeader(
+                    immersive: true,
+                    squareArtwork: squareArtwork,
+                    title: 'Album',
+                    expandedHeight: 400,
+                    showTitleInAppBar: false,
+                    background: const ColoredBox(
+                      key: artworkKey,
+                      color: Colors.orange,
+                    ),
+                    actions: AlbumPlayActions(
+                      playLabel: 'Play',
+                      shuffleTooltip: 'Shuffle',
+                      onPlay: () => plays++,
+                      onShuffle: () {},
+                    ),
+                  ),
+                  slivers: const [
+                    SliverToBoxAdapter(child: Text('Track list')),
+                    SliverToBoxAdapter(child: SizedBox(height: 2000)),
+                  ],
+                ),
+              ),
+            ),
+          );
+          await tester.pumpAndSettle();
+          final artwork = find.byKey(artworkKey);
+          final play = find.text('Play');
+          final tracks = find.text('Track list');
+          final originalArt = tester.getRect(artwork);
+          final originalPlay = tester.getRect(play);
+          final originalTracks = tester.getRect(tracks);
+          final originalBack = tester.getRect(find.byTooltip('Back'));
+          final element = tester.element(artwork);
+          final gesture = await tester.startGesture(const Offset(195, 250));
+          await gesture.moveBy(const Offset(0, 150));
+          await tester.pump();
+          final stretchedArt = tester.getRect(artwork);
+          expect(controller.offset, lessThan(0));
+          if (reduceMotion) {
+            expect(stretchedArt.size, originalArt.size);
+          } else {
+            expect(stretchedArt.width, greaterThan(originalArt.width));
+            expect(
+              stretchedArt.width / originalArt.width,
+              closeTo(stretchedArt.height / originalArt.height, 0.001),
+            );
+            expect(stretchedArt.top, closeTo(originalArt.top, 0.01));
+          }
+          expect(tester.getSize(play), originalPlay.size);
+          expect(tester.getRect(play).top, greaterThan(originalPlay.top));
+          expect(tester.getRect(tracks).top, greaterThan(originalTracks.top));
+          expect(tester.getRect(find.byTooltip('Back')), originalBack);
+          expect(play.hitTestable(), findsOneWidget);
+          expect(tester.element(artwork), same(element));
+          await gesture.up();
+          await tester.pumpAndSettle();
+          expect(tester.getRect(artwork), originalArt);
+          expect(tester.getRect(play), originalPlay);
+          await tester.tap(play);
+          expect(plays, 1);
+          expect(tester.takeException(), isNull);
+        },
+      );
+    }
+  }
+
   for (final brightness in Brightness.values) {
     for (final scale in [1.0, 2.0]) {
       testWidgets(