fix(artist): zoom artwork during pull-down stretching

lib/widgets/mornye_artist_header.dart

@@ -157,9 +157,10 @@ class MornyeArtistHeader extends StatelessWidget {
   final String? logoUrl;
   final Widget? badge;
 
+  // A SliverMainAxisGroup clamps negative overlap, preventing this header from
+  // receiving the overscroll used for its stretch animation.
   @override
-  Widget build(BuildContext context) =>
+  Widget build(BuildContext context) => buildSlivers(context).single;
-      SliverMainAxisGroup(slivers: buildSlivers(context));
 
   List<Widget> buildSlivers(BuildContext context) {
     final surface = Theme.of(context).colorScheme.surface;
@@ -206,6 +207,7 @@ class MornyeArtistHeader extends StatelessWidget {
               32;
           return SliverAppBar(
             pinned: true,
+            stretch: !MediaQuery.disableAnimationsOf(context),
             expandedHeight: expandedHeight - MediaQuery.paddingOf(context).top,
             backgroundColor: surface,
             surfaceTintColor: Colors.transparent,
@@ -233,6 +235,7 @@ class MornyeArtistHeader extends StatelessWidget {
             ),
             flexibleSpace: FlexibleSpaceBar(
               collapseMode: CollapseMode.pin,
+              stretchModes: const [StretchMode.zoomBackground],
               background: Stack(
                 fit: StackFit.expand,
                 children: [
@@ -366,7 +369,30 @@ class _ArtistCollapsingArtwork extends ConsumerWidget {
                 sigmaY: blur,
                 tileMode: TileMode.clamp,
               ),
-              child: RepaintBoundary(child: child),
+              child: LayoutBuilder(
+                builder: (context, constraints) {
+                  final height = settings?.maxExtent ?? constraints.maxHeight;
+                  final zoom = height > 0
+                      ? (constraints.maxHeight / height).clamp(
+                          1.0,
+                          double.infinity,
+                        )
+                      : 1.0;
+                  // Stretch the photograph uniformly around its top edge.
+                  // Identity and actions remain outside this transform, moving
+                  // down with the sliver without growing along with the image.
+                  return OverflowBox(
+                    alignment: Alignment.topCenter,
+                    minHeight: height,
+                    maxHeight: height,
+                    child: Transform.scale(
+                      scale: zoom,
+                      alignment: Alignment.topCenter,
+                      child: RepaintBoundary(child: child),
+                    ),
+                  );
+                },
+              ),
             ),
           ),
           if (blurEnabled && fade < 1)

test/mornye_detail_headers_test.dart

@@ -222,6 +222,67 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  testWidgets('pulling the artist header zooms only the artwork', (
+    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);
+    const artworkKey = ValueKey('stretch-artwork');
+    await tester.pumpWidget(
+      ProviderScope(
+        child: MaterialApp(
+          theme: MornyeTheme.build(Brightness.dark),
+          home: Scaffold(
+            body: CustomScrollView(
+              physics: const BouncingScrollPhysics(
+                parent: AlwaysScrollableScrollPhysics(),
+              ),
+              slivers: const [
+                MornyeArtistHeader(
+                  name: 'Artist',
+                  artwork: ColoredBox(key: artworkKey, color: Colors.orange),
+                  actions: [Text('Artist action')],
+                  showTitle: false,
+                ),
+                SliverToBoxAdapter(child: Text('Album list')),
+                SliverToBoxAdapter(child: SizedBox(height: 2000)),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    final artwork = find.byKey(artworkKey);
+    final action = find.text('Artist action');
+    final albums = find.text('Album list');
+    final originalArt = tester.getRect(artwork);
+    final originalAction = tester.getRect(action);
+    final originalAlbums = tester.getRect(albums);
+    final element = tester.element(artwork);
+    final gesture = await tester.startGesture(const Offset(195, 350));
+    await gesture.moveBy(const Offset(0, 150));
+    await tester.pump();
+    final stretchedArt = tester.getRect(artwork);
+    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(action), originalAction.size);
+    expect(tester.getRect(action).top, greaterThan(originalAction.top));
+    expect(tester.getRect(albums).top, greaterThan(originalAlbums.top));
+    expect(tester.element(artwork), same(element));
+    await gesture.up();
+    await tester.pumpAndSettle();
+    expect(tester.getRect(artwork), originalArt);
+    expect(tester.getRect(action), originalAction);
+    expect(tester.takeException(), isNull);
+  });
+
   for (final brightness in Brightness.values) {
     for (final scale in [1.0, 2.0]) {
       testWidgets(