fix(download): make picker drag dismissal natural

lib/widgets/app_bottom_sheet.dart

@@ -40,6 +40,39 @@ class AppSheetHandle extends StatelessWidget {
   }
 }
 
+/// A modal-sheet surface whose height and inner scroll position share one drag.
+///
+/// The child must attach the supplied [ScrollController] to its primary
+/// vertical scroll view. Pulling down at the top then moves the whole surface;
+/// releasing either restores it or dismisses it at the minimum extent.
+class AppDraggableSheet extends StatelessWidget {
+  const AppDraggableSheet({
+    super.key,
+    required this.builder,
+    this.initialChildSize = 0.88,
+    this.minChildSize = 0.25,
+    this.maxChildSize = 0.88,
+  });
+
+  final ScrollableWidgetBuilder builder;
+  final double initialChildSize;
+  final double minChildSize;
+  final double maxChildSize;
+
+  @override
+  Widget build(BuildContext context) {
+    return DraggableScrollableSheet(
+      expand: false,
+      snap: true,
+      shouldCloseOnMinExtent: true,
+      initialChildSize: initialChildSize,
+      minChildSize: minChildSize,
+      maxChildSize: maxChildSize,
+      builder: builder,
+    );
+  }
+}
+
 /// Standard chrome for modal sheet content: drag handle, optional title block,
 /// height cap, keyboard inset and bottom safe area, so each sheet only supplies
 /// its own body.

lib/widgets/download_service_picker.dart

@@ -13,6 +13,7 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
   final String? coverUrl;
   final void Function(String quality, String service) onSelect;
   final String? recommendedService;
+  final ScrollController? scrollController;
 
   const DownloadServicePicker({
     super.key,
@@ -21,6 +22,7 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
     this.coverUrl,
     required this.onSelect,
     this.recommendedService,
+    this.scrollController,
   });
 
   @override
@@ -42,12 +44,16 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
       useRootNavigator: true,
       backgroundColor: colorScheme.surfaceContainerHigh,
       isScrollControlled: true,
-      builder: (context) => DownloadServicePicker(
-        trackName: trackName,
-        artistName: artistName,
-        coverUrl: coverUrl,
-        onSelect: onSelect,
-        recommendedService: recommendedService,
+      enableDrag: false,
+      builder: (context) => AppDraggableSheet(
+        builder: (context, scrollController) => DownloadServicePicker(
+          trackName: trackName,
+          artistName: artistName,
+          coverUrl: coverUrl,
+          onSelect: onSelect,
+          recommendedService: recommendedService,
+          scrollController: scrollController,
+        ),
       ),
     );
   }
@@ -120,6 +126,7 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
 
     return SafeArea(
       child: SingleChildScrollView(
+        controller: widget.scrollController,
         child: Column(
           mainAxisSize: MainAxisSize.min,
           crossAxisAlignment: CrossAxisAlignment.start,

test/design_system_test.dart

@@ -259,6 +259,64 @@ void main() {
       expect(find.text('body'), findsOneWidget);
     });
 
+    testWidgets('draggable content moves as one surface and dismisses', (
+      tester,
+    ) async {
+      const sheetKey = ValueKey<String>('scrollable-sheet');
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: AppTheme.light(),
+          home: Scaffold(
+            body: Builder(
+              builder: (context) => ElevatedButton(
+                onPressed: () => showModalBottomSheet<void>(
+                  context: context,
+                  isScrollControlled: true,
+                  // Disable the route recognizer so the draggable surface,
+                  // rather than the modal's fallback gesture, is under test.
+                  enableDrag: false,
+                  builder: (_) => AppDraggableSheet(
+                    builder: (_, scrollController) => Material(
+                      key: sheetKey,
+                      child: ListView(
+                        controller: scrollController,
+                        children: const [
+                          SizedBox(height: 800, child: Text('sheet body')),
+                        ],
+                      ),
+                    ),
+                  ),
+                ),
+                child: const Text('open'),
+              ),
+            ),
+          ),
+        ),
+      );
+
+      await tester.tap(find.text('open'));
+      await tester.pumpAndSettle();
+      expect(find.byKey(sheetKey), findsOneWidget);
+
+      final initialTop = tester.getTopLeft(find.byKey(sheetKey)).dy;
+      final gesture = await tester.startGesture(
+        tester.getCenter(find.byKey(sheetKey)),
+      );
+      await gesture.moveBy(const Offset(0, 160));
+      await tester.pump();
+
+      expect(
+        tester.getTopLeft(find.byKey(sheetKey)).dy,
+        greaterThan(initialTop + 100),
+      );
+
+      await gesture.moveBy(const Offset(0, 260));
+      await gesture.up();
+      await tester.pumpAndSettle();
+
+      expect(find.byKey(sheetKey), findsNothing);
+    });
+
     testWidgets('sheet shape comes from the token scale', (tester) async {
       final shape =
           AppTheme.light().bottomSheetTheme.shape! as RoundedRectangleBorder;