ui(settings): theme picker exit motion + trigger expand parity

lib/features/settings/theme_picker_button.dart

@@ -76,7 +76,10 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
       material.ScrollController();
   final material.TextEditingController _searchController =
       material.TextEditingController();
+  final material.ValueNotifier<bool> _menuOpen =
+      material.ValueNotifier<bool>(false);
   bool _triggerHovered = false;
+  bool _closingWithExit = false;
   String? _previewThemeId;
   String? _previewThemeLabel;
   QueryaTheme? _previewTheme;
@@ -97,9 +100,26 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
     _searchController.removeListener(_onSearchChanged);
     _searchController.dispose();
     _scrollController.dispose();
+    _menuOpen.dispose();
     super.dispose();
   }
 
+  /// Plays exit fade-slide, then removes the [MenuAnchor] overlay (#499).
+  Future<void> _closeWithExit() async {
+    if (!_controller.isOpen || _closingWithExit) return;
+    _closingWithExit = true;
+    _menuOpen.value = false;
+    final duration = context.motionDuration(QueryaMotion.standard);
+    if (duration > QueryaMotion.instant) {
+      await Future<void>.delayed(duration);
+    }
+    if (!mounted) return;
+    if (_controller.isOpen) {
+      _controller.close();
+    }
+    _closingWithExit = false;
+  }
+
   void _resetPreviewState() {
     _previewDebounce?.cancel();
     _previewRequestSerial++;
@@ -192,6 +212,14 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
 
     final anchor = material.MenuAnchor(
       controller: _controller,
+      onOpen: () {
+        _closingWithExit = false;
+        _menuOpen.value = true;
+      },
+      onClose: () {
+        _closingWithExit = false;
+        _menuOpen.value = false;
+      },
       crossAxisUnconstrained: false,
       alignmentOffset: material.Offset(
         0,
@@ -223,10 +251,13 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
         ),
       ),
       menuChildren: [
-        material.SizedBox(
-          width: menuWidth,
-          height: menuHeight,
-          child: _buildMenuPanel(context, cs),
+        _ThemePickerMenuEnter(
+          openNotifier: _menuOpen,
+          child: material.SizedBox(
+            width: menuWidth,
+            height: menuHeight,
+            child: _buildMenuPanel(context, cs),
+          ),
         ),
       ],
       builder: (context, controller, child) {
@@ -354,7 +385,7 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
                           widget.onSelected(theme.id);
                           _clearSearch();
                           _resetPreviewState();
-                          _controller.close();
+                          unawaited(_closeWithExit());
                         },
                       );
                     },
@@ -403,16 +434,10 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
               ? material.MainAxisSize.max
               : material.MainAxisSize.min,
           children: [
-            material.Expanded(
-              child: material.Text(
-                _triggerLabel,
-                maxLines: 1,
-                overflow: material.TextOverflow.ellipsis,
-                style: QueryaDropdownTokens.triggerTextStyle(
-                  context,
-                  _enabled ? cs.popoverForeground : cs.mutedForeground,
-                ),
-              ),
+            _triggerLabelText(
+              context: context,
+              cs: cs,
+              expand: widget.expandToParent || fieldWidth != null,
             ),
             material.SizedBox(width: chevronGap),
             material.Icon(
@@ -433,7 +458,7 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
         onTap: _enabled
             ? () {
                 if (controller.isOpen) {
-                  controller.close();
+                  unawaited(_closeWithExit());
                 } else {
                   _clearSearch();
                   _resetPreviewState();
@@ -446,6 +471,61 @@ class _ThemePickerButtonState extends material.State<ThemePickerButton> {
       ),
     );
   }
+
+  material.Widget _triggerLabelText({
+    required material.BuildContext context,
+    required ColorScheme cs,
+    required bool expand,
+  }) {
+    final text = material.Text(
+      _triggerLabel,
+      maxLines: 1,
+      overflow: material.TextOverflow.ellipsis,
+      style: QueryaDropdownTokens.triggerTextStyle(
+        context,
+        _enabled ? cs.popoverForeground : cs.mutedForeground,
+      ),
+    );
+    if (expand) {
+      return material.Expanded(child: text);
+    }
+    return text;
+  }
+}
+
+/// Enter/exit fade-slide for theme menu body while the overlay stays mounted.
+class _ThemePickerMenuEnter extends material.StatelessWidget {
+  const _ThemePickerMenuEnter({
+    required this.openNotifier,
+    required this.child,
+  });
+
+  final material.ValueNotifier<bool> openNotifier;
+  final material.Widget child;
+
+  @override
+  material.Widget build(material.BuildContext context) {
+    final duration = context.motionDuration(QueryaMotion.standard);
+    final enter = context.motionCurve(QueryaMotion.enter);
+    final exit = context.motionCurve(QueryaMotion.exit);
+    return material.ValueListenableBuilder<bool>(
+      valueListenable: openNotifier,
+      builder: (context, open, _) {
+        final curve = open ? enter : exit;
+        return material.AnimatedSlide(
+          offset: open ? material.Offset.zero : const material.Offset(0, -0.04),
+          duration: duration,
+          curve: curve,
+          child: material.AnimatedOpacity(
+            opacity: open ? 1 : 0,
+            duration: duration,
+            curve: curve,
+            child: child,
+          ),
+        );
+      },
+    );
+  }
 }
 
 class _ThemePickerRow extends material.StatefulWidget {

test/features/settings/theme_picker_button_test.dart

@@ -581,6 +581,60 @@ void main() {
 
       expect(picked, ThemeController.builtinQueryaLightId);
     });
+
+    testWidgets('compact trigger uses min mainAxisSize (no forced Expanded)',
+        (tester) async {
+      await tester.pumpWidget(
+        queryaThemeTestShell(
+          child: material.Scaffold(
+            body: ThemePickerButton(
+              themes: _fakeThemes(3),
+              selectedThemeId: 'theme-0',
+              onSelected: (_) {},
+            ),
+          ),
+        ),
+      );
+      await tester.pump();
+
+      final rows = tester.widgetList<material.Row>(find.byType(material.Row));
+      final triggerRow = rows.firstWhere(
+        (row) => row.mainAxisSize == material.MainAxisSize.min,
+      );
+      expect(triggerRow.mainAxisSize, material.MainAxisSize.min);
+      expect(
+        triggerRow.children.whereType<material.Expanded>(),
+        isEmpty,
+      );
+    });
+
+    testWidgets('selecting theme keeps overlay briefly for exit motion',
+        (tester) async {
+      final themes = _fakeThemes(5);
+      await tester.pumpWidget(
+        queryaThemeTestShell(
+          child: material.Scaffold(
+            body: ThemePickerButton(
+              themes: themes,
+              selectedThemeId: 'theme-0',
+              onSelected: (_) {},
+            ),
+          ),
+        ),
+      );
+      await tester.pump();
+
+      await tester.tap(find.text('Theme 00'));
+      await tester.pumpAndSettle();
+      expect(find.byType(material.ListView), findsOneWidget);
+
+      await tester.tap(find.text('Theme 01'));
+      await tester.pump(); // start exit; overlay still mounted
+      expect(find.byType(material.ListView), findsOneWidget);
+
+      await tester.pumpAndSettle();
+      expect(find.byType(material.ListView), findsNothing);
+    });
   });
 
   group('filterThemeDefinitions metadata', () {