feat(todo): dialogs on the desktop, the tabs reordered, a task's path and menu (ADR 0033, D11 to D14)

- halkyon_ui: showAdaptiveSheet shows a dialog on Linux, macOS and Windows
  at every width (bottom sheets stay on phones and tablets below expanded
  windows), so Learn and Train follow; SheetScaffold takes a heading in
  the title's place and may leave out its close button.
- Todo: the tabs are Inbox, Today, Upcoming, Browse, Today still opening;
  `serverpod start` launches the app on Linux, as it has no web build.
- A task's sheet shows where the task is (its project, an icon once tasks
  are above it, and the tasks above it, each opening what it names) and a
  ⋮ menu in place of its close button: when it was added (its UUID v7),
  Duplicate with its sub-tasks, hiding its done sub-tasks (synced in its
  payload), Close in the pane, Delete after asking. The description's icon
  stays by its first line.
- A row names its project and section at the end of its date's line; every
  menu entry has its icon.
- Learn: a studyset's path starts at the Library tab's icon, named by its
  tooltip.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_ui/lib/src/widget/adaptive_sheet.dart

@@ -7,14 +7,16 @@ import 'package:halkyon_ui/src/layout/window_size.dart';
 import 'package:lucide_icons_flutter/lucide_icons.dart';
 import 'package:material_ui/material_ui.dart';
 
-/// Shows [builder]'s sheet, usually a [SheetScaffold], as a bottom sheet in
-/// windows below expanded and as a dialog from there on; completes with the
-/// sheet's result either way.
+/// Shows [builder]'s sheet, usually a [SheetScaffold], as a bottom sheet on
+/// phones and tablets in windows below expanded, and as a dialog from there
+/// on and on the desktop (Linux, macOS, Windows) at every width; completes
+/// with the sheet's result either way.
 ///
 /// Expanded rather than Material's medium, because a bottom sheet is a touch
 /// surface: medium windows are mostly tablets, expanded ones mostly
 /// desktops, where a sheet rising from the bottom of a monitor reads as a
-/// phone screen moved over.
+/// phone screen moved over. That holds for a narrow window on the desktop
+/// too, so there it is always a dialog (the developer's, 1 Nov 2026).
 ///
 /// A sheet that asks before discarding changes (with a `PopScope`) passes
 /// [swipeable] false: a bottom sheet swiped away closes without asking its
@@ -26,7 +28,7 @@ Future<T?> showAdaptiveSheet<T>(
   required WidgetBuilder builder,
   bool swipeable = true,
 }) {
-  if (!context.windowSize.isAtLeastExpanded) {
+  if (!context.windowSize.isAtLeastExpanded && !_onDesktop) {
     return showModalBottomSheet<T>(
       context: context,
       useRootNavigator: true,
@@ -46,8 +48,11 @@ Future<T?> showAdaptiveSheet<T>(
   return showDialog<T>(
     context: context,
     builder: (context) => Dialog(
-      // More room than an alert's default: sheets hold forms and lists.
-      insetPadding: const EdgeInsets.symmetric(horizontal: 40, vertical: 32),
+      // More room than an alert's default: sheets hold forms and lists; and
+      // in a narrow desktop window less margin, so the form keeps its width.
+      insetPadding: context.windowSize.isAtLeastMedium
+          ? const EdgeInsets.symmetric(horizontal: 40, vertical: 32)
+          : const EdgeInsets.symmetric(horizontal: 16, vertical: 24),
       clipBehavior: Clip.antiAlias,
       child: _Presentation(
         isDialog: true,
@@ -58,6 +63,17 @@ Future<T?> showAdaptiveSheet<T>(
   );
 }
 
+/// Whether the app runs on the desktop, where sheets are dialogs at every
+/// width.
+bool get _onDesktop => switch (defaultTargetPlatform) {
+  TargetPlatform.linux ||
+  TargetPlatform.macOS ||
+  TargetPlatform.windows => true,
+  TargetPlatform.android ||
+  TargetPlatform.iOS ||
+  TargetPlatform.fuchsia => false,
+};
+
 /// Tells a [SheetScaffold] how it shows: as a dialog or a bottom sheet, and
 /// whether a drag handle sits above it.
 class const _Presentation({
@@ -96,6 +112,15 @@ class const SheetScaffold({
   /// The sheet's title.
   required final String title,
 
+  /// Shown in the title's place where set, such as a path to what the sheet
+  /// holds; [title] still names the sheet.
+  final Widget? heading,
+
+  /// Whether a close button ends the header. A sheet whose [action] is a
+  /// menu holding Close leaves it out; it still closes by back, a swipe, a
+  /// tap beside it or Escape.
+  final bool closeButton = true,
+
   /// The content; a scroll view holds it, so it is a plain column rather
   /// than a list.
   required final Widget body,
@@ -163,7 +188,9 @@ class const SheetScaffold({
         inset(
           _Header(
             title: title,
+            heading: heading,
             action: action,
+            closeButton: closeButton,
             onClose: busy
                 ? null
                 : onClose ?? () => Navigator.of(context).maybePop(),
@@ -261,26 +288,31 @@ class const SheetScaffold({
 /// swiped at all.
 class const _Header({
   required final String title,
+  required final Widget? heading,
   required final Widget? action,
+  required final bool closeButton,
   required final VoidCallback? onClose,
 }) extends StatelessWidget {
   @override
   Widget build(BuildContext context) => Row(
     children: [
       Expanded(
-        child: Text(
-          title,
-          style: Theme.of(context).textTheme.titleMedium,
-          maxLines: 1,
-          overflow: TextOverflow.ellipsis,
-        ),
+        child:
+            heading ??
+            Text(
+              title,
+              style: Theme.of(context).textTheme.titleMedium,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+            ),
       ),
       ?action,
-      IconButton(
-        tooltip: HalkyonUiLocalizations.of(context).close,
-        icon: const Icon(LucideIcons.x),
-        onPressed: onClose,
-      ),
+      if (closeButton)
+        IconButton(
+          tooltip: HalkyonUiLocalizations.of(context).close,
+          icon: const Icon(LucideIcons.x),
+          onPressed: onClose,
+        ),
     ],
   );
 }

packages/halkyon_ui/test/widget/adaptive_sheet_test.dart

@@ -48,7 +48,8 @@ void main() {
     await tester.pumpAndSettle();
   }
 
-  testWidgets('is a bottom sheet below expanded windows', (tester) async {
+  testWidgets('is a bottom sheet below expanded windows on a phone or a '
+      'tablet', (tester) async {
     await open(tester, width: 839);
 
     expect(find.byType(BottomSheet), findsOneWidget);
@@ -62,6 +63,23 @@ void main() {
     expect(find.byType(BottomSheet), findsNothing);
   });
 
+  for (final platform in [
+    TargetPlatform.linux,
+    TargetPlatform.macOS,
+    TargetPlatform.windows,
+  ]) {
+    testWidgets('is a dialog on the desktop however narrow the window '
+        '(${platform.name})', (tester) async {
+      debugDefaultTargetPlatformOverride = platform;
+      addTearDown(() => debugDefaultTargetPlatformOverride = null);
+      await open(tester, width: 400);
+
+      expect(find.byType(Dialog), findsOneWidget);
+      expect(find.byType(BottomSheet), findsNothing);
+      debugDefaultTargetPlatformOverride = null;
+    });
+  }
+
   for (final width in [400.0, 1200.0]) {
     testWidgets('keeps its close button and footer in view above a long body '
         '(${width.round()} wide)', (tester) async {
@@ -184,6 +202,43 @@ void main() {
     });
   });
 
+  testWidgets("a heading of its own takes the title's place, and the close "
+      'button may give way to its action', (tester) async {
+    tester.view.physicalSize = const Size(400, 900);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+    await tester.pumpWidget(
+      MaterialApp(
+        localizationsDelegates: HalkyonUiLocalizations.localizationsDelegates,
+        supportedLocales: HalkyonUiLocalizations.supportedLocales,
+        home: Scaffold(
+          body: Builder(
+            builder: (context) => TextButton(
+              onPressed: () => showAdaptiveSheet<void>(
+                context,
+                builder: (context) => const SheetScaffold(
+                  title: 'Task',
+                  heading: Text('Inbox › Shopping'),
+                  closeButton: false,
+                  action: Text('More'),
+                  body: Text('Body'),
+                ),
+              ),
+              child: const Text('Open'),
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.tap(find.text('Open'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Inbox › Shopping'), findsOneWidget);
+    expect(find.text('Task'), findsNothing);
+    expect(find.byTooltip('Close'), findsNothing);
+    expect(find.text('More'), findsOneWidget);
+  });
+
   testWidgets('a body that fits shows no lines', (tester) async {
     await open(tester, width: 400);