feat(todo): the open sidebar lists favourites and the project tree, folds kept

Todo's open sidebar is laid out as Todoist's (the developer's decisions
of 10 Nov 2026): the favourite projects, filters and labels, then the
projects as a tree with their open counts, sub-projects folding. Browse
and the sidebar share their rows (project_lists.dart) and their folds,
which the device now keeps per person (FoldedProjects,
folded_projects.json in the person's folder) instead of forgetting them
at each start.

Whats-New: On a wide screen, the open sidebar lists your favourites and projects; folded sub-projects stay folded.
Whats-New-De: Auf breiten Bildschirmen zeigt die geöffnete Seitenleiste deine Favoriten und Projekte; eingeklappte Unterprojekte bleiben eingeklappt.

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

apps/todo/halkyon_todo_flutter/test/app/todo_app_test.dart

@@ -26,6 +26,7 @@ import 'package:halkyon_todo_flutter/src/feature/label/model/label.dart';
 import 'package:halkyon_todo_flutter/src/feature/location/data/location_reminder_gateway.dart';
 import 'package:halkyon_todo_flutter/src/feature/location/model/task_location.dart';
 import 'package:halkyon_todo_flutter/src/feature/location/widget/location_picker.dart';
+import 'package:halkyon_todo_flutter/src/feature/project/data/folded_projects.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/data/project_repository.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/model/project.dart';
 import 'package:halkyon_todo_flutter/src/feature/project/model/project_view.dart';
@@ -95,6 +96,9 @@ void main() {
   late MemoryLocationGateway locationGateway;
   late FakeSpeechInput speech;
 
+  /// The projects folded in Browse and the sidebar.
+  late FoldedProjects folded;
+
   /// How many syncs ran.
   late int syncs;
 
@@ -128,6 +132,7 @@ void main() {
     weather = FakeWeather();
     locationGateway = MemoryLocationGateway();
     speech = FakeSpeechInput();
+    folded = FoldedProjects();
     store = MemoryInstanceStore();
     looks = MemoryLookStore();
     gateway = FakeAuthGateway();
@@ -233,6 +238,7 @@ void main() {
               reminders: reminders,
               locationReminders: locationGateway,
               calendarFeeds: calendarFeeds,
+              foldedProjects: folded,
             );
           },
         ),
@@ -4778,6 +4784,96 @@ void main() {
         expect(find.byKey(NavigationFrame.sidebarKey), findsOneWidget);
         expect(looks.writes.last.sidebarOpen, isTrue);
       });
+
+      /// Seeds Home, a favourite, with its sub-project Garden, where Weed
+      /// is open, and Work, where Report is; opens the sidebar.
+      Future<Map<String, String>> openWithProjects(WidgetTester tester) async {
+        await start(tester, usedBefore: true);
+        final ids = await tester.runAsync(() async {
+          final projects = ProjectRepository(projectRows, keys);
+          final home = await projects.save(
+            const ProjectContent(name: 'Home', position: 1, favorite: true),
+          );
+          final garden = await projects.save(
+            ProjectContent(name: 'Garden', position: 2, parentId: home),
+          );
+          final work = await projects.save(
+            const ProjectContent(name: 'Work', position: 3),
+          );
+          final tasks = TaskRepository(taskRows, keys);
+          await tasks.add(TaskContent(title: 'Weed', projectId: garden));
+          await tasks.add(TaskContent(title: 'Report', projectId: work));
+          return {'Home': home, 'Garden': garden, 'Work': work};
+        });
+        projectRows.bringRemoteChanges();
+        taskRows.bringRemoteChanges();
+        tester.view.physicalSize = const Size(1200, 900);
+        await tester.pumpAndSettle();
+        await tester.tap(find.byTooltip('Open sidebar'));
+        await tester.pumpAndSettle();
+        return ids!;
+      }
+
+      Finder inSidebar(Finder finder) => find.descendant(
+        of: find.byKey(NavigationFrame.sidebarKey),
+        matching: finder,
+      );
+
+      testWidgets('open, it lists the favourites, then the projects as a '
+          'tree with their open tasks counted', (tester) async {
+        await openWithProjects(tester);
+
+        // The test's language is American English.
+        final favorites = tester.getTopLeft(inSidebar(find.text('Favorites')));
+        final projects = tester.getTopLeft(inSidebar(find.text('Projects')));
+        expect(favorites.dy, lessThan(projects.dy));
+        final homes = inSidebar(find.text('Home'));
+        expect(homes, findsNWidgets(2), reason: 'a favourite and a project');
+        expect(tester.getTopLeft(homes.first).dy, lessThan(projects.dy));
+        expect(
+          tester.getTopLeft(inSidebar(find.text('Garden'))).dx,
+          greaterThan(tester.getTopLeft(homes.last).dx),
+          reason: 'indented under its parent',
+        );
+        expect(
+          find.descendant(
+            of: find.ancestor(
+              of: inSidebar(find.text('Garden')),
+              matching: find.byType(ListTile),
+            ),
+            matching: find.text('1'),
+          ),
+          findsOneWidget,
+        );
+      });
+
+      testWidgets('folding a project there folds it in Browse too, kept on '
+          'the device', (tester) async {
+        final ids = await openWithProjects(tester);
+
+        await tester.tap(inSidebar(find.byTooltip('Hide sub-projects')));
+        await tester.pumpAndSettle();
+
+        expect(inSidebar(find.text('Garden')), findsNothing);
+        expect(folded.isFolded(ids['Home']!), isTrue);
+        await tester.tap(inSidebar(find.text('Browse')));
+        await tester.pumpAndSettle();
+        expect(find.text('Garden'), findsNothing);
+        expect(
+          find.byTooltip('Show sub-projects'),
+          findsNWidgets(2),
+          reason: "the sidebar's and Browse's",
+        );
+      });
+
+      testWidgets('a project tapped there opens', (tester) async {
+        await openWithProjects(tester);
+
+        await tester.tap(inSidebar(find.text('Work')));
+        await tester.pumpAndSettle();
+
+        expect(find.text('Report'), findsOneWidget);
+      });
     });
 
     group("a project's linked calendar (D39, the developer's decisions of "

apps/todo/halkyon_todo_flutter/test/feature/project/folded_projects_test.dart

@@ -0,0 +1,51 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_todo_flutter/src/feature/project/data/folded_projects.dart';
+
+/// Which projects' sub-projects are folded away, kept per device (the
+/// developer's decision of 10 Nov 2026), in Browse and the sidebar alike.
+void main() {
+  late Directory folder;
+  late File file;
+
+  setUp(() {
+    folder = Directory.systemTemp.createTempSync('folded');
+    file = File('${folder.path}/folded_projects.json');
+  });
+  tearDown(() => folder.deleteSync(recursive: true));
+
+  test('nothing is folded at first', () async {
+    final folded = await FoldedProjects.open(file);
+
+    expect(folded.isFolded('school'), isFalse);
+  });
+
+  test('a fold is kept for the next start, an unfold too', () async {
+    final folded = await FoldedProjects.open(file);
+    var told = 0;
+    folded.addListener(() => told++);
+
+    await folded.toggle('school');
+    await folded.toggle('home');
+    await folded.toggle('home');
+
+    expect(told, 3);
+    final again = await FoldedProjects.open(file);
+    expect(again.isFolded('school'), isTrue);
+    expect(again.isFolded('home'), isFalse);
+  });
+
+  test('a damaged file folds nothing', () async {
+    file.writeAsStringSync('{"school": ');
+
+    expect((await FoldedProjects.open(file)).isFolded('school'), isFalse);
+  });
+
+  test('without a file it folds for this session alone', () async {
+    final folded = FoldedProjects();
+    await folded.toggle('school');
+
+    expect(folded.isFolded('school'), isTrue);
+  });
+}