feat(todo): a task done ticks on phones and chimes on desktops

The developer's request of 10 Nov 2026: completing a task should feel like
something. `CompletionFeedback`, held by `TodoDevice` and handed to each
person's `TodoPerson`, gives a light haptic tick on Android and iOS and, on
desktops, a short quiet chime of our own: two soft bell tones a fifth apart,
synthesized by `apps/todo/tool/completion_sound.dart` into
`assets/sounds/task_done.wav`, so it needs no one's licence. A task's check
and the selection's Complete call it once, however many tasks are done;
an undo is silent.

Settings' Tasks turns the chime off on a desktop, kept per device in
`<app support>/completion_feedback.json`; a phone is offered no switch. A
device that can't play loses only the sound. The player is `audioplayers`,
as Learn's sounds: on Linux it links GStreamer, so Todo's snap gains the
`audio-playback` plug and GStreamer's headers to build, as Learn's recipe has.

Whats-New: Completing a task now gives a light tap on phones and a short chime on computers, which Settings › Tasks turns off.
Whats-New-De: Eine erledigte Aufgabe gibt jetzt auf dem Handy ein leichtes Tippen und am Computer einen kurzen Klang, den du unter Einstellungen › Aufgaben ausschaltest.

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

@@ -42,6 +42,7 @@ import 'package:halkyon_todo_flutter/src/feature/section/data/section_repository
 import 'package:halkyon_todo_flutter/src/feature/section/model/section.dart';
 import 'package:halkyon_todo_flutter/src/feature/settings/data/settings_repository.dart';
 import 'package:halkyon_todo_flutter/src/feature/settings/model/todo_settings.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/data/completion_feedback.dart';
 import 'package:halkyon_todo_flutter/src/feature/task/data/task_repository.dart';
 import 'package:halkyon_todo_flutter/src/feature/task/model/repeat.dart';
 import 'package:halkyon_todo_flutter/src/feature/task/model/task.dart';
@@ -99,6 +100,12 @@ void main() {
   /// The projects folded in Browse and the sidebar.
   late FoldedProjects folded;
 
+  /// What the device did as tasks were done: `tick` or `chime`, in order.
+  late List<String> felt;
+
+  /// What a task done feels like: a phone's unless a test says.
+  late CompletionFeedback completion;
+
   /// How many syncs ran.
   late int syncs;
 
@@ -133,6 +140,11 @@ void main() {
     locationGateway = MemoryLocationGateway();
     speech = FakeSpeechInput();
     folded = FoldedProjects();
+    felt = [];
+    completion = CompletionFeedback(
+      tick: () async => felt.add('tick'),
+      chime: () async => felt.add('chime'),
+    );
     store = MemoryInstanceStore();
     looks = MemoryLookStore();
     gateway = FakeAuthGateway();
@@ -239,6 +251,7 @@ void main() {
               locationReminders: locationGateway,
               calendarFeeds: calendarFeeds,
               foldedProjects: folded,
+              completionFeedback: completion,
             );
           },
         ),
@@ -3917,13 +3930,16 @@ void main() {
       await tester.pumpAndSettle();
       expect(find.text('Water plants'), findsNothing);
       expect(find.text('Task done'), findsOneWidget);
+      expect(felt, ['tick'], reason: "a phone's tick");
 
       await tester.tap(find.text('Undo'));
       await tester.pumpAndSettle();
       expect(find.text('Water plants'), findsOneWidget);
+      expect(felt, ['tick'], reason: 'nothing on an undo');
 
       await tester.tap(find.byTooltip('Mark as done'));
       await tester.pumpAndSettle();
+      expect(felt, ['tick', 'tick']);
       await tester.tap(find.byTooltip('Display'));
       await tester.pumpAndSettle();
       await tester.tap(find.text('Completed tasks'));
@@ -6023,6 +6039,7 @@ void main() {
         await tester.pumpAndSettle();
         expect(find.text('Water plants'), findsNothing);
         expect(find.text('2 tasks done'), findsOneWidget);
+        expect(felt, ['tick'], reason: 'once for both');
         await tester.tap(find.text('Undo'));
         await tester.pumpAndSettle();
         expect(find.text('Water plants'), findsOneWidget);
@@ -6708,6 +6725,58 @@ void main() {
         );
       });
 
+      testWidgets("a desktop's chime of a task done is turned off in Tasks, "
+          'for the device; a phone, which ticks, is offered none', (
+        tester,
+      ) async {
+        await start(tester, usedBefore: true);
+        await openSettings(tester);
+        expect(find.text('Sound when done'), findsNothing);
+
+        await tester.pumpWidget(const SizedBox());
+        completion = CompletionFeedback(
+          sounds: true,
+          tick: () async => felt.add('tick'),
+          chime: () async => felt.add('chime'),
+        );
+        await start(tester, usedBefore: true);
+        await seed(
+          tester,
+          TaskContent(title: 'Water plants', projectId: inbox()),
+        );
+        await goTab(tester, 'Inbox');
+        await tester.tap(find.byTooltip('Mark as done'));
+        await tester.pumpAndSettle();
+        expect(felt, ['chime']);
+        // The undo's snack bar gone first, as it would be by the time.
+        ScaffoldMessenger.of(
+          tester.element(find.byType(SnackBar)),
+        ).removeCurrentSnackBar();
+        await tester.pumpAndSettle();
+
+        await openSettings(tester);
+        await tapInSettings(tester, 'Sound when done');
+        expect(completion.soundOn, isFalse);
+        expect(
+          tester
+              .widget<SwitchListTile>(
+                find.widgetWithText(SwitchListTile, 'Sound when done'),
+              )
+              .value,
+          isFalse,
+        );
+        await tester.pageBack();
+        await tester.pumpAndSettle();
+        await seed(
+          tester,
+          TaskContent(title: 'Post letter', projectId: inbox()),
+        );
+        await goTab(tester, 'Inbox');
+        await tester.tap(find.byTooltip('Mark as done'));
+        await tester.pumpAndSettle();
+        expect(felt, ['chime'], reason: 'quiet now');
+      });
+
       testWidgets('a task added with a time gets the automatic reminder; '
           'reminders are snoozed for as long as set', (tester) async {
         await start(tester, usedBefore: true);

apps/todo/halkyon_todo_flutter/test/feature/task/completion_feedback_test.dart

@@ -0,0 +1,83 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_todo_flutter/src/feature/task/data/completion_feedback.dart';
+import 'package:path/path.dart' as p;
+
+void main() {
+  late int ticks;
+  late int chimes;
+
+  setUp(() {
+    ticks = 0;
+    chimes = 0;
+  });
+
+  Future<void> tick() async => ticks++;
+  Future<void> chime() async => chimes++;
+
+  test('a phone ticks once a task is done, and offers no sound', () async {
+    final feedback = CompletionFeedback(tick: tick, chime: chime);
+
+    await feedback.completed();
+
+    expect(feedback.offersSound, isFalse);
+    expect((ticks, chimes), (1, 0));
+  });
+
+  test('a desktop chimes, while its sound is on, and never ticks', () async {
+    final feedback = CompletionFeedback(
+      sounds: true,
+      tick: tick,
+      chime: chime,
+    );
+    expect(feedback.offersSound, isTrue);
+    expect(feedback.soundOn, isTrue, reason: 'on at first');
+
+    await feedback.completed();
+    expect((ticks, chimes), (0, 1));
+
+    await feedback.setSoundOn(on: false);
+    await feedback.completed();
+    expect((ticks, chimes), (0, 1));
+  });
+
+  test("a sound that can't play takes nothing with it", () async {
+    final feedback = CompletionFeedback(
+      sounds: true,
+      chime: () async => throw StateError('no GStreamer'),
+    );
+
+    await expectLater(feedback.completed(), completes);
+  });
+
+  group('kept on the device', () {
+    late Directory folder;
+
+    setUp(() async {
+      folder = await Directory.systemTemp.createTemp('completion');
+      addTearDown(() => folder.delete(recursive: true));
+    });
+
+    test('the sound turned off stays off when the app opens again', () async {
+      final file = File(p.join(folder.path, 'completion_feedback.json'));
+      final feedback = await CompletionFeedback.open(file, sounds: true);
+      var changes = 0;
+      feedback.addListener(() => changes++);
+
+      await feedback.setSoundOn(on: false);
+      expect(changes, 1);
+
+      final again = await CompletionFeedback.open(file, sounds: true);
+      expect(again.soundOn, isFalse);
+    });
+
+    test('a file that is no setting leaves the sound on', () async {
+      final file = File(p.join(folder.path, 'completion_feedback.json'));
+      await file.writeAsString('not json');
+      expect((await CompletionFeedback.open(file, sounds: true)).soundOn, true);
+      await file.writeAsString('[1]');
+      expect((await CompletionFeedback.open(file, sounds: true)).soundOn, true);
+    });
+  });
+}