Sounds: survive an audio device that crashes the app on open

A Windows friend's 1.3.0 dies about a second in on every start, right
around the 2 s audio warm-up (no Dart error, no close lines). Opening the
device is now logged and leaves audio-init.pending until it returns; a
start that finds it skips sounds instead of crashing again, and a sound
preview in Settings tries once more.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/test/sound_engine_test.dart

@@ -1,3 +1,4 @@
+import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:flutter_test/flutter_test.dart';
@@ -147,4 +148,46 @@ void main() {
       expect(b.deinits, 1);
     });
   });
+
+  group('crash mark', () {
+    late Directory dir;
+    setUp(() => dir = Directory.systemTemp.createTempSync('sound_mark'));
+    tearDown(() => dir.deleteSync(recursive: true));
+
+    test('exists only while the device opens', () async {
+      final mark = '${dir.path}/audio-init.pending';
+      var seen = false;
+      final b = _MarkBackend(() => seen = File(mark).existsSync());
+      final e = SoundEngine(backend: b)..crashMark = mark;
+      expect(await e.warmUp(), isTrue);
+      expect(seen, isTrue, reason: 'there while opening');
+      expect(File(mark).existsSync(), isFalse, reason: 'gone once open');
+    });
+
+    test('left by a crash: sounds stay off, a preview tries again', () async {
+      final mark = '${dir.path}/audio-init.pending';
+      File(mark).writeAsStringSync('opening the audio device');
+      final b = _FakeBackend();
+      final e = SoundEngine(backend: b)..crashMark = mark;
+      await e.play('chat', 'k', _bytes, volume: 1);
+      expect(b.inits, 0, reason: 'never opened after a crash');
+      expect(b.plays, isEmpty);
+      e.retry();
+      await e.play('chat', 'k', _bytes, volume: 1);
+      expect(b.inits, 1);
+      expect(b.plays, hasLength(1));
+      expect(File(mark).existsSync(), isFalse);
+    });
+  });
+}
+
+class _MarkBackend extends _FakeBackend {
+  final void Function() onInit;
+  _MarkBackend(this.onInit);
+
+  @override
+  Future<void> init() async {
+    onInit();
+    await super.init();
+  }
 }