test(dfu): cover retry failures and sequence wrap cases

test/service/dfu_protocol_test.dart

@@ -67,6 +67,19 @@ void main() {
       expect(frames[1].bytes.length, universalShifterDfuFrameSizeBytes);
       expect(frames[1].bytes.sublist(1, 18), image.sublist(63, 80));
     });
+
+    test('uses deterministic wrapping sequence numbers from custom start', () {
+      final image = List<int>.generate(
+          3 * universalShifterDfuFramePayloadSizeBytes,
+          (index) => index & 0xFF);
+
+      final frames = DfuProtocol.buildDataFrames(image, startSequence: 0xFE);
+
+      expect(frames.length, 3);
+      expect(frames[0].sequence, 0xFE);
+      expect(frames[1].sequence, 0xFF);
+      expect(frames[2].sequence, 0x00);
+    });
   });
 
   group('DfuProtocol sequence and ACK helpers', () {

test/service/firmware_update_service_test.dart

@@ -66,6 +66,32 @@ void main() {
       await transport.dispose();
     });
 
+    test('fails after bounded retries when ACK progress times out', () async {
+      final transport = _FakeFirmwareUpdateTransport(suppressDataAcks: true);
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultWindowSize: 1,
+        defaultAckTimeout: const Duration(milliseconds: 40),
+        maxNoProgressRetries: 2,
+      );
+
+      final image = List<int>.generate(90, (index) => index & 0xFF);
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 10,
+      );
+
+      expect(result.isErr(), isTrue);
+      expect(result.unwrapErr().toString(), contains('Upload stalled'));
+      expect(result.unwrapErr().toString(), contains('after 3 retries'));
+      expect(transport.controlWrites.last, [universalShifterDfuOpcodeAbort]);
+      expect(transport.sequenceWriteCount(0), 3);
+      expect(service.currentProgress.state, DfuUpdateState.failed);
+
+      await service.dispose();
+      await transport.dispose();
+    });
+
     test('cancel sends ABORT and reports aborted state', () async {
       final firstFrameSent = Completer<void>();
       final transport = _FakeFirmwareUpdateTransport(
@@ -201,6 +227,45 @@ void main() {
       await service.dispose();
       await transport.dispose();
     });
+
+    test('handles deterministic ACK sequence wrap-around across 0xFF->0x00',
+        () async {
+      const frameCount = 260;
+      final transport = _FakeFirmwareUpdateTransport();
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultWindowSize: 16,
+        defaultAckTimeout: const Duration(milliseconds: 100),
+      );
+
+      final image = List<int>.generate(
+        frameCount * universalShifterDfuFramePayloadSizeBytes,
+        (index) => index & 0xFF,
+      );
+
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 16,
+      );
+
+      expect(result.isOk(), isTrue);
+
+      var ffToZeroTransitions = 0;
+      for (var i = 1; i < transport.ackNotifications.length; i++) {
+        if (transport.ackNotifications[i - 1] == 0xFF &&
+            transport.ackNotifications[i] == 0x00) {
+          ffToZeroTransitions += 1;
+        }
+      }
+
+      expect(ffToZeroTransitions, greaterThanOrEqualTo(2));
+      expect(service.currentProgress.lastAckedSequence, 0x03);
+      expect(service.currentProgress.sentBytes, image.length);
+      expect(service.currentProgress.state, DfuUpdateState.completed);
+
+      await service.dispose();
+      await transport.dispose();
+    });
   });
 }
 
@@ -226,6 +291,7 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
 
   final List<List<int>> controlWrites = <List<int>>[];
   final List<List<int>> dataWrites = <List<int>>[];
+  final List<int> ackNotifications = <int>[];
   final List<String> postFinishSteps = <String>[];
   final Set<int> _droppedOnce = <int>{};
   int _lastAck = 0xFF;
@@ -254,9 +320,7 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
     if (opcode == universalShifterDfuOpcodeStart) {
       _lastAck = 0xFF;
       _expectedSequence = 0;
-      scheduleMicrotask(() {
+      _scheduleAck(0xFF);
-        _ackController.add([0xFF]);
-      });
     }
 
     if (opcode == universalShifterDfuOpcodeAbort) {
@@ -283,9 +347,7 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
 
     if (shouldDrop) {
       _droppedOnce.add(sequence);
-      scheduleMicrotask(() {
+      _scheduleAck(_lastAck);
-        _ackController.add([_lastAck]);
-      });
       return Ok(null);
     }
 
@@ -294,13 +356,19 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
       _expectedSequence = (_expectedSequence + 1) & 0xFF;
     }
 
-    scheduleMicrotask(() {
+    _scheduleAck(_lastAck);
-      _ackController.add([_lastAck]);
-    });
 
     return Ok(null);
   }
 
+  void _scheduleAck(int sequence) {
+    final ack = sequence & 0xFF;
+    ackNotifications.add(ack);
+    scheduleMicrotask(() {
+      _ackController.add([ack]);
+    });
+  }
+
   @override
   Future<Result<void>> waitForExpectedResetDisconnect({
     required Duration timeout,