feat: recover bootloader OTA transfers

lib/pages/device_details_page.dart

@@ -497,10 +497,6 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
   }
 
   Future<FirmwareUpdateService?> _ensureFirmwareUpdateService() async {
-    final shifter = _shifterService;
-    if (shifter == null) {
-      return null;
-    }
     if (_firmwareUpdateService != null) {
       return _firmwareUpdateService;
     }
@@ -513,7 +509,7 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
 
     final service = FirmwareUpdateService(
       transport: ShifterFirmwareUpdateTransport(
-        shifterService: shifter,
+        shifterService: _shifterService,
         bluetoothController: bluetooth,
         buttonDeviceId: widget.deviceAddress,
       ),
@@ -585,7 +581,6 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
       return;
     }
 
-    await _startStatusStreamingIfNeeded();
     final updater = await _ensureFirmwareUpdateService();
     if (!mounted) {
       return;
@@ -872,9 +867,10 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
         currentConnectionStatus == ConnectionStatus.connected;
     final hasDeviceAccess =
         isCurrentConnected && _shifterService != null && _latestStatus != null;
+    final canUseFirmwareUpdate = isCurrentConnected;
     final canSelectFirmware =
-        hasDeviceAccess && !_isSelectingFirmware && !_isFirmwareUpdateBusy;
+        canUseFirmwareUpdate && !_isSelectingFirmware && !_isFirmwareUpdateBusy;
-    final canStartFirmware = hasDeviceAccess &&
+    final canStartFirmware = canUseFirmwareUpdate &&
         !_isSelectingFirmware &&
         !_isFirmwareUpdateBusy &&
         _selectedFirmware != null;
@@ -907,8 +903,26 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
                     status: _latestStatus,
                   ),
                   const SizedBox(height: 20),
-                  if (hasDeviceAccess) ...[
+                  if (canUseFirmwareUpdate) ...[
+                    _FirmwareUpdateCard(
+                      selectedFirmware: _selectedFirmware,
+                      progress: _dfuProgress,
+                      isSelecting: _isSelectingFirmware,
+                      isStarting: _isStartingFirmwareUpdate,
+                      canSelect: canSelectFirmware,
+                      canStart: canStartFirmware,
+                      phaseText: _dfuPhaseText(_dfuProgress.state),
+                      statusText: _firmwareUserMessage,
+                      formattedProgressBytes:
+                          '${_formatBytes(_dfuProgress.sentBytes)} / ${_formatBytes(_dfuProgress.totalBytes)}',
+                      onSelectFirmware: _selectFirmwareFile,
+                      onStartUpdate: _startFirmwareUpdate,
+                      expectedOffsetHex:
+                          '0x${_dfuProgress.expectedOffset.toRadixString(16).padLeft(8, '0').toUpperCase()}',
+                    ),
                     const SizedBox(height: 16),
+                  ],
+                  if (hasDeviceAccess) ...[
                     _StatusBanner(
                       status: _latestStatus,
                       onTap: _showStatusHistory,
@@ -1009,23 +1023,6 @@ class _DeviceDetailsPageState extends ConsumerState<DeviceDetailsPage> {
                         ),
                       ),
                     ),
-                    const SizedBox(height: 16),
-                    _FirmwareUpdateCard(
-                      selectedFirmware: _selectedFirmware,
-                      progress: _dfuProgress,
-                      isSelecting: _isSelectingFirmware,
-                      isStarting: _isStartingFirmwareUpdate,
-                      canSelect: canSelectFirmware,
-                      canStart: canStartFirmware,
-                      phaseText: _dfuPhaseText(_dfuProgress.state),
-                      statusText: _firmwareUserMessage,
-                      formattedProgressBytes:
-                          '${_formatBytes(_dfuProgress.sentBytes)} / ${_formatBytes(_dfuProgress.totalBytes)}',
-                      onSelectFirmware: _selectFirmwareFile,
-                      onStartUpdate: _startFirmwareUpdate,
-                      expectedOffsetHex:
-                          '0x${_dfuProgress.expectedOffset.toRadixString(16).padLeft(8, '0').toUpperCase()}',
-                    ),
                   ] else if (isCurrentConnected) ...[
                     _PairingRequiredCard(
                       isChecking: _isPairingCheckRunning,

lib/service/firmware_update_service.dart

@@ -12,11 +12,13 @@ class FirmwareUpdateService {
   FirmwareUpdateService({
     required FirmwareUpdateTransport transport,
     this.defaultStatusTimeout = const Duration(seconds: 2),
-    this.defaultBootloaderConnectTimeout = const Duration(seconds: 20),
+    this.defaultBootloaderConnectTimeout = const Duration(seconds: 60),
     this.defaultPostFinishResetTimeout = const Duration(seconds: 8),
     this.defaultReconnectTimeout = const Duration(seconds: 12),
     this.defaultVerificationTimeout = const Duration(seconds: 5),
+    this.queueFullBackoff = const Duration(milliseconds: 200),
     this.maxNoProgressRetries = 5,
+    this.maxReconnectResumeAttempts = 3,
   }) : _transport = transport;
 
   final FirmwareUpdateTransport _transport;
@@ -25,7 +27,9 @@ class FirmwareUpdateService {
   final Duration defaultPostFinishResetTimeout;
   final Duration defaultReconnectTimeout;
   final Duration defaultVerificationTimeout;
+  final Duration queueFullBackoff;
   final int maxNoProgressRetries;
+  final int maxReconnectResumeAttempts;
 
   final StreamController<DfuUpdateProgress> _progressController =
       StreamController<DfuUpdateProgress>.broadcast();
@@ -87,8 +91,17 @@ class FirmwareUpdateService {
         reconnectTimeout ?? defaultReconnectTimeout;
     final effectiveVerificationTimeout =
         verificationTimeout ?? defaultVerificationTimeout;
-    final normalizedSessionId = sessionId & 0xFF;
+    final rawSessionId = sessionId & 0xFF;
+    final normalizedSessionId = rawSessionId == 0 ? 1 : rawSessionId;
     final imageCrc32 = BootloaderDfuProtocol.crc32(imageBytes);
+    final startPayload = BootloaderDfuStartPayload(
+      totalLength: imageBytes.length,
+      imageCrc32: imageCrc32,
+      appStart: appStart,
+      imageVersion: imageVersion,
+      sessionId: normalizedSessionId,
+      flags: flags.rawValue,
+    );
 
     _isRunning = true;
     _cancelRequested = false;
@@ -114,30 +127,25 @@ class FirmwareUpdateService {
     try {
       _throwIfCancelled();
       _emitProgress(state: DfuUpdateState.enteringBootloader);
+      final alreadyInBootloader = await _isConnectedToBootloader();
+      if (!alreadyInBootloader) {
         final enterResult = await _transport.enterBootloader();
+        final appDisconnectResult = await _transport.waitForAppDisconnect(
+          timeout: effectiveBootloaderConnectTimeout,
+        );
+        if (appDisconnectResult.isErr()) {
           if (enterResult.isErr()) {
             throw _DfuFailure(
               'Failed to request bootloader DFU mode: ${enterResult.unwrapErr()}',
             );
           }
-
-      final appDisconnectResult = await _transport.waitForAppDisconnect(
-        timeout: effectiveBootloaderConnectTimeout,
-      );
-      if (appDisconnectResult.isErr()) {
           throw _DfuFailure(
             'Device did not disconnect into bootloader mode: ${appDisconnectResult.unwrapErr()}',
           );
         }
 
         _emitProgress(state: DfuUpdateState.connectingBootloader);
-      final bootloaderConnectResult = await _transport.connectToBootloader(
+        await _connectToBootloader(timeout: effectiveBootloaderConnectTimeout);
-        timeout: effectiveBootloaderConnectTimeout,
-      );
-      if (bootloaderConnectResult.isErr()) {
-        throw _DfuFailure(
-          'Could not connect to bootloader DFU mode: ${bootloaderConnectResult.unwrapErr()}',
-        );
       }
 
       final mtuResult =
@@ -161,17 +169,8 @@ class FirmwareUpdateService {
       await _readInitialStatus();
 
       _emitProgress(state: DfuUpdateState.erasing);
-      final startStatus = await _writeControlAndWaitForStatus(
+      final startStatus = await _sendStartAndWaitForStatus(
-        BootloaderDfuProtocol.encodeStartPayload(
+        startPayload,
-          BootloaderDfuStartPayload(
-            totalLength: imageBytes.length,
-            imageCrc32: imageCrc32,
-            appStart: appStart,
-            imageVersion: imageVersion,
-            sessionId: normalizedSessionId,
-            flags: flags.rawValue,
-          ),
-        ),
         timeout: effectiveStatusTimeout,
       );
       _requireOkStatus(
@@ -187,7 +186,9 @@ class FirmwareUpdateService {
         imageBytes: imageBytes,
         sessionId: normalizedSessionId,
         payloadSize: payloadSize,
+        startPayload: startPayload,
         statusTimeout: effectiveStatusTimeout,
+        bootloaderConnectTimeout: effectiveBootloaderConnectTimeout,
       );
 
       _emitProgress(state: DfuUpdateState.finishing);
@@ -289,6 +290,7 @@ class FirmwareUpdateService {
 
   Future<void> _subscribeToStatus() async {
     await _statusSubscription?.cancel();
+    _statusStreamError = null;
     _statusSubscription = _transport.subscribeToStatus().listen(
       _handleStatusPayload,
       onError: (Object error) {
@@ -313,15 +315,19 @@ class FirmwareUpdateService {
     required List<int> imageBytes,
     required int sessionId,
     required int payloadSize,
+    required BootloaderDfuStartPayload startPayload,
     required Duration statusTimeout,
+    required Duration bootloaderConnectTimeout,
   }) async {
     var expectedOffset = _currentProgress.expectedOffset;
     var retriesWithoutProgress = 0;
+    var reconnectResumeAttempts = 0;
 
     while (expectedOffset < imageBytes.length) {
       _throwIfCancelled();
-      _throwIfStatusStreamErrored();
+      _throwIfStatusStreamErrored(recoverable: true);
 
+      try {
         final frame = BootloaderDfuProtocol.buildDataFrame(
           imageBytes: imageBytes,
           sessionId: sessionId,
@@ -335,15 +341,20 @@ class FirmwareUpdateService {
 
         if (status.code == DfuBootloaderStatusCode.queueFull ||
             status.code == DfuBootloaderStatusCode.stateError) {
+          if (status.code == DfuBootloaderStatusCode.queueFull) {
+            await _delayWithCancel(queueFullBackoff);
+          }
           final recoveredStatus = await _requestStatus(timeout: statusTimeout);
           _requireOkStatus(
             recoveredStatus,
             sessionId: sessionId,
             operation: 'GET_STATUS after ${_statusLabel(status)}',
           );
-        expectedOffset =
+          expectedOffset = recoveredStatus.expectedOffset
-            recoveredStatus.expectedOffset.clamp(0, imageBytes.length).toInt();
+              .clamp(0, imageBytes.length)
+              .toInt();
           _emitTransferProgress(recoveredStatus, imageBytes.length);
+          reconnectResumeAttempts = 0;
           continue;
         }
 
@@ -364,29 +375,135 @@ class FirmwareUpdateService {
             sessionId: sessionId,
             operation: 'GET_STATUS after no progress',
           );
-        expectedOffset =
+          expectedOffset = recoveredStatus.expectedOffset
-            recoveredStatus.expectedOffset.clamp(0, imageBytes.length).toInt();
+              .clamp(0, imageBytes.length)
+              .toInt();
           _emitTransferProgress(recoveredStatus, imageBytes.length);
           continue;
         }
 
         retriesWithoutProgress = 0;
+        reconnectResumeAttempts = 0;
         expectedOffset = nextOffset;
         _emitTransferProgress(status, imageBytes.length);
+      } on _DfuFailure catch (failure) {
+        if (!failure.recoverable ||
+            reconnectResumeAttempts >= maxReconnectResumeAttempts) {
+          rethrow;
         }
+        reconnectResumeAttempts += 1;
+        final recoveredStatus = await _recoverTransferStatus(
+          timeout: statusTimeout,
+          bootloaderConnectTimeout: bootloaderConnectTimeout,
+          failure: failure,
+        );
+        if (recoveredStatus.isOk &&
+            recoveredStatus.sessionId == 0 &&
+            recoveredStatus.expectedOffset == 0) {
+          _emitProgress(
+            state: DfuUpdateState.erasing,
+            sentBytes: 0,
+            expectedOffset: 0,
+          );
+          final startStatus = await _sendStartAndWaitForStatus(
+            startPayload,
+            timeout: statusTimeout,
+          );
+          _requireOkStatus(
+            startStatus,
+            sessionId: sessionId,
+            expectedOffset: 0,
+            operation: 'START after reconnect',
+          );
+          expectedOffset = 0;
+          retriesWithoutProgress = 0;
+          _emitProgress(state: DfuUpdateState.transferring);
+          continue;
+        }
+        _requireOkStatus(
+          recoveredStatus,
+          sessionId: sessionId,
+          operation: 'GET_STATUS after reconnect',
+        );
+        expectedOffset =
+            recoveredStatus.expectedOffset.clamp(0, imageBytes.length).toInt();
+        _emitTransferProgress(recoveredStatus, imageBytes.length);
+        _emitProgress(state: DfuUpdateState.transferring);
+        continue;
+      }
+    }
+  }
+
+  Future<bool> _isConnectedToBootloader() async {
+    final result = await _transport.isConnectedToBootloader();
+    if (result.isErr()) {
+      throw _DfuFailure(
+        'Could not check bootloader DFU connection: ${result.unwrapErr()}',
+      );
+    }
+    return result.unwrap();
+  }
+
+  Future<void> _connectToBootloader({required Duration timeout}) async {
+    final bootloaderConnectResult = await _transport.connectToBootloader(
+      timeout: timeout,
+    );
+    if (bootloaderConnectResult.isErr()) {
+      throw _DfuFailure(
+        'Could not connect to bootloader DFU mode: ${bootloaderConnectResult.unwrapErr()}',
+      );
+    }
+  }
+
+  Future<DfuBootloaderStatus> _sendStartAndWaitForStatus(
+    BootloaderDfuStartPayload payload, {
+    required Duration timeout,
+  }) {
+    return _writeControlAndWaitForStatus(
+      BootloaderDfuProtocol.encodeStartPayload(payload),
+      timeout: timeout,
+    );
+  }
+
+  Future<DfuBootloaderStatus> _recoverTransferStatus({
+    required Duration timeout,
+    required Duration bootloaderConnectTimeout,
+    required _DfuFailure failure,
+  }) async {
+    await _statusSubscription?.cancel();
+    _statusSubscription = null;
+    _statusSignal = null;
+    _latestStatus = null;
+    _statusStreamError = null;
+    _statusEventCount = 0;
+    _emitProgress(
+      state: DfuUpdateState.connectingBootloader,
+      errorMessage: failure.message,
+    );
+    await _connectToBootloader(timeout: bootloaderConnectTimeout);
+    await _subscribeToStatus();
+    _emitProgress(state: DfuUpdateState.waitingForStatus);
+    return _requestStatus(timeout: timeout);
   }
 
   Future<DfuBootloaderStatus> _writeControlAndWaitForStatus(
     List<int> payload, {
     required Duration timeout,
+    bool recoverable = false,
   }) async {
     final eventCount = _statusEventCount;
     final result = await _transport.writeControl(payload);
     if (result.isErr()) {
       throw _DfuFailure(
-          'Failed to write bootloader control command: ${result.unwrapErr()}');
+        'Failed to write bootloader control command: ${result.unwrapErr()}',
+        recoverable: recoverable,
+      );
     }
-    return _waitForStatus(afterEventCount: eventCount, timeout: timeout);
+    return _waitForStatus(
+      afterEventCount: eventCount,
+      timeout: timeout,
+      recoverable: recoverable,
+    );
   }
 
   Future<DfuBootloaderStatus> _writeDataFrameAndWaitForStatus(
@@ -398,28 +515,35 @@ class FirmwareUpdateService {
     if (result.isErr()) {
       throw _DfuFailure(
         'Failed sending DFU data at offset ${frame.offset}: ${result.unwrapErr()}',
+        recoverable: true,
       );
     }
-    return _waitForStatus(afterEventCount: eventCount, timeout: timeout);
+    return _waitForStatus(
+      afterEventCount: eventCount,
+      timeout: timeout,
+      recoverable: true,
+    );
   }
 
   Future<DfuBootloaderStatus> _requestStatus({required Duration timeout}) {
     return _writeControlAndWaitForStatus(
       BootloaderDfuProtocol.encodeGetStatusPayload(),
       timeout: timeout,
+      recoverable: true,
     );
   }
 
   Future<DfuBootloaderStatus> _waitForStatus({
     required int afterEventCount,
     required Duration timeout,
+    bool recoverable = false,
   }) async {
     final deadline = DateTime.now().add(timeout);
     var observedEvents = afterEventCount;
 
     while (true) {
       _throwIfCancelled();
-      _throwIfStatusStreamErrored();
+      _throwIfStatusStreamErrored(recoverable: recoverable);
 
       if (_statusEventCount > observedEvents && _latestStatus != null) {
         return _latestStatus!;
@@ -427,14 +551,16 @@ class FirmwareUpdateService {
 
       final remaining = deadline.difference(DateTime.now());
       if (remaining <= Duration.zero) {
-        throw const _DfuFailure(
+        throw _DfuFailure(
           'Timed out waiting for bootloader DFU status. Reconnect and retry the update.',
+          recoverable: recoverable,
         );
       }
 
       final gotEvent = await _waitForNextStatusEvent(
         afterEventCount: observedEvents,
         timeout: remaining,
+        recoverable: recoverable,
       );
       if (gotEvent) {
         observedEvents = _statusEventCount - 1;
@@ -445,6 +571,7 @@ class FirmwareUpdateService {
   Future<bool> _waitForNextStatusEvent({
     required int afterEventCount,
     required Duration timeout,
+    required bool recoverable,
   }) async {
     if (_statusEventCount > afterEventCount) {
       return true;
@@ -467,7 +594,7 @@ class FirmwareUpdateService {
     }
 
     _throwIfCancelled();
-    _throwIfStatusStreamErrored();
+    _throwIfStatusStreamErrored(recoverable: recoverable);
     return _statusEventCount > afterEventCount;
   }
 
@@ -584,10 +711,21 @@ class FirmwareUpdateService {
     }
   }
 
-  void _throwIfStatusStreamErrored() {
+  Future<void> _delayWithCancel(Duration duration) async {
+    if (duration <= Duration.zero) {
+      return;
+    }
+    await Future.any<void>([
+      Future<void>.delayed(duration),
+      _cancelSignal?.future ?? Future<void>.value(),
+    ]);
+    _throwIfCancelled();
+  }
+
+  void _throwIfStatusStreamErrored({bool recoverable = false}) {
     final error = _statusStreamError;
     if (error != null) {
-      throw _DfuFailure(error);
+      throw _DfuFailure(error, recoverable: recoverable);
     }
   }
 
@@ -600,6 +738,8 @@ class FirmwareUpdateService {
 }
 
 abstract interface class FirmwareUpdateTransport {
+  Future<Result<bool>> isConnectedToBootloader();
+
   Future<Result<void>> enterBootloader();
 
   Future<Result<void>> waitForAppDisconnect({required Duration timeout});
@@ -630,15 +770,39 @@ class ShifterFirmwareUpdateTransport implements FirmwareUpdateTransport {
     required this.buttonDeviceId,
   });
 
-  final ShifterService shifterService;
+  final ShifterService? shifterService;
   final BluetoothController bluetoothController;
   final String buttonDeviceId;
 
   String? _bootloaderDeviceId;
 
+  @override
+  Future<Result<bool>> isConnectedToBootloader() async {
+    final currentState = bluetoothController.currentConnectionState;
+    if (currentState.$1 != ConnectionStatus.connected ||
+        currentState.$2 == null) {
+      return Ok(false);
+    }
+
+    final statusResult = await bluetoothController.readCharacteristic(
+      currentState.$2!,
+      universalShifterControlServiceUuid,
+      universalShifterDfuStatusCharacteristicUuid,
+    );
+    if (statusResult.isErr()) {
+      return Ok(false);
+    }
+    _bootloaderDeviceId = currentState.$2;
+    return Ok(true);
+  }
+
   @override
   Future<Result<void>> enterBootloader() {
-    return shifterService.writeCommand(UniversalShifterCommand.enterDfu);
+    final shifter = shifterService;
+    if (shifter == null) {
+      return Future.value(bail('Normal app control service is not available.'));
+    }
+    return shifter.writeCommand(UniversalShifterCommand.enterDfu);
   }
 
   @override
@@ -774,10 +938,17 @@ class ShifterFirmwareUpdateTransport implements FirmwareUpdateTransport {
   Future<Result<void>> verifyDeviceReachable(
       {required Duration timeout}) async {
     try {
-      final statusResult = await shifterService.readStatus().timeout(timeout);
+      final statusResult = await bluetoothController
+          .readCharacteristic(
+            buttonDeviceId,
+            universalShifterControlServiceUuid,
+            universalShifterStatusCharacteristicUuid,
+          )
+          .timeout(timeout);
       if (statusResult.isErr()) {
         return Err(statusResult.unwrapErr());
       }
+      CentralStatus.fromBytes(statusResult.unwrap());
       return Ok(null);
     } on TimeoutException {
       return bail(
@@ -874,9 +1045,10 @@ class ShifterFirmwareUpdateTransport implements FirmwareUpdateTransport {
 }
 
 class _DfuFailure implements Exception {
-  const _DfuFailure(this.message);
+  const _DfuFailure(this.message, {this.recoverable = false});
 
   final String message;
+  final bool recoverable;
 
   @override
   String toString() => message;

test/service/firmware_update_service_test.dart

@@ -24,6 +24,7 @@ void main() {
 
       expect(result.isOk(), isTrue);
       expect(transport.steps, [
+        'isConnectedToBootloader',
         'enterBootloader',
         'waitForAppDisconnect',
         'connectToBootloader',
@@ -48,6 +49,63 @@ void main() {
       await transport.dispose();
     });
 
+    test('starts directly when already connected to bootloader', () async {
+      final image = _validImage(80);
+      final transport = _FakeFirmwareUpdateTransport(
+        totalBytes: image.length,
+        alreadyInBootloader: true,
+      );
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultStatusTimeout: const Duration(milliseconds: 100),
+      );
+
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 8,
+      );
+
+      expect(result.isOk(), isTrue);
+      expect(transport.steps, [
+        'isConnectedToBootloader',
+        'negotiateMtu',
+        'readStatus',
+        'waitForBootloaderDisconnect',
+        'reconnectForVerification',
+        'verifyDeviceReachable',
+      ]);
+      expect(
+          transport.controlWrites.first.first, universalShifterDfuOpcodeStart);
+
+      await service.dispose();
+      await transport.dispose();
+    });
+
+    test('tolerates enter bootloader write error when app disconnects',
+        () async {
+      final image = _validImage(80);
+      final transport = _FakeFirmwareUpdateTransport(
+        totalBytes: image.length,
+        failEnterBootloader: true,
+      );
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultStatusTimeout: const Duration(milliseconds: 100),
+      );
+
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 12,
+      );
+
+      expect(result.isOk(), isTrue);
+      expect(transport.steps, contains('waitForAppDisconnect'));
+      expect(service.currentProgress.state, DfuUpdateState.completed);
+
+      await service.dispose();
+      await transport.dispose();
+    });
+
     test('backs off on queue-full status and resumes from GET_STATUS',
         () async {
       final image = _validImage(80);
@@ -80,6 +138,84 @@ void main() {
       await transport.dispose();
     });
 
+    test('reconnects and resumes from status after transient data failure',
+        () async {
+      final image = _validImage(130);
+      final transport = _FakeFirmwareUpdateTransport(
+        totalBytes: image.length,
+        failDataWriteAtOffsetOnce:
+            universalShifterBootloaderDfuMaxPayloadSizeBytes,
+      );
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultStatusTimeout: const Duration(milliseconds: 100),
+        defaultBootloaderConnectTimeout: const Duration(milliseconds: 100),
+      );
+
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 13,
+      );
+
+      expect(result.isOk(), isTrue);
+      expect(
+        transport.steps.where((step) => step == 'connectToBootloader').length,
+        2,
+      );
+      expect(
+        transport.controlWrites
+            .where((write) => write.first == universalShifterDfuOpcodeGetStatus)
+            .length,
+        1,
+      );
+      expect(
+        transport.dataWriteOffsets
+            .where(
+              (offset) =>
+                  offset == universalShifterBootloaderDfuMaxPayloadSizeBytes,
+            )
+            .length,
+        2,
+      );
+      expect(service.currentProgress.state, DfuUpdateState.completed);
+
+      await service.dispose();
+      await transport.dispose();
+    });
+
+    test('restarts START when reconnect status has no active session',
+        () async {
+      final image = _validImage(80);
+      final transport = _FakeFirmwareUpdateTransport(
+        totalBytes: image.length,
+        failDataWriteAtOffsetOnce:
+            universalShifterBootloaderDfuMaxPayloadSizeBytes,
+        resetSessionOnRecoveryStatus: true,
+      );
+      final service = FirmwareUpdateService(
+        transport: transport,
+        defaultStatusTimeout: const Duration(milliseconds: 100),
+        defaultBootloaderConnectTimeout: const Duration(milliseconds: 100),
+      );
+
+      final result = await service.startUpdate(
+        imageBytes: image,
+        sessionId: 14,
+      );
+
+      expect(result.isOk(), isTrue);
+      expect(
+        transport.controlWrites
+            .where((write) => write.first == universalShifterDfuOpcodeStart)
+            .length,
+        2,
+      );
+      expect(service.currentProgress.state, DfuUpdateState.completed);
+
+      await service.dispose();
+      await transport.dispose();
+    });
+
     test('fails with bootloader status error on rejected START', () async {
       final image = _validImage(40);
       final transport = _FakeFirmwareUpdateTransport(
@@ -147,15 +283,23 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
   _FakeFirmwareUpdateTransport({
     required this.totalBytes,
     this.startStatusCode = DfuBootloaderStatusCode.ok,
+    this.alreadyInBootloader = false,
+    this.failEnterBootloader = false,
     this.queueFullOnFirstData = false,
     this.suppressFirstDataStatus = false,
+    this.failDataWriteAtOffsetOnce,
+    this.resetSessionOnRecoveryStatus = false,
     this.onDataWrite,
   });
 
   final int totalBytes;
   final DfuBootloaderStatusCode startStatusCode;
+  final bool alreadyInBootloader;
+  final bool failEnterBootloader;
   final bool queueFullOnFirstData;
   final bool suppressFirstDataStatus;
+  final int? failDataWriteAtOffsetOnce;
+  final bool resetSessionOnRecoveryStatus;
   final void Function()? onDataWrite;
 
   final StreamController<List<int>> _statusController =
@@ -167,12 +311,23 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
 
   int _sessionId = 0;
   int _expectedOffset = 0;
+  int _connectCount = 0;
+  bool _sentDataFailure = false;
   bool _sentQueueFull = false;
   bool _suppressedDataStatus = false;
 
+  @override
+  Future<Result<bool>> isConnectedToBootloader() async {
+    steps.add('isConnectedToBootloader');
+    return Ok(alreadyInBootloader);
+  }
+
   @override
   Future<Result<void>> enterBootloader() async {
     steps.add('enterBootloader');
+    if (failEnterBootloader) {
+      return bail('app disconnected before write response');
+    }
     return Ok(null);
   }
 
@@ -185,6 +340,7 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
   @override
   Future<Result<void>> connectToBootloader({required Duration timeout}) async {
     steps.add('connectToBootloader');
+    _connectCount += 1;
     return Ok(null);
   }
 
@@ -212,6 +368,10 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
       _expectedOffset = 0;
       _scheduleStatus(startStatusCode, _sessionId, 0);
     } else if (opcode == universalShifterDfuOpcodeGetStatus) {
+      if (resetSessionOnRecoveryStatus && _connectCount > 1) {
+        _sessionId = 0;
+        _expectedOffset = 0;
+      }
       _scheduleStatus(DfuBootloaderStatusCode.ok, _sessionId, _expectedOffset);
     } else if (opcode == universalShifterDfuOpcodeFinish) {
       _scheduleStatus(DfuBootloaderStatusCode.ok, payload[1], totalBytes);
@@ -229,6 +389,11 @@ class _FakeFirmwareUpdateTransport implements FirmwareUpdateTransport {
     final offset = _readLeU32(frame, 1);
     dataWriteOffsets.add(offset);
 
+    if (failDataWriteAtOffsetOnce == offset && !_sentDataFailure) {
+      _sentDataFailure = true;
+      return bail('simulated BLE write failure');
+    }
+
     if (queueFullOnFirstData && !_sentQueueFull) {
       _sentQueueFull = true;
       _scheduleStatus(