anchor.diff:        flow.id,
       ),
       errorsAreFatal: true,
  -    onExit: resultPort.sendPort,
  +    onExit: exitPort.sendPort,
       onError: errorPort.sendPort,
     );
     final Completer<R> result = Completer<R>();
  
positive.code: }
  
  Future<void> _spawn<Q, R>(_IsolateConfiguration<Q, FutureOr<R>> configuration) async {
    R result;
    await Timeline.timeSync(
      configuration.debugLabel,
      () async {
        final FutureOr<R> applicationResult = await configuration.apply();
        result = await applicationResult;
      },
      flow: Flow.step(configuration.flowId),
    );
  
negative.code:   final Flow flow = Flow.begin();
    Timeline.startSync('$debugLabel: start', flow: flow);
    final ReceivePort resultPort = ReceivePort();
    final ReceivePort exitPort = ReceivePort();
    final ReceivePort errorPort = ReceivePort();
    Timeline.finishSync();
    final Isolate isolate = await Isolate.spawn<_IsolateConfiguration<Q, FutureOr<R>>>(
  