anchor.diff:      flow: Flow.step(configuration.flowId),
     );
     Timeline.timeSync(
  -    '${configuration.debugLabel}: returning result',
  -    () { configuration.resultPort.send(result); },
  +    '${configuration.debugLabel}: exiting and returning a result', () {},
       flow: Flow.step(configuration.flowId),
     );
  +  Isolate.exit(configuration.resultPort, result);
   }
  
positive.code:   resultPort.close();
    exitPort.close();
    errorPort.close();
    isolate.kill();
    Timeline.finishSync();
    return result.future;
  }
  
negative.code:   final ReceivePort exitPort = ReceivePort();
    final ReceivePort errorPort = ReceivePort();
    Timeline.finishSync();
    await Isolate.spawn<_IsolateConfiguration<Q, FutureOr<R>>>(
      _spawn,
      _IsolateConfiguration<Q, FutureOr<R>>(
        callback,
  