我不明白为什么下面代码中addItem方法抛出的错误没有在try-catch块中捕获

void main() async {
  var executor = Executor();
  var stream = Stream.fromIterable([0, 1, 2, 3, 4, 5, 6, 7]);
  try {
    await for (var _ in stream) {
      executor.submit(() => demoMethod());
    }
    await executor.execute();
  } catch (e) {
    print(e);
  }
}

Future<void> demoMethod() async {
  var list = [1, 2, 3, 1, 4, 5];
  var executor = Executor();
  var test = Test();

  for (var element in list) {
    executor.submit(() => test.addItem(element));
  }

  await executor.execute();
  test.list.forEach(print);
}

class Test {
  var list = <int>[];

  Future<void> addItem(int i) async {
    if (list.contains(i)) {
      throw Exception('Item exists');
    }
    list.add(i);
  }
}

class Executor {
  final List<Future<void>> _futures = [];
  bool _disposed = false;

  void submit(Future<void> Function() computation) {
    if (!_disposed) {
      _futures.add(computation());
    } else {
      throw Exception('Executor is already disposed');
    }
  }

  Future<void> execute() async {
    await Future.wait(_futures, eagerError: true);
    _disposed = true;
  }
}

但以下代码能够正确捕获错误

void main() async {
  var executor = Executor();
  try {
    for (var i = 0; i < 10; i++) {
      executor.submit(() => demoMethod());
    }
    await executor.execute();
  } catch (e) {
    print(e);
  }
}

我猜这与流处理有关。