Question

An AI wrote this Flutter code to parse and process a large analytics payload, claiming it 'runs in the background with async'. The UI still freezes for ~600ms when it runs and the frame counter drops to zero during the parse. Why doesn't `async` help here, and how would you fix it?

1Future<List<Event>> processPayload(String raw) async {2  final json = jsonDecode(raw);                 // big payload3  final events = <Event>[];4  for (final e in json['events']) {5    events.add(_transform(e));                   // CPU-heavy per item6  }7  return events;8}