How should you properly design a message queuing and delivery confirmation system, ensuring a message genuinely sent while a WebSocket connection was temporarily disconnected is properly and reliably delivered once that particular connection actually genuinely reconnects?

A genuinely robust real time messaging system typically maintains a genuine local queue of messages that still genuinely need to actually be sent, properly adding a given message to that queue immediately when a user actually genuinely sends it, and only actually removing that particular message from the queue once the server genuinely confirms it was actually successfully received, meaning if the connection genuinely happens to drop before that particular confirmation ever actually arrives, the message genuinely remains properly queued and is automatically resent the very instant the connection genuinely successfully reconnects, ensuring no message is ever accidentally silently lost due to a genuinely temporary connectivity interruption.

class MessageQueue {
  final List<PendingMessage> _pending = [];

  void send(String message) {
    final pending = PendingMessage(message);
    _pending.add(pending);
    channel.sink.add(jsonEncode({'id': pending.id, 'text': message}));
  }

  void onAck(String id) => _pending.removeWhere((m) => m.id == id);
}