queueSend method

@override Future<String> queueSend(String requestUri)

Queue a send for OFFLINE-first delivery (invariant 4): durably persist the send INTENT (the same ZIP-321 URI) and return immediately — no network, no signing, no money movement. It survives a process kill and proposes → signs → broadcasts on the next online sync (proposing at SEND time, not now, is what stops a long-queued send from ever carrying a stale anchor). Returns the opaque queued-send id; throws queuedSendsFull at the durable cap (a real send is never silently dropped).

Implementation

@override
Future<String> queueSend(String requestUri) async {
  queueCount++;
  lastQueueUri = requestUri;
  if (queueThrows != null) throw queueThrows!;
  return queuedId;
}