processEvent(event, ...args) {
    if (!event.event_id) {
      console.error(event);
      throw new Error(`Missing "event_id" on event`);
    }
    if (!event.type) {
      console.error(event);
      throw new Error(`Missing "type" on event`);
    }
    const eventProcessor = this.EventProcessors[event.type];
    if (!eventProcessor) {
      throw new Error(
        `Missing conversation event processor for "${event.type}"`,
      );
    }
    return eventProcessor.call(this, event, ...args);
  }
Process an event from the WebSocket server and compose items
@param {Object} event
@param  {...any} args
@returns {item: import('./client.js').ItemType | null, delta: ItemContentDeltaType | null}