Method cancelTask

src/prompt/WorkflowManager.ts:436–440

* 取消任务

(id: string, reason: string)

   * 取消任务
   */
  public cancelTask(id: string, reason: string): WorkflowTask {
    const task = this.updateTask(id, { status: 'cancelled' });
    this.addTaskNote(id, `任务被取消: ${reason}`);
    return task;
  }

  /**
   * 添加任务备注