Improve pipeline thread consumer task cancellation

Because the pipeline thread consumer is single-threaded and runs tasks sequentially, there's the real possibility that a single bad task could starve it.

For now, Ctrl+C should cancel whatever task is running. This may indeed include background tasks...

But some ideas for improving this are:

• A key-chord to cancel/unblock the pipeline thread when something other than console input is being run
• A monitor thread to supervise the pipeline thread that:
  • Logs when tasks drag on
  • Alerts users to long running tasks
  • Allows cancellation
  • Can completely reset the main runspace...

未指定文件、测试或入口点。先定位 pipeline 线程消费者，并跟踪其现有的 Ctrl+C 取消路径；在修改之前，明确需要的取消和监控行为。完成标准应包括一种已达成共识的方法，以防止长时间运行的任务使消费者得不到调度。