heartbeat

--screenshots should take an option of: off, on, only-on-failure or space-efficient.

space-efficient be the default in heartbeat and would retain just the last step's screenshot on successful runs, and retain all steps on errors. This is important because screenshots, even with the efficiency gains we've recently gotten, just take up too much space and cost too much. Even a handful

这里的路由和server通信是否可以用一个长连接来维护更好