Eliminate need to restart receiver when sender is restarted

[stapelberg]

Currently, the receiver needs to be restarted when the sender is restarted:

• sender stops
• receiver still prints stats messages, pipeline still playing
• once sender restarts (!), receiver prints PAUSED, then prints READY, and hangs

We should check if the converse is also true, and make it so that no restarts are necessary either way.