In spite of a solid blue light on the WiFi dongle, the RPI disk activity light seemed to indicate the bot was still running.packet_write_wait: Connection to 10.0.0.188 port 22: Broken pipe
I pulled the USB WiFi dongle out and then reinserted it. Surprise - it started blinking again and I was able to remote ssh into it.
Any ideas what can hang both the built-in WiFi and the USB WiFi?