How does it loop, if at all? Does it just restart at the end after it falls out of `main()`?

This is definitely something I'd like to try. Gotta figure out where to run the server... maybe a good time to figure out how to do custom Home Assistant add-ons.

How long do those batteries last you? Even with the deep sleep, I imagine doing the WiFi handshake every time is going to be expensive.

As far as I understand it has a deep-sleep" timer that wakes it every X minutes (mine every 30). This gives me approximately 1 Month with 4 AA rechargeable. Larger sleep intervals, other esp dev boards or larger rechargeable will increase this.