Indeed... or the Go library fsm[1] based on javascript-state-machine. I thought I'd use them both in a game I'm building, but I'm leaning towards the idea that the UI state is just the state that's already in the server's model.

I'm happy that the ability to generate GraphViz drawings has already helped me find a bug, at design time!

[1] https://github.com/looplab/fsm