Fantastic, I'd been daydreaming about doing similar for a while!

Do I understand correctly that the Quint code is not needed 'at runtime', that it's there for model-based testing of the XState implementation?

Right. Quint is not used in runtime and is not supposed to be. It's a strong testing layer. But there's much more to it. My bigger idea is that I would generate whatever implementation from it, hopefully, with an agentic loop - the MBT test is a natural feedback harness to leave coding overnight. So dnd-rust at some point, maybe? If someone develops a game, they would be able to generate a core logic in rust for bevy, in c# for unity, in (whatever it's used there) for godot. That's in an ideal world.

Yes that's exactly what I started thinking, this is great work - thank you!