This seems mostly ok. The only thing that (imo) wouldn't pass code review is that big honking loop at https://github.com/achristmascarl/rainfrog/blob/main/src/app.... That thing needs to be refactored down to be readable, with individual logic chunks being put into their own functions and tidied up a bit.

That's not really Rust-specific, obviously, but all the `match` and `if let` and whatever other Rust stuff looks fine, so it's what I've got.