right now we don't have a good way to send a python enum (or our wrapper around a python enum) to/from rust, right?

Nope. If it’s numeric, we have some prior art in https://github.com/pantsbuild/pants/blob/198b8faaf1e0e926ff2beaa8a899b4d3bb327b21/src/rust/engine/logging/src/lib.rs#L57-L69 but there’s nothing nice at the moment 🙂