Except anyhow is compatible in that direction. io::Error and thiserror types will automatically convert to anyhow errors.

In my experience it's not quite as automatic as you'd hope. I always often to throw in stuff like `.map_err(Into::into)` or `Ok(foo?)` to convert the errors.

Not the end of the world but I do think defending the proliferation of error types in typical Rust projects is copium.

Yes, `?` automatically does `.into()`.

There are plenty of reasons you can complain about Rust's error handling, but "proliferation of error types" feels like a misunderstanding of how Rust error handling works in the first place.