Lots of nice stuff, since we are also in rust I see a lot of similar pattern in our codebase. I think your oneone crate could be split, we would probably be interested to collaborate on an http/2 support. We also have our own internal forgiving parser. It is an interesting thing to build tooling that must intentionally go beyond a spec since you basically have to reimplement all the primitives.

Couldn't it use vim itself for multiplexing?

you should really drop this. I don't what MitmProxy uses, but I know that I can just download it from here

https://mitmproxy.org/downloads

and it just works - I am not gonna try another program if I have to install these other parts to get it working