There are lots of situations where we want to spawn a new process (e.g. git add -p, vim), give stdin and stdout to that process, then wait for the process to finish, and rerender. There is a PR up looking at how to do this in the context of opening vim for a file, but after the subprocess finishes, the app gets very glitchy. This is probably the number one blocker to a lot of functionality that would be great to have in the app.