https://github.com/jerome-pouiller/reredirect/
Ended up using dtach. Needs to be run ahead of time, but very direct and minimal stdin/stdout piping tool that's worked great with everything I've thrown at it. https://github.com/crigler/dtach
at least I think it would be possible to do "switch to another full terminal window, no splits, no status bar" without being a terminal emulator, I haven't tried.