I'm normally not a BSD user. I'm more familiar with "screen" than "tmux". To me, a "terminal multiplexer" is a physical piece of hardware. It has numerous slow serial lines to which one may attach terminals, modems, or consoles. It time-multiplexes them to/from a single high-speed link, typically by interleaving the streams of data bit by bit.

I don't see tmux being available as a library that I could link into my emulator. If it can be a library, then yes my emulator could implement the tmux protocol. This turns out to be almost exactly what I was proposing, with the terminal state implemented by a library within the emulator. I'd just be missing the user-friendly aspect of automatically popping up the terminal windows when my emulator starts, but perhaps that could be arranged by having the emulator start xterm running tmux.

This is comparable to using vnc protocol for VGA. I have this implemented, but nobody likes to use it. Everybody prefers the built-in video window to show the guest's VGA.

If you meant to not link in the tmux code though, that won't work.

Instead of insisting that there is a terminal emulator issue on the client side, I insist that there not be a distinct client. The code that tracks terminal state (cursor position, current character attributes, etc.) pretty much needs to live in the emulator. That is the only reasonable way to ensure that the state can be saved and restored by the emulator. Actually displaying this state could be done by connecting a client (annoying) or just by popping up a window.

Another nice thing about having the terminal windows built into the emulator is that they all go away when the emulator does, even if that is a crash.