The chat I mentioned above linked this issue, which, to be honest, I skimmed and said, ok, yeah, Astra's right, ControlMaster seems maybe like a big no go, then never tried. https://github.com/mobile-shell/mosh/issues/24

I tend to have ~20+ tabs open and each one has it's own tmux session inside of it, with multiple windows. I do think that making a terminal that can script and control multiple tmux sessions via control mode is, sort of, the longer destination ahead for me! That'll be exciting.