A trick I've found is not attaching to that session, but starting a new session sharing all underlying windows. The model in tmux is [session]->[windows]->[panes], but something I did not realize until recently is that [session] can be multiple.

So rather than `tmux attach -t 0` use `tmux new-session -t 0`, allowing you to interact with the same windows without disturbing the other session.

Terminal A: 300x10 lines (long across, but short) Terminal B: 120x30 lines (standard new terminal size)

I have a tmux session running in A; I open terminal B, and attach to it with -new-session. My first pane is trimmed to the height of Terminal A.

If I do prefix-c (create new pane), the new pane is now the size of Terminal B - hurray!

But if I open Terminal C, which is yet another size, and attach to my existing session, it resizes every pane in Terminal B to the size of Terminal C; and when I disconnect from Terminal C, those panes do not appear to switch back to what they now should be, unconstrained by Terminal C.

(If I didn't explain this clearly, I can provide some screenshots later.)

I might be misunderstanding, but could you not use `tmux new-session -t 0` again for the third terminal?

> and when I disconnect from Terminal C, those panes do not appear to switch back to what they now should be, unconstrained by Terminal C.

Odd. Unrelated to your earlier issue, but that's not what I'd expect or am seeing when I try to reproduce is locally.

(Also, good to see you again, digitally - how's your hemisphere?)

I basically want an untouched session to go into a screensaver mode where it no longer controls the terminal size.

It's certainly not the end of the world to detach them, but I'd rather not. And detaching before I leave a session is just busywork.