Issue description

It would be nice to have a hook that gets triggered when a tmux pane/client is focussed but does not receive any user input (keyboard or mouse) for a period of time. Activity monitors like WakaTime pause logging time when user has not pressed any keystrokes. The hook would be activated only when a pane/client is focussed but does not receive any user input for a certain length of time.

The monitor-silence hook seems insufficient as it seems to not just track user input but program output too, and doesn't seem to care about being focussed pane or not.

Required information

Please provide the following information:

• tmux version (tmux -V) 3.3-next.
• Platform (uname -sp) Darwin arm.
• $TERM inside and outside of tmux (echo $TERM) xterm-256color, tmux-256color.