when I run tmux kill-session, it sends SIGHUP to all processes that are running. This often isn't enough for my purposes, and I want to send SIGINT or SIGKILL.
A command like this would do the trick:
tmux list-panes -s -F "#{pane_pid} #{pane_current_command}" | grep -v tmux | awk '{print $1}' | xargs kill -9
(From this answer.)
How can I run this everytime I call kill-session? Apparently there is no before-kill-session hook.