gistfile1.sh

myscope=$(cat /proc/$PPID/cgroup | rev | cut -d/ -f1 | rev);

swaymsg -m -t subscribe '["window"]' \
  | jq '.container.pid' \
  | (while read pid; do cat /proc/$pid/cgroup | cut -d: -f3- ; done) \
  | (rev | cut -d '/' -f1 | rev | grep -E '^run-[[:alnum:]].*\.scope$') \
  | (
    last="";
    while read scope; do 
      if [ ! -z "$last" ] && [ "$last" != "$myscope" ]; then
        printf "exiting %s, freezing\n" "$last"; 
        (set -x; systemctl kill --user --signal STOP "$last"); 
      fi ;
      (set -x; systemctl kill --user --signal CONT "$scope");
      last="$scope";
    done
  )