Function count_tree 

fn count_tree(
    p: &mut Popups,
    node: &str,
    exists: &dyn Fn(&str) -> bool,
    depth: usize,
) -> usize

Popup panes open or being opened anywhere below node: its own, and theirs, and so on. Records stay with each popup’s direct opener, so when a pane in the middle of a chain closes, the subtree under it still counts for whichever pane is now its root.