Function force_kill_tree 

pub fn force_kill_tree(pid: u32, started_at_ms: u64) -> usize

Kill pid and every descendant at once (SIGKILL on Unix, TerminateProcess on Windows), leaves first, after re-checking that pid is still the process started at started_at_ms (0 = unknown, judged by PID alone). One OS snapshot. Returns how many processes it signalled.