Function kill_process_group 

fn kill_process_group(child: &Child, signal: c_int, signal_name: &str)

Send signal to an entire process group in one shot (negated pid — see the two public wrappers below for why this targets a whole group, not just one process). Shared by both so the return-value handling — a silently-ignored failure would otherwise let a genuinely-failed kill (anything but the expected “already empty” ESRCH) read as a successful teardown — lives in exactly one place. Logs on any failure OTHER than ESRCH (the routine no-op case: the group was already empty, e.g. a prior SIGTERM’s own graceful shutdown already reaped it).