The adopted-worker monitor polled liveness at 1 Hz forever (a `ps` subprocess per tick on macOS). It now parks on the kernel's exit notification (Linux pidfd, macOS kqueue EVFILT_PROC/NOTE_EXIT, both awaited through tokio's AsyncFd), with a clearly marked 30 s liveness poll only where the watch cannot register. pa-core's open_pidfd now returns io::Result so the wait can tell ESRCH (already exited) from an unwatchable pid. The adopted arm matches the Child arm's shape: it waits for the exit, then honors the stop flags.