Function respawn_if_requested 

pub fn respawn_if_requested() -> Option<u32>

If a respawn was requested, launch a detached child running the captured launch command (now the new on-disk binary), and return its PID.

Call this after the daemon has torn down, so the listening port is free. The child is detached (new session on unix; DETACHED_PROCESS on windows) and inherits this process’s stdio, so it logs wherever the daemon did. A bare process has no supervisor, so if the child fails to start the service stays down until restarted by hand (the previous binary remains as a .bak).