On boot as it's loading players, their file descriptor ID was saved, so it loads it up and resumes talking to the socket. It also loads the ID of the server socket descriptor. No need to send information to a new process as it just loads the previous game state.
If you're curious: https://github.com/borlak/acmud/blob/7c2442dfccfc28364fc399a...
And: https://github.com/borlak/acmud/blob/7c2442dfccfc28364fc399a...