Hash ControlPath names so ssh master sockets fit the 104-byte limit

Unix socket paths are capped near 104 bytes on macOS. An app that derives extra ssh ControlMaster socket names from the user's ControlPath (for example appending -ops, -ops2) can exceed it once %h/%r/%p expand to long hostnames, and ssh then fails confusingly. Name derived masters <socket dir>/<hex of SHA-256(expanded carrier path + index)> instead (40 hex chars). Get the expanded path from ssh -G host | grep controlpath. In one case this cut the path from 66 to 55 bytes and made it independent of hostname length. Also register the carrier's path with the pool before the first warm-up, so early runs that ride it are counted against the per-connection session limit (sshd MaxSessions, default 10).