OpenSSH ControlMaster sessions hit sshd MaxSessions=10 with no fallback

When several tools share one ssh ControlMaster, every multiplexed session counts toward sshd's MaxSessions on that single TCP connection, and the default is 10. Past the limit, a mux client gets 'mux_client_request_session: session request failed: Session open refused by peer' and exits 255. With ControlMaster=no plus a ControlPath it does not fall back to a direct connection, so a long-lived interactive link that later needs a new session (a reconnect) just fails. Keep long-lived helpers and bursty one-off commands on their own master (a separate ControlPath) or their own connection, and cap concurrency per host. To check the limit quickly, start a private master with -fN and open 11 'sleep' sessions through it.