QNX 6 / SCO OpenServer 5 only. sshd-session can keep root privileges on
platforms that lack file-descriptor passing and need root for PTY
allocation, via GatewayPorts and StreamLocalForwarding. Linux supports
file-descriptor passing, so this code path is not used in Echo's build.
OpenSSH 10.6 also forcibly disables those options on the affected
platforms.
https://www.openssh.com/releasenotes.html#10.6
https://security-tracker.debian.org/tracker/CVE-2026-106589