On SSH sessions to headless servers, DBUS_SESSION_BUS_ADDRESS and
XDG_RUNTIME_DIR may not be set even when the user's systemd instance
is running via linger. This causes 'systemctl --user' to fail with
'Failed to connect to bus: No medium found', breaking gateway
restart/start/stop as a service and falling back to foreground mode.
Add _ensure_user_systemd_env() that detects the standard D-Bus socket
at /run/user/<UID>/bus and sets the env vars before any systemctl --user
call. Called from _systemctl_cmd() so all existing call sites benefit
automatically with zero changes.
Fixes: gateway restart falling back to foreground on headless servers
teknium1
452ba35804