be9c2bd19c
A system-level gateway unit has no ordering against user@<uid>.service and linger may be enabled after boot, so the bus can appear after the one-shot adoption in run_gateway() ran. Derive XDG_RUNTIME_DIR/DBUS_SESSION_BUS_ADDRESS fresh for the availability probe and every scoped spawn (cron worker, Kanban worker, PTY/pipe terminal spawns, scope cleanup) so the 60s failure TTL can actually recover. Refs #104893.