docs: def exit_on_signal():
      """
      Install a signal handler for HUP, INT, and TERM to call exit, allowing clean shutdown.
      When running a universe environment, it's important to shut down the container when the
      agent dies so you should either call this or otherwise arrange to exit on signals.
      """
      def shutdown(signal, frame):
          logger.warn('Received signal %s: exiting', signal)
          sys.exit(128+signal)
      signal.signal(signal.SIGHUP, shutdown)
      signal.signal(signal.SIGINT, shutdown)
      signal.signal(signal.SIGTERM, shutdown)