code: func check(err error) {
  	if err == nil {
  		return
  	}
  
  	buildMU.Lock()
  	defer buildMU.Unlock()
  	build.Status = pb.Status_INFRA_FAILURE
  	build.SummaryMarkdown = fmt.Sprintf("run_annotations failure: `%s`", err)
  	client.WriteBuild(build)
  	fmt.Fprintln(os.Stderr, err)
  	os.Exit(1)
  }
docs: // check marks the build as INFRA_FAILURE and exits with code 1 if err is not nil.