code: func logAnnotatedErr(ctx context.Context, err error, f string, args ...interface{}) {
  	if err == nil {
  		return
  	}
  
  	nargs := make([]interface{}, len(args)+1)
  	nargs[copy(nargs, args)] = strings.Join(errors.RenderStack(err), "\n")
  
  	if f == "" {
  		f = "Captured error stack:"
  	}
  	log.Errorf(ctx, f+"\n%s", nargs...)
  }
docs: // logAnnotatedErr logs the full stack trace from an annotated error to the
  // installed logger at error level.