code: func BackgroundWithID(ctx context.Context) context.Context {
  	id := ctx.Value(RequestIDContextKey)
  	ctx = context.Background()
  	if id == nil {
  		return ctx
  	}
  	return WithRequestID(ctx, id.(string))
  }
docs: // BackgroundWithID returns a new background context with an existing
  // request ID in ctx, if any.