can't embed file into markdown documents,help

[spaceychen]

my envirment:

• macos Ventura 13.7.6
• Node v22.18.0
• Rspress v1.45.1

According to docs alias, embed a.js to a.md, I want to render sourcecode, but render "undefined".

project file directory

codes # demo code
  |__a.js
docs // markdown
  |__a.md

codes/a.js file

function test(){
 return "hello world"
}

docs/a.md file
ps: the escape character used to avoid being rendered by github, it does not exist in the actual document.

code demo
\```js file="@js/a.js"
\```

rspress.config.ts file

import * as path from 'node:path';
import { defineConfig } from 'rspress/config';
import pkg from './package.json';
const { license, author,repository } = pkg;

export default defineConfig({
  base: '/language/',
  root: path.join(__dirname, 'docs'),
  title: 'language',
  head: [],
  route: {
    include: ['docs/**/*.md'],
    cleanUrls: true,
  },
  builderConfig: {
    resolve: {
      alias: {
        "@js":"codes/js",  // watch this!!!
      },
    },
  },
);

How should I do ?