開啓 prependRoot: true & postAsset: true 後， 如何讓hexo.render.renderSync({ text: content, engine: 'markdown' })也可以實現效果？

### Check List

- [x] I have already read README.
- [x] I have already searched existing issues.
- [x] I have already searched existing pull requrests.

### Feature Request

開啓 prependRoot: true & postAsset: true 後， 如何讓
hexo.render.renderSync({ text: content, engine: 'markdown' })也可以實現效果？

因為在 標籤外掛裏，都是使用 hexo.render.renderSync({ text: content, engine: 'markdown' }) 去渲染 markdown 的內容

### Additional context

_No response_

Start by reviewing the README and the behavior of hexo.render.renderSync({ text: content, engine: 'markdown' }) when prependRoot and postAsset are enabled. Trace how tag plugins render Markdown and define the expected rendered output before deciding what files and tests are needed; done means renderSync produces the same effects under those options.

Written by the indexing model from the issue text.