Add full post content to RSS feed

[Copilot]

RSS feed currently only includes post descriptions. Readers cannot view full articles without visiting the site.

Changes

• Render full markdown to HTML: Use @astrojs/markdown-remark to process post bodies with the same plugin chain as the main site (syntax highlighting, typography transforms, GitHub mentions, external link handling, etc.)

• Performance optimization: Create markdown processor at module level to avoid recreation on each request

• Backward compatible: Maintain existing description field alongside new content field

Implementation

// Module-level processor with site plugins
const markdownProcessor = createMarkdownProcessor({
  remarkPlugins: [remarkGfm, remarkEmoji, remarkSmartypants, ...],
  rehypePlugins: [rehypeSlug, rehypeAutolinkHeadings, ...],
  shikiConfig: { themes: { light: 'github-light', dark: 'github-dark' } }
});

export async function GET(context: APIContext) {
  const processor = await markdownProcessor;
  const items = await Promise.all(
    sortedPosts.map(async (post) => {
      const result = await processor.render(post.body, { frontmatter: post.data });
      return { ...item, content: result.code };
    })
  );
  // ...
}

Feed size increases from 105KB to 2.5MB reflecting full content inclusion.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>RSS feed should contain full post</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Custom agent used: code
Specialized agent for code changes in this Astro project including JavaScript/TypeScript, Astro components, and SCSS/CSS

• Fixes RSS feed should contain full post #1624

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