blog: publish an RSS feed

Six long essays and no way to subscribe: /rss.xml and /feed.xml both
answered 404, so an aggregator had nothing to poll.

Adds @astrojs/rss and a /rss.xml route, newest first — the reverse of the
index, which reads oldest first the way a bibliography does. Items carry
the excerpt rather than the body: the posts run to thousands of words with
KaTeX and highlighted code, none of which survives a feed reader intact.

Discovery goes in the head on every page; /blog also carries a visible
link, since a reader who wants the feed should not have to view source.

Claude-Session: https://claude.ai/code/session_01S3mVZMgbynFxc2N874K9nH

Author: redcpp

package-lock.json

@@ -19,6 +19,7 @@
   },
   "dependencies": {
     "@astrojs/mdx": "^7.0.8",
+    "@astrojs/rss": "^4.0.19",
     "@astrojs/sitemap": "^3.7.3",
     "@resvg/resvg-js": "^2.6.2",
     "astro": "^7.2.9",

package.json

@@ -47,6 +47,12 @@ const fontHref =
     <link rel="manifest" href="/site.webmanifest" />
     <meta name="theme-color" content="#FCFCFA" />
     <link rel="sitemap" href="/sitemap-index.xml" />
+    <link
+      rel="alternate"
+      type="application/rss+xml"
+      title="Diego Said — Writing"
+      href="/rss.xml"
+    />
 
     {/* Open Graph */}
     <meta property="og:title" content={title} />

src/layouts/BaseLayout.astro

@@ -20,6 +20,12 @@ const posts = (await getCollection('blog')).sort(
     <p class="mt-3 text-[17px] text-muted leading-relaxed">
       Long-form essays on protocol design, distributed systems, and AI infrastructure.
     </p>
+    <a
+      href="/rss.xml"
+      class="inline-block mt-4 font-mono text-[13px] text-muted hover:text-accent transition-colors"
+    >
+      RSS
+    </a>
     <div class="mt-12 border-t border-rule divide-y divide-rule">
       {
         posts.map((post) => (

src/pages/blog/index.astro

@@ -0,0 +1,38 @@
+import rss from '@astrojs/rss';
+import type { APIContext } from 'astro';
+import { getCollection } from 'astro:content';
+
+/**
+ * Feed for /blog.
+ *
+ * Newest first — the reverse of the index page, which reads oldest first the
+ * way a bibliography does. A reader pulls the feed to see what is new.
+ *
+ * Items carry the excerpt, not the post body. The posts run to several thousand
+ * words with KaTeX and highlighted code, none of which survives a feed reader
+ * intact, so the description is the blurb and the link is the article.
+ */
+export async function GET(context: APIContext) {
+  const posts = (await getCollection('blog')).sort(
+    (a, b) => b.data.date.valueOf() - a.data.date.valueOf(),
+  );
+
+  return rss({
+    title: 'Diego Said — Writing',
+    description:
+      'Long-form essays on protocol design, distributed systems, and AI infrastructure.',
+    // Set in astro.config; the type is nullable because a site-less config is
+    // legal, so fall back rather than emit a feed full of relative links.
+    site: context.site ?? 'https://diegosaid.com',
+    items: posts.map((post) => ({
+      title: post.data.title,
+      description: post.data.excerpt,
+      pubDate: post.data.date,
+      categories: post.data.tags,
+      // Trailing slash: Cloudflare Pages 308-redirects the bare form, and a
+      // feed reader that follows the redirect would record a different id.
+      link: `/blog/${post.id}/`,
+    })),
+    customData: '<language>en-us</language>',
+  });
+}