Add llms-full.txt and AI-readability signals to the docs (#2911)

docs/middleware.ts

@@ -0,0 +1,56 @@
+// Vercel Routing Middleware (https://vercel.com/docs/routing-middleware):
+// serves the markdown mirror of a docs page when the client prefers it via
+// `Accept: text/markdown`. Runs only on Vercel deployments.
+import type { MiddlewareHandler } from 'astro'
+import { next, rewrite } from '@vercel/functions'
+import { preferredFormat } from './lib/accept'
+import { markdownUrlFromDocsUrl } from './lib/markdown-url'
+import { redirects } from './lib/redirects'
+
+// Astro picks this file up as its own middleware (`srcDir` is the project
+// root) and requires an `onRequest` export; the real logic is Vercel-only.
+export const onRequest: MiddlewareHandler = (_context, nextHandler) => nextHandler()
+
+export const config = {
+  // extensionless paths outside the asset directories — the html docs pages
+  matcher: '/((?!(?:dist|preview|img|static|css|js)/)(?!.*\\.).*)',
+}
+
+const alternate = (path: string, type: string) => `<${path}>; rel="alternate"; type="${type}"`
+
+export default function middleware(request: Request) {
+  const url = new URL(request.url)
+
+  // renamed pages fall through to their 301; negotiation reruns on the target
+  if (Object.hasOwn(redirects, url.pathname)) return next()
+
+  const format = preferredFormat(request.headers.get('accept'))
+
+  if (format === 'markdown') {
+    const htmlPath = url.pathname
+    url.pathname = markdownUrlFromDocsUrl(url.pathname)
+    return rewrite(url, {
+      headers: {
+        Link: alternate(htmlPath, 'text/html'),
+        Vary: 'Accept',
+      },
+    })
+  }
+
+  if (format === 'none') {
+    return new Response('Not acceptable. This page is available as text/html or text/markdown.\n', {
+      status: 406,
+      headers: {
+        'Content-Type': 'text/plain; charset=utf-8',
+        'Vary': 'Accept',
+      },
+    })
+  }
+
+  return next({
+    headers: {
+      Link: alternate(markdownUrlFromDocsUrl(url.pathname), 'text/markdown'),
+      Vary: 'Accept',
+    },
+  })
+}