Fix homepage markdown content negotiation

The CloudFront Lambda rewrote `/` with `Accept: text/markdown` to an
invalid `.md` URI, causing a 502 LambdaValidationError. Homepage has no
flattened markdown equivalent, so route to `/llms.txt` — the
agent-oriented markdown index of the site. Same handling for
`/index.html`.

Also set `Content-Type: text/markdown` on `llms.txt` at upload time, so
content negotiation responses and direct requests both advertise the
correct media type.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dvdksn

.github/workflows/deploy.yml

@@ -103,6 +103,15 @@ jobs:
             --exclude "*" \
             --include "*.pf_meta" \
             --include "*.pf_fragment"
+      -
+        name: Set markdown Content-Type on llms.txt
+        if: ${{ env.DOCS_S3_BUCKET != '' }}
+        run: |
+          aws --region ${{ env.DOCS_AWS_REGION }} s3 cp \
+            s3://${{ env.DOCS_S3_BUCKET }}/llms.txt \
+            s3://${{ env.DOCS_S3_BUCKET }}/llms.txt \
+            --content-type="text/markdown" \
+            --metadata-directive="REPLACE"
       -
         name: Update Cloudfront config
         if: ${{ env.DOCS_CLOUDFRONT_ID != '' }}

hack/releaser/cloudfront-lambda-redirects.js

@@ -68,8 +68,11 @@ exports.handler = (event, context, callback) => {
     // If it's not a file, treat it as a directory
     if (!hasFileExtension) {
         if (wantsMarkdown) {
-            // Markdown files are flattened: /path/to/page.md not /path/to/page/index.md
-            uri = uri.replace(/\/$/, '') + '.md';
+            // Markdown files are flattened: /path/to/page.md not /path/to/page/index.md.
+            // Homepage has no flattened equivalent, so serve llms.txt as the
+            // agent-oriented markdown index of the site.
+            const stripped = uri.replace(/\/$/, '');
+            uri = stripped === '' ? '/llms.txt' : stripped + '.md';
         } else {
             // HTML uses directory structure with index.html
             if (!uri.endsWith("/")) {
@@ -79,8 +82,9 @@ exports.handler = (event, context, callback) => {
         }
         request.uri = uri;
     } else if (wantsMarkdown && uri.endsWith('/index.html')) {
-        // If requesting index.html but wants markdown, use the flattened .md file
-        uri = uri.replace(/\/index\.html$/, '.md');
+        // If requesting index.html but wants markdown, use the flattened .md file.
+        // Root index.html has no flattened equivalent, so serve llms.txt instead.
+        uri = uri === '/index.html' ? '/llms.txt' : uri.replace(/\/index\.html$/, '.md');
         request.uri = uri;
     }