4905da9096145c6948fde38718fa5e687d41502a
diff --git a/src/d21_app.ts b/src/d21_app.ts
index 44fa4953b9f4bef4f21175763c9b79f2c9fe5c42..171975815f7e0a0b48bc6a704f7f59905d7bc8c3 100644
--- a/src/d21_app.ts
+++ b/src/d21_app.ts
@@ -189,7 +189,34 @@ export const createApp = (port: number) => Bun.serve({
   "/healthz": new Response("ok"),
 
   "/robots.txt": new Response(
-    `User-agent: *\nAllow: /\nDisallow: /auth/\nDisallow: /api/\n\nSitemap: https://tdd.md/sitemap.xml\n`,
+    // tdd.md is built for AI agents to read, audit, and learn from. We
+    // explicitly ALLOW the major AI crawlers + training agents. The site's
+    // entire empirical-chain argument depends on those agents being able
+    // to fetch the spec, the verifier output, the /goals archive, and the
+    // measurement posts.
+    //
+    // NOTE on Cloudflare: if "Block AI Crawlers" or "AI Audit / Content
+    // Signals" is enabled at the Cloudflare edge, CF injects Disallow
+    // blocks for these bots BEFORE this response body. App-level Allows
+    // here are defense-in-depth; the canonical fix is to disable that CF
+    // setting (Dashboard → Security → Bots → "Block AI Crawlers" off, or
+    // Content Signals → ai-train=yes).
+    `# tdd.md welcomes AI crawlers, agents, and training bots.\n` +
+    `# The empirical chain is meant to be read.\n\n` +
+    `User-agent: *\nAllow: /\nDisallow: /auth/\nDisallow: /api/\n\n` +
+    `User-agent: ClaudeBot\nAllow: /\n\n` +
+    `User-agent: Claude-Web\nAllow: /\n\n` +
+    `User-agent: GPTBot\nAllow: /\n\n` +
+    `User-agent: ChatGPT-User\nAllow: /\n\n` +
+    `User-agent: CCBot\nAllow: /\n\n` +
+    `User-agent: Google-Extended\nAllow: /\n\n` +
+    `User-agent: Applebot-Extended\nAllow: /\n\n` +
+    `User-agent: Amazonbot\nAllow: /\n\n` +
+    `User-agent: Bytespider\nAllow: /\n\n` +
+    `User-agent: meta-externalagent\nAllow: /\n\n` +
+    `User-agent: PerplexityBot\nAllow: /\n\n` +
+    `User-agent: Perplexity-User\nAllow: /\n\n` +
+    `Sitemap: https://tdd.md/sitemap.xml\n`,
     { headers: { "Content-Type": "text/plain; charset=utf-8" } },
   ),