feat: serve llms.txt so agents can discover the send API

Adds an llmstxt.org-format usage spec at the repo root, bundled into the
worker as a text module and served at GET /llms.txt. /llms.txt is the only
GET route; all other GETs still return 405, so crawlers and link previews
cannot trigger a Telegram message.

README.md

@@ -18,6 +18,8 @@ The worker forwards `text` to Telegram as-is (no prepended metadata). For reques
 
 ### For AI agents / Claude Code routines
 
+Machine-readable usage spec: [`llms.txt`](llms.txt), served at `GET https://miti-telegram.miti99.workers.dev/llms.txt`. It is the only GET route; every other GET returns 405, so no crawler or link preview can trigger a message.
+
 Read this section first, do not probe.
 
 - **One POST per intended message.** Do not send a `"test"` payload to verify the endpoint — every successful POST forwards to Telegram, so probes spam the inbox.

index.js

@@ -1,3 +1,5 @@
+import LLMS_TXT from './llms.txt';
+
 export default {
   async fetch(request, env, ctx) {
     // Handle CORS preflight requests
@@ -6,13 +8,29 @@ export default {
         status: 204,
         headers: {
           'Access-Control-Allow-Origin': '*',
-          'Access-Control-Allow-Methods': 'POST, OPTIONS',
+          'Access-Control-Allow-Methods': 'GET, POST, OPTIONS',
           'Access-Control-Allow-Headers': 'Content-Type',
           'Access-Control-Max-Age': '86400',
         },
       });
     }
 
+    // Usage spec for AI agents. Read-only: GET never forwards to Telegram,
+    // so crawlers and link previewers cannot trigger a message.
+    if (request.method === 'GET' || request.method === 'HEAD') {
+      const { pathname } = new URL(request.url);
+
+      if (pathname === '/llms.txt') {
+        return new Response(request.method === 'HEAD' ? null : LLMS_TXT, {
+          headers: {
+            'Content-Type': 'text/plain; charset=utf-8',
+            'Cache-Control': 'public, max-age=3600',
+            'Access-Control-Allow-Origin': '*',
+          },
+        });
+      }
+    }
+
     if (request.method !== 'POST') {
       return new Response('Method not allowed', {
         status: 405,

llms.txt

@@ -0,0 +1,20 @@
+# miti-telegram
+
+> Cloudflare Worker that forwards a text message to Miti's Telegram inbox. Messages are sent with POST; there is no GET send endpoint.
+
+Send a message:
+
+```
+POST https://miti-telegram.miti99.workers.dev/
+Content-Type: application/json
+
+{"text": "<your message>"}
+```
+
+`application/x-www-form-urlencoded` with `text=<your message>` is also accepted.
+
+Responses: `{"success":true}` on success. `400` — missing `text`, or unsupported `Content-Type`. `405` — any method other than POST or OPTIONS; GET reaches only `/llms.txt` and cannot send. `500` — worker misconfiguration, not caller-fixable.
+
+## Optional
+
+- [Full rules for agents](https://github.com/tiennm99/miti-telegram#for-ai-agents--claude-code-routines): one POST per intended message, never probe the endpoint, never retry on 2xx.