feat: add <no-reply/> silent marker for agent opt-out (#196)

* feat: add {{NO_REPLY}} silent marker for agent opt-out

Allow the agent to respond with {{NO_REPLY}} to suppress message
delivery for messages that don't warrant a reply. The marker is
checked in three places: the streaming edit guard (prefix match to
prevent partial sends), finalizeMessage(), and the post-stream
response handler.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* refactor: use <no-reply/> XML marker instead of {{NO_REPLY}}

Switch to XML-style self-closing tag for consistency with the XML
envelope format used elsewhere, and because LLMs produce well-formed
XML tags more reliably than template syntax.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add no-reply hint to group chat envelopes

Agents created outside lettabot (via ADE, Letta Cloud) won't have the
system prompt telling them about <no-reply/>. Adding the hint to group
chat envelopes makes the opt-out mechanism self-documenting.

Written by Cameron ◯ Letta Code

"Silence is one of the great arts of conversation." -- Marcus Tullius Cicero

---------

Co-authored-by: Gabriele Sarti <gabriele.sarti996@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

package-lock.json

@@ -7,6 +7,7 @@
     "": {
       "name": "lettabot",
       "version": "1.0.0",
+      "hasInstallScript": true,
       "license": "Apache-2.0",
       "dependencies": {
         "@clack/prompts": "^0.11.0",

src/core/bot.ts

@@ -443,6 +443,15 @@ export class LettaBot {
       
       // Helper to finalize and send current accumulated response
       const finalizeMessage = async () => {
+        // Check for silent marker - agent chose not to reply
+        if (response.trim() === '<no-reply/>') {
+          console.log('[Bot] Agent chose not to reply (no-reply marker)');
+          sentAnyMessage = true;
+          response = '';
+          messageId = null;
+          lastUpdate = Date.now();
+          return;
+        }
         if (response.trim()) {
           try {
             if (messageId) {
@@ -521,8 +530,10 @@ export class LettaBot {
             response += streamMsg.content;
             
             // Stream updates only for channels that support editing (Telegram, Slack)
+            // Hold back streaming edits while response could still become <no-reply/>
             const canEdit = adapter.supportsEditing?.() ?? true;
-            if (canEdit && Date.now() - lastUpdate > 500 && response.length > 0) {
+            const mayBeNoReply = '<no-reply/>'.startsWith(response.trim());
+            if (canEdit && !mayBeNoReply && Date.now() - lastUpdate > 500 && response.length > 0) {
               try {
                 if (messageId) {
                   await adapter.editMessage(msg.chatId, messageId, response);
@@ -600,6 +611,13 @@ export class LettaBot {
         clearInterval(typingInterval);
       }
       
+      // Check for silent marker - agent chose not to reply
+      if (response.trim() === '<no-reply/>') {
+        console.log('[Bot] Agent chose not to reply (no-reply marker)');
+        sentAnyMessage = true;
+        response = '';
+      }
+
       // Send final response
       if (response.trim()) {
         try {

src/core/formatter.test.ts

@@ -180,6 +180,18 @@ describe('formatMessageEnvelope', () => {
       const result = formatMessageEnvelope(msg);
       expect(result).toContain('**Mentioned**: yes');
     });
+
+    it('includes no-reply hint for group chats', () => {
+      const msg = createMessage({ isGroup: true });
+      const result = formatMessageEnvelope(msg);
+      expect(result).toContain('<no-reply/>');
+    });
+
+    it('omits no-reply hint for DMs', () => {
+      const msg = createMessage({ isGroup: false });
+      const result = formatMessageEnvelope(msg);
+      expect(result).not.toContain('no-reply');
+    });
   });
 
   describe('format hints', () => {

src/core/formatter.ts

@@ -231,6 +231,7 @@ function buildChatContextLines(msg: InboundMessage, options: EnvelopeOptions): s
     if (msg.wasMentioned) {
       lines.push(`- **Mentioned**: yes`);
     }
+    lines.push(`- **Hint**: To skip replying, respond with exactly: \`<no-reply/>\``);
   } else {
     lines.push(`- **Type**: Direct message`);
   }

src/core/system-prompt.ts

@@ -6,6 +6,8 @@ export const SYSTEM_PROMPT = `You are a self-improving AI agent with advanced me
 
 You are connected to a multi-channel messaging system (LettaBot) that allows you to communicate with users across Telegram, Slack, Discord, WhatsApp, and Signal. You run on a remote server and can execute tools, manage files, and interact with various services.
 
+Not every message requires a response. Before replying, consider whether your response adds value. In group chats especially, avoid replying to messages not directed at you, simple acknowledgments, or conversations between other users. Quality over quantity — only reply when you have something meaningful to contribute.
+
 # Communication System
 
 You communicate through multiple channels and trigger types. Understanding when your messages are delivered is critical:
@@ -68,6 +70,21 @@ During heartbeats and background tasks:
 
 You don't need to notify the user about everything. Use judgment about what's worth interrupting them for.
 
+## Choosing Not to Reply
+
+Not all messages warrant a response. If a message doesn't need a reply, respond with exactly:
+
+\`<no-reply/>\`
+
+This suppresses the message so nothing is sent to the user. Use this for:
+- Messages in a group not directed at you
+- Simple acknowledgments (e.g., "ok", "thanks", thumbs up)
+- Conversations between other users you don't need to join
+- Notifications or updates that don't require a response
+- Messages you've already addressed
+
+When in doubt, prefer \`<no-reply/>\` over a low-value response. Users appreciate an agent that knows when to stay quiet.
+
 ## Available Channels
 
 - **telegram** - Telegram messenger