feat: add reply/quoted message context support

Add generic reply context fields to NewMessage (reply_to_message_id,
reply_to_message_content, reply_to_sender_name) so any channel can
pass quoted message context to the agent.

- Add thread_id and reply_to_* fields to NewMessage interface
- Add DB migration for reply context columns on messages table
- Update storeMessage/getMessagesSince/getNewMessages to persist and
  retrieve reply fields
- Render reply context as <quoted_message> XML in formatMessages
- Add DB and formatting tests

Co-Authored-By: Alfred-the-buttler <leon.alfred.bot@gmail.com>
Co-Authored-By: moktamd <moktamd@users.noreply.github.com>
Co-Authored-By: gurixs-carson <gurixs-carson@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db.test.ts

@@ -142,6 +142,86 @@ describe('storeMessage', () => {
   });
 });
 
+// --- reply context persistence ---
+
+describe('reply context', () => {
+  it('stores and retrieves reply_to fields', () => {
+    storeChatMetadata('group@g.us', '2024-01-01T00:00:00.000Z');
+
+    storeMessage({
+      id: 'reply-1',
+      chat_jid: 'group@g.us',
+      sender: '123',
+      sender_name: 'Alice',
+      content: 'Yes, on my way!',
+      timestamp: '2024-01-01T00:00:01.000Z',
+      reply_to_message_id: '42',
+      reply_to_message_content: 'Are you coming tonight?',
+      reply_to_sender_name: 'Bob',
+    });
+
+    const messages = getMessagesSince(
+      'group@g.us',
+      '2024-01-01T00:00:00.000Z',
+      'Andy',
+    );
+    expect(messages).toHaveLength(1);
+    expect(messages[0].reply_to_message_id).toBe('42');
+    expect(messages[0].reply_to_message_content).toBe(
+      'Are you coming tonight?',
+    );
+    expect(messages[0].reply_to_sender_name).toBe('Bob');
+  });
+
+  it('returns null for messages without reply context', () => {
+    storeChatMetadata('group@g.us', '2024-01-01T00:00:00.000Z');
+
+    store({
+      id: 'no-reply',
+      chat_jid: 'group@g.us',
+      sender: '123',
+      sender_name: 'Alice',
+      content: 'Just a normal message',
+      timestamp: '2024-01-01T00:00:01.000Z',
+    });
+
+    const messages = getMessagesSince(
+      'group@g.us',
+      '2024-01-01T00:00:00.000Z',
+      'Andy',
+    );
+    expect(messages).toHaveLength(1);
+    expect(messages[0].reply_to_message_id).toBeNull();
+    expect(messages[0].reply_to_message_content).toBeNull();
+    expect(messages[0].reply_to_sender_name).toBeNull();
+  });
+
+  it('retrieves reply context via getNewMessages', () => {
+    storeChatMetadata('group@g.us', '2024-01-01T00:00:00.000Z');
+
+    storeMessage({
+      id: 'reply-2',
+      chat_jid: 'group@g.us',
+      sender: '456',
+      sender_name: 'Carol',
+      content: 'Agreed',
+      timestamp: '2024-01-01T00:00:01.000Z',
+      reply_to_message_id: '99',
+      reply_to_message_content: 'We should meet',
+      reply_to_sender_name: 'Dave',
+    });
+
+    const { messages } = getNewMessages(
+      ['group@g.us'],
+      '2024-01-01T00:00:00.000Z',
+      'Andy',
+    );
+    expect(messages).toHaveLength(1);
+    expect(messages[0].reply_to_message_id).toBe('99');
+    expect(messages[0].reply_to_sender_name).toBe('Dave');
+  });
+});
+
 // --- getMessagesSince ---
 
 describe('getMessagesSince', () => {