Strip leaked metadata from LLM responses

The local LLM was echoing back [Server context: ...] metadata lines
in its responses despite prompt instructions not to. Now stripped
via regex before sending to Discord.

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

cogs/chat.py

@@ -1,6 +1,7 @@
 import asyncio
 import logging
 import random
+import re
 from collections import deque
 from pathlib import Path
 
@@ -160,7 +161,13 @@ class ChatCog(commands.Cog):
         if typing_ctx:
             await typing_ctx.__aexit__(None, None, None)
 
-        if response is None:
+        # Strip leaked metadata the LLM may echo back
+        if response:
+            response = re.sub(r"\[Server context:[^\]]*\]\n?", "", response)
+            response = re.sub(r"\[Replying to bot's message:[^\]]*\]\n?", "", response)
+            response = response.strip()
+
+        if not response:
             log_channel = discord.utils.get(message.guild.text_channels, name="bcs-log")
             if log_channel:
                 try: