Fix Qwen 400 template errors and add retry logic

- Add _assistant_msg_dict() to serialize assistant messages as plain dicts
  with content normalized from None to "", preventing Qwen's jinja template
  from rejecting tool-call messages with content=null
- Apply fix in all three agent loops (_run_agent_inner, run_reflection_agent,
  run_life_event_reflection)
- Replace error-to-chat fallback with silent logging + up to 3 retries
  (2s apart) before giving up

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

bot.py

@@ -678,6 +678,24 @@ async def send_image_to_channel(url: str, channel: discord.abc.Messageable, capt
         return f"Failed to fetch or send image: {exc}"
 
 
+def _assistant_msg_dict(msg) -> dict:
+    """Serialize an assistant ChatCompletionMessage to a plain dict.
+
+    Qwen's jinja template rejects content=null, so we normalize it to "".
+    """
+    d: dict = {"role": "assistant", "content": msg.content or ""}
+    if msg.tool_calls:
+        d["tool_calls"] = [
+            {
+                "id": tc.id,
+                "type": "function",
+                "function": {"name": tc.function.name, "arguments": tc.function.arguments},
+            }
+            for tc in msg.tool_calls
+        ]
+    return d
+
+
 def _ensure_user_tail(messages: list) -> None:
     """Qwen's chat template requires a non-empty user message as the last message."""
     if not messages:
@@ -750,7 +768,7 @@ async def _run_agent_inner(messages: list, channel: discord.abc.Messageable | No
         if not msg.tool_calls:
             return msg.content
 
-        kwargs["messages"].append(msg)
+        kwargs["messages"].append(_assistant_msg_dict(msg))
 
         for tc in msg.tool_calls:
             args = json.loads(tc.function.arguments)
@@ -822,7 +840,7 @@ async def run_reflection_agent(messages: list, max_turns: int) -> tuple[str, str
         if not msg.tool_calls:
             break
 
-        kwargs["messages"].append(msg)
+        kwargs["messages"].append(_assistant_msg_dict(msg))
 
         for tc in msg.tool_calls:
             args = json.loads(tc.function.arguments)
@@ -875,7 +893,7 @@ async def run_life_event_reflection(messages: list):
         if not msg.tool_calls:
             break
 
-        kwargs["messages"].append(msg)
+        kwargs["messages"].append(_assistant_msg_dict(msg))
 
         for tc in msg.tool_calls:
             args = json.loads(tc.function.arguments)
@@ -1244,11 +1262,17 @@ async def on_message(message: discord.Message):
     messages = [{"role": "system", "content": system_content}] + list(history)[:-1] + [current_msg]
 
     async with message.channel.typing():
+        reply = None
+        for attempt in range(3):
             try:
                 reply = await run_agent(messages, channel=message.channel)
+                break
             except Exception as exc:
-            reply = f"Error: {exc}"
+                log.error(f"[agent] Error (attempt {attempt + 1}/3): {exc}")
+                if attempt == 2:
                     history.pop()
+                    return
+                await asyncio.sleep(2)
 
     if reply:
         history.append({"role": "assistant", "content": reply})