Ensure message sent to LLMCallEvent for Anthropic is serializable (#6135)

Messages sent as part of `LLMCallEvent` for Anthropic were not fully serializable
The example below shows TextBlock and ToolUseBlocks inside the content of messages - these throw downsteam errors in apps like AGS (or event sinks) that expect serializable dicts inside the LLMCallEvent.
```
[
{'role': 'user', 'content': 'What is the weather in New York?'}, 
{'role': 'assistant', 'content': [TextBlock(citations=None, text='I can help you find the weather in New York. Let me check that for you.', type='text'), ToolUseBlock(id='toolu_016W8g55GejYGBzRRrcsnt7M', input={'city': 'New York'}, name='get_weather', type='tool_use')]}, 
{'role': 'user', 'content': [{'type': 'tool_result', 'tool_use_id': 'toolu_016W8g55GejYGBzRRrcsnt7M', 'content': 'The weather in New York is 73 degrees and Sunny.'}]}
]


```
This PR attempts to first serialize content of anthropic messages before they are passed to `LLMCallEvent`

```
[
{'role': 'user', 'content': 'What is the weather in New York?'}, 
{'role': 'assistant', 'content': [{'citations': None, 'text': 'I can help you find the weather in New York. Let me check that for you.', 'type': 'text'}, {'id': 'toolu_016W8g55GejYGBzRRrcsnt7M', 'input': {'city': 'New York'}, 'name': 'get_weather', 'type': 'tool_use'}]}, 
{'role': 'user', 'content': [{'type': 'tool_result', 'tool_use_id': 'toolu_016W8g55GejYGBzRRrcsnt7M', 'content': 'The weather in New York is 73 degrees and Sunny.'}]}
]

```

Author: victordibia

Diff for: python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py

@@ -432,6 +432,25 @@ def __init__(
         self._total_usage = RequestUsage(prompt_tokens=0, completion_tokens=0)
         self._actual_usage = RequestUsage(prompt_tokens=0, completion_tokens=0)
 
+    def _serialize_message(self, message: MessageParam) -> Dict[str, Any]:
+        """Convert an Anthropic MessageParam to a JSON-serializable format."""
+        if isinstance(message, dict):
+            result: Dict[str, Any] = {}
+            for key, value in message.items():
+                if key == "content" and isinstance(value, list):
+                    serialized_blocks: List[Any] = []
+                    for block in value:  # type: ignore
+                        if isinstance(block, BaseModel):
+                            serialized_blocks.append(block.model_dump())
+                        else:
+                            serialized_blocks.append(block)
+                    result[key] = serialized_blocks
+                else:
+                    result[key] = value
+            return result
+        else:
+            return {"role": "unknown", "content": str(message)}
+
     def _merge_system_messages(self, messages: Sequence[LLMMessage]) -> Sequence[LLMMessage]:
         """
         Merge continuous system messages into a single message.
@@ -573,10 +592,11 @@ async def create(
             prompt_tokens=result.usage.input_tokens,
             completion_tokens=result.usage.output_tokens,
         )
+        serializable_messages: List[Dict[str, Any]] = [self._serialize_message(msg) for msg in anthropic_messages]
 
         logger.info(
             LLMCallEvent(
-                messages=cast(List[Dict[str, Any]], anthropic_messages),
+                messages=serializable_messages,
                 response=result.model_dump(),
                 prompt_tokens=usage.prompt_tokens,
                 completion_tokens=usage.completion_tokens,

Diff for: python/packages/autogen-ext/tests/models/test_anthropic_model_client.py

@@ -317,13 +317,9 @@ async def test_anthropic_multimodal() -> None:
 async def test_anthropic_serialization() -> None:
     """Test serialization and deserialization of component."""
 
-    api_key = os.getenv("ANTHROPIC_API_KEY")
-    if not api_key:
-        pytest.skip("ANTHROPIC_API_KEY not found in environment variables")
-
     client = AnthropicChatCompletionClient(
         model="claude-3-haiku-20240307",
-        api_key=api_key,
+        api_key="api-key",
     )
 
     # Serialize and deserialize
@@ -336,6 +332,42 @@ async def test_anthropic_serialization() -> None:
     assert isinstance(loaded_model_client, AnthropicChatCompletionClient)
 
 
+@pytest.mark.asyncio
+async def test_anthropic_message_serialization_with_tools(caplog: pytest.LogCaptureFixture) -> None:
+    """Test that complex messages with tool calls are properly serialized in logs."""
+    api_key = os.getenv("ANTHROPIC_API_KEY")
+    if not api_key:
+        pytest.skip("ANTHROPIC_API_KEY not found in environment variables")
+
+    # Use existing tools from the test file
+    pass_tool = FunctionTool(_pass_function, description="Process input text", name="process_text")
+    add_tool = FunctionTool(_add_numbers, description="Add two numbers together", name="add_numbers")
+
+    client = AnthropicChatCompletionClient(
+        model="claude-3-haiku-20240307",
+        api_key=api_key,
+    )
+
+    # Set up logging capture - capture all loggers
+    with caplog.at_level(logging.INFO):
+        # Make a request that should trigger a tool call
+        await client.create(
+            messages=[
+                SystemMessage(content="Use the tools available to help the user."),
+                UserMessage(content="Process the text 'hello world' using the process_text tool.", source="user"),
+            ],
+            tools=[pass_tool, add_tool],
+        )
+
+        # Look for any log containing serialized messages, not just with 'LLMCallEvent'
+        serialized_message_logs = [
+            record for record in caplog.records if '"messages":' in str(record.msg) or "messages" in str(record.msg)
+        ]
+
+        # Verify we have at least one log with serialized messages
+        assert len(serialized_message_logs) > 0, "No logs with serialized messages found"
+
+
 @pytest.mark.asyncio
 async def test_anthropic_muliple_system_message() -> None:
     """Test multiple system messages in a single request."""
@@ -347,7 +379,6 @@ async def test_anthropic_muliple_system_message() -> None:
         model="claude-3-haiku-20240307",
         api_key=api_key,
     )
-
     # Test multiple system messages
     messages: List[LLMMessage] = [
         SystemMessage(content="When you say anything Start with 'FOO'"),