Fix bug arising from instantiation of CallToolResult class

[meerkat-citronella]

In mcp_aggregator.py, CallToolResult is being instantiated incorrectly. message is being passed as a string instead of content which should be a list of TextContent. It is causing the following error:

Traceback (most recent call last):
  File "/path/to/project/.venv/lib/python3.12/site-packages/mcp_agent/workflows/llm/augmented_llm.py", line 373, in call_tool
    result = await self.aggregator.call_tool(tool_name, tool_args)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/.venv/lib/python3.12/site-packages/mcp_agent/agents/agent.py", line 205, in call_tool
    return await super().call_tool(name, arguments)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/.venv/lib/python3.12/site-packages/mcp_agent/mcp/mcp_aggregator.py", line 323, in call_tool
    return await try_call_tool(server_connection.session)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/.venv/lib/python3.12/site-packages/mcp_agent/mcp/mcp_aggregator.py", line 306, in try_call_tool
    return CallToolResult(
    ^^^^^^^^^^^^^^^
  File "/path/to/project/.venv/lib/python3.12/site-packages/pydantic/main.py", line 214, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for CallToolResult
content
  Field required [type=missing, input_value={'message': "Failed to ca...er 'my_server': "}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.10/v/missing

Instantiating CallToolResult like:

CallToolResult(isError=True, message=f"my error msg")

is inconsistent with the other uses of CallToolResult in agent.py, augmented_llm.py, augmented_llm_openai.py, and swarm.py, which instantiate it thusly:

return CallToolResult(
                    isError=True,
                    content=[TextContent(type="text", text=f"my error msg")],
                )

I have updated the instantiation of CallToolResult to align with agent.py, augment_llm.py, etc. and the above error no longer occurs.

[saqadri]

Awesome catch, thank you @meerkat-citronella!