* add regression test for dict content in AssistantMessage
Tests the fix for pydantic validation error when send_message tool
returns dict content like {'tofu': 1, 'mofu': 1, 'bofu': 1}.
The test verifies that dict content is properly serialized to JSON
string before creating AssistantMessage.
* improve type annotation for validate_function_response
Changed return type from Any to str | dict[str, Any] to match actual
behavior. This enables static type checkers (pyright, mypy) to catch
type mismatches like the AssistantMessage bug.
With proper type annotations, pyright would have caught:
error: Argument of type "str | dict[str, Any]" cannot be assigned
to parameter "content" of type "str"
This prevents future bugs where dict is passed to string-only fields.
* add regression test for dict content in AssistantMessage
Moved test into existing test_message_manager.py suite alongside other
message conversion tests.
Tests the fix for pydantic validation error when send_message tool
returns dict content like {'tofu': 1, 'mofu': 1, 'bofu': 1}.
The test verifies that dict content is properly serialized to JSON
string before creating AssistantMessage.