[Lanre Shittu (Shizoqua)]

Description

Fixes #3516.

_execute_call_section_async only checked that parsed tool arguments were a JSON object for registered Tools. Functions in custom_functions were called with whatever json.loads returned, so "null", "[1, 2]" or "\"text\"" reached them as None, a list or a string, and a function reading args["x"] crashed the whole send.

The object check now runs before either kind of function is called. Custom functions get the same handling as tools: a malformed_arguments output the model can recover from, or a ValueError when fail_on_missing_function=True. Unregistered names still return function_not_found.

Tests and Documentation

Added tests in tests/unit/prompt_target/target/test_openai_response_target.py:

• null, a list and a string are returned as malformed_arguments with invoked=False, and the custom function is never awaited.
• With fail_on_missing_function=True, the same input raises ValueError and the custom function is never awaited.

No docs or notebooks changed, so JupyText was not needed.

[Richard Lundeen (richlundeen)]

Looks good. Custom functions now use the same JSON-object argument check and error result as registered tools. Unknown function handling stays unchanged.

Reviewed with GitHub Copilot.