fix(types): exclude *args/**kwargs from the signature schema

[BlueX888]

Summary

get_schema_from_signature now skips *args and **kwargs parameters instead of turning them into schema properties.

Why

get_schema_from_signature built a Pydantic model from every parameter in the signature, including the var-positional (*args) and var-keyword (**kwargs) ones (src/outlines/types/utils.py:199). Since such parameters have no default, they became required properties of the generated schema, even though they can never be bound by ** unpacking. This violates the invariant documented in the docstring (src/outlines/types/utils.py:193): every JSON object valid to the output schema must be passable to the function with **:

def fn(a: int, *args: str): ...

schema = get_schema_from_signature(fn)  # required: ["a", "args"]
fn(**{"a": 1, "args": "x"})           # TypeError: fn() got an unexpected keyword argument 'args'

When the function does have a **kwargs parameter to absorb them, the values silently land in **kwargs under their own names instead of the variadic parameters they represent.

Changes

• src/outlines/types/utils.py: skip parameters whose kind is VAR_POSITIONAL or VAR_KEYWORD in get_schema_from_signature.
• tests/types/test_types_utils.py: regression test test_get_schema_from_signature_ignores_var_parameters.

Testing

$ pytest tests/types/test_types_utils.py::test_get_schema_from_signature_ignores_var_parameters   # on main
FAILED ... AssertionError: assert ['a', 'args', 'b', 'kwargs'] == ['a', 'b']

$ pytest tests/types/test_types_utils.py::test_get_schema_from_signature_ignores_var_parameters   # with this fix
1 passed

$ pytest tests/types/
347 passed

$ pre-commit run --all-files
check for merge conflicts................................................Passed
debug statements (python)................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
mypy.....................................................................Passed
ruff.....................................................................Passed