fix(core): read tool args without Pydantic property shadowing

[hsusul]

Summary

FuncSchema.to_call_args() used getattr() to recover tool arguments from the generated Pydantic model. For parameters named model_extra or model_fields_set, that hits BaseModel properties instead of the validated fields, so the tool is invoked with None or a set of field names even though JSON validation succeeded.

This is distinct from #3547 / #3572, which were about names that crash create_model(). These names build and validate successfully, then silently pass the wrong values.

Reproduction

from agents.function_schema import function_schema

def search(query: str, model_extra: str) -> str:
    return f"{query}:{model_extra}"

fs = function_schema(search, use_docstring_info=False)
parsed = fs.params_pydantic_model.model_validate(
    {"query": "hello", "model_extra": "gpt-4.1"}
)
args, kwargs = fs.to_call_args(parsed)
print(args)  # Before: ['hello', None]

Solution

Read instance __dict__ first so Pydantic properties cannot shadow tool parameters. Nested model objects are preserved (unlike model_dump()).

Test plan

• Added regression tests for model_extra and model_fields_set
• uv run pytest tests/test_function_schema.py tests/test_function_tool.py (101 passed)
• uv run ruff format / ruff check on the changed files
• uv run pyright on the changed files
• git diff --check clean

Issue number

N/A — no matching open issue. Adjacent reserved-name construction failures (#3547, #3549, #3572) were closed wontfix; this path is a silent wrong-argument bug after successful schema construction.

Checks

• I've added new tests, if relevant
• I've run targeted format, lint, typecheck, and tests on the changed files
• I've run .agents/skills/code-change-verification/scripts/run.sh (full make format currently fails on an unrelated pre-existing E501 in .agents/skills/implementation-final-review/scripts/test_skill_contract.py on main)
• If using Codex, I've run /review before submitting this PR

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-24T22:17:24.759602Z	6fc29a5	New commits
🔒 Security Review	✅ Completed 2026-08-24T22:18:25.043970Z	6fc29a5	New commits

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