fix: make sure items etc. is passed to mcp tools

[MagnusS0]

Describe your changes

This patch fixes a bug in convert_openapi_to_mcp_tools where array‑typed parameters lost their items sub‑schema and caused downstream function‑calling errors.

• Deep‑copy each parameter’s full schema instead of rebuilding only its type
• Preserve items, format, enum, default, etc., for all path, query, and body parameters
• No change to overall behaviour, tool definitions, HTTP mapping, and response docs remain the same

All existing tests still pass with same coverage.

Issue

OpenAI, Gemini and other providers expects 'items' in array schema in tools to be defined.
When converting these where removed from the OpenAPI schema leading to the below error.

I got this error in both Cursor and using PydanticAI.

pydantic_ai.exceptions.ModelHTTPError: status_code: 400, model_name: gpt-4.1-mini, body: {'message': "Invalid schema for function 'update_tags': In context=('properties', 'tags'), array schema missing items.", 'type': 'invalid_request_error', 'param': 'tools[3].function.parameters', 'code': 'invalid_function_parameters'}

Checklist before requesting a review

• Added relevant tests
• Run ruff & mypy
• All tests pass

========================================================================= tests coverage ==========================================================================
_________________________________________________________ coverage: platform linux, python 3.12.2-final-0 _________________________________________________________

Name                                Stmts   Miss  Cover   Missing
-----------------------------------------------------------------
fastapi_mcp/__init__.py                 5      0   100%
fastapi_mcp/openapi/__init__.py         0      0   100%
fastapi_mcp/openapi/convert.py        151     14    91%   46-47, 52-53, 116-119, 122, 126-128, 211, 234
fastapi_mcp/openapi/utils.py           79      5    94%   15, 143, 145, 147, 161
fastapi_mcp/server.py                 165     19    88%   167-170, 198, 222, 234, 242, 248-251, 267, 278-279, 302-305, 330, 334
fastapi_mcp/transport/__init__.py       0      0   100%
fastapi_mcp/transport/sse.py           59      0   100%
fastapi_mcp/types.py                    0      0   100%
fastapi_mcp/utils/__init__.py           0      0   100%
-----------------------------------------------------------------
TOTAL                                 459     38    92%
Coverage XML written to file coverage.xml
Required test coverage of 80% reached. Total coverage: 91.72%
======================================================================= 67 passed in 14.82s =======================================================================

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!

[shira-ayal]

Hi !
Thanks for contributing and using the library.
Can you please add a unit test for the line I marked?
Other than this, seems alright :)

[MagnusS0]

Will do!
And thanks for building an awesome library 😄