fix: Remove display_name for non-Vertex file uploads

[ystory]

Description

When using the Google.GenAI backend (GEMINI_API), file uploads fail if the file_data or inline_data parts of the request contain a display_name. The Gemini API (non-Vertex) does not support this attribute, causing a ValueError.

This commit updates the _preprocess_request method in the Gemini class to sanitize the request. It now iterates through all content parts and sets display_name to None if the determined backend is GEMINI_API. This ensures compatibility, similar to the existing handling of the labels attribute.

Fixes #1182

Testing Plan

1. Unit Tests

• Added a new parameterized test test_preprocess_request_handles_backend_specific_fields to tests/unittests/models/test_google_llm.py.
• This test verifies:
  • When the backend is GEMINI_API, display_name in file_data and inline_data is correctly set to None.
  • When the backend is VERTEX_AI, display_name remains unchanged.
• All unit tests passed successfully.

pytest ./tests/unittests/models/test_google_llm.py                                    ░▒▓ ✔  adk-python   base   system   21:14:02  
============================================================================================ test session starts ============================================================================================
platform darwin -- Python 3.12.10, pytest-8.3.5, pluggy-1.6.0
rootdir: /Users/leo/PycharmProjects/adk-python
configfile: pyproject.toml
plugins: anyio-4.9.0, langsmith-0.3.42, asyncio-0.26.0, mock-3.14.0, xdist-3.6.1
asyncio: mode=Mode.AUTO, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 20 items                                                                                                                                                                                          

tests/unittests/models/test_google_llm.py ....................                                                                                                                                        [100%]

============================================================================================ 20 passed in 3.19s =============================================================================================

2. Manual End-to-End (E2E) Test
I manually verified the fix using adk web. The test was configured to use a Google AI Studio API key, which is the scenario where the bug occurs.

• Before the fix:
  When uploading a file, the request failed with the error: {"error": "display_name parameter is not supported in Gemini API."}. This confirms the bug.

• After the fix:
  With the patch applied, the same file upload was processed successfully. The agent correctly analyzed the file and responded without errors.

[darien-schettler]

Thanks for implementing this! It fixes issue correct?

[ystory]

Thanks for implementing this! It fixes issue correct?

Hi @darien-schettler,
Yes, I believe this fixes it. I was facing the same problem, and your detailed issue was very helpful. This patch works on my end. However, I'd appreciate it if you could let me know if you think there's anything missing, just in case.
Thanks!