fix(litellm): collect all tools so native tools aren't dropped

[vup903]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: ADK bug — LiteLlm: native tools silently dropped when routing through a proxy gateway #6091

Problem:

When ADK's LiteLlm integration is used through a proxy gateway, native/built-in tools (tools without function_declarations, e.g. google_search) are silently dropped and never reach the gateway. _get_completion_inputs gated all tool conversion on llm_request.config.tools[0].function_declarations, so:

• a Tool carrying only native tools produced tools=None (the reported bug), and
• any Tool past index 0 was ignored entirely — the list comprehension only ever touched tools[0], which is the underlying root cause; native-tool dropping is the most common way people hit it.

Solution:

Loop over all llm_request.config.tools instead of only index 0: convert function_declarations through the existing _function_declaration_to_tool_param path, and serialize native tools via model_dump(by_alias=True, exclude_none=True) into the same combined list. Function and native tools are always sent together; ADK does not pre-emptively guess provider support, so an unsupported schema is rejected by the provider/proxy like any other unsupported parameter (per maintainer guidance on the issue).

The identical tools[0]-only slice in _build_request_log is fixed the same way for consistency (debug-log only; does not change what is sent).

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Added to tests/unittests/models/test_litellm.py:

• test_get_completion_inputs_serializes_native_only_tool — a native-only Tool is serialized instead of dropped.
• test_get_completion_inputs_mixed_native_and_function_tools — both a native tool and a function tool reach the request.
• test_get_completion_inputs_collects_tools_beyond_index_zero — function tools on config.tools[1:] are no longer ignored.
• test_get_completion_inputs_no_tools_returns_none — regression: no tools still yields tools=None.

$ pytest tests/unittests/models/test_litellm.py -q
345 passed, 4 warnings in 16.40s

Manual End-to-End (E2E) Tests:

For the OpenAI path I ran ADK's LiteLlm against a local litellm proxy and confirmed native tools now appear in the outgoing request body (before this change the body carried no tools). I don't have a Vertex AI environment, so the Vertex-via-proxy path is covered here by wire-shape assertions against a mocked OpenAI-compatible backend — a check on a real Vertex proxy during review would be appreciated (@surajksharma07 offered a second pair of eyes on the Vertex-side wire shape).

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[adk-bot]

Thank you @vup903 for your contribution! 🎉

Your changes have been successfully imported and merged via Copybara in commit c429d75.

Closing this PR as the changes are now in the main branch.