fix(lite_llm): exclude llm_client from model_dump to fix build_graph …

[ammarfitwalla]

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

• Closes: adk web build_graph crashes with LiteLlm model due to non-serializable LiteLLMClient #5367 https://github.com/google/adk-python/issues/5367

Testing Plan

Unit Tests:

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

Added test_lite_llm_model_dump_excludes_llm_client in tests/unittests/models/test_litellm.py.
This test asserts that llm_client is absent from model_dump(mode="python", exclude_none=True) output.
246 passed, 1 warning in 6.15s

Manual End-to-End (E2E) Tests:

Unable to perform E2E testing at this time due to lack of a LiteLLM-compatible API key.
The unit test directly covers the root cause — llm_client being present in model_dump() output — which is the exact field that causes the PydanticSerializationError in the builder serialization path.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

The builder endpoint in adk_web_server.py serializes agent fields via model_dump().
For LiteLlm, this included llm_client -- a LiteLLMClient instance that Pydantic
cannot serialize, causing:
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize
unknown type: <class 'google.adk.models.lite_llm.LiteLLMClient'>

Fix: Mark llm_client with exclude=True in its Pydantic Field definition.
This drops it from model_dump() output while keeping the client fully functional at runtime.

# Before
llm_client: LiteLLMClient = Field(default_factory=LiteLLMClient)

# After
llm_client: LiteLLMClient = Field(default_factory=LiteLLMClient, exclude=True)

[rohityan]

Hi @ammarfitwalla , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Please fix formatting errors by running autoformat.sh

[ammarfitwalla]

Hi @ammarfitwalla , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Please fix formatting errors by running autoformat.sh

Fixed the formatting by running pyink. Thanks for the quick review!