feat: Add tool_choice config to LlmAgent for controlling tool invocation

[Oxygen56]

Summary

Adds a tool_choice field to LlmAgent that maps provider-agnostic values (auto, required, none) to Google GenAI's ToolConfig / FunctionCallingConfig.

Changes

• llm_agent.py: tool_choice field with Literal type and docstring
• base_llm_flow.py: Maps tool_choice → types.ToolConfig(function_calling_config=...)
• tests/unittests/agents/test_tool_choice.py: 8 unit tests

Testing Plan

pytest tests/unittests/agents/test_tool_choice.py -v

Tests cover:

• Field declaration existence and default value
• tool_choice="required" → FunctionCallingConfigMode.ANY
• tool_choice="none" → FunctionCallingConfigMode.NONE
• tool_choice="auto" / unset → no config forced
• Full ToolConfig structure verification

🤖 Generated with Claude Code
Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com

[google-cla]

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[adk-bot]

Response from ADK Triaging Agent

Hello @Oxygen56, thank you for creating this PR to add tool_choice configuration!

This is a great feature, but to help us review and merge your contribution, could you please address the following items according to our contribution guidelines:

1. Contributor License Agreement (CLA): It looks like the Google CLA check has failed. Please visit https://cla.developers.google.com/ to sign or verify your agreement.
2. Testing Plan & Unit Tests: Please include a testing plan section in your PR description describing how you tested this change. Additionally, please add or update unit tests (under tests/unittests/) for your new feature.
3. Logs/Screenshots: Since this is a new feature, please provide logs or a screenshot of the fix working in action (for example, demonstrating that the tool choice constraint behaves as expected).

These details will help our reviewers process your PR much faster. Thank you!

[rohityan]

Hi @Oxygen56 , Thank you for your contribution! It appears you haven't yet signed the Contributor License Agreement (CLA). Please visit https://cla.developers.google.com/ to complete the signing process. Once the CLA is signed, we'll be able to proceed with the review of your PR. Thank you!

[adk-bot]

🔍 ADK Pull Request Analysis: PR #5984

Title: feat: Add tool_choice config to LlmAgent for controlling tool invocation
Author: @Oxygen56
Status: open

---

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• The Google CLA Bot has flagged that the contributor has not yet signed the agreement.
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Next Steps for the Contributor

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[Oxygen56]

@adk-bot CLA has been signed. Ready for re-review.

[Oxygen56]

@rohityan @adk-bot All checks are now passing (cla/google ✅, header-check ✅, pr-analyze ✅, check-changes ✅). The CLA has been signed and there are no remaining blockers.

Ready for review — thanks for your time!