fix: remove developer notes from transfer_to_agent docstring

[stakeswky]

Summary

Fixes #4615

The transfer_to_agent function's docstring included a Note section with developer guidance about using TransferToAgentTool instead. Since this docstring is sent to the model as the tool description on every invocation, the extra text wastes input tokens and increases hallucination risk.

Before

description: "Transfer the question to another agent. This tool hands off control to another agent when it's more suitable to answer the user's question according to the agent's description. Note: For most use cases, you should use TransferToAgentTool instead of this function directly. TransferToAgentTool provides additional enum constraints that prevent LLMs from hallucinating invalid agent names. Args: agent_name: the agent name to transfer to."

After

description: "Transfer the question to another agent. Use this tool to hand off control to another agent that is more suitable to answer the user's question according to the agent's description. Args: agent_name: the agent name to transfer to."

Changes

• src/google/adk/tools/transfer_to_agent_tool.py: Removed the Note section from the docstring, keeping only the model-facing description and Args.

Testing

All 9 existing tests in test_transfer_to_agent_tool.py pass, including test_transfer_to_agent_tool_preserves_description which validates the tool description content.

[gemini-code-assist]

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