Allow user confirmation before transfer_to_agent in Google ADK

Is your feature request related to a problem? Please describe.
In Google ADK, control transfer to a sub-agent is currently performed automatically through the transfer_to_agent tool. However, when there are many agents and some of them provide similar functionality, it may be unclear to the end user which agent will actually receive control. This lack of transparency can lead to confusion or an unintended choice.

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Describe the solution you’d like
Introduce an option for the user to confirm the transfer of control.
For example, when transfer_to_agent is triggered, the system could:
• display a list of available sub-agents,
• allow the user to pick the desired one,
• confirm the transfer after the selection.

This interactive step would make the process more transparent and give the user full control over agent selection.

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Describe alternatives you’ve considered
• Implementing filtering or selection logic in code, but this still removes direct user involvement and adds extra complexity.
• Creating an intermediate “dispatcher” agent that asks the user, but this approach feels over-engineered and complicates the architecture.

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Additional context
This feature would be especially helpful when:
• multiple agents have overlapping capabilities (e.g., several support or domain-specific agents),
• explicit confirmation is critical, such as for financial operations or configuration changes