Instructions for AgentTool summarization

[sgpstefanov]

I'm reading the docs about wrapping an agent as a tool using AgentTool - https://google.github.io/adk-docs/tools/function-tools/#customization
I see that there's a skip_summarization option.
This is where I learn that some responses have automatic summarization.
Could you show me where the prompt for this summarization step is? I can't seem to find it in the code base.