I created this article for the purpose of entering the All Things Agentic Hackathon. TL;DR — An ADK output_key writes into the session of the agent that declares it. In-process that session is shared, so it looks like state flows.
Source: [Dev.to](https://dev.to/arjunganesh/what-100-test-coverage-missed-state-across-google-adk-a2a-boundaries-29i1)