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Lifecycle hooks and resource factories manage behavior around the agent without turning that behavior into tools. Author them in root lifecycle/, or package reusable functionality as a Harnest Extension with its own lifecycle/ folder. Lifecycle is root-owned. SubAgents cannot add private lifecycle hooks and factories.

Application resources

Start, publish, share, and close application dependencies.

Invocation hooks

Observe or transform agent, model, and tool execution.

Output policy

Select public narration, tool activity, provider reasoning, and model metadata.

Native integrations

Add ADK plugins or LangGraph middleware when portable hooks are not enough.

Harnest Extensions

Package typed SDK access and declared runtime contributions.