Lifecycle

Lifecycle extensions manage behavior around the agent without turning that behavior into tools.

Need	Use
Start and close a dependency	Application resource
Publish a value to agent code	Context resource
Observe or transform execution	Invocation hook
Control public SubAgent narration	Output policy
Add framework-specific behavior	Native integration
Add application HTTP routes	HTTP route factory
Store sessions or checkpoints	Storage factory
Store session-owned media	Asset store
Authenticate or resolve credentials	Security factory
Export traces or logs	Telemetry exporter

Lifecycle is root-owned. SubAgents cannot add private lifecycle extensions.

Application resources

Start, publish, share, and close application dependencies.

Observe or transform agent, model, and tool execution.

Decide whether intermediate SubAgent narration becomes public.

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

Boundary	Page
Sessions and checkpoints	Checkpoints and storage
Caller identity and downstream tokens	Authentication and credentials
Logs, traces, and audit events	Telemetry
Application-specific HTTP contracts	Custom HTTP endpoints
Typed media and asset references	Typed multimodal contracts
Decorator signatures and cardinality	Runtime extension reference