Agent Sessions can coordinate work

What changed

Agent Sessions can now find other Sessions, create a new same-Agent Session, and send durable work to another Session. Session creation and sending require per-call approval, and completed actions link directly to the target Session from chat.

Why this matters to the user

Users can delegate bounded work across Session timelines without keeping the originating tool call open. Requests and completion results survive ordinary app restarts.

What the user should do

Nothing — approve Session creation or sending when the requested delegation is expected.

Notes for release manager

Delivery is asynchronous and at-most-once at the model-turn boundary; external tool side effects cannot be made exactly-once across a crash.