useMessages

Subscribe to a scoped messages stream. Pass stream and optionally a subagent/subgraph snapshot (or any namespaced target).

Contract:

• At the root (no target) this returns stream.messages directly — no extra subscription is opened. stream.messages is the live merge of messages-channel token deltas and values.messages snapshots (see UseStreamReturn.messages), so token-by-token streaming here depends on the backend emitting messages channel events. Backends that only emit values updates will render full turns at once rather than streaming.
• For any other namespace, the mount triggers a ref-counted messages subscription scoped to that namespace. Unmounting the last component that watches this namespace closes the subscription automatically.

Messages are always BaseMessage class instances from @langchain/core/messages.