useMessageMetadata

Read metadata recorded for a specific message id — today exposes parentCheckpointId, the checkpoint the message was first seen on. Designed for fork / edit flows:

const { parentCheckpointId } = useMessageMetadata(stream, msg.id) ?? {};
if (parentCheckpointId) {
  await stream.submit(input, { forkFrom: { checkpointId: parentCheckpointId } });
}

Returns undefined when the id isn't known yet (e.g. the server hasn't emitted parent_checkpoint for that message, or the message arrived via messages-channel deltas only and no values snapshot has landed for it yet).