The namespace of the turn's scopes (TurnScopes.namespace).
Optional turnOn a turn with no learner: the explicit id of the user whose turn it is, when it is not the session's learner.
Optional conversationThe turn's conversation id: the session's row collects it, so forgetUser deletes the conversation's thread.
The turn a recorded or guarded write belongs to, as the GMI read it from that turn's own preparation: a learner's turn keys the write to the learner; a turn with no learner keys it to the agent and the session, under the session form's namespace, with a second user's explicit id in
turnUserId.