When the turn this transcript belongs to began, in milliseconds since epoch.
A provider that withholds the final transcript until its reply has finished
generating should set this, so the user message can be placed on the session
timeline where the turn happened rather than where the transcript arrived.
When the turn this transcript belongs to began, in milliseconds since epoch.
A provider that withholds the final transcript until its reply has finished generating should set this, so the user message can be placed on the session timeline where the turn happened rather than where the transcript arrived.