I’d pick 1.
I did a Helpdesk chat application which is a little different than the concern here.
I had a lobby room and a room for each user.
The helpdesk admin joins the users room after the user turns up in the lobby.
The lobby room is used to indicate presence.
It has worked OK so far. I think the question is scale.
I’d pick whatever most closely resembles communication in the real world.
