soulfind tells a room about a new member, the new member included, before
it sends them the room's member list. The roster was started from that
echo, so for a moment after joining a room read as holding nobody but us,
and `room users` returns on the first roster it sees: it could print only
the asking user. That is the flake in room_users_lists_who_is_in_the_room.
A join or leave now only updates a roster the server has sent in full,
which is also what room_members already promised for a room we have not
joined. The e2e test waits for the resident's own member list instead of a
fixed second, so it no longer races the resident's join either.
Michel de Graaf
7060d3521a