Since the unread rooms stream was scoped per user, posting a message
publishes the room id once to each member of the room. Each publish is a
round trip to Redis, made one after another inside the request, so the time
to post a message grows with the size of the room and in a big room is far
more than the rest of the request.
The fanout now runs in Message::BroadcastUnreadRoomJob, so the poster no
longer waits for it. Who gets the notice and what it says are unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NuTtwJKhb77Dv7EQqv2C3C
Marcello Costagliola