Link to problem area:

https://spec.matrix.org/v1.5/server-server-api/#get_matrixfederationv1publicrooms
https://spec.matrix.org/v1.5/client-server-api/#get_matrixclientv3publicrooms

Issue

Neither the C-S nor federation /publicRooms APIs make it clear if servers may return rooms that they are no longer resident in (or cannot handle a join request for some other reason).

If servers can return rooms that they are no longer resident in, how is the client supposed to join the room, given there is no server list?