Since this is a co-op game and I don't care about cheating I could have just made stamina wholly client-authoritative, but I don't want to rule out having stamina available on the server as well, even if it's slightly out sometimes. I've found that having the server decide when "exhausted" happens even if the client slightly disagrees works fine, wheras real-time replication from server->client of stamina looks terrible in the UI even with smoothing because of the lag & variable replication rate