From what I see with other clients (DSub, Ultrasonic, substreamer), they send a ping when registering the server to validate address/user/password. At this point you would get the supportExtensions field and save it with the server information you already save.
Doesn’t Symfonium do this initial ping to validate address/user/password?
Yes I do amongst other tests, but servers are upgraded during their life time that will need to request the supported endpoints anyway again without running the wizard. Probably based on the fact that the server version have changed in any query return.
Anyway exposing the field in ping does not hurt and works for me.