So what I've done for now wrt !postActiv exception handling improvement, is just put everything together, in a central file for server exception, /classes/ServerException.php

This file includes the descendant classes for exceptions that fall under that type.

I have also assigned what I believe to be the sanest HTTP status code as error codes for each, but they may be subject to chance if the actual causes of the errors turn out to not be what the documentation that exists says they are.