Note that the released source code is pretty different from the actual running site. In particular, all the rsvp code that caused the problem is not in the released source.

The HN source code is in the Arc language. See my site http://files.arcfn.com/doc/index.html for Arc documentation, specifically http://files.arcfn.com/doc/srv.html for the web server internals (including why links expire). Also see the App Server page which explains account management.

If you want to hack on this, there's a small but enthusiastic Arc community at http://arclanguage.org/forum