On the contrary that is a classic challenge checker on pgc. The first one was written in native PHP and have access to all data. Only the site developer could create them
The new checker system is using a lua sandbox and are more limiting because other people can write them. Then they have to be more limiting for security and other reasons.
There are others and som have planing tools. if you search for 360° Challenge and you will find the most common special checker.
They are easy to identify if you find them in search etc because "View source" "Download source" and "Tag Script" button as not active when you find them.
They are not tested in the background and can be found on the challenge maps by excluding challenges that you have passed or failed. The will be som new lua checker that ether results in error for you or have not been autochecked but most will be old checker.
It is mostly 360° Challenge except a few others
There is a problem writing in i gsak when i now think about it and that is that the macro language is quit limiting and not that fast. There are no object and max 50 arrays and that will be a problem i suspect. To do thing fast in GSAK you have to do them in the SQLite database part and i dont think this is subtile for an sql implantation.
I thin the esiest implementation is to write a external program that takes a gpx och csv with caches as input