getting referral ids for Moodle course enrolments

There was a request to store and report the referral ids passed via GET request from another site onto one of our Moodle instances. I turned to ChatGPT (free) for help. 

For the immediate need of getting referral ids from past logs, it suggested some python code. Which, of course, did not work on the first try. But 5 iterations later, got something useful out of it, which is shared at
https://github.com/hn-88/moodle-plugin-local-referrals/tree/main/temporary%20python%20code 

Then, it suggested writing a local plugin, and also suggested skeleton code. But the suggested code would not work if the user was not logged in to our site before clicking the referral link on the external site. It suggested saving the referral code to $SESSION. But that did not seem to work. Debugging to the Apache error log using lines like 
error_log('[local_referrals] function on_user_enrolled() ... ');
the referral id in $SESSION was being set to null when the user was logging in to our site.

Tried asking gemini.google.com (free) since ChatGPT seemed to be caught in a loop and unable to provide a fix. Gemini immediately looked up Moodle documentation and said that clearing the session (starting a new session) when a user logs on to Moodle is a known feature - and so we should store the referral id elsewhere - either in the database or in a cookie. Gemini in "Deep Research" mode also wrote a couple of essays about the issue, which could be summarized as my earlier sentence!

Then Gemini generated some code, but the code was incomplete. Asked ChatGPT to complete it - then asked Gemini to correct the errors introduced by ChatGPT - and the result is at
https://github.com/hn-88/moodle-plugin-local-referrals/ 

Some excerpts from the chats with ChatGPT and Gemini are in the wiki of that github repo - 
https://github.com/hn-88/moodle-plugin-local-referrals/wiki