Sorry it has taken me so long, but I've finally uploaded the source code and my level solving tool here: https://github.com/mkamener/pathslider
I haven't actually tried to run/build the project for many years, and it is using an older version of Godot, so I can't guarantee it is all working. But feel free to do whatever you want with it :)
I abandoned my effort to port the game from Godot 2.x to Godot 4.x. The process was hard and was too big for me given my time and skill. Recently, I decided to ask Claude Code to create a PWA Web App from scratch using the Godot 2.x source as the spec. After about 1 hour and $24.63, this is the result. I have only started testing the game, but so far so good. Check it out! https://pathsliderweb.amayfield26.workers.dev/