I tested it, it works, and it's a very laborious plugin. Congratulations!
Some of the new features don't work (yet), but I think you'll get them to work (Y-shaped or T-shaped stairs).
The profile editor is very interesting (at least for me).
May I use it as inspiration for my other plugins?
In return, I could try to organize your source code better. 7625 lines in a single sheet is a bit too much and difficult to manage.

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