How to add editor-only per-face box handles?

Godot Version

v4.3.dev5.official [89f70e98d]

Question

Hello everyone,

Does anybody know how to add a 3D editor-only wireframe box and most importantly the new per-face box handles on new custom elements?

I want to create a very simple stairs generator that would use a user-defined bounding box as well as min and max values for stair height and length to automatically determine stairs count and then spawn appropriate meshes in editor.

Here’s the commit where the per-face handles were implemented in the engine. It comes with a short showcase video. I looked at the examples implemented in that commit but it’s far from helping me enough. I have also looked through the 3D gizmo plugins tutorial.

Implementation can be in GDScript or C#. I don’t mind going the GDExtensions route either.

Image showing the per-face handles:
image

Thank you for your time!