I would think SolveSpace would be a much better target for this. It's got its own GUI system so probably pretty trivial to get running in the browser.

Oh yeah look somebody did it 4 years ago: https://github.com/TrevorDArcyEvans/solve-space-web

Plus SolveSpace is actually a good CAD app, especially for simple stuff. (For complex stuff the only good open source option is FreeCAD.)