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.)
Ok, solve space is cool. But let me know when it’s ready to tackle more than a “hello world” level design problem.
This is something that is being done by the core maintainer(s?) now; it’s linked off the main site.