Unrelated but BTW FreeCAD is fully python scriptable. In fact, as I understand it, every operation is first translated to python code.
Yeah, and it outright isn't documented.
There is also Cascade Studio (Demo). Sadly development has stalled, it was a really cool project.
Probably not at all what OP is looking for though since TinkerCAD is just sketch/primitive type workflow, not like openscad.
Someone posted this https://webvm.io/alpine.html in another community and it made me think of this post. I've never used webvm and I suspect there are many downsides but seemed relevant and the demo seems to be able to run a full desktop environment. You have to find a CAD software that supports Linux though which is a controversial topic at best.
Check out Kasm too, you can easily install blender into it.
Might I ask, why exactly do you feel the need to have a webapp for CAD rather than a hard client?