Thanks for asking. Core ops are OCCT. It's got great primitives and tolerant modeling. For performance purposes, I've implemented my own algorithms for hidden line rendering, tessellation, and others. I've spent my whole career (15 years+) working on and around kernels.

More detail for the curious: it’s C++ compiled to WebAssembly and runs entirely client-side with a WebGL2 renderer, so there’s no server round-trip for geometry. OCCT does booleans, fillets, and STEP. I replaced its mesher with my own tessellator because BRepMesh was the bottleneck at scale, and hidden-line/Make2D are custom too. Happy to go deeper on any of it.