A Fail-Safe Exact Kernel for Rational Sphere-Plane CSG with a Machine-Checked Combinatorial Boundary

Companion preprint. We present an exact, deterministic boundary kernel for regularized Boolean CSG over rational spheres and planes, with a Lean-checked combinatorial closure rule, a fail-safe outcome classification, and benchmark artifacts. The deposit includes the paper PDF, SHA-256 list, and a source-and-artifact archive. The source archive contains the GPL research kernel, Lean proofs, test vectors, artifact tables, and reproduction scripts. Licenses: paper CC BY 4.0; research code and Lean proofs GPL-3.0-or-later; artifact data CC BY 4.0. The Axiom product QA core is not included.