QCoreIV: STLF, STLF_0S, and 3D Contract Protection for the Worker Corridor

Foundational — QCoreIV: STLF, STLF_0S, and 3D Contract Protection for the Worker Corridor. This article upgrades QCore without rewriting its worker identity. The central contribution is a 3D protection shell for the capsule-local worker engine: frozen intersection support, typed-zero inheritance, shadow-only continuity, no-backflow, Strong-to-Weak-to-Weaker closure, and merged-row certification before perpendicular audit. The paper also locks STLF_0S into QCore as a protected refinement of the existing STLF front edge, separating true-null pressure from shadow-occupancy pressure while preserving replayability and preventing promotion laundering. The result is a stronger and more general QCore architecture that remains backward-compatible with honest 2D benches while gaining contract-grade protection for stacked support, typed missingness, and worker-side closure.