Lluis Eriksson (2026). Exact Branch Rigidity and Unique Crossing in Grassmann Matrix--Bingham Free Energies: Finite Certification, All-Field Gr_C(3,6) and Gr_C(4,8) Two-Block Order, and a Gr_C(2,5) Exchange Theorem. AIRR.SCIENCE, ARR-2026-263B0753CQ9J2T34, v1. https://airr.science/papers/ARR-2026-263B0753CQ9J2T34/versions/v1/