This document formalizes the Sector Alignment Stress Test, a permutation-based audit designed to distinguish geometric–modular alignment from modular structure alone within synthetic network models �. HMM_Methods_Appendix_v1.pdf None The procedure operates by: Holding network topology fixed, Randomly permuting sector labels, Recomputing entropy and edge-leakage metrics, Comparing aligned vs. permuted outcomes. By separating structural geometry from label assignment, the test identifies whether observed entropy reduction or identity concentration arises from genuine geometric–modular alignment or from modular partitioning alone. The method is model-agnostic within the defined network class but makes no claims beyond synthetic or explicitly defined systems. Its purpose is diagnostic: to detect structural coupling between geometry and modular assignment under controlled permutation.