Advanced Spectral Diagnostics for 2D MHD Turbulence: The Xu-Auditor Protocol

This technical report presents the Xu-Auditor protocol, a lightweight spectral-fidelity auditing framework designed for high-resolution pseudo-spectral Magnetohydrodynamic (MHD) simulations. While standard global invariants often fail to detect localized numerical pathologies, this protocol identifies nonphysical energy accumulation (spectral blocking) through two complementary metrics: the Blocking Index (BI) and a Spectral-consistency score ($\rho$). Using the canonical 2D Orszag-Tang benchmark at $N=256$, we demonstrate the discovery of a distinct spectral break at $t=0.266$. This anomaly serves as an early warning for the loss of physical fidelity, occurring before traditional diagnostics show significant degradation. This work provides the theoretical basis and numerical validation for routine spectral auditing in computational fluid dynamics. Keywords: MHD Turbulence, Pseudo-spectral methods, Orszag-Tang, Spectral Blocking, Numerical Fidelity, Python.