Mesoscopic Structural Risk Diagnostics for Constraint-Based Quantum Architectures: Layer II

Scalable quantum architectures are increasingly constrained by mesoscopic structural effects that emerge prior to hardware realization. While a foundational admissibility layer establishes spectral consistency of scaling families, admissibility alone doesnot ensure favorable physical scaling behavior as architectures grow. This work introduces a second diagnostic layer aimed at quantifying architecture-level structural risk under controlled growth. Assuming admissibility has been verified, we analyze parametrized architectural graph families and extract a minimal set of physically interpretable observables derived from a symmetric structural operator. By examining the scaling of load concentration, mediation overhead, and perturbationinduced amplification, we estimate global and local growth exponents and define a Relative Structural Risk Index (SRI) for comparative assessment across architectures. The framework is evaluated on multiple architectural families, including linear chains, planar grids, centralized star topologies, modular hierarchical constructions, and a constraintmediated architecture inspired by parity-based encodings. The results indicate that spectrally admissible architectures can nonetheless exhibit substantially different mesoscopic scaling regimes. The proposed diagnostic layer functions as a pre-hardware structural assessment instrument, supporting architecture-level decisions prior to layout optimization, hardware prototyping, or error-correction design.