Preprint. Part III of the Epistemic Hygiene framework. This paper presents the methodological and validation architecture for the diagnostic framework developed in Access Collapse (Isopahkala 2026a) and Epistemic Hygiene in Practice (Isopahkala 2026b). We clarify the structure of the Z-depth metric by distinguishing formal minimal reconstruction depth from operational depth observed in analyst practice. The framework's instruments are organised into a three-level hierarchy: boundary conditions (d, s), the meta-diagnostic operator (Z-depth), and the diagnostic operator (Φ-gate). We introduce the binding diagnosis instrument, which captures the implicit structural features preventing evaluation of claims through a location × reason pair. The paper also specifies a full validation protocol with four measurement layers: Φ-status agreement, Z-depth convergence, binding-diagnosis convergence, and reconstruction-path similarity. Pre-registered success criteria and falsification conditions are defined for future empirical validation studies.