Related Work: De Jesus, Elias. (2026). Diagnostic Map of Constraint-Coupled Vacua in String-Inspired Models. Zenodo. https://doi.org/10.5281/zenodo.18320070 This technical note introduces and empirically validates Conditional Geometric Relational Diagnostics (c-GRD), a falsifiable diagnostic framework for analyzing constraint topology in complex physical systems. c-GRD extends Two-Boundary Inference (TBI) by generating conditional, pre-registrable predictions of three types: (I) relational invariance, (II) forbidden regions, and (III) regime transitions, expressed through a signed radial coordinate \rho = \ln(R/\sqrt{e}) constructed from dimensionless observable ratios. The framework is validated using galaxy dynamics data from the Radial Acceleration Relation (RAR) and low-multipole CMB power spectra. Results show: (i) a localized and asymmetric regime transition in RAR at \rho = 0, coincident with the empirically established MOND acceleration scale; (ii) a correct null result for CMB low-\ell data where no transition is physically expected; (iii) strong relational variance suppression (≈90%) in acceleration ratios relative to null expectation; and (iv) strict or marginal compliance with pre-registered forbidden regions consistent with measurement scatter. c-GRD is explicitly diagnostic, not predictive of numerical constants, and does not advocate any specific theory of gravity or cosmology. Its relevance to string theory lies in providing a constraint-topology and duality-oriented diagnostic language for large theory spaces and landscapes, clarifying why predictivity may be structurally limited in the absence of boundary accessibility or global compression constraints.