H₀ as an Interface-Dependent Stress Test: Evidence for Local Consistency and Global Non-Closure

This technical note presents a controlled stress test of the Hubble constant (H₀) within an interface-dependent inferential framework, using ACT DR6 CMB lensing and BAO likelihoods analyzed both independently and jointly. Rather than proposing a resolution of the H₀ tension or introducing new physical mechanisms, the analysis is explicitly diagnostic. By applying constrained H₀ priors and tracking the resulting redistribution of χ² contributions across observational interfaces, the study probes how local consistency can coexist with global non-closure. The results show that: H₀ constraints are locally absorbable within specific observational interfaces, the resulting residuals systematically migrate between likelihood components rather than being eliminated, no single global configuration achieves full closure without redistributing inferential tension. These findings support an interpretation in which cosmological tensions act as interface-dependent stress tests rather than indicators of missing parameters or new physics. The work is aligned with regime-based and non-closure methodologies and is intended as a contribution to the structured analysis of inferential limits in contemporary cosmology. No claims of resolution, unification, or new ontological structure are advanced. The results are presented solely as empirical diagnostics of model-interface interactions and domains of validity.