Isotropy of the z ≈ 0.65 expansion anomaly: a test of the Vaidya-FRW accretion framework

In a companion paper we derived H = Ṁ/M from Vaidya-FRW junction conditions, detecting a localized accretion enhancement at z_c ≈ 0.63 at 2.9σ in combined supernova, BAO, and CMB data. Because the interior scale factor couples to the total horizon mass M(v), a scalar with no angular dependence, the framework requires this signal to be spatially isotropic. We test this prediction by splitting Pantheon+ supernovae into hemispheres aligned with three CMB anomaly axes and fitting independently. All inter-hemisphere tensions are below 0.35σ. The signal is detected at 2.6-2.8σ in every hemisphere. The Gaussian clump parameters are 10-50× more stable across sky cuts than w₀w_a, whose best-fit values fragment by Δw_a = 0.16-0.36 between hemispheres. Both results, isotropy of the signal and fragmentation of smooth parameterizations, were predicted in [1].