Non-Invariant Cosmological Estimators: Structural Theorems, Empirical Evidence from Pantheon+, and Physical Realization in MRUV Cosmology

We demonstrate that the universality of the Hubble constant H_0 is not a structural identity of cosmological inference but an additional assumption. Two model-independent theorems are established: (1) the Non-Commutativity Theorem, showing that GLS estimators applied to luminosity distance data over finite redshift windows suffer a systematic bias DeltaH = K*z_max + O(z_max^2), with K generically non-zero for any smooth cosmology with nonlinear D_L(z); and (2) the Non-Equivalence Theorem, establishing that estimators acting on physically distinct domains are structurally non-equivalent without an explicit domain-bridging assumption. We further establish a new structural result: window-invariant estimation is possible if and only if the observable lies exactly in the inferential subspace span{z}. Writing the observable as y = a*z + r, any nonlinear residual r not identically zero generically induces estimator drift. The condition beta = 0 corresponds to a non-robust fine-tuned cancellation, identifying H_0 universality as a degenerate case of inferential subspace closure rather than a physical prediction. Operational application to Pantheon+SH0ES (N = 1701 Type Ia supernovae) yields beta = -9.8 +/- 1.2 km/s/Mpc at 8.2-sigma significance, robust across three weight schemes and three z_min cuts. A null-test on mock LambdaCDM data confirms zero drift (0.2-sigma). MRUV cosmology predicts beta_pred = -7.23 +/- 0.86 km/s/Mpc (1.7-sigma consistency). CDG-2 (M_dyn/M_* ~ 1670) is reproduced without non-baryonic matter. Increasing observational precision alone cannot resolve the Hubble tension if inference remains structurally non-invariant.