Resolution of the Reactor Antineutrino and Gallium Anomalies: Substrate Boundary Acoustic Impedance, Non-Oscillatory Transmission Loss, and the Elimination of eV-Scale Sterile Neutrinos in an Elastically Pre-Stressed Vacuum

Short-baseline reactor antineutrino experiments (Daya Bay, RENO, Double Chooz, PROSPECT, STEREO) consistently report an integral flux deficit of R_RAA = 0.945 ± 0.018 relative to Huber-Mueller conversion predictions. Simultaneously, radioactive source calibrations of gallium experiments (GALLEX, SAGE, BEST) exhibit an even deeper capture rate deficit of R_BEST = 0.79 ± 0.05. Standard model extensions invoke a light sterile neutrino (Δm_41^2 ~ 1 eV^2), which creates acute tensions with muon-neutrino disappearance limits (MINOS+, IceCube, MicroBooNE) and conflicts with cosmological constraints on relativistic species (ΔN_eff < 0.2 from Planck). Building upon our foundational series on the physical vacuum as an elastically pre-stressed continuum, we show that these deficits are not flavor oscillations, but classical elastodynamic boundary transmission losses. In our ontology, neutrinos are unbound transverse torsional shear wavepackets propagating through the pre-stressed substrate. In a reactor fuel core or Mega-Curie source, the extreme concentration of nuclear mass solitons compresses the local continuum, elevating its localized acoustic impedance (Z_core > Z_0). Crossing the mechanical interface into free vacuum induces acoustic reflection and boundary dissipation. We derive the analytical transmission coefficient T_trans = 4 Z_0 Z_core / (Z_0 + Z_core)^2 ≈ 0.947 for reactor fuel lattices and T_BEST ≈ 0.81 for compact chromium sources, matching observational data without sterile neutrinos, resolving the short-baseline anomalies under Occam's razor while preserving N_eff ≡ 3.04.