Transport-Dominated Frame Error and a Conservative Low-Dissipation Correction on D3Q125

Central-Hermite sensing and collision suppress translation-induced cross-order coupling in fixed-velocity kinetic models, but this local improvement does not automatically control macroscopic frame error. We isolate the source of boost-dependent error in a D3Q125 finite-volume kinetic solver by separating collision, spectrally exact periodic streaming, first-order upwind transport, higher-order time integration, and low-dissipation spatial transport. Collision-only diagnostics are frame robust to roundoff, whereas first-order upwind transport produces percent-level changes in fitted shear-wave viscosity. Replacing forward Euler by SSPRK2 does not improve the error, while spectrally exact periodic streaming reduces it by about four orders of magnitude. A second-order Lax-Wendroff flux reduces the median smooth-wave boost error by 99.78% relative to first-order upwind and gives approximately second-order convergence in the smooth regime. For steep profiles, unlimited Lax-Wendroff can generate negative populations. We therefore combine a conservative interface-flux limiter with a local collision positivity limiter. The resulting method preserves mass, momentum, and kinetic energy to floating-point accumulation accuracy, maintains nonnegative populations to numerical tolerance, and roughly halves the median steep-profile macroscopic field error relative to upwind while retaining essentially the same accuracy as unlimited Lax-Wendroff. A separate boosted acoustic-entropy-wave benchmark confirms the same hierarchy without relying on shear-viscosity fitting: Lax-Wendroff reduces the median combined frame discrepancy by 97.53% relative to upwind, while SSPRK2 does not repair the first-order spatial error. The results distinguish collision-level frame robustness from full-solver frame accuracy and identify boost-dependent numerical dissipation in the spatial discretization as the dominant error source in the tested regime.