A Fixed-Direction Solar-System Lorentz-Violation Target: the s-bar^TX Boost-Dipole of de Sitter-Unruh Modified Inertia

A timestamped, falsifiable prediction note for the planetary-ephemeris community (INPOP / EPM / DE). The de Sitter-Unruh modified-inertia account of the MOND acceleration scale (a0 = cH_Lambda/Z = 9.36e-11 m/s^2, Z=sqrt(32pi/3)) is a PREFERRED-FRAME theory: the de Sitter-Unruh bath of the cosmological horizon defines a preferred rest frame, the cosmic (CMB) frame, which is a Standard-Model-Extension (SME) gravity-sector background s-bar_munu. The Solar System's motion at v=369.8 km/s toward the CMB apex (beta=v/c=1.23e-3) gives the otherwise-isotropic background a forced time-space (boost) component s-bar^TX proportional to beta, aligned with that apex. PREDICTION (specific and falsifiable): s-bar^TX ~ 8.7e-10, CPT-EVEN only, with a FIXED sky direction = the CMB apex (l,b)=(264.0, 48.3) deg; (RA,Dec)~(168,-7) deg -- NOT a free coefficient to marginalize, but a dipole locked to a known point on the sky (one fewer degree of freedom than a generic SME search). The current bound (Hees et al. 2015, planetary ephemerides) is |s-bar^TX| <~ 1.3e-9, so the prediction sits ~1.5x under the present limit. DECISIVE MEASUREMENT: a dedicated s-bar^TX dipole fit (orbital dynamics + light propagation in the Time-Transfer Formalism) reaching sigma ~ 4e-10 (a factor ~1.5-2 beyond the present sensitivity) will DETECT a dipole of ~8.7e-10 aligned with the CMB apex, or EXCLUDE it. The data are in hand -- INPOP/EPM/DE planetary ranging, the Cassini Saturn arc (extended), Mars-orbiter ranging, and BepiColombo Mercury ranging (arrival 2026) -- so this is ANALYSIS-LIMITED, not data-limited. HONEST SCOPE: the direction and CPT-even character are robust consequences of 'preferred frame = CMB frame'; the magnitude is framework-specific (inherits the author's a0->s_munu component ledger, +-O(1)). This is a test of the gravity-sector preferred frame ONLY -- a theory of gravity and the dark sector, NOT a theory of everything; the Standard-Model matter sector is untouched. The framework passes every other named gravity-sector bound (LLR, INPOP/Cassini gamma, atom interferometry, pulsar alpha2, VLBI); s-bar^TX is its tightest exposure, which is why it is the one most worth a dedicated fit. Reproducible from the public repository. Supplements the author's published de Sitter-Unruh papers (DOI 10.5281/zenodo.20973740, 10.5281/zenodo.20965016).