Substrate-Frame Pre-Registration: Pre-Registered Observer-Frame Predictions for Independent Low-Redshift SN Ia Data

This document pre-registers five observer-frame predictions on the directional structure of the foreground-coupled distance-modulus residual field in Type Ia supernovae. The claim is that the residual field carries a principal axis ~30 degrees from the Virgo-Perseus axis on Pantheon+, with four locked structural signatures (anti-cone amplification, secondary maximum-signal direction, antipodal hemispheric asymmetry, perpendicular-vs-parallel anisotropy) along/perpendicular/antipodal to that axis. Before Rubin Year-1 data are released, this document locks the five subsample-direction tests (S-Y1-A through S-Y1-E) with thresholds calibrated on Pantheon+. Reproduction on the independent Rubin Y1 sample is the test. This pre-registration is filed as a separate Zenodo deposit from the foreground-coupling Mishkat pre-registration because the two claims are mechanistically distinct: foreground coupling modulates SN brightness via line-of-sight stellar material, whereas observer-frame substrate locking is a directional/anisotropic claim about the residual field's principal-axis structure. Each pre-registration is independently falsifiable.