No-contig α junction now inferred per-TRAJ (TRAJ_JUNCTION_RESIDUES, 52 genes from validated B1 contig reads; source 'j_inferred') instead of blanket N — wrong for ~30% of α. Unmapped J → N (canonical_fallback). validate_sequences cross-checks the α seam against the J gene's germline residue (#242/#236). j_inferred is still not contig-verified (gate #243/#244 unchanged). Closes #242.