1step,rule,n_before,n_after,n_removed,rationale21,drop months before 1992-03-01 (first training row; lag/neworder availability),417,415,2,TASK.md ridge spec: training rows start at s=1992-03-0132,drop months s with s+1 > last origin 2026-08-01 (target not available at origin),415,413,2,information rule: training target y_{s+1} must be dated <= t4