ROWCOL-03 QC FAIL (rms 52.9 unchanged by erosion) proved the junk edge
columns are FULLY covered with DEFINED-BUT-WRONG back-projection values
(left-edge convert_direct artifact class) - erosion cannot see them:
- exclude a 16px frame-edge band from the content-excluded estimator by
  geometry (ROWCOL_BP_EDGE_MARGIN); those lines take the legacy fallback;
- physical cap in the per-line merge: a content-excluded line value over
  max_abs cannot be line noise - use legacy (also blunts any future
  ROWCOL-01-class estimator failure).

RT conditioning: profile HPF now applies ONLY when rowcol_um_sigma==0.
Stacking it on the UM measurement double-high-passed the row-offset
estimate ((1-G10)(1-G8)): removed fraction at period ~20 rows dropped
96% -> 91%, residual mid-band line noise x2 - measured merged RT-RENDER
rows metric 10.60 (ROWCOL-02, pre-rework) -> 18.73 (ROWCOL-03). Single
sigma-10 high-pass removes strictly more noise at every period than the
old sigma-8-only path and protects the LoG band at least as well.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>