derive cleaner min-4px YOLO corpus

docs/reviews/2026-08-09-ai-assisted-checkpoint-review.md

@@ -161,3 +161,29 @@ The edge sample shows expected clipped buildings under the 0.35 minimum-visible
 policy. Raising that value may reduce partial-target pressure, but it must be a
 separately versioned ablation because removing all 5,079 rows without checking
 the original visible fraction would be unsound.
+
+## Derived min-4px experimental corpus
+
+The row-level finding was converted into a new immutable derived corpus rather
+than changing the historical dataset. The derivation is checksum-bound to the
+79,192-label source summary and removes only labels whose smallest 512-tile
+dimension is below 4 pixels. It retains all 252 tiles and 77,380 labels; no
+positive tile became empty, and no source file was overwritten.
+
+Fresh audits report zero sub-4-pixel labels, zero invalid or missing label
+files, zero exact/high-IoU duplicates and zero reconstructed cross-split
+object groups. Extreme-aspect labels fall from 26 to 10, possible nesting from
+43 to 41 and tile-edge rows from 5,079 to 4,840. The complete four-page visual
+render was inspected again. Pure-background tiles remain visibly empty, sparse
+contexts remain distinct and the ten remaining elongated labels predominantly
+match plausible long structures.
+
+The generic quality auditor still reports `needs_attention` because normalized
+median box area `0.000641` is below its conservative `0.001` warning threshold.
+That corresponds to median dimensions near 12 by 13 pixels at source tile
+resolution and is not a failed minimum-dimension gate. The warning remains
+visible; it was not suppressed or relabelled as success.
+
+This min-4px version is the preferred experimental successor to the legacy
+min-3px corpus. It explicitly remains ineligible for governed training until
+real human review and all release-contract evidence exist.