test(M00): add landmark-region visual diff

docs/CAMERA_POSE_SWEEP.md

@@ -54,4 +54,10 @@ A WMO-ready joint grid fixed yaw at 10 degrees and evaluated pitch `[-25, -20, -
 
 The grid therefore has no approved joint optimum. Full-frame color error continues to trade landmark framing against large terrain regions. The manifest remains unchanged. The next registration method must score an approved inn/road/tree landmark region or explicit landmark coordinates rather than the entire image.
 
+## Common landmark region — 2026-07-12
+
+The comparator accepts an optional common screen rectangle through `--region x,y,width,height`; the sweep runner exposes it as `-ComparisonRegion x,y,width,height`. Coordinates are integer pixels in the shared reference/candidate image space. Both images must have identical dimensions and the rectangle must be fully inside them. Omitting the option preserves full-frame behavior.
+
+The existing 15 WMO-ready Goldshire candidates were rescored inside `[300,100,1400,650]`, covering the reference facade/chimney and nearby trees. ROI error ranked FOV 38/yaw 10/pitch -15 first at `0.081777` with changed-pixel ratio `0.697185`. This is an interior pitch candidate and improves on the full-frame grass preference, but human inspection still rejects manifest calibration: the facade is too large, its upper part is cropped, and the rectangle retains substantial road/terrain pixels. A common rectangle is useful diagnostic weighting, not semantic landmark registration. Explicit approved landmark coordinates or a mask remain necessary.
+
 During this run the sweep orchestration was hardened in two ways: expected comparator exit code `1` is now collected through an explicit child process, and viewport dimensions are explicit. A reference/candidate `size_mismatch` now fails before ranking instead of producing an empty metric.