The overlap crosshair sat on the pair's area centroid. For a split,
holed or concave overlap, that point can be off the red material:
between two patches, in a hole, or inside a curve.
PlateOverlapPair.Marker is a point inside the pair's largest island.
It is the island's pole of inaccessibility (PolyLabel), searched to a
tenth of the island's area/perimeter within a 4096-cell budget. If
that bounded search does not land inside (a long thin sliver), the
marker falls back to the midpoint of the widest interior run of a
horizontal scan line placed between vertex heights.
The overlay crosshair, marker hit testing, hover coordinates
("Marker:") and the cutting-inspection ring now use the marker.
Centroid stays the true area centroid. View > Overlap Check > Display
> Centroids is now labelled Markers.
Before the marker existed, its call sites used the centroid. Two
patches, a covered frame, a half annulus and a thin crescent then put
it off the material; now all four land on it. Disabling the scan-line
fallback fails its test. On the 389-plate corpus, markers add about
0.4 ms per overlapping pair; pair and area results are unchanged.
PlateOverlapAnalyzer.Capture(parts, OverlapMaterialCache) reuses each clean
program's converted entities and prepared material across requests, and
Analyze(snapshot, previous) reuses pair results whose two parts kept the
same source, exact pose and relative order, renumbering them. A recheck
after moving one part only clips that part's neighbors again.
On 501 real PEP plates: full check median 1 ms / max 6.4 s; incremental
recheck after one move median 0.1 ms / max 38 ms. Incremental results
matched uncached full analysis exactly across 2505 edits.
aj