Merge branch 'fix/bestfit-overlap-test'

Fixes BestFit overlap check to agree with the geometry BuildParts
actually places, resolving BestFitOverlapTests.KeptPairs_NoOverlap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

OpenNest.Engine/BestFit/PairEvaluator.cs

@@ -58,19 +58,6 @@ namespace OpenNest.Engine.BestFit
             part2.Location = candidate.Part2Offset;
             part2.UpdateBounds();
 
-            // Overlap check — perimeter vs perimeter. Uses Collision.HasOverlap (full polygon
-            // clip) rather than Shape.Intersects (edge-crossing only), which misses containment-
-            // style overlaps where one perimeter's boundary never crosses the other's.
-            var shape1 = GetPerimeterShape(part1);
-            var shape2 = GetPerimeterShape(part2);
-            var overlaps =
-                shape1 != null
-                && shape2 != null
-                && Collision.HasOverlap(
-                    shape1.ToPolygonWithTolerance(OverlapChordTolerance),
-                    shape2.ToPolygonWithTolerance(OverlapChordTolerance)
-                );
-
             // Convex hull vertices from perimeter polygons only
             var allPoints = GetPartVertices(part1);
             allPoints.AddRange(GetPartVertices(part2));
@@ -106,7 +93,9 @@ namespace OpenNest.Engine.BestFit
 
             var trueArea = candidate.Drawing.Area * 2;
 
-            // Normalize to landscape (width >= height) for consistent display.
+            // Normalize to landscape (width >= height) for consistent display. Do this before
+            // the overlap check so bestRotation already matches the final OptimalRotation that
+            // BuildParts will apply.
             if (bestHeight > bestWidth)
             {
                 var tmp = bestWidth;
@@ -115,6 +104,33 @@ namespace OpenNest.Engine.BestFit
                 bestRotation += Angle.HalfPI;
             }
 
+            // Overlap check — perimeter vs perimeter, in the same final orientation BuildParts
+            // uses downstream. Uses Collision.HasOverlap (full polygon clip) rather than
+            // Shape.Intersects (edge-crossing only), which misses containment-style overlaps
+            // where one perimeter's boundary never crosses the other's. Checking pre-rotation
+            // geometry here (rather than rotating part1/part2 first, matching BuildParts) would
+            // tessellate arcs at a different orientation than the geometry actually gets placed
+            // with, letting tangent-corner slivers slip through in one frame but not the other.
+            if (!bestRotation.IsEqualTo(0))
+            {
+                var pairBounds = (
+                    (IEnumerable<IBoundable>)new IBoundable[] { part1, part2 }
+                ).GetBoundingBox();
+                var center = pairBounds.Center;
+                part1.Rotate(-bestRotation, center);
+                part2.Rotate(-bestRotation, center);
+            }
+
+            var shape1 = GetPerimeterShape(part1);
+            var shape2 = GetPerimeterShape(part2);
+            var overlaps =
+                shape1 != null
+                && shape2 != null
+                && Collision.HasOverlap(
+                    shape1.ToPolygonWithTolerance(OverlapChordTolerance),
+                    shape2.ToPolygonWithTolerance(OverlapChordTolerance)
+                );
+
             return new BestFitResult
             {
                 Candidate = candidate,