fix(reporting): fill parts whose arc ends carry post roundoff

The nest report joined contour segments only within 1e-12, but converted
arcs rebuild their end from the start radius and end angle. Rounded or
incremental programs (end radius a few 1e-7 off the start radius, which
the report's own validator accepts up to Tolerance.Epsilon) left every
arc a hair short of the next move, so outlines split into open pieces
and N26-27K's parts printed unshaded as if they had tab gaps.

Join within Tolerance.Epsilon instead, still far below ShapeBuilder's
welding tolerance and real tab gaps.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Reporting/NestReportGeometry.cs

@@ -165,10 +165,14 @@ internal static class NestReportGeometry
             throw Error(context, "nonfinite geometry coordinate.");
     }
 
-    // Only absorb floating-point trig roundoff, never ShapeBuilder's welding tolerance.
-    // A deliberate tab/rapid interruption is never joined by contour construction.
+    // Converted arcs rebuild their end from center, start radius and end angle, so a program
+    // arc whose end radius differs from its start radius (rounded or incremental posts; the
+    // validator accepts up to Tolerance.Epsilon) misses the next move's exact start by that
+    // much. Absorb only that, never ShapeBuilder's larger welding tolerance: a deliberate
+    // tab/rapid interruption is never joined by contour construction.
     private static bool SamePoint(ReportPoint first, ReportPoint second) =>
-        System.Math.Abs(first.X - second.X) <= 1e-12 && System.Math.Abs(first.Y - second.Y) <= 1e-12;
+        System.Math.Abs(first.X - second.X) <= Tolerance.Epsilon
+        && System.Math.Abs(first.Y - second.Y) <= Tolerance.Epsilon;
 
     private static InvalidOperationException Error(string context, string message) => new($"{context}: {message}");
 }

OpenNest.Tests/Reporting/NestReportGeometryTests.cs

@@ -79,6 +79,27 @@ public class NestReportGeometryTests
         Assert.True(geometry.StrokeOnly);
     }
 
+    [Fact]
+    public void Capture_ClosesOutlineWhoseArcEndpointIsRebuiltWithRoundoff()
+    {
+        // Posted/rounded programs carry arcs whose end radius differs slightly from the start
+        // radius; the converted arc's rebuilt end then misses the next move's start by that much.
+        var nest = NestReportTestData.CreateNest();
+        var codes = nest.Plates[0].Parts[0].Program.Codes;
+        codes.Clear();
+        codes.Add(new RapidMove(0, 0));
+        codes.Add(new LinearMove(10, 0));
+        codes.Add(new ArcMove(new Vector(12.000004, 2), new Vector(10, 2), RotationType.CCW));
+        codes.Add(new LinearMove(12.000004, 10));
+        codes.Add(new LinearMove(0, 10));
+        codes.Add(new LinearMove(0, 0));
+        var geometry = NestReportBuilder.Capture(nest, NestReportTestData.GeneratedAt).Plates[0].Parts[0].Geometry;
+        var contour = Assert.Single(geometry.Contours);
+        Assert.True(contour.Closed);
+        Assert.Equal(5, contour.Segments.Length);
+        Assert.False(geometry.StrokeOnly);
+    }
+
     [Fact]
     public void Capture_ExcludedLayersCannotConnectSeparateMaterialPaths()
     {