fix(core): arc bounding box inflated for near-zero sweep arcs

Arcs with sweep angles smaller than Tolerance.Epsilon were treated as
full circles by IsBetweenRad's shortcut check, causing UpdateBounds to
expand the bounding box to Center ± Radius. This made zoom-to-fit zoom
out far beyond the actual part extents.

Skip cardinal angle expansion when sweep is near-zero so the bounding
box uses only the arc's start/end points.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Core/Geometry/Arc.cs

@@ -404,10 +404,12 @@ namespace OpenNest.Geometry
                 maxY = startpt.Y;
             }
 
+            var sweep = SweepAngle();
+            if (sweep > Tolerance.Epsilon)
+            {
                 var angle1 = StartAngle;
                 var angle2 = EndAngle;
 
-            // switch the angle to counter clockwise.
                 if (IsReversed)
                     Generic.Swap(ref angle1, ref angle2);
 
@@ -424,6 +426,7 @@ namespace OpenNest.Geometry
 
                 if (Angle.IsBetweenRad(Angle.TwoPI, angle1, angle2))
                     maxX = Center.X + Radius;
+            }
 
             boundingBox.X = minX;
             boundingBox.Y = minY;

OpenNest.Tests/Geometry/EllipseConverterTests.cs

@@ -2,14 +2,18 @@ using OpenNest.Geometry;
 using OpenNest.IO;
 using OpenNest.Math;
 using Xunit;
+using Xunit.Abstractions;
 using System.Linq;
 
 namespace OpenNest.Tests.Geometry;
 
 public class EllipseConverterTests
 {
+    private readonly ITestOutputHelper _output;
     private const double Tol = 1e-10;
 
+    public EllipseConverterTests(ITestOutputHelper output) => _output = output;
+
     [Fact]
     public void EvaluatePoint_AtZero_ReturnsMajorAxisEnd()
     {
@@ -245,6 +249,26 @@ public class EllipseConverterTests
         }
     }
 
+    [Fact]
+    public void DxfImport_ArcBoundingBoxes_Diagnostic()
+    {
+        var path = @"C:\Users\aisaacs\Desktop\11ga tab.dxf";
+        if (!System.IO.File.Exists(path)) return;
+
+        var result = Dxf.Import(path);
+        var all = (System.Collections.Generic.IEnumerable<IBoundable>)result.Entities;
+        var bbox = all.GetBoundingBox();
+        _output.WriteLine($"Overall: X={bbox.X:F4} Y={bbox.Y:F4} W={bbox.Length:F4} H={bbox.Width:F4}");
+
+        for (var i = 0; i < result.Entities.Count; i++)
+        {
+            var e = result.Entities[i];
+            var b = e.BoundingBox;
+            var flag = (b.Length > 1 || b.Width > 1) ? " ***" : "";
+            _output.WriteLine($"{i + 1,3}. {e.GetType().Name,-8} X={b.X:F4} Y={b.Y:F4} W={b.Length:F4} H={b.Width:F4}{flag}");
+        }
+    }
+
     [Fact]
     public void ToOpenNest_FlippedNormalZ_ProducesCorrectArcs()
     {