feat: add WeldGapTabSplit implementation

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

OpenNest.Tests/Splitting/SplitFeatureTests.cs

@@ -1,9 +1,53 @@
+using System.Linq;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests.Splitting;
 
 public class SplitFeatureTests
 {
+    [Fact]
+    public void WeldGapTabSplit_Vertical_TabsOnNegativeSide()
+    {
+        var feature = new WeldGapTabSplit();
+        var line = new SplitLine(50.0, CutOffAxis.Vertical);
+        var parameters = new SplitParameters
+        {
+            Type = SplitType.WeldGapTabs,
+            TabWidth = 2.0,
+            TabHeight = 0.25,
+            TabCount = 2
+        };
+
+        var result = feature.GenerateFeatures(line, 0.0, 100.0, parameters);
+
+        // Positive side (right): single straight line (no tabs)
+        Assert.Single(result.PositiveSideEdge);
+        Assert.IsType<Line>(result.PositiveSideEdge[0]);
+
+        // Negative side (left): has tab protrusions — more than 1 entity
+        Assert.True(result.NegativeSideEdge.Count > 1);
+
+        // All entities should be lines
+        Assert.All(result.NegativeSideEdge, e => Assert.IsType<Line>(e));
+
+        // First entity starts at extent start, last ends at extent end
+        var first = (Line)result.NegativeSideEdge[0];
+        var last = (Line)result.NegativeSideEdge[^1];
+        Assert.Equal(0.0, first.StartPoint.Y, 6);
+        Assert.Equal(100.0, last.EndPoint.Y, 6);
+
+        // Tabs protrude in the negative-X direction (left of split line)
+        var tabEntities = result.NegativeSideEdge.Cast<Line>().ToList();
+        var minX = tabEntities.Min(l => System.Math.Min(l.StartPoint.X, l.EndPoint.X));
+        Assert.Equal(50.0 - 0.25, minX, 6); // tabHeight = 0.25
+    }
+
+    [Fact]
+    public void WeldGapTabSplit_Name()
+    {
+        Assert.Equal("Weld-Gap Tabs", new WeldGapTabSplit().Name);
+    }
+
     [Fact]
     public void StraightSplit_Vertical_ProducesSingleLineEachSide()
     {