feat: add VerticalRemnantEngine and HorizontalRemnantEngine

Two new engine classes subclassing DefaultNestEngine that override
CreateComparer, PreferredDirection, and BuildAngles to optimize for
preserving side remnants. Both registered in NestEngineRegistry and
covered by 6 integration tests.

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

OpenNest.Engine/HorizontalRemnantEngine.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Engine;
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// Optimizes for the largest top-side horizontal drop.
+    /// Scores by count first, then minimizes Y-extent.
+    /// Prefers vertical nest direction and angles that keep parts narrow in Y.
+    /// </summary>
+    public class HorizontalRemnantEngine : DefaultNestEngine
+    {
+        public HorizontalRemnantEngine(Plate plate) : base(plate) { }
+
+        public override string Name => "Horizontal Remnant";
+
+        public override string Description => "Optimizes for largest top-side horizontal drop";
+
+        protected override IFillComparer CreateComparer() => new HorizontalRemnantComparer();
+
+        public override NestDirection? PreferredDirection => NestDirection.Vertical;
+
+        public override List<double> BuildAngles(NestItem item, double bestRotation, Box workArea)
+        {
+            var baseAngles = new List<double> { bestRotation, bestRotation + Angle.HalfPI };
+            baseAngles.Sort((a, b) => RotatedHeight(item, a).CompareTo(RotatedHeight(item, b)));
+            return baseAngles;
+        }
+
+        private static double RotatedHeight(NestItem item, double angle)
+        {
+            var bb = item.Drawing.Program.BoundingBox();
+            var cos = System.Math.Abs(System.Math.Cos(angle));
+            var sin = System.Math.Abs(System.Math.Sin(angle));
+            return bb.Length * cos + bb.Width * sin;
+        }
+    }
+}

OpenNest.Engine/NestEngineRegistry.cs

@@ -24,6 +24,14 @@ namespace OpenNest
             Register("NFP",
                 "NFP-based mixed-part nesting with simulated annealing",
                 plate => new NfpNestEngine(plate));
+
+            Register("Vertical Remnant",
+                "Optimizes for largest right-side vertical drop",
+                plate => new VerticalRemnantEngine(plate));
+
+            Register("Horizontal Remnant",
+                "Optimizes for largest top-side horizontal drop",
+                plate => new HorizontalRemnantEngine(plate));
         }
 
         public static IReadOnlyList<NestEngineInfo> AvailableEngines => engines;

OpenNest.Engine/VerticalRemnantEngine.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Engine;
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// Optimizes for the largest right-side vertical drop.
+    /// Scores by count first, then minimizes X-extent.
+    /// Prefers horizontal nest direction and angles that keep parts narrow in X.
+    /// </summary>
+    public class VerticalRemnantEngine : DefaultNestEngine
+    {
+        public VerticalRemnantEngine(Plate plate) : base(plate) { }
+
+        public override string Name => "Vertical Remnant";
+
+        public override string Description => "Optimizes for largest right-side vertical drop";
+
+        protected override IFillComparer CreateComparer() => new VerticalRemnantComparer();
+
+        public override NestDirection? PreferredDirection => NestDirection.Horizontal;
+
+        public override List<double> BuildAngles(NestItem item, double bestRotation, Box workArea)
+        {
+            var baseAngles = new List<double> { bestRotation, bestRotation + Angle.HalfPI };
+            baseAngles.Sort((a, b) => RotatedWidth(item, a).CompareTo(RotatedWidth(item, b)));
+            return baseAngles;
+        }
+
+        private static double RotatedWidth(NestItem item, double angle)
+        {
+            var bb = item.Drawing.Program.BoundingBox();
+            var cos = System.Math.Abs(System.Math.Cos(angle));
+            var sin = System.Math.Abs(System.Math.Sin(angle));
+            return bb.Width * cos + bb.Length * sin;
+        }
+    }
+}