feat: add plate creation and upgrade-vs-new evaluation

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

OpenNest.Engine/MultiPlateNester.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using System.Linq;
 using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
+using OpenNest.Math;
 
 namespace OpenNest
 {
@@ -92,5 +93,76 @@ namespace OpenNest
 
             return viable;
         }
+
+        public struct UpgradeDecision
+        {
+            public bool ShouldUpgrade;
+            public double UpgradeCost;
+            public double NewPlateCost;
+        }
+
+        public static Plate CreatePlate(Plate template, List<PlateOption> options, Box minBounds)
+        {
+            var plate = new Plate(template.Size)
+            {
+                PartSpacing = template.PartSpacing,
+                Quadrant = template.Quadrant,
+            };
+            plate.EdgeSpacing = new Spacing
+            {
+                Left = template.EdgeSpacing.Left,
+                Right = template.EdgeSpacing.Right,
+                Top = template.EdgeSpacing.Top,
+                Bottom = template.EdgeSpacing.Bottom,
+            };
+
+            if (options == null || options.Count == 0 || minBounds == null)
+                return plate;
+
+            // Find smallest option that fits the part (by cost ascending).
+            var sorted = options.OrderBy(o => o.Cost).ToList();
+
+            foreach (var option in sorted)
+            {
+                var workW = option.Width - template.EdgeSpacing.Left - template.EdgeSpacing.Right;
+                var workL = option.Length - template.EdgeSpacing.Top - template.EdgeSpacing.Bottom;
+
+                var fitsNormal = workW >= minBounds.Width - Tolerance.Epsilon
+                              && workL >= minBounds.Length - Tolerance.Epsilon;
+                var fitsRotated = workW >= minBounds.Length - Tolerance.Epsilon
+                               && workL >= minBounds.Width - Tolerance.Epsilon;
+
+                if (fitsNormal || fitsRotated)
+                {
+                    plate.Size = new Size(option.Width, option.Length);
+                    return plate;
+                }
+            }
+
+            // No option fits — use template size.
+            return plate;
+        }
+
+        public static UpgradeDecision EvaluateUpgradeVsNew(
+            PlateOption currentSize,
+            PlateOption upgradeSize,
+            PlateOption newPlateSize,
+            double salvageRate,
+            double estimatedNewPlateUtilization)
+        {
+            var upgradeCost = upgradeSize.Cost - currentSize.Cost;
+
+            var newPlateCost = newPlateSize.Cost;
+            var remnantFraction = 1.0 - estimatedNewPlateUtilization;
+            var salvageCredit = remnantFraction * newPlateSize.Cost * salvageRate;
+            var netNewCost = newPlateCost - salvageCredit;
+
+            return new UpgradeDecision
+            {
+                ShouldUpgrade = upgradeCost < netNewCost,
+                UpgradeCost = upgradeCost,
+                NewPlateCost = netNewCost,
+            };
+        }
     }
 }