feat: wire IFillComparer through PairFiller and StripeFiller

PairFiller now accepts an optional IFillComparer (defaulting to
DefaultFillComparer) and uses it in EvaluateCandidates and
EvaluateCandidate/FillPattern instead of raw FillScore comparisons.
PairsFillStrategy passes context.Policy?.Comparer through.
StripeFiller derives _comparer from FillContext.Policy in its
constructor and uses it in Fill() instead of FillScore comparisons.

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

OpenNest.Engine/Fill/PairFiller.cs

@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
+using OpenNest.Engine;
 
 namespace OpenNest.Engine.Fill
 {
@@ -29,11 +30,13 @@ namespace OpenNest.Engine.Fill
 
         private readonly Size plateSize;
         private readonly double partSpacing;
+        private readonly IFillComparer comparer;
 
-        public PairFiller(Size plateSize, double partSpacing)
+        public PairFiller(Size plateSize, double partSpacing, IFillComparer comparer = null)
         {
             this.plateSize = plateSize;
             this.partSpacing = partSpacing;
+            this.comparer = comparer ?? new DefaultFillComparer();
         }
 
         public PairFillResult Fill(NestItem item, Box workArea,
@@ -61,7 +64,6 @@ namespace OpenNest.Engine.Fill
             int plateNumber, CancellationToken token, IProgress<NestProgress> progress)
         {
             List<Part> best = null;
-            var bestScore = default(FillScore);
             var sinceImproved = 0;
             var effectiveWorkArea = workArea;
 
@@ -72,12 +74,10 @@ namespace OpenNest.Engine.Fill
                     token.ThrowIfCancellationRequested();
 
                     var filled = EvaluateCandidate(candidates[i], drawing, effectiveWorkArea);
-                    var score = FillScore.Compute(filled, effectiveWorkArea);
 
-                    if (score > bestScore)
+                    if (comparer.IsBetter(filled, best, effectiveWorkArea))
                     {
                         best = filled;
-                        bestScore = score;
                         sinceImproved = 0;
                         effectiveWorkArea = TryReduceWorkArea(filled, targetCount, workArea, effectiveWorkArea);
                     }
@@ -87,7 +87,7 @@ namespace OpenNest.Engine.Fill
                     }
 
                     NestEngineBase.ReportProgress(progress, NestPhase.Pairs, plateNumber, best, workArea,
-                        $"Pairs: {i + 1}/{candidates.Count} candidates, best = {bestScore.Count} parts");
+                        $"Pairs: {i + 1}/{candidates.Count} candidates, best = {best?.Count ?? 0} parts");
 
                     if (i + 1 >= EarlyExitMinTried && sinceImproved >= EarlyExitStaleLimit)
                     {
@@ -101,7 +101,7 @@ namespace OpenNest.Engine.Fill
                 Debug.WriteLine("[PairFiller] Cancelled mid-phase, using results so far");
             }
 
-            Debug.WriteLine($"[PairFiller] Best pair result: {bestScore.Count} parts, density={bestScore.Density:P1}");
+            Debug.WriteLine($"[PairFiller] Best pair result: {best?.Count ?? 0} parts");
             return best ?? new List<Part>();
         }
 
@@ -147,7 +147,7 @@ namespace OpenNest.Engine.Fill
             var pairParts = candidate.BuildParts(drawing);
             var engine = new FillLinear(workArea, partSpacing);
             var angles = BuildTilingAngles(candidate);
-            return FillHelpers.FillPattern(engine, pairParts, angles, workArea);
+            return FillHelpers.FillPattern(engine, pairParts, angles, workArea, comparer);
         }
 
         private static List<double> BuildTilingAngles(BestFitResult candidate)

OpenNest.Engine/Fill/StripeFiller.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
+using OpenNest.Engine;
 using OpenNest.Engine.BestFit;
 using OpenNest.Engine.Strategies;
 using OpenNest.Geometry;
@@ -18,6 +19,7 @@ public class StripeFiller
 
     private readonly FillContext _context;
     private readonly NestDirection _primaryAxis;
+    private readonly IFillComparer _comparer;
 
     /// <summary>
     /// When true, only complete stripes are placed — no partial rows/columns.
@@ -35,6 +37,7 @@ public class StripeFiller
     {
         _context = context;
         _primaryAxis = primaryAxis;
+        _comparer = context.Policy?.Comparer ?? new DefaultFillComparer();
     }
 
     public List<Part> Fill()
@@ -49,7 +52,6 @@ public class StripeFiller
         var strategyName = _primaryAxis == NestDirection.Horizontal ? "Row" : "Column";
 
         List<Part> bestParts = null;
-        var bestScore = default(FillScore);
 
         for (var i = 0; i < bestFits.Count; i++)
         {
@@ -82,22 +84,20 @@ public class StripeFiller
                     if (result == null || result.Count == 0)
                         continue;
 
-                    var score = FillScore.Compute(result, workArea);
                     Debug.WriteLine($"[StripeFiller] {strategyName} candidate {i} {dirLabel}: " +
                         $"angle={Angle.ToDegrees(angle):F1}°, N={count}, waste={waste:F2}, " +
                         $"grid={result.Count} parts");
 
-                    if (bestParts == null || score > bestScore)
+                    if (_comparer.IsBetter(result, bestParts, workArea))
                     {
                         bestParts = result;
-                        bestScore = score;
                     }
                 }
             }
 
             NestEngineBase.ReportProgress(_context.Progress, NestPhase.Custom,
                 _context.PlateNumber, bestParts, workArea,
-                $"{strategyName}: {i + 1}/{bestFits.Count} pairs, best = {bestScore.Count} parts");
+                $"{strategyName}: {i + 1}/{bestFits.Count} pairs, best = {bestParts?.Count ?? 0} parts");
         }
 
         return bestParts ?? new List<Part>();

OpenNest.Engine/Strategies/PairsFillStrategy.cs

@@ -11,7 +11,8 @@ namespace OpenNest.Engine.Strategies
 
         public List<Part> Fill(FillContext context)
         {
-            var filler = new PairFiller(context.Plate.Size, context.Plate.PartSpacing);
+            var comparer = context.Policy?.Comparer;
+            var filler = new PairFiller(context.Plate.Size, context.Plate.PartSpacing, comparer);
             var result = filler.Fill(context.Item, context.WorkArea,
                 context.PlateNumber, context.Token, context.Progress);