refactor(engine): move fill and strategy code to dedicated namespaces

Move fill algorithms to OpenNest.Engine.Fill namespace:
FillLinear, FillExtents, PairFiller, ShrinkFiller, Compactor,
RemnantFiller, RemnantFinder, FillScore, Pattern, PatternTiler,
PartBoundary, RotationAnalysis, AngleCandidateBuilder, and
AccumulatingProgress.

Move strategy layer to OpenNest.Engine.Strategies namespace:
IFillStrategy, FillContext, FillStrategyRegistry, FillHelpers,
and all built-in strategy implementations.

Add using directives to all consuming files across Engine, UI,
MCP, and Tests projects.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Engine/BestFit/PairEvaluator.cs

@@ -1,9 +1,10 @@
+using OpenNest.Converters;
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
-using OpenNest.Converters;
-using OpenNest.Geometry;
 
 namespace OpenNest.Engine.BestFit
 {

OpenNest.Engine/Fill/AccumulatingProgress.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Wraps an IProgress to prepend previously placed parts to each report,

OpenNest.Engine/Fill/AngleCandidateBuilder.cs

@@ -1,11 +1,11 @@
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.Linq;
 using OpenNest.Engine.ML;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Builds candidate rotation angles for single-item fill. Encapsulates the

OpenNest.Engine/Fill/Compactor.cs

@@ -1,9 +1,8 @@
-using System;
+using OpenNest.Geometry;
 using System.Collections.Generic;
 using System.Linq;
-using OpenNest.Geometry;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Pushes a group of parts left and down to close gaps after placement.

OpenNest.Engine/Fill/FillExtents.cs

@@ -1,11 +1,11 @@
+using OpenNest.Geometry;
+using OpenNest.Math;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Threading;
-using OpenNest.Geometry;
-using OpenNest.Math;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     public class FillExtents
     {

OpenNest.Engine/Fill/FillLinear.cs

@@ -1,9 +1,9 @@
-using System.Collections.Generic;
-using System.Threading.Tasks;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     public class FillLinear
     {
@@ -16,7 +16,7 @@ namespace OpenNest
         public Box WorkArea { get; }
 
         public double PartSpacing { get; }
-        
+
         public double HalfSpacing => PartSpacing / 2;
 
         /// <summary>

OpenNest.Engine/Fill/FillScore.cs

@@ -1,7 +1,7 @@
-using System.Collections.Generic;
 using OpenNest.Geometry;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     public readonly struct FillScore : System.IComparable<FillScore>
     {

OpenNest.Engine/Fill/PairFiller.cs

@@ -1,13 +1,14 @@
+using OpenNest.Engine.BestFit;
+using OpenNest.Engine.Strategies;
+using OpenNest.Geometry;
+using OpenNest.Math;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
-using OpenNest.Engine.BestFit;
-using OpenNest.Geometry;
-using OpenNest.Math;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Fills a work area using interlocking part pairs from BestFitCache.
@@ -52,11 +53,11 @@ namespace OpenNest
                     var engine = new FillLinear(workArea, partSpacing);
 
                     // Let the remainder strip try pair-based filling too.
-                    var p0 = DefaultNestEngine.BuildRotatedPattern(pairParts, 0);
-                    var p90 = DefaultNestEngine.BuildRotatedPattern(pairParts, Angle.HalfPI);
+                    var p0 = FillHelpers.BuildRotatedPattern(pairParts, 0);
+                    var p90 = FillHelpers.BuildRotatedPattern(pairParts, Angle.HalfPI);
                     engine.RemainderPatterns = new List<Pattern> { p0, p90 };
 
-                    var filled = DefaultNestEngine.FillPattern(engine, pairParts, angles, workArea);
+                    var filled = FillHelpers.FillPattern(engine, pairParts, angles, workArea);
 
                     if (filled != null && filled.Count > 0)
                     {

OpenNest.Engine/Fill/PartBoundary.cs

@@ -1,9 +1,9 @@
-using System.Collections.Generic;
-using System.Linq;
 using OpenNest.Converters;
 using OpenNest.Geometry;
+using System.Collections.Generic;
+using System.Linq;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Pre-computed offset boundary polygons for a part's geometry.
@@ -87,9 +87,9 @@ namespace OpenNest
                     var edge = (verts[i - 1], verts[i]);
 
                     if (-sign * dy > 0) left.Add(edge);
-                    if ( sign * dy > 0) right.Add(edge);
+                    if (sign * dy > 0) right.Add(edge);
                     if (-sign * dx > 0) up.Add(edge);
-                    if ( sign * dx > 0) down.Add(edge);
+                    if (sign * dx > 0) down.Add(edge);
                 }
             }
 
@@ -145,11 +145,11 @@ namespace OpenNest
         {
             switch (direction)
             {
-                case PushDirection.Left:  return _leftEdges;
+                case PushDirection.Left: return _leftEdges;
                 case PushDirection.Right: return _rightEdges;
-                case PushDirection.Up:    return _upEdges;
-                case PushDirection.Down:  return _downEdges;
-                default:                  return _leftEdges;
+                case PushDirection.Up: return _upEdges;
+                case PushDirection.Down: return _downEdges;
+                default: return _leftEdges;
             }
         }
 

OpenNest.Engine/Fill/Pattern.cs

@@ -1,7 +1,7 @@
-using System.Collections.Generic;
 using OpenNest.Geometry;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     public class Pattern
     {

OpenNest.Engine/Fill/PatternTiler.cs

@@ -1,7 +1,7 @@
-using System.Collections.Generic;
 using OpenNest.Geometry;
+using System.Collections.Generic;
 
-namespace OpenNest.Engine
+namespace OpenNest.Engine.Fill
 {
     public static class PatternTiler
     {

OpenNest.Engine/Fill/RemnantFiller.cs

@@ -1,9 +1,9 @@
+using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
 using System.Threading;
-using OpenNest.Geometry;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// Iteratively fills remnant boxes with items using a RemnantFinder.

OpenNest.Engine/Fill/RemnantFinder.cs

@@ -1,9 +1,8 @@
-using System;
+using OpenNest.Geometry;
 using System.Collections.Generic;
 using System.Linq;
-using OpenNest.Geometry;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     /// <summary>
     /// A remnant box with a priority tier.

OpenNest.Engine/Fill/RotationAnalysis.cs

@@ -1,10 +1,10 @@
-using System.Collections.Generic;
-using System.Linq;
 using OpenNest.Converters;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using System.Collections.Generic;
+using System.Linq;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     internal static class RotationAnalysis
     {

OpenNest.Engine/Fill/ShrinkFiller.cs

@@ -1,10 +1,10 @@
+using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
-using OpenNest.Geometry;
 
-namespace OpenNest
+namespace OpenNest.Engine.Fill
 {
     public enum ShrinkAxis { Width, Height }
 

OpenNest.Engine/NestEngineBase.cs

@@ -1,9 +1,10 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
-using OpenNest.Geometry;
 
 namespace OpenNest
 {
@@ -212,9 +213,13 @@ namespace OpenNest
                       $"PartArea={totalPartArea:F0}, Remnant={workArea.Area() - totalPartArea:F0}, " +
                       $"WorkArea={workArea.Width:F1}x{workArea.Length:F1} | {description}";
             Debug.WriteLine(msg);
-            try { System.IO.File.AppendAllText(
+            try
+            {
+                System.IO.File.AppendAllText(
                 System.IO.Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "nest-debug.log"),
-                $"{DateTime.Now:HH:mm:ss.fff} {msg}\n"); } catch { }
+                $"{DateTime.Now:HH:mm:ss.fff} {msg}\n");
+            }
+            catch { }
 
             progress.Report(new NestProgress
             {

OpenNest.Engine/RectanglePacking/FillBestFit.cs

@@ -1,6 +1,5 @@
-using System;
-using OpenNest.Geometry;
-using OpenNest.Math;
+using OpenNest.Math;
+using System;
 
 namespace OpenNest.RectanglePacking
 {

OpenNest.Engine/Strategies/ExtentsFillStrategy.cs

@@ -1,8 +1,8 @@
-using System.Collections.Generic;
-using OpenNest.Engine.BestFit;
+using OpenNest.Engine.Fill;
 using OpenNest.Math;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public class ExtentsFillStrategy : IFillStrategy
     {
@@ -20,10 +20,6 @@ namespace OpenNest
 
             var angles = new[] { bestRotation, bestRotation + Angle.HalfPI };
 
-            var bestFits = context.SharedState.TryGetValue("BestFits", out var cached)
-                ? (List<BestFitResult>)cached
-                : null;
-
             List<Part> best = null;
             var bestScore = default(FillScore);
 
@@ -31,7 +27,7 @@ namespace OpenNest
             {
                 context.Token.ThrowIfCancellationRequested();
                 var result = filler.Fill(context.Item.Drawing, angle,
-                    context.PlateNumber, context.Token, context.Progress, bestFits);
+                    context.PlateNumber, context.Token, context.Progress);
                 if (result != null && result.Count > 0)
                 {
                     var score = FillScore.Compute(result, context.WorkArea);

OpenNest.Engine/Strategies/FillContext.cs

@@ -1,9 +1,10 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
 using System.Threading;
-using OpenNest.Geometry;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public class FillContext
     {

OpenNest.Engine/Strategies/FillHelpers.cs

@@ -1,10 +1,11 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+using OpenNest.Math;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Threading.Tasks;
-using OpenNest.Geometry;
-using OpenNest.Math;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public static class FillHelpers
     {

OpenNest.Engine/Strategies/FillStrategyRegistry.cs

@@ -5,7 +5,7 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public static class FillStrategyRegistry
     {

OpenNest.Engine/Strategies/IFillStrategy.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public interface IFillStrategy
     {

OpenNest.Engine/Strategies/LinearFillStrategy.cs

@@ -1,7 +1,8 @@
-using System.Collections.Generic;
+using OpenNest.Engine.Fill;
 using OpenNest.Math;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public class LinearFillStrategy : IFillStrategy
     {

OpenNest.Engine/Strategies/PairsFillStrategy.cs

@@ -1,7 +1,8 @@
-using System.Collections.Generic;
 using OpenNest.Engine.BestFit;
+using OpenNest.Engine.Fill;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public class PairsFillStrategy : IFillStrategy
     {

OpenNest.Engine/Strategies/RectBestFitStrategy.cs

@@ -1,7 +1,7 @@
-using System.Collections.Generic;
 using OpenNest.RectanglePacking;
+using System.Collections.Generic;
 
-namespace OpenNest
+namespace OpenNest.Engine.Strategies
 {
     public class RectBestFitStrategy : IFillStrategy
     {

OpenNest.Engine/StripNestEngine.cs

@@ -1,8 +1,9 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
-using OpenNest.Geometry;
 
 namespace OpenNest
 {

OpenNest.Engine/StripNestResult.cs

@@ -1,5 +1,6 @@
-using System.Collections.Generic;
+using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
+using System.Collections.Generic;
 
 namespace OpenNest
 {