fix(engine): use required spacing, not a sampled gap, when resequencing shrink-fill strips

SortStrips measured the gap between only the first two strips in original
placement order and replayed that single value between every strip after
reordering by height/width. Real (non-uniform) geometry produces varying
inter-strip gaps, so resequencing could expand the total footprint beyond
the plate's already-fitted work area, crashing StripPlateNester with
"Candidate placement falls outside the usable stock area." Using the
actual required spacing guarantees the resequenced span never exceeds
the original, since real gaps are always >= spacing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -74,12 +74,13 @@ GPU-accelerated pair evaluation for best-fit nesting. `GpuPairEvaluator` impleme
 Training data collection for ML angle prediction. `TrainingDatabase` stores per-angle nesting results in SQLite via EF Core for offline model training.
 
 ### OpenNest.Benchmark (console app, depends on Core + Engine + IO)
-Compares registered `NestEngineBase` implementations against each other on real `.nest` files. Fully generic — it never hardcodes drawing geometry, just reads whatever drawings/quantities/plate settings each input file already has.
+Compares registered `INestingEngine` implementations against each other on real `.nest` files. Each engine solves the whole job — it owns its own multi-plate/size strategy rather than being handed one already-sized plate at a time. Fully generic — it never hardcodes drawing geometry, just reads whatever drawings/quantities/plate settings each input file already has.
 
 - `JobLoader` builds `BenchmarkJob`s from a `.nest` file or a folder of them via `NestReader`, using every drawing with `Quantity.Required > 0`. `--sheet-sizes` can sweep a fixed list of plate sizes instead of each file's own.
-- `BenchmarkRunner` gives each (job, engine) pair a fresh `Plate`/`NestItem` list (`BenchmarkJob.CreatePlate()`/`CreateItems()`) so engines can't see each other's mutated state, then calls the engine's `Nest()` and times it.
-- `NestValidator` checks the returned layout: every part inside `Plate.WorkArea()`, every pair at least `Plate.PartSpacing` apart (checked geometrically via each part's own world-space polygon, inflated by the spacing — works on arbitrary concave/holed shapes, not just bounding boxes), and no drawing over its requested quantity. An invalid or throwing run scores zero for that job.
-- Scoring matches `Plate.Utilization()` (placed drawing area / full sheet area, `Plate.Area()`). If an engine placed every requested part, ties are broken by the smaller used-bounding-box (`Report`'s ranking rule) — a more compact layout leaves a bigger usable remnant.
+- `BenchmarkJob.BuildNestJob(maxPlates)` converts the job into a `NestJob`: one `NestJobPart` per requested drawing (via `DrawingJobMapper.FromDrawing`) and one `NestPlateStock` per candidate sheet size (unlimited quantity — the engine decides how many of each size it uses).
+- `BenchmarkRunner` calls each engine's `INestingEngine.Solve(NestJob)` once per job, under a wall-clock timeout so a runaway or hanging engine can't stall the whole benchmark run, then materializes the result back into legacy `Plate`/`Part` objects via `NestResultMaterializer` for scoring.
+- `NestValidator` checks the returned layout: every part inside `Plate.WorkArea()`, every pair at least `Plate.PartSpacing` apart (checked geometrically via each part's own world-space polygon, inflated by the spacing — works on arbitrary concave/holed shapes, not just bounding boxes), and no drawing over its requested quantity. An invalid, throwing, or timed-out run scores zero for that job.
+- Scoring matches `Plate.Utilization()` (placed drawing area / full sheet area, `Plate.Area()`). If an engine placed every requested part, ties are broken by fewer plates used (`Report`'s ranking rule) — using fewer sheets to do the same job wastes less material.
 - `--engines Name1,Name2` filters to specific registered engines (default: all); `--csv <path>` writes a flat per-job CSV alongside the console report.
 
 ### OpenNest.Mcp (console app, depends on Core + Engine + IO)

OpenNest.Benchmark/BenchmarkJob.cs

@@ -41,50 +41,20 @@ namespace OpenNest.Benchmark
         public int TotalRequestedQuantity => Requests.Sum(r => r.Quantity);
 
         /// <summary>
-        /// A blank plate carrying only the job's spacing/quadrant template.
-        /// MultiPlateNester.CreatePlate copies these settings onto whichever
-        /// size it ultimately picks; its Size is only the fallback used when
-        /// nothing in the candidate pool fits, so it's set to the largest
-        /// candidate rather than an arbitrary one.
+        /// Builds the whole-job request this job represents: one NestJobPart per
+        /// requested drawing, and one NestPlateStock per candidate sheet size
+        /// (unlimited quantity - the engine under test decides how many of each
+        /// size it actually uses, and how demand splits across plates). The
+        /// engine owns its own multi-plate/size strategy; this harness no
+        /// longer picks plate sizes on the engine's behalf.
         /// </summary>
-        public Plate CreateTemplatePlate()
+        public NestJob BuildNestJob(int maxPlates)
         {
-            var fallbackSize = CandidateSizes
-                .OrderByDescending(s => s.Width * s.Length)
-                .FirstOrDefault();
-
-            return new Plate(fallbackSize)
-            {
-                EdgeSpacing = EdgeSpacing,
-                PartSpacing = PartSpacing,
-                Quadrant = Quadrant,
-            };
-        }
-
-        /// <summary>
-        /// The candidate sizes as PlateOptions for MultiPlateNester.CreatePlate.
-        /// Cost is area-proportional since no real per-size material pricing is
-        /// available here - this only affects which size is preferred when more
-        /// than one candidate fits, favoring the smaller/cheaper sheet.
-        /// </summary>
-        public List<PlateOption> BuildPlateOptions()
-        {
-            return CandidateSizes
-                .Select(s => new PlateOption { Width = s.Width, Length = s.Length, Cost = s.Width * s.Length })
-                .ToList();
-        }
-
-        public List<NestItem> CreateItems()
-        {
-            return Requests.Select(r => new NestItem
-            {
-                Drawing = r.Drawing,
-                Quantity = r.Quantity,
-                Priority = r.Priority,
-                StepAngle = r.StepAngle,
-                RotationStart = r.RotationStart,
-                RotationEnd = r.RotationEnd,
-            }).ToList();
+            var parts = Requests.Select(r =>
+                DrawingJobMapper.FromDrawing(r.Drawing.Id.ToString(), r.Drawing, r.Quantity));
+            var stock = CandidateSizes.Select(size =>
+                new NestPlateStock(size.ToString(1), size, null, PartSpacing, EdgeSpacing, Quadrant));
+            return new NestJob(parts, stock, new NestJobOptions("Default", maxPlates));
         }
     }
 }

OpenNest.Benchmark/BenchmarkRunner.cs

@@ -7,23 +7,23 @@ using System.Threading;
 namespace OpenNest.Benchmark
 {
     /// <summary>
-    /// Runs every candidate engine against every job. A job may need several
-    /// plates to place everything it asks for; this drives that loop itself,
-    /// since NestEngineBase.Nest() fills exactly one already-sized plate and
-    /// has no say in picking its own size. For each plate the loop needs, the
-    /// smallest candidate size that fits the largest still-unplaced drawing is
-    /// chosen via the codebase's own MultiPlateNester.CreatePlate, then the
-    /// engine's Nest() fills that plate with whatever of the remaining items
-    /// fit. This is applied identically to every engine, so no engine gets to
-    /// (or has to) implement sheet-size selection itself.
+    /// Runs every candidate engine against every job. Each engine is a full
+    /// INestingEngine: it owns its own plate/size selection and multi-plate
+    /// strategy for the whole job, rather than being handed one already-sized
+    /// plate at a time by this harness. A per-run timeout guards against a
+    /// runaway or hanging engine — cooperative cancellation, so it reliably
+    /// stops engines built on NestJobRunner (all four built-ins) but can't
+    /// forcibly interrupt an engine that never checks its token.
     /// </summary>
     public static class BenchmarkRunner
     {
-        /// <summary>Safety cap so a degenerate engine (placing almost nothing
-        /// per plate) can't loop indefinitely.</summary>
+        /// <summary>Physical-sheet cap passed to every job's NestJobOptions.MaxPlates.</summary>
         private const int MaxPlates = 40;
 
-        public static List<JobResult> Run(List<BenchmarkJob> jobs, IReadOnlyList<NestEngineInfo> engines)
+        /// <summary>Wall-clock budget for one engine solving one job.</summary>
+        private static readonly TimeSpan SolveTimeout = TimeSpan.FromMinutes(5);
+
+        public static List<JobResult> Run(List<BenchmarkJob> jobs, IReadOnlyList<NestingEngineInfo> engines)
         {
             var results = new List<JobResult>(jobs.Count * engines.Count);
 
@@ -38,60 +38,58 @@ namespace OpenNest.Benchmark
             return results;
         }
 
-        private static JobResult RunOne(BenchmarkJob job, NestEngineInfo engineInfo)
+        private static JobResult RunOne(BenchmarkJob job, NestingEngineInfo engineInfo)
         {
-            var template = job.CreateTemplatePlate();
-            var options = job.BuildPlateOptions();
-            var remaining = job.CreateItems();
             var requested = job.TotalRequestedQuantity;
-
-            var plateRuns = new List<(Plate Plate, List<Part> Parts)>();
-            string engineError = null;
             var sw = Stopwatch.StartNew();
 
             try
             {
-                while (remaining.Any(i => i.Quantity > 0) && plateRuns.Count < MaxPlates)
+                var nestJob = job.BuildNestJob(MaxPlates);
+                var engine = engineInfo.Factory();
+                using var cts = new CancellationTokenSource(SolveTimeout);
+                var jobResult = engine.Solve(nestJob, null, cts.Token);
+
+                var materialized = NestResultMaterializer.Materialize(nestJob, jobResult);
+                var plateRuns = materialized.Nest.Plates
+                    .Select(plate => (Plate: plate, Parts: plate.Parts.ToList()))
+                    .ToList();
+
+                var requirements = job.Requests.ToDictionary<DrawingRequest, Drawing, (string Name, int Quantity)>(
+                    r => materialized.DrawingsByPartId[r.Drawing.Id.ToString()],
+                    r => (r.Drawing.Name, r.Quantity),
+                    ReferenceEqualityComparer.Instance);
+
+                var validation = NestValidator.Validate(plateRuns, requirements);
+                var totalPlaced = plateRuns.Sum(pr => pr.Parts.Count);
+                var placedArea = validation.Valid ? plateRuns.Sum(pr => pr.Parts.Sum(p => p.BaseDrawing.Area)) : 0;
+                var plateArea = plateRuns.Sum(pr => pr.Plate.Area());
+
+                var sizeBreakdown = plateRuns
+                    .GroupBy(pr => pr.Plate.Size.ToString(1))
+                    .OrderByDescending(g => g.Count())
+                    .ToDictionary(g => g.Key, g => g.Count());
+
+                sw.Stop();
+
+                return new JobResult
                 {
-                    var largest = remaining
-                        .Where(i => i.Quantity > 0)
-                        .OrderByDescending(i => BoundsArea(i))
-                        .First();
-
-                    var plate = MultiPlateNester.CreatePlate(template, options, largest.Drawing.Program.BoundingBox());
-                    var engine = engineInfo.Factory(plate);
-                    var itemsClone = CloneItems(remaining);
-
-                    var parts = engine.Nest(itemsClone, null, CancellationToken.None) ?? new List<Part>();
-
-                    if (parts.Count == 0)
-                    {
-                        // Not even the largest available candidate size could fit
-                        // the current largest remaining part - stop here rather
-                        // than loop forever; whatever's left is reported unplaced.
-                        break;
-                    }
-
-                    plateRuns.Add((plate, parts));
-
-                    foreach (var item in remaining)
-                    {
-                        var placed = parts.Count(p => p.BaseDrawing.Id == item.Drawing.Id);
-
-                        if (placed > 0)
-                            item.Quantity = System.Math.Max(0, item.Quantity - placed);
-                    }
-                }
+                    EngineName = engineInfo.Name,
+                    JobName = job.Name,
+                    Valid = validation.Valid,
+                    Violations = validation.Violations,
+                    PartsPlaced = totalPlaced,
+                    PartsRequested = requested,
+                    PlacedArea = placedArea,
+                    PlateArea = plateArea,
+                    PlatesUsed = plateRuns.Count,
+                    SizeBreakdown = sizeBreakdown,
+                    ElapsedMs = sw.ElapsedMilliseconds,
+                };
             }
-            catch (Exception ex)
-            {
-                engineError = $"{ex.GetType().Name}: {ex.Message}";
-            }
-
-            sw.Stop();
-
-            if (engineError != null)
+            catch (OperationCanceledException)
             {
+                sw.Stop();
                 return new JobResult
                 {
                     EngineName = engineInfo.Name,
@@ -99,53 +97,22 @@ namespace OpenNest.Benchmark
                     Valid = false,
                     PartsRequested = requested,
                     ElapsedMs = sw.ElapsedMilliseconds,
-                    Error = engineError,
+                    Error = $"Timed out after {SolveTimeout.TotalMinutes:F0} minute(s)",
                 };
             }
-
-            var validation = NestValidator.Validate(plateRuns, job);
-            var totalPlaced = plateRuns.Sum(pr => pr.Parts.Count);
-            var placedArea = validation.Valid ? plateRuns.Sum(pr => pr.Parts.Sum(p => p.BaseDrawing.Area)) : 0;
-            var plateArea = plateRuns.Sum(pr => pr.Plate.Area());
-
-            var sizeBreakdown = plateRuns
-                .GroupBy(pr => pr.Plate.Size.ToString(1))
-                .OrderByDescending(g => g.Count())
-                .ToDictionary(g => g.Key, g => g.Count());
-
-            return new JobResult
+            catch (Exception ex)
             {
-                EngineName = engineInfo.Name,
-                JobName = job.Name,
-                Valid = validation.Valid,
-                Violations = validation.Violations,
-                PartsPlaced = totalPlaced,
-                PartsRequested = requested,
-                PlacedArea = placedArea,
-                PlateArea = plateArea,
-                PlatesUsed = plateRuns.Count,
-                SizeBreakdown = sizeBreakdown,
-                ElapsedMs = sw.ElapsedMilliseconds,
-            };
-        }
-
-        private static double BoundsArea(NestItem item)
-        {
-            var bb = item.Drawing.Program.BoundingBox();
-            return bb.Width * bb.Length;
-        }
-
-        private static List<NestItem> CloneItems(List<NestItem> items)
-        {
-            return items.Select(i => new NestItem
-            {
-                Drawing = i.Drawing,
-                Quantity = i.Quantity,
-                Priority = i.Priority,
-                StepAngle = i.StepAngle,
-                RotationStart = i.RotationStart,
-                RotationEnd = i.RotationEnd,
-            }).ToList();
+                sw.Stop();
+                return new JobResult
+                {
+                    EngineName = engineInfo.Name,
+                    JobName = job.Name,
+                    Valid = false,
+                    PartsRequested = requested,
+                    ElapsedMs = sw.ElapsedMilliseconds,
+                    Error = $"{ex.GetType().Name}: {ex.Message}",
+                };
+            }
         }
     }
 }

OpenNest.Benchmark/NestValidator.cs

@@ -25,7 +25,14 @@ namespace OpenNest.Benchmark
     /// </summary>
     public static class NestValidator
     {
-        public static ValidationResult Validate(List<(Plate Plate, List<Part> Parts)> plateRuns, BenchmarkJob job)
+        /// <summary>
+        /// requirements maps each materialized part's BaseDrawing (by reference - materialized
+        /// Drawing instances are freshly reconstructed per NestResultMaterializer.Materialize, so
+        /// identity must never be inferred from Name, which is only incidentally seeded from the
+        /// originating NestJobPart id) to its original quantity limit and display name.
+        /// </summary>
+        public static ValidationResult Validate(List<(Plate Plate, List<Part> Parts)> plateRuns,
+            IReadOnlyDictionary<Drawing, (string Name, int Quantity)> requirements)
         {
             var result = new ValidationResult();
             var allParts = plateRuns.SelectMany(pr => pr.Parts).ToList();
@@ -33,45 +40,46 @@ namespace OpenNest.Benchmark
             if (allParts.Count == 0)
                 return result;
 
-            ValidateQuantities(allParts, job, result);
+            ValidateQuantities(allParts, requirements, result);
 
             foreach (var (plate, parts) in plateRuns)
             {
                 if (parts.Count == 0)
                     continue;
 
-                ValidateBounds(parts, plate, result);
+                ValidateBounds(parts, plate, requirements, result);
                 ValidateAreaBudget(parts, plate, result);
-                ValidateSpacing(parts, plate.PartSpacing, result);
+                ValidateSpacing(parts, plate.PartSpacing, requirements, result);
             }
 
             return result;
         }
 
-        private static void ValidateQuantities(List<Part> parts, BenchmarkJob job, ValidationResult result)
+        private static void ValidateQuantities(List<Part> parts,
+            IReadOnlyDictionary<Drawing, (string Name, int Quantity)> requirements, ValidationResult result)
         {
-            var allowed = job.Requests.ToDictionary(r => r.Drawing.Id, r => r.Quantity);
             var placedCounts = parts
-                .GroupBy(p => p.BaseDrawing.Id)
+                .GroupBy<Part, Drawing>(p => p.BaseDrawing, ReferenceEqualityComparer.Instance)
                 .ToDictionary(g => g.Key, g => g.Count());
 
-            foreach (var (drawingId, placed) in placedCounts)
+            foreach (var (drawing, placed) in placedCounts)
             {
-                if (!allowed.TryGetValue(drawingId, out var max))
+                if (!requirements.TryGetValue(drawing, out var requirement))
                 {
-                    result.Violations.Add($"Placed drawing id={drawingId} which was not requested for this job");
+                    result.Violations.Add($"Placed drawing '{drawing.Name}' which was not requested for this job");
                     continue;
                 }
 
-                if (placed > max)
+                if (placed > requirement.Quantity)
                 {
-                    var name = parts.First(p => p.BaseDrawing.Id == drawingId).BaseDrawing.Name;
-                    result.Violations.Add($"'{name}': placed {placed} across all plates but only {max} were requested");
+                    result.Violations.Add(
+                        $"'{requirement.Name}': placed {placed} across all plates but only {requirement.Quantity} were requested");
                 }
             }
         }
 
-        private static void ValidateBounds(List<Part> parts, Plate plate, ValidationResult result)
+        private static void ValidateBounds(List<Part> parts, Plate plate,
+            IReadOnlyDictionary<Drawing, (string Name, int Quantity)> requirements, ValidationResult result)
         {
             var workArea = plate.WorkArea();
 
@@ -87,7 +95,7 @@ namespace OpenNest.Benchmark
                 if (outLeft || outBottom || outRight || outTop)
                 {
                     result.Violations.Add(
-                        $"'{part.BaseDrawing.Name}' at ({part.Location.X:F2},{part.Location.Y:F2}) falls outside the work area " +
+                        $"'{DisplayName(part, requirements)}' at ({part.Location.X:F2},{part.Location.Y:F2}) falls outside the work area " +
                         $"of a {plate.Size} plate");
                 }
             }
@@ -116,7 +124,8 @@ namespace OpenNest.Benchmark
             }
         }
 
-        private static void ValidateSpacing(List<Part> parts, double spacing, ValidationResult result)
+        private static void ValidateSpacing(List<Part> parts, double spacing,
+            IReadOnlyDictionary<Drawing, (string Name, int Quantity)> requirements, ValidationResult result)
         {
             var worldPolygons = new Polygon[parts.Count];
             var inflatedPolygons = new Polygon[parts.Count];
@@ -140,12 +149,18 @@ namespace OpenNest.Benchmark
                     if (Collision.HasOverlap(inflatedPolygons[i], worldPolygons[j]))
                     {
                         result.Violations.Add(
-                            $"'{parts[i].BaseDrawing.Name}' and '{parts[j].BaseDrawing.Name}' are closer than the required spacing ({spacing:F3})");
+                            $"'{DisplayName(parts[i], requirements)}' and '{DisplayName(parts[j], requirements)}' are closer than the required spacing ({spacing:F3})");
                     }
                 }
             }
         }
 
+        /// <summary>Friendly name for a violation message, falling back to the materialized
+        /// Drawing's own Name (the raw partId string) if this part wasn't in requirements at all -
+        /// that mismatch is already reported by ValidateQuantities, so this is display-only.</summary>
+        private static string DisplayName(Part part, IReadOnlyDictionary<Drawing, (string Name, int Quantity)> requirements) =>
+            requirements.TryGetValue(part.BaseDrawing, out var requirement) ? requirement.Name : part.BaseDrawing.Name;
+
         /// <summary>
         /// Extracts a part's perimeter as a world-space polygon, optionally inflated
         /// outward by the given spacing, mirroring Part.Intersects' own geometry

OpenNest.Benchmark/Program.cs

@@ -3,6 +3,7 @@ using OpenNest.Benchmark;
 using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 
 return BenchmarkConsole.Run(args);
@@ -40,7 +41,10 @@ static class BenchmarkConsole
             return 1;
         }
 
-        var engines = NestEngineRegistry.AvailableEngines;
+        var enginesDir = Path.Combine(AppContext.BaseDirectory, "Engines");
+        NestingEngineRegistry.LoadPlugins(enginesDir);
+
+        var engines = NestingEngineRegistry.AvailableEngines;
 
         if (options.EngineNames.Count > 0)
         {
@@ -51,7 +55,7 @@ static class BenchmarkConsole
             if (engines.Count == 0)
             {
                 Console.Error.WriteLine("None of the requested engines are registered. Available: " +
-                    string.Join(", ", NestEngineRegistry.AvailableEngines.Select(e => e.Name)));
+                    string.Join(", ", NestingEngineRegistry.AvailableEngines.Select(e => e.Name)));
                 return 1;
             }
         }
@@ -133,21 +137,21 @@ static class BenchmarkConsole
                 Console.Error.WriteLine($"Warning: could not parse sheet size '{token}', skipping");
         }
 
-        return sizes;
+        return sizes.Distinct().ToList();
     }
 
     private static void PrintUsage()
     {
-        Console.Error.WriteLine("OpenNest.Benchmark - compare registered nesting engines on a set of .nest files");
+        Console.Error.WriteLine("OpenNest.Benchmark - compare registered whole-job nesting engines on a set of .nest files");
         Console.Error.WriteLine();
         Console.Error.WriteLine("For each .nest file, every drawing with quantity > 0 is nested (mixed together),");
-        Console.Error.WriteLine("once per registered engine. This is a full nest, not a single fixed-size plate:");
-        Console.Error.WriteLine("as many plates as needed are created, one at a time, each sized by picking the");
-        Console.Error.WriteLine("smallest candidate sheet size that fits the largest still-unplaced drawing -");
-        Console.Error.WriteLine("applied identically to every engine, since Nest() itself has no say over its");
-        Console.Error.WriteLine("own plate's size. Scoring: aggregate material utilization across every plate");
-        Console.Error.WriteLine("used, then (if everything requested was placed) fewer plates as the tie-break.");
-        Console.Error.WriteLine("An invalid layout (out of bounds, overlapping, or over-quantity) scores zero.");
+        Console.Error.WriteLine("once per registered INestingEngine. Each engine is handed the full job - every");
+        Console.Error.WriteLine("requested part and the whole pool of candidate sheet sizes - and owns its own");
+        Console.Error.WriteLine("multi-plate/size strategy: how many plates it uses, of which sizes, and how");
+        Console.Error.WriteLine("demand splits across them. Scoring: aggregate material utilization across every");
+        Console.Error.WriteLine("plate used, then (if everything requested was placed) fewer plates as the");
+        Console.Error.WriteLine("tie-break. An invalid layout (out of bounds, overlapping, or over-quantity), a");
+        Console.Error.WriteLine("thrown exception, or a run exceeding its time budget all score zero.");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Usage:");
         Console.Error.WriteLine("  OpenNest.Benchmark <file.nest | folder> [options]");

OpenNest.Engine.Tests/Fill/SortStripsTests.cs

@@ -0,0 +1,46 @@
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Fill;
+
+public class SortStripsTests
+{
+    private static Part MakeRectPart(double x, double y, double w, double h)
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new OpenNest.CNC.RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new OpenNest.CNC.LinearMove(new Vector(0, 0)));
+        var drawing = new Drawing("rect", pgm);
+        return new Part(drawing, new Vector(x, y));
+    }
+
+    [Fact]
+    public void SortColumnsByHeight_NonUniformGaps_DoesNotExceedOriginalSpan()
+    {
+        // Three columns with non-uniform gaps between them (5, then 1) and heights
+        // ordered so the sort-by-height pass must reorder them (tallest first, then
+        // shortest, then medium). The tallest column's original position leaves a
+        // 5-unit gap to its neighbor; that single sampled gap must not get replayed
+        // as the spacing for the whole staircase once it's no longer the leading pair.
+        var tall = MakeRectPart(0, 0, 10, 30);    // Left 0-10,  gap of 5 to next
+        var shortCol = MakeRectPart(15, 0, 5, 5); // Left 15-20, gap of 1 to next
+        var medium = MakeRectPart(21, 0, 20, 15); // Left 21-41
+
+        var originalRight = new[] { tall, shortCol, medium }.Max(p => p.BoundingBox.Right);
+        var originalLeft = new[] { tall, shortCol, medium }.Min(p => p.BoundingBox.Left);
+        var originalSpan = originalRight - originalLeft;
+
+        var parts = new List<Part> { tall, shortCol, medium };
+        IterativeShrinkFiller.SortColumnsByHeight(parts, spacing: 1.0);
+
+        var newRight = parts.Max(p => p.BoundingBox.Right);
+        var newLeft = parts.Min(p => p.BoundingBox.Left);
+        var newSpan = newRight - newLeft;
+
+        Assert.True(newSpan <= originalSpan + 1e-9,
+            $"Resequenced columns must not exceed the original footprint: original span {originalSpan}, new span {newSpan}");
+    }
+}

OpenNest.Engine.Tests/Jobs/FixedStrategyNestingEngineTests.cs

@@ -0,0 +1,43 @@
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class FixedStrategyNestingEngineTests
+{
+    [Fact]
+    public void ForcesConfiguredStrategyRegardlessOfJobOptions()
+    {
+        var engine = new FixedStrategyNestingEngine("Strip");
+        // The job itself declares an unknown strategy; if FixedStrategyNestingEngine
+        // didn't override it, PlateNesterFactory would reject it with NotSupportedException.
+        var job = FiniteStockJobTests.Job(1, new NestJobOptions("Not A Real Strategy"));
+
+        var result = engine.Solve(job);
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+    }
+
+    [Fact]
+    public void PreservesJobMaxPlates()
+    {
+        var engine = new FixedStrategyNestingEngine("Default");
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(100, 100)), 6);
+        var stock = new NestPlateStock("sheet", new Size(220, 220), quantity: null, partSpacing: 2.0,
+            edgeSpacing: new Spacing(5.0, 5.0, 5.0, 5.0), quadrant: 1);
+        var job = new NestJob(new[] { part }, new[] { stock }, new NestJobOptions("Default", maxPlates: 1));
+
+        var result = engine.Solve(job);
+
+        Assert.Equal(NestJobStatus.Incomplete, result.Status);
+        Assert.Equal(NestJobStopReason.PlateLimitReached, result.StopReason);
+        Assert.Single(result.Plates);
+    }
+
+    [Fact]
+    public void RejectsNullOrWhitespaceStrategyAtConstruction()
+    {
+        Assert.Throws<ArgumentException>(() => new FixedStrategyNestingEngine(null));
+        Assert.Throws<ArgumentException>(() => new FixedStrategyNestingEngine("  "));
+    }
+}

OpenNest.Engine.Tests/Jobs/NestingEngineRegistryTests.cs

@@ -0,0 +1,49 @@
+using Xunit;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestingEngineRegistryTests
+{
+    [Fact]
+    public void BuiltInStrategiesAreRegistered()
+    {
+        var names = NestingEngineRegistry.AvailableEngines.Select(e => e.Name).ToList();
+
+        Assert.Contains("Default", names);
+        Assert.Contains("Strip", names);
+        Assert.Contains("Vertical Remnant", names);
+        Assert.Contains("Horizontal Remnant", names);
+    }
+
+    [Fact]
+    public void EachBuiltInFactoryProducesAWorkingEngine()
+    {
+        foreach (var info in NestingEngineRegistry.AvailableEngines)
+        {
+            var engine = info.Factory();
+            var result = engine.Solve(FiniteStockJobTests.Job(1));
+
+            Assert.Equal(NestJobStatus.Complete, result.Status);
+        }
+    }
+
+    [Fact]
+    public void DuplicateNameIsSkipped()
+    {
+        var before = NestingEngineRegistry.AvailableEngines.Count;
+
+        NestingEngineRegistry.Register("Default", "duplicate", () => new FixedStrategyNestingEngine("Default"));
+
+        Assert.Equal(before, NestingEngineRegistry.AvailableEngines.Count);
+    }
+
+    [Fact]
+    public void LoadPluginsAgainstMissingDirectoryIsANoOp()
+    {
+        var before = NestingEngineRegistry.AvailableEngines.Count;
+
+        NestingEngineRegistry.LoadPlugins(Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString()));
+
+        Assert.Equal(before, NestingEngineRegistry.AvailableEngines.Count);
+    }
+}

OpenNest.Engine/Fill/IterativeShrinkFiller.cs

@@ -219,8 +219,10 @@ namespace OpenNest.Engine.Fill
             if (strips.Count <= 1)
                 return;
 
-            var gap = stripMin(strips[1]) - stripMax(strips[0]);
-
+            // Use the required clearance as the inter-strip gap, not a gap sampled from one
+            // original pair: actual placement gaps vary for irregular/mixed-size geometry, and
+            // replaying a larger sampled gap across every reordered pair can push the trailing
+            // strip past the original (already plate-fitted) footprint.
             strips.Sort((a, b) => sortMetric(a).CompareTo(sortMetric(b)));
 
             var pos = primaryEdge(parts[0].BoundingBox);
@@ -236,7 +238,7 @@ namespace OpenNest.Engine.Fill
                         part.Offset(offset);
                 }
 
-                pos = stripMax(s) + gap;
+                pos = stripMax(s) + spacing;
             }
 
             parts.Clear();

OpenNest.Engine/Jobs/FixedStrategyNestingEngine.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Threading;
+
+namespace OpenNest;
+
+/// <summary>
+/// Adapts one fixed IPlateNester strategy to the whole-job INestingEngine contract, so it can compete
+/// as a full job solver alongside model-submitted engines. Delegates all multi-plate/size selection to
+/// NestJobRunner; only the placement strategy key is forced, overriding whatever the job itself declared.
+/// </summary>
+public sealed class FixedStrategyNestingEngine : INestingEngine
+{
+    private readonly string strategy;
+    private readonly NestJobRunner runner = new(PlateNesterFactory.Create);
+
+    public FixedStrategyNestingEngine(string strategy)
+    {
+        if (string.IsNullOrWhiteSpace(strategy))
+            throw new ArgumentException("Strategy cannot be null or whitespace.", nameof(strategy));
+        this.strategy = strategy;
+    }
+
+    public NestJobResult Solve(NestJob job, IProgress<NestJobProgress> progress = null, CancellationToken token = default)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+        var forced = new NestJob(job.Parts, job.Plates, new NestJobOptions(strategy, job.Options.MaxPlates));
+        return runner.Solve(forced, progress, token);
+    }
+}

OpenNest.Engine/Jobs/NestingEngineInfo.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace OpenNest;
+
+/// <summary>Display metadata plus a fresh-instance factory for one registered whole-job engine.</summary>
+public class NestingEngineInfo
+{
+    public NestingEngineInfo(string name, string description, Func<INestingEngine> factory)
+    {
+        Name = name;
+        Description = description;
+        Factory = factory;
+    }
+
+    public string Name { get; }
+    public string Description { get; }
+    public Func<INestingEngine> Factory { get; }
+}

OpenNest.Engine/Jobs/NestingEngineRegistry.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+
+namespace OpenNest;
+
+/// <summary>
+/// Registry of whole-job INestingEngine implementations, parallel to NestEngineRegistry (which is for
+/// the legacy single-plate NestEngineBase). The four production strategies are exposed here through
+/// FixedStrategyNestingEngine so they compete on equal footing with model-submitted engines. Unlike
+/// NestEngineRegistry, this has no ActiveEngineName/global-selection concept — callers choose an engine
+/// explicitly from AvailableEngines.
+/// </summary>
+public static class NestingEngineRegistry
+{
+    private static readonly List<NestingEngineInfo> engines = new();
+
+    static NestingEngineRegistry()
+    {
+        Register("Default", "Multi-phase nesting (Linear, Pairs, RectBestFit, Remainder)",
+            () => new FixedStrategyNestingEngine("Default"));
+
+        Register("Strip", "Strip-based nesting for mixed-drawing layouts",
+            () => new FixedStrategyNestingEngine("Strip"));
+
+        Register("Vertical Remnant", "Optimizes for largest right-side vertical drop",
+            () => new FixedStrategyNestingEngine("Vertical Remnant"));
+
+        Register("Horizontal Remnant", "Optimizes for largest top-side horizontal drop",
+            () => new FixedStrategyNestingEngine("Horizontal Remnant"));
+    }
+
+    public static IReadOnlyList<NestingEngineInfo> AvailableEngines => engines;
+
+    public static void Register(string name, string description, Func<INestingEngine> factory)
+    {
+        if (engines.Any(e => e.Name.Equals(name, StringComparison.OrdinalIgnoreCase)))
+        {
+            Debug.WriteLine($"[NestingEngineRegistry] Duplicate engine '{name}' skipped");
+            return;
+        }
+
+        engines.Add(new NestingEngineInfo(name, description, factory));
+    }
+
+    /// <summary>Scans *.dll in directory for non-abstract INestingEngine types with a public
+    /// parameterless constructor, registering each under its CLR type name. Mirrors
+    /// NestEngineRegistry.LoadPlugins's per-assembly/per-type isolation: one bad plugin never
+    /// prevents the rest from loading.</summary>
+    public static void LoadPlugins(string directory)
+    {
+        if (!Directory.Exists(directory))
+            return;
+
+        foreach (var dll in Directory.GetFiles(directory, "*.dll"))
+        {
+            try
+            {
+                var assembly = Assembly.LoadFrom(dll);
+
+                foreach (var type in assembly.GetTypes())
+                {
+                    if (type.IsAbstract || !typeof(INestingEngine).IsAssignableFrom(type))
+                        continue;
+
+                    var ctor = type.GetConstructor(Type.EmptyTypes);
+
+                    if (ctor == null)
+                    {
+                        Debug.WriteLine($"[NestingEngineRegistry] Skipping {type.Name}: no parameterless constructor");
+                        continue;
+                    }
+
+                    try
+                    {
+                        Register(type.Name, string.Empty, () => (INestingEngine)ctor.Invoke(null));
+                        Debug.WriteLine($"[NestingEngineRegistry] Loaded plugin engine: {type.Name}");
+                    }
+                    catch (Exception ex)
+                    {
+                        Debug.WriteLine($"[NestingEngineRegistry] Failed to register {type.Name}: {ex.Message}");
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"[NestingEngineRegistry] Failed to load assembly {Path.GetFileName(dll)}: {ex.Message}");
+            }
+        }
+    }
+}

OpenNest.Engine/OpenNest.Engine.csproj

@@ -6,6 +6,7 @@
   </PropertyGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="OpenNest.Tests" />
+    <InternalsVisibleTo Include="OpenNest.Engine.Tests" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />

README.md

@@ -168,7 +168,7 @@ dotnet run --project OpenNest.Console/OpenNest.Console.csproj -- project.zip ext
 
 ## Benchmarking Nest Engines
 
-`OpenNest.Benchmark` compares every registered `NestEngineBase` implementation against each other on a set of `.nest` files, scoring by material utilization:
+`OpenNest.Benchmark` compares every registered `INestingEngine` implementation against each other on a set of `.nest` files, scoring by material utilization. Each engine owns its own multi-plate/size strategy for the whole job — how many plates it uses, of which sizes, and how demand splits across them:
 
 ```bash
 # Benchmark all registered engines against every .nest file in a folder
@@ -179,7 +179,9 @@ dotnet run --project OpenNest.Benchmark/OpenNest.Benchmark.csproj -- job.nest \
   --sheet-sizes 48x96,60x96,60x120,72x120,72x144 --engines Default,Astra,Claude --csv results.csv
 ```
 
-An engine's layout is rejected (scoring zero for that job) if any part falls outside the work area, any two parts are closer than the required spacing, or a drawing gets more parts placed than requested.
+An engine's layout is rejected (scoring zero for that job) if any part falls outside the work area, any two parts are closer than the required spacing, or a drawing gets more parts placed than requested. A run that doesn't finish within its time budget also scores zero, as a timeout.
+
+Custom competitor engines can be added by dropping a DLL implementing `INestingEngine` with a public parameterless constructor into the `Engines/` directory next to the benchmark executable; each one is registered under its own CLR type name. This is a separate plugin contract from the desktop app's `NestEngineRegistry`/`NestEngineBase` (which requires a `(Plate)` constructor) — a `NestEngineBase` plugin dropped into the benchmark's `Engines/` folder is silently skipped, since the benchmark only ever solves whole jobs.
 
 ## Project Structure
 
@@ -213,7 +215,7 @@ OpenNest.sln
 | **OpenNest.Gpu** | GPU-accelerated bitmap overlap detection for best-fit pair evaluation using ILGPU. |
 | **OpenNest.Posts.Cincinnati** | Post-processor plugin for Cincinnati CL-707/800/900/940/CLX laser cutting machines. Outputs Cincinnati-format G-code with material library, kerf compensation, and pierce logic. |
 | **OpenNest.Mcp** | MCP (Model Context Protocol) server exposing nesting operations as tools for AI assistants. |
-| **OpenNest.Benchmark** | Runs every registered nest engine against a set of `.nest` files and scores them by material utilization, so engine implementations can be compared head-to-head. |
+| **OpenNest.Benchmark** | Runs every registered whole-job nesting engine (`INestingEngine`) against a set of `.nest` files and scores them by material utilization, so competing engines — each owning its own multi-plate strategy — can be compared head-to-head. |
 | **OpenNest.Tests** | 89 test files covering core geometry, fill strategies, splitting, bending, BOM import, post-processing, and the API. |
 
 ## Nesting Engines