feat(api): accept complete nesting jobs and report fulfillment

Task 6 of the whole-job engine API: adapt the public NestRequest/NestRunner/
NestResponse surface to delegate to the whole-job runner instead of a manual
quantity loop.

- NestRequest: optional explicit Plates stock list (null keeps the legacy
  unlimited SheetSize fallback; empty list means no available stock),
  optional per-part Id (derived as part-{index} when absent), and an explicit
  PlacementStrategy that takes precedence over the legacy Strategy.
- NestRequestPlate: one physical-stock type (id, size, quantity, spacing,
  quadrant).
- NestRunner: imports each DXF once, propagates priority/rotation constraints,
  runs a single NestJobRunner solve, materializes ID/pose placements exactly
  once, and reports aggregate utilization as total placed part area over total
  physical sheet area.
- NestResponse: exposes status, stop reason, part fulfillment, stock usage,
  and plate-to-stock mapping; .nestquote save/load gains a schema version and
  reports completion as unknown for old archives lacking fulfillment metadata.
- Tests: extend the Api request/runner/persistence suites for legacy SheetSize,
  explicit mixed finite stock, stock exhaustion, weighted utilization, old
  archive loading, and new-archive round trips.

Verification: cross-compiles clean on net8.0-windows (Linux). The Api tests
require a Windows runner (net8.0-windows) and are NOT executed here; the
delegated engine logic is covered by the 70-test net8.0 Engine.Tests suite
(committed in Task 5). Windows runtime verification remains outstanding.

OpenNest.Api/NestRequest.cs

@@ -6,10 +6,18 @@ namespace OpenNest.Api;
 public class NestRequest
 {
     public IReadOnlyList<NestRequestPart> Parts { get; init; } = [];
+    /// <summary>
+    /// Explicit available physical stock. Null keeps the legacy unlimited SheetSize fallback;
+    /// an empty list deliberately means no stock is available.
+    /// </summary>
+    public IReadOnlyList<NestRequestPlate> Plates { get; init; }
     public Size SheetSize { get; init; } = new(60, 120);
+    /// <summary>Built-in whole-job placement strategy. Explicit values take precedence over legacy Strategy.</summary>
+    public string PlacementStrategy { get; init; } = "Default";
     public string Material { get; init; } = "Steel, A1011 HR";
     public double Thickness { get; init; } = 0.06;
     public double Spacing { get; init; } = 0.1;
+    /// <summary>Legacy compatibility setting; Auto maps to the Default whole-job strategy.</summary>
     public NestStrategy Strategy { get; init; } = NestStrategy.Auto;
     public CutParameters Cutting { get; init; } = CutParameters.Default;
 }

OpenNest.Api/NestRequestPart.cs

@@ -2,6 +2,8 @@ namespace OpenNest.Api;
 
 public class NestRequestPart
 {
+    /// <summary>Optional stable requirement identity. NestRunner derives part-{requestIndex} when omitted.</summary>
+    public string Id { get; init; }
     public string DxfPath { get; init; }
     public int Quantity { get; init; } = 1;
     public bool AllowRotation { get; init; } = true;

OpenNest.Api/NestRequestPlate.cs

@@ -0,0 +1,15 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Api;
+
+/// <summary>One explicit physical-stock type for a whole nesting job.</summary>
+public class NestRequestPlate
+{
+    public string Id { get; init; }
+    public Size Size { get; init; }
+    /// <summary>Available physical sheets; null means unlimited.</summary>
+    public int? Quantity { get; init; }
+    public double PartSpacing { get; init; }
+    public Spacing EdgeSpacing { get; init; }
+    public int Quadrant { get; init; } = 1;
+}

OpenNest.Api/NestResponse.cs

@@ -1,18 +1,40 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.IO.Compression;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using System.Threading.Tasks;
 using OpenNest.IO;
 
 namespace OpenNest.Api;
 
+/// <summary>Stable fulfillment metadata for one requested part identity.</summary>
+public sealed record NestPartFulfillment(string PartId, int Requested, int Placed, int Unplaced);
+
+/// <summary>Physical-sheet usage for one stock identity.</summary>
+public sealed record NestStockUsage(string StockId, int Used, int? Remaining);
+
+/// <summary>Maps each materialized physical sheet to its source stock identity.</summary>
+public sealed record NestPlateStockMapping(int PlateIndex, string StockId);
+
 public class NestResponse
 {
+    public const int CurrentSchemaVersion = 2;
+
+    /// <summary>Zero identifies an archive written before response metadata was versioned.</summary>
+    public int SchemaVersion { get; init; } = CurrentSchemaVersion;
     public int SheetCount { get; init; }
+    /// <summary>Placed-part area divided by total materialized physical-sheet area, as a 0.0–1.0 ratio.</summary>
     public double Utilization { get; init; }
     public TimeSpan CutTime { get; init; }
     public TimeSpan Elapsed { get; init; }
+    /// <summary>Null means an older archive did not record whole-job fulfillment status.</summary>
+    public NestJobStatus? Status { get; init; }
+    public NestJobStopReason? StopReason { get; init; }
+    public IReadOnlyList<NestPartFulfillment> Fulfillment { get; init; } = [];
+    public IReadOnlyList<NestStockUsage> StockUsage { get; init; } = [];
+    public IReadOnlyList<NestPlateStockMapping> PlateStockMappings { get; init; } = [];
     public Nest Nest { get; init; }
     public NestRequest Request { get; init; }
 
@@ -20,7 +42,8 @@ public class NestResponse
     {
         PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
         WriteIndented = true,
-        IncludeFields = true  // Required for OpenNest.Geometry.Size (public fields)
+        IncludeFields = true, // Required for OpenNest.Geometry.Size and Spacing public fields.
+        Converters = { new JsonStringEnumConverter() }
     };
 
     public async Task SaveAsync(string path)
@@ -28,32 +51,34 @@ public class NestResponse
         using var fs = new FileStream(path, FileMode.Create);
         using var zip = new ZipArchive(fs, ZipArchiveMode.Create);
 
-        // Write request.json
         var requestEntry = zip.CreateEntry("request.json");
         await using (var stream = requestEntry.Open())
         {
             await JsonSerializer.SerializeAsync(stream, Request, JsonOptions);
         }
 
-        // Write response.json (metrics only)
-        var metrics = new
-        {
-            SheetCount,
-            Utilization,
-            CutTimeTicks = CutTime.Ticks,
-            ElapsedTicks = Elapsed.Ticks
-        };
+        // Keep persisted data versioned and detached from the live mutable Nest graph.
         var responseEntry = zip.CreateEntry("response.json");
         await using (var stream = responseEntry.Open())
         {
-            await JsonSerializer.SerializeAsync(stream, metrics, JsonOptions);
+            await JsonSerializer.SerializeAsync(stream, new NestResponseArchiveDto
+            {
+                SchemaVersion = CurrentSchemaVersion,
+                SheetCount = SheetCount,
+                Utilization = Utilization,
+                CutTimeTicks = CutTime.Ticks,
+                ElapsedTicks = Elapsed.Ticks,
+                Status = Status,
+                StopReason = StopReason,
+                Fulfillment = Fulfillment is null ? [] : new List<NestPartFulfillment>(Fulfillment),
+                StockUsage = StockUsage is null ? [] : new List<NestStockUsage>(StockUsage),
+                PlateStockMappings = PlateStockMappings is null ? [] : new List<NestPlateStockMapping>(PlateStockMappings)
+            }, JsonOptions);
         }
 
-        // Write embedded nest.nest via NestWriter → MemoryStream → ZIP entry
         var nestEntry = zip.CreateEntry("nest.nest");
         using var nestMs = new MemoryStream();
-        var writer = new NestWriter(Nest);
-        writer.Write(nestMs);
+        new NestWriter(Nest).Write(nestMs);
         nestMs.Position = 0;
         await using (var stream = nestEntry.Open())
         {
@@ -66,25 +91,34 @@ public class NestResponse
         using var fs = new FileStream(path, FileMode.Open, FileAccess.Read);
         using var zip = new ZipArchive(fs, ZipArchiveMode.Read);
 
-        // Read request.json
         var requestEntry = zip.GetEntry("request.json")
             ?? throw new InvalidOperationException("Missing request.json in .nestquote file");
         NestRequest request;
         await using (var stream = requestEntry.Open())
         {
-            request = await JsonSerializer.DeserializeAsync<NestRequest>(stream, JsonOptions);
+            request = await JsonSerializer.DeserializeAsync<NestRequest>(stream, JsonOptions)
+                ?? throw new InvalidOperationException("Invalid request.json in .nestquote file");
         }
 
-        // Read response.json
         var responseEntry = zip.GetEntry("response.json")
             ?? throw new InvalidOperationException("Missing response.json in .nestquote file");
-        JsonElement metricsJson;
+        NestResponseArchiveDto archive;
+        var hasSchemaVersion = false;
+        var hasStatusMetadata = false;
         await using (var stream = responseEntry.Open())
+        using (var document = await JsonDocument.ParseAsync(stream))
         {
-            metricsJson = await JsonSerializer.DeserializeAsync<JsonElement>(stream, JsonOptions);
+            var root = document.RootElement;
+            hasSchemaVersion = root.TryGetProperty("schemaVersion", out _);
+            hasStatusMetadata = root.TryGetProperty("status", out _) ||
+                root.TryGetProperty("stopReason", out _) ||
+                root.TryGetProperty("fulfillment", out _) ||
+                root.TryGetProperty("stockUsage", out _) ||
+                root.TryGetProperty("plateStockMappings", out _);
+            archive = root.Deserialize<NestResponseArchiveDto>(JsonOptions)
+                ?? throw new InvalidOperationException("Invalid response.json in .nestquote file");
         }
 
-        // Read embedded nest.nest via NestReader(Stream)
         var nestEntry = zip.GetEntry("nest.nest")
             ?? throw new InvalidOperationException("Missing nest.nest in .nestquote file");
         Nest nest;
@@ -95,18 +129,37 @@ public class NestResponse
                 await stream.CopyToAsync(nestMs);
             }
             nestMs.Position = 0;
-            var reader = new NestReader(nestMs);
-            nest = reader.Read();
+            nest = new NestReader(nestMs).Read();
         }
 
         return new NestResponse
         {
-            SheetCount = metricsJson.GetProperty("sheetCount").GetInt32(),
-            Utilization = metricsJson.GetProperty("utilization").GetDouble(),
-            CutTime = TimeSpan.FromTicks(metricsJson.GetProperty("cutTimeTicks").GetInt64()),
-            Elapsed = TimeSpan.FromTicks(metricsJson.GetProperty("elapsedTicks").GetInt64()),
+            SchemaVersion = hasSchemaVersion ? archive.SchemaVersion : 0,
+            SheetCount = archive.SheetCount,
+            Utilization = archive.Utilization,
+            CutTime = TimeSpan.FromTicks(archive.CutTimeTicks),
+            Elapsed = TimeSpan.FromTicks(archive.ElapsedTicks),
+            Status = hasStatusMetadata ? archive.Status : null,
+            StopReason = hasStatusMetadata ? archive.StopReason : null,
+            Fulfillment = hasStatusMetadata ? archive.Fulfillment ?? [] : [],
+            StockUsage = hasStatusMetadata ? archive.StockUsage ?? [] : [],
+            PlateStockMappings = hasStatusMetadata ? archive.PlateStockMappings ?? [] : [],
             Nest = nest,
             Request = request
         };
     }
+
+    private sealed class NestResponseArchiveDto
+    {
+        public int SchemaVersion { get; init; }
+        public int SheetCount { get; init; }
+        public double Utilization { get; init; }
+        public long CutTimeTicks { get; init; }
+        public long ElapsedTicks { get; init; }
+        public NestJobStatus? Status { get; init; }
+        public NestJobStopReason? StopReason { get; init; }
+        public List<NestPartFulfillment> Fulfillment { get; init; } = [];
+        public List<NestStockUsage> StockUsage { get; init; } = [];
+        public List<NestPlateStockMapping> PlateStockMappings { get; init; } = [];
+    }
 }

OpenNest.Api/NestRunner.cs

@@ -11,125 +11,167 @@ namespace OpenNest.Api;
 
 public static class NestRunner
 {
+    private const string LegacyStockId = "legacy-sheet";
+
     public static Task<NestResponse> RunAsync(
         NestRequest request,
         IProgress<NestProgress> progress = null,
         CancellationToken token = default)
     {
-        if (request.Parts.Count == 0)
+        ArgumentNullException.ThrowIfNull(request);
+        var requestParts = request.Parts ?? throw new ArgumentException("Request parts must not be null.", nameof(request));
+        if (requestParts.Count == 0)
             throw new ArgumentException("Request must contain at least one part.", nameof(request));
 
         var sw = Stopwatch.StartNew();
+        var parts = IdentifyParts(requestParts);
+        var importedByPath = new Dictionary<string, Drawing>(StringComparer.Ordinal);
+        var jobParts = new List<NestJobPart>(parts.Count);
 
-        // 1. Import DXFs → Drawings
-        var drawings = new List<Drawing>();
-        foreach (var part in request.Parts)
+        foreach (var part in parts)
         {
-            if (!File.Exists(part.DxfPath))
-                throw new FileNotFoundException($"DXF file not found: {part.DxfPath}", part.DxfPath);
+            token.ThrowIfCancellationRequested();
+            if (!File.Exists(part.Request.DxfPath))
+                throw new FileNotFoundException($"DXF file not found: {part.Request.DxfPath}", part.Request.DxfPath);
 
-            Drawing drawing;
+            if (!importedByPath.TryGetValue(part.Request.DxfPath, out var drawing))
+            {
                 try
                 {
-                drawing = CadImporter.ImportDrawing(part.DxfPath,
-                    new CadImportOptions { Quantity = part.Quantity });
+                    drawing = CadImporter.ImportDrawing(part.Request.DxfPath,
+                        new CadImportOptions { Quantity = part.Request.Quantity });
                 }
-            catch (System.Exception ex)
+                catch (Exception exception)
                 {
-                throw new InvalidOperationException(
-                    $"Failed to import DXF: {part.DxfPath}", ex);
+                    throw new InvalidOperationException($"Failed to import DXF: {part.Request.DxfPath}", exception);
                 }
 
                 if (drawing.Program == null || drawing.Program.Codes.Count == 0)
-                throw new InvalidOperationException($"Failed to import DXF: {part.DxfPath}");
+                    throw new InvalidOperationException($"Failed to import DXF: {part.Request.DxfPath}");
 
-            drawings.Add(drawing);
+                importedByPath.Add(part.Request.DxfPath, drawing);
             }
 
-        // 2. Build NestItems
-        var items = new List<NestItem>();
-        for (var i = 0; i < request.Parts.Count; i++)
-        {
-            var part = request.Parts[i];
-            items.Add(new NestItem
-            {
-                Drawing = drawings[i],
-                Quantity = part.Quantity,
-                Priority = part.Priority,
-                StepAngle = part.AllowRotation ? 0 : OpenNest.Math.Angle.TwoPI,
-            });
+            ConfigureDrawingForRequirement(drawing, part.Request);
+            jobParts.Add(DrawingJobMapper.FromDrawing(part.Id, drawing, part.Request.Quantity));
         }
 
-        // 3. Multi-plate loop
-        var nest = new Nest();
+        var job = new NestJob(jobParts, CreateStock(request),
+            new NestJobOptions(ResolvePlacementStrategy(request)));
+        var jobProgress = progress == null ? null : new JobProgressBridge(progress);
+        var result = new NestJobRunner(PlateNesterFactory.Create).Solve(job, jobProgress, token);
+
+        // This is the sole translation from immutable result poses to mutable legacy output objects.
+        var materialized = NestResultMaterializer.Materialize(job, result);
+        var nest = materialized.Nest;
         nest.Thickness = request.Thickness;
         nest.Material = new Material(request.Material);
-        var remaining = items.Select(item => item.Quantity).ToList();
 
-        while (remaining.Any(q => q > 0))
-        {
-            token.ThrowIfCancellationRequested();
+        var timingInfo = Timing.GetTimingInfo(nest);
+        var cutTime = Timing.CalculateTime(timingInfo, request.Cutting);
+        sw.Stop();
 
-            var plate = new Plate(request.SheetSize)
+        return Task.FromResult(new NestResponse
         {
-                PartSpacing = request.Spacing,
-            };
-
-            // Build items for this pass with remaining quantities
-            var passItems = new List<NestItem>();
-            for (var i = 0; i < items.Count; i++)
-            {
-                if (remaining[i] <= 0) continue;
-                passItems.Add(new NestItem
-                {
-                    Drawing = items[i].Drawing,
-                    Quantity = remaining[i],
-                    Priority = items[i].Priority,
-                    StepAngle = items[i].StepAngle,
+            SheetCount = nest.Plates.Count,
+            Utilization = CalculateUtilization(nest),
+            CutTime = cutTime,
+            Elapsed = sw.Elapsed,
+            Status = result.Status,
+            StopReason = result.StopReason,
+            Fulfillment = result.Fulfillment
+                .Select(value => new NestPartFulfillment(value.PartId, value.Requested, value.Placed, value.Unplaced))
+                .ToArray(),
+            StockUsage = result.StockUsage
+                .Select(value => new NestStockUsage(value.StockId, value.Used, value.Remaining))
+                .ToArray(),
+            PlateStockMappings = result.Plates
+                .Select(value => new NestPlateStockMapping(value.PlateIndex, value.StockId))
+                .ToArray(),
+            Nest = nest,
+            Request = request
         });
     }
 
-            // Run engine
-            var engine = NestEngineRegistry.Create(plate);
-            var parts = engine.Nest(passItems, progress, token);
-
-            if (parts.Count == 0)
-                break; // No progress — part doesn't fit on fresh sheet
-
-            // Add parts to plate and nest
-            foreach (var p in parts)
-                plate.Parts.Add(p);
-
-            nest.Plates.Add(plate);
-
-            // Deduct placed quantities
-            foreach (var p in parts)
+    private static IReadOnlyList<IdentifiedRequestPart> IdentifyParts(IReadOnlyList<NestRequestPart> requestParts)
     {
-                var idx = drawings.IndexOf(p.BaseDrawing);
-                if (idx >= 0)
-                    remaining[idx]--;
+        var identified = new List<IdentifiedRequestPart>(requestParts.Count);
+        var ids = new HashSet<string>(StringComparer.Ordinal);
+        for (var index = 0; index < requestParts.Count; index++)
+        {
+            var part = requestParts[index] ?? throw new ArgumentException("Request parts must not contain null entries.", nameof(requestParts));
+            var id = part.Id ?? $"part-{index}";
+            if (string.IsNullOrWhiteSpace(id))
+                throw new ArgumentException("Part IDs must not be blank.", nameof(requestParts));
+            if (!ids.Add(id))
+                throw new ArgumentException("Part IDs must be unique.", nameof(requestParts));
+            identified.Add(new IdentifiedRequestPart(id, part));
+        }
+
+        return identified;
+    }
+
+    private static IReadOnlyList<NestPlateStock> CreateStock(NestRequest request)
+    {
+        if (request.Plates is null)
+        {
+            return
+            [
+                new NestPlateStock(LegacyStockId, request.SheetSize, quantity: null,
+                    partSpacing: request.Spacing)
+            ];
+        }
+
+        var stock = new List<NestPlateStock>(request.Plates.Count);
+        foreach (var plate in request.Plates)
+        {
+            if (plate is null)
+                throw new ArgumentException("Request plates must not contain null entries.", nameof(request));
+            stock.Add(new NestPlateStock(plate.Id, plate.Size, plate.Quantity, plate.PartSpacing,
+                plate.EdgeSpacing, plate.Quadrant));
+        }
+
+        return stock;
+    }
+
+    private static void ConfigureDrawingForRequirement(Drawing drawing, NestRequestPart part)
+    {
+        drawing.Priority = part.Priority;
+        drawing.Constraints ??= new NestConstraints();
+        if (!part.AllowRotation)
+        {
+            // A zero legacy step means automatic rotation to DrawingJobMapper, so lock it explicitly.
+            drawing.Constraints.StepAngle = OpenNest.Math.Angle.TwoPI;
+            drawing.Constraints.StartAngle = 0;
+            drawing.Constraints.EndAngle = 0;
         }
     }
 
-        // 4. Compute timing
-        var timingInfo = Timing.GetTimingInfo(nest);
-        var cutTime = Timing.CalculateTime(timingInfo, request.Cutting);
-
-        sw.Stop();
-
-        // 5. Build response
-        var response = new NestResponse
+    private static string ResolvePlacementStrategy(NestRequest request) => request.PlacementStrategy ?? request.Strategy switch
     {
-            SheetCount = nest.Plates.Count,
-            Utilization = nest.Plates.Count > 0
-                ? nest.Plates.Average(p => p.Utilization())
-                : 0,
-            CutTime = cutTime,
-            Elapsed = sw.Elapsed,
-            Nest = nest,
-            Request = request
+        NestStrategy.Auto => "Default",
+        _ => throw new NotSupportedException($"Unknown legacy nesting strategy: {request.Strategy}.")
     };
 
-        return Task.FromResult(response);
+    private static double CalculateUtilization(Nest nest)
+    {
+        var sheetArea = nest.Plates.Sum(plate => plate.Area());
+        if (sheetArea == 0) return 0;
+        var placedArea = nest.Plates.Sum(plate => plate.Parts
+            .Where(part => !part.BaseDrawing.IsCutOff)
+            .Sum(part => part.BaseDrawing.Area));
+        return placedArea / sheetArea;
+    }
+
+    private sealed record IdentifiedRequestPart(string Id, NestRequestPart Request);
+
+    private sealed class JobProgressBridge(IProgress<NestProgress> progress) : IProgress<NestJobProgress>
+    {
+        public void Report(NestJobProgress value)
+        {
+            ArgumentNullException.ThrowIfNull(value);
+            if (value.LegacyProgress is not null)
+                progress.Report(value.LegacyProgress);
+        }
     }
 }

OpenNest.Engine.Tests/Jobs/FiniteStockJobTests.cs

@@ -0,0 +1,183 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class FiniteStockJobTests
+{
+    internal static NestJob Job(int? stock = 3, NestJobOptions? options = null) => new(
+        new[] { new NestJobPart("p", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle()), 3) },
+        new[] { new NestPlateStock("s", new Size(100, 200), stock) }, options);
+
+    internal sealed class Nester(Func<PlatePlacementRequest, PlateCandidate> place) : IPlateNester
+    {
+        public int Calls { get; private set; }
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default) { Calls++; return place(request); }
+    }
+
+    internal static PlateCandidate One(PlatePlacementRequest request) => new(new[]
+        { new NestJobPlacement(request.Parts[0].Id, 99, 0, 0, 0) });
+
+    [Theory]
+    [InlineData(3, 3, 0, NestJobStatus.Complete, NestJobStopReason.Completed)]
+    [InlineData(2, 2, 1, NestJobStatus.Incomplete, NestJobStopReason.StockExhausted)]
+    [InlineData(0, 0, 3, NestJobStatus.Incomplete, NestJobStopReason.StockExhausted)]
+    public void DemandAndPhysicalStockAreAccountedFromPlacements(int stock, int placed, int left,
+        NestJobStatus status, NestJobStopReason reason)
+    {
+        var requests = new List<int>();
+        var nester = new Nester(r => { requests.Add(r.Parts[0].Quantity); return One(r); });
+        var job = Job(stock);
+        var result = new NestJobRunner(_ => nester).Solve(job);
+        Assert.Equal(status, result.Status);
+        Assert.Equal(reason, result.StopReason);
+        Assert.Equal(placed, result.Plates.Count);
+        Assert.All(result.Plates, p => Assert.Single(p.Placements));
+        Assert.Equal(Enumerable.Range(0, placed), result.Plates.SelectMany(p => p.Placements).Select(p => p.InstanceIndex));
+        Assert.Equal(Enumerable.Range(0, placed).Select(i => 3 - i), requests);
+        Assert.Equal(new PartFulfillment("p", 3, placed, left), Assert.Single(result.Fulfillment));
+        Assert.Equal(new StockUsage("s", placed, stock - placed), Assert.Single(result.StockUsage));
+        Assert.Equal(3, job.Parts[0].Quantity);
+        Assert.Equal(stock, job.Plates[0].Quantity);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData(3)]
+    public void NoPlacementStopsWithoutConsumingStock(int? stock)
+    {
+        var nester = new Nester(_ => new PlateCandidate(Array.Empty<NestJobPlacement>()));
+        var result = new NestJobRunner(_ => nester).Solve(Job(stock));
+        Assert.Equal(1, nester.Calls);
+        Assert.Empty(result.Plates);
+        Assert.Equal(NestJobStatus.Incomplete, result.Status);
+        Assert.Equal(NestJobStopReason.NoPlacementFound, result.StopReason);
+        Assert.Equal(new StockUsage("s", 0, stock), Assert.Single(result.StockUsage));
+    }
+
+    [Fact]
+    public void PlateLimitStopsUnlimitedStock()
+    {
+        var result = new NestJobRunner(_ => new Nester(One)).Solve(Job(null, new NestJobOptions(maxPlates: 2)));
+        Assert.Equal(2, result.Plates.Count);
+        Assert.Equal(NestJobStopReason.PlateLimitReached, result.StopReason);
+        Assert.Equal(new StockUsage("s", 2, null), Assert.Single(result.StockUsage));
+    }
+
+    [Fact]
+    public void CancellationImmediatelyAfterEngineReturnThrowsWithoutCommit()
+    {
+        using var cts = new CancellationTokenSource();
+        var commits = new List<NestJobProgress>();
+        var nester = new Nester(r => { cts.Cancel(); return One(r); });
+        Assert.Throws<OperationCanceledException>(() => new NestJobRunner(_ => nester)
+            .Solve(Job(), new InlineProgress(commits.Add), cts.Token));
+        Assert.DoesNotContain(commits, p => p.Stage == NestJobStage.PlateCommitted);
+    }
+
+    [Fact]
+    public void InitialCancellationSkipsEngine()
+    {
+        using var cts = new CancellationTokenSource();
+        cts.Cancel();
+        Assert.Throws<OperationCanceledException>(() => new NestJobRunner(_ => throw new Exception("called"))
+            .Solve(Job(), token: cts.Token));
+    }
+
+    [Theory]
+    [InlineData("unknown", 0, 0, 0, 1)]
+    [InlineData("p", double.NaN, 0, 0, 1)]
+    [InlineData("p", 0, double.PositiveInfinity, 0, 1)]
+    [InlineData("p", 0, 0, double.NaN, 1)]
+    [InlineData("p", 0, 0, 0, 4)]
+    public void InvalidCandidateThrows(string id, double x, double y, double rotation, int count)
+    {
+        var nester = new Nester(_ => new PlateCandidate(Enumerable.Range(0, count)
+            .Select(i => new NestJobPlacement(id, i, x, y, rotation))));
+        Assert.Throws<InvalidOperationException>(() => new NestJobRunner(_ => nester).Solve(Job()));
+    }
+
+    [Fact]
+    public void NullCandidateAndUnknownStrategyAreExplicitErrors()
+    {
+        Assert.Throws<InvalidOperationException>(() => new NestJobRunner(_ => new Nester(_ => null!)).Solve(Job()));
+        Assert.Throws<NotSupportedException>(() => new NestJobRunner(_ => null!).Solve(Job(options: new NestJobOptions("missing"))));
+    }
+
+    [Fact]
+    public void MixedStockCanBeEvaluated()
+    {
+        var job = Job();
+        var mixed = new NestJob(job.Parts, job.Plates.Concat(new[] { new NestPlateStock("other", new Size(20, 10), 2) }));
+        var result = new NestJobRunner(_ => new Nester(One)).Solve(mixed);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+    }
+
+    [Theory]
+    [InlineData(0, 20, 0, 1)]
+    [InlineData(10, double.NaN, 0, 1)]
+    [InlineData(10, 20, -1, 1)]
+    [InlineData(10, 20, double.PositiveInfinity, 1)]
+    [InlineData(10, 20, 0, 5)]
+    public void InvalidStockSettingsRejected(double width, double length, double spacing, int quadrant)
+    {
+        var job = new NestJob(Job().Parts, new[] { new NestPlateStock("s", new Size(width, length), 1, spacing, quadrant: quadrant) });
+        Assert.Throws<ArgumentException>(() => new NestJobRunner(_ => new Nester(One)).Solve(job));
+    }
+
+    [Fact]
+    public void InvalidEdgesAndGeometryRejected()
+    {
+        var runner = new NestJobRunner(_ => new Nester(One));
+        foreach (var edges in new[] { new Spacing(-1, 0, 0, 0), new Spacing(0, double.NaN, 0, 0), new Spacing(1000, 1000, 1000, 1000) })
+            Assert.Throws<ArgumentException>(() => runner.Solve(new NestJob(Job().Parts,
+                new[] { new NestPlateStock("s", new Size(100, 200), edgeSpacing: edges) })));
+        var program = TestDrawingFactory.Rectangle();
+        program.LineTo(double.NaN, 0);
+        Assert.Throws<ArgumentException>(() => runner.Solve(new NestJob(new[]
+            { new NestJobPart("p", PartGeometrySnapshot.FromProgram(program), 1) }, Job().Plates)));
+    }
+
+    [Fact]
+    public void InvalidContractInputsAreRejected()
+    {
+        var job = Job();
+        Assert.Throws<ArgumentNullException>(() => new NestJobRunner(_ => new Nester(One)).Solve(null!));
+        Assert.Throws<ArgumentException>(() => new NestJob(new NestJobPart[] { null! }, job.Plates));
+        Assert.Throws<ArgumentException>(() => new NestJob(job.Parts.Concat(job.Parts), job.Plates));
+        Assert.Throws<ArgumentException>(() => new NestJob(job.Parts, job.Plates.Concat(job.Plates)));
+        Assert.Throws<ArgumentOutOfRangeException>(() => new NestJobPart("p", job.Parts[0].Geometry, 0));
+        Assert.Throws<ArgumentOutOfRangeException>(() => new NestPlateStock("s", new Size(1, 1), -1));
+        Assert.Throws<ArgumentOutOfRangeException>(() => new NestJobOptions(maxPlates: 0));
+    }
+
+    [Fact]
+    public void RunnerFactoriesAreInstanceScopedAndReceiveExactStrategyKeys()
+    {
+        var keys = new List<string>();
+        var first = new NestJobRunner(key => { keys.Add(key); return new Nester(One); });
+        var second = new NestJobRunner(key => { keys.Add(key); return new Nester(_ => new PlateCandidate(Array.Empty<NestJobPlacement>())); });
+        Assert.Equal(NestJobStatus.Complete, first.Solve(Job(options: new NestJobOptions("custom-A"))).Status);
+        Assert.Equal(NestJobStopReason.NoPlacementFound, second.Solve(Job(options: new NestJobOptions("custom-B"))).StopReason);
+        Assert.Equal(NestJobStatus.Complete, first.Solve(Job(options: new NestJobOptions("custom-A"))).Status);
+        Assert.Equal(new[] { "custom-A", "custom-B", "custom-A" }, keys);
+    }
+
+    [Fact]
+    public void CancellationAfterAnEarlierCommitStillThrowsRatherThanReturningPartialResult()
+    {
+        using var cts = new CancellationTokenSource();
+        var calls = 0;
+        var commits = new List<NestJobProgress>();
+        var nester = new Nester(r => { if (++calls == 2) cts.Cancel(); return One(r); });
+        Assert.Throws<OperationCanceledException>(() => new NestJobRunner(_ => nester)
+            .Solve(Job(), new InlineProgress(commits.Add), cts.Token));
+        Assert.Equal(1, Assert.Single(commits.Where(p => p.Stage == NestJobStage.PlateCommitted)).CommittedParts);
+        Assert.Equal(2, calls);
+    }
+
+    private sealed class InlineProgress(Action<NestJobProgress> report) : IProgress<NestJobProgress>
+    {
+        public void Report(NestJobProgress value) => report(value);
+    }
+}

OpenNest.Engine.Tests/Jobs/JobAdapterTests.cs

@@ -0,0 +1,162 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class JobAdapterTests
+{
+    [Fact]
+    public void LegacyMutationsCannotDoubleSubtractOrReachCallerObjects()
+    {
+        var drawing = new Drawing("same name", TestDrawingFactory.Rectangle());
+        drawing.Quantity.Required = 9;
+        var item = new NestItem { Drawing = drawing, Quantity = 3, Priority = 7, StepAngle = 0 };
+        var sourcePlate = new Plate(100, 200) { Quantity = 3, PartSpacing = 2 };
+        var job = new NestJob(new[] { DrawingJobMapper.FromItem("requirement", item) },
+            new[] { DrawingJobMapper.FromPlate("stock", sourcePlate, 3) });
+        var quantities = new List<int>();
+        var adapter = new LegacyPlateNesterAdapter(p => new MutatingEngine(p, items =>
+        {
+            var privateItem = Assert.Single(items);
+            quantities.Add(privateItem.Quantity);
+            Assert.NotSame(drawing, privateItem.Drawing);
+            Assert.Equal(0, privateItem.StepAngle);
+            Assert.Equal(7, privateItem.Priority);
+            var part = new Part(privateItem.Drawing);
+            privateItem.Quantity = 0;
+            privateItem.Drawing.Quantity.Required = 0;
+            return new List<Part> { part };
+        }));
+        var result = new NestJobRunner(_ => adapter).Solve(job);
+        var materialized = NestResultMaterializer.Materialize(job, result);
+        Assert.Equal(new[] { 3, 2, 1 }, quantities);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(3, materialized.Nest.Plates.Count);
+        Assert.All(materialized.Nest.Plates, p => { Assert.Equal(1, p.Quantity); Assert.Single(p.Parts); });
+        var outputDrawing = materialized.DrawingsByPartId["requirement"];
+        Assert.Equal(3, outputDrawing.Quantity.Required);
+        Assert.Equal(3, outputDrawing.Quantity.Nested);
+        Assert.All(materialized.Nest.Plates, p => Assert.Same(outputDrawing, p.Parts[0].BaseDrawing));
+        Assert.NotSame(drawing, outputDrawing);
+        Assert.Equal(9, drawing.Quantity.Required);
+        Assert.Equal(0, drawing.Quantity.Nested);
+        Assert.Equal(3, item.Quantity);
+        Assert.Equal(3, sourcePlate.Quantity);
+        Assert.Empty(sourcePlate.Parts);
+        Assert.Equal(2, sourcePlate.PartSpacing);
+        Assert.Equal(PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle()).Motions,
+            PartGeometrySnapshot.FromProgram(drawing.Program).Motions);
+    }
+
+    [Fact]
+    public void ReferenceIdentityNotNamesControlsLegacyPlacements()
+    {
+        var drawing = new Drawing("duplicate", TestDrawingFactory.Rectangle());
+        var job = new NestJob(new[] { DrawingJobMapper.FromDrawing("a", drawing, 1),
+            DrawingJobMapper.FromDrawing("b", drawing, 1) }, FiniteStockJobTests.Job(1).Plates);
+        var adapter = new LegacyPlateNesterAdapter(p => new MutatingEngine(p, items =>
+        {
+            Assert.NotSame(items[0].Drawing, items[1].Drawing);
+            foreach (var item in items) item.Drawing.Name = "identical";
+            return new List<Part>
+            {
+                new Part(items[0].Drawing, new Vector(0, 0)),
+                new Part(items[1].Drawing, new Vector(10, 0))
+            };
+        }));
+        var result = new NestJobRunner(_ => adapter).Solve(job);
+        Assert.Equal(new[] { "a", "b" }, result.Plates[0].Placements.Select(p => p.PartId));
+        var output = NestResultMaterializer.Materialize(job, result);
+        Assert.NotSame(output.DrawingsByPartId["a"], output.DrawingsByPartId["b"]);
+        Assert.All(output.DrawingsByPartId.Values, d => Assert.Equal(1, d.Quantity.Nested));
+    }
+
+    [Fact]
+    public void UnknownPrivateDrawingIsRejectedEvenWithMatchingName()
+    {
+        var adapter = new LegacyPlateNesterAdapter(p => new MutatingEngine(p, items => new List<Part>
+            { new(new Drawing(items[0].Drawing.Name, TestDrawingFactory.Rectangle())) }));
+        Assert.Throws<InvalidOperationException>(() => new NestJobRunner(_ => adapter).Solve(FiniteStockJobTests.Job()));
+        Assert.Throws<NotSupportedException>(() => LegacyPlateNesterAdapter.Create("not registered"));
+    }
+
+    [Fact]
+    public void ExactGeometryRoundTripsIncludingOriginArcHoleAndMode()
+    {
+        var program = TestDrawingFactory.Rectangle();
+        program.Offset(-17.123456789, 5.25);
+        program.MoveTo(-14, 9);
+        program.ArcTo(-14, 9, -13, 9, RotationType.CW);
+        ((ArcMove)program.Codes[^1]).Layer = LayerType.Cut;
+        var drawing = new Drawing("shape", program);
+        var part = DrawingJobMapper.FromDrawing("p", drawing, 1);
+        var snapshot = part.Geometry.Motions.ToArray();
+        ((Motion)program.Codes[1]).EndPoint = new Vector(999, 888);
+        Assert.Equal(snapshot, part.Geometry.Motions);
+        var roundTrip = DrawingJobMapper.ToProgram(part.Geometry);
+        Assert.Equal(snapshot, PartGeometrySnapshot.FromProgram(roundTrip).Motions);
+        Assert.Equal(program.Mode, roundTrip.Mode);
+        roundTrip.Codes.Clear();
+        Assert.Equal(snapshot, part.Geometry.Motions);
+        var incremental = new Program(Mode.Incremental);
+        incremental.MoveTo(5, -3);
+        incremental.LineTo(7, 4);
+        var incrementalSnapshot = PartGeometrySnapshot.FromProgram(incremental);
+        Assert.Equal(Mode.Incremental, DrawingJobMapper.ToProgram(incrementalSnapshot).Mode);
+        Assert.Equal(incrementalSnapshot.Motions,
+            PartGeometrySnapshot.FromProgram(DrawingJobMapper.ToProgram(incrementalSnapshot)).Motions);
+    }
+
+    [Fact]
+    public void RealDefaultEngineRunsFromDrawingThroughMaterialization()
+    {
+        var drawing = new Drawing("generated asymmetric rectangle", TestDrawingFactory.Rectangle(13, 7));
+        drawing.Quantity.Required = 1;
+        var job = new NestJob(new[] { DrawingJobMapper.FromDrawing("rectangle", drawing, 1) },
+            new[] { new NestPlateStock("sheet", new Size(40, 60), 1, 1, new Spacing(2, 2, 2, 2)) });
+        var result = new NestJobRunner(LegacyPlateNesterAdapter.Create).Solve(job);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(new StockUsage("sheet", 1, 0), Assert.Single(result.StockUsage));
+        var pose = Assert.Single(Assert.Single(result.Plates).Placements);
+        var output = NestResultMaterializer.Materialize(job, result);
+        var physicalPlate = Assert.Single(output.Nest.Plates);
+        var placed = Assert.Single(physicalPlate.Parts);
+        Assert.Equal(1, physicalPlate.Quantity);
+        Assert.Same(output.DrawingsByPartId["rectangle"], placed.BaseDrawing);
+        Assert.Equal(pose.X, placed.Location.X);
+        Assert.Equal(pose.Y, placed.Location.Y);
+        Assert.Equal(pose.Rotation, placed.Rotation, 10);
+        Assert.Equal(1, placed.BaseDrawing.Quantity.Nested);
+        Assert.Equal(0, drawing.Quantity.Nested);
+        Assert.Equal(1, drawing.Quantity.Required);
+        var bounds = placed.BoundingBox;
+        var work = physicalPlate.WorkArea();
+        Assert.True(bounds.Left >= work.Left - 1e-6 && bounds.Bottom >= work.Bottom - 1e-6);
+        Assert.True(bounds.Right <= work.Right + 1e-6 && bounds.Top <= work.Top + 1e-6);
+    }
+
+    [Fact]
+    public void MaterializationRotatesAboutSnapshotOriginThenTranslates()
+    {
+        var program = TestDrawingFactory.Rectangle();
+        program.Offset(-5, 3);
+        var job = new NestJob(new[] { new NestJobPart("p", PartGeometrySnapshot.FromProgram(program), 1) },
+            FiniteStockJobTests.Job(1).Plates);
+        var result = new NestJobRunner(_ => new FiniteStockJobTests.Nester(_ => new PlateCandidate(new[]
+            { new NestJobPlacement("p", 0, 23, 31, 0.7) }))).Solve(job);
+        var output = NestResultMaterializer.Materialize(job, result);
+        var part = output.Nest.Plates[0].Parts[0];
+        var expected = new Vector(-5, 3).Rotate(0.7);
+        Assert.Equal(expected.X, ((Motion)part.Program.Codes[0]).EndPoint.X, 10);
+        Assert.Equal(expected.Y, ((Motion)part.Program.Codes[0]).EndPoint.Y, 10);
+        Assert.Equal(new Vector(23, 31), part.Location);
+    }
+
+    private sealed class MutatingEngine(Plate plate, Func<List<NestItem>, List<Part>> nest) : NestEngineBase(plate)
+    {
+        public override string Name => "test";
+        public override string Description => "mutates private demand";
+        public override List<Part> Nest(List<NestItem> items, IProgress<NestProgress> progress, CancellationToken token)
+            => nest(items);
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobCancellationTests.cs

@@ -0,0 +1,114 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestJobCancellationTests
+{
+    [Fact]
+    public void PreTrialCancellationSkipsCandidateWorkAndPreservesInput()
+    {
+        using var cancellation = new CancellationTokenSource();
+        cancellation.Cancel();
+        var nester = new CancellableNester(_ => new PlateCandidate(Array.Empty<NestJobPlacement>()));
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 3)), 1);
+        var sourceGeometry = part.Geometry.Motions.ToArray();
+        var stock = new NestPlateStock("stock", new Size(20, 30), 1);
+        var job = new NestJob(new[] { part }, new[] { stock });
+
+        Assert.Throws<OperationCanceledException>(() => new NestJobRunner(_ => nester).Solve(job, token: cancellation.Token));
+
+        Assert.Equal(0, nester.Calls);
+        Assert.Equal(sourceGeometry, job.Parts[0].Geometry.Motions);
+        Assert.Equal(1, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+    }
+
+    [Fact]
+    public void CancellationDuringCandidateThrowsWithoutCommitOrInputMutation()
+    {
+        using var cancellation = new CancellationTokenSource();
+        var reports = new List<NestJobProgress>();
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 3)), 1);
+        var sourceGeometry = part.Geometry.Motions.ToArray();
+        var stock = new NestPlateStock("stock", new Size(20, 30), 1);
+        var job = new NestJob(new[] { part }, new[] { stock });
+        var nester = new CancellableNester((_, token) =>
+        {
+            cancellation.Cancel();
+            token.ThrowIfCancellationRequested();
+            return new PlateCandidate(Array.Empty<NestJobPlacement>());
+        });
+
+        Assert.Throws<OperationCanceledException>(() => new NestJobRunner(_ => nester)
+            .Solve(job, new InlineProgress(reports.Add), cancellation.Token));
+
+        Assert.Equal(1, nester.Calls);
+        Assert.DoesNotContain(reports, report => report.Stage == NestJobStage.PlateCommitted);
+        Assert.Equal(sourceGeometry, job.Parts[0].Geometry.Motions);
+        Assert.Equal(1, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+    }
+
+    [Fact]
+    public void LegacyProgressIsWrappedWithCurrentCandidateContext()
+    {
+        var reports = new List<NestJobProgress>();
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 3)), 1);
+        var job = new NestJob(new[] { part }, new[] { new NestPlateStock("stock", new Size(20, 30), 1) });
+        var runner = new NestJobRunner(_ => new LegacyPlateNesterAdapter(plate => new ReportingEngine(plate)));
+
+        var result = runner.Solve(job, new InlineProgress(reports.Add));
+
+        Assert.Equal(NestJobStopReason.NoPlacementFound, result.StopReason);
+        var legacy = Assert.Single(reports.Where(report => report.LegacyProgress != null));
+        Assert.Equal(NestJobStage.EvaluatingCandidate, legacy.Stage);
+        Assert.Equal("stock", legacy.StockId);
+        Assert.Equal(0, legacy.PlateIndex);
+        Assert.Equal(0, legacy.CommittedPlates);
+        Assert.Equal(0, legacy.CommittedParts);
+        Assert.Equal("legacy detail", legacy.LegacyProgress!.Description);
+    }
+
+    private sealed class InlineProgress(Action<NestJobProgress> report) : IProgress<NestJobProgress>
+    {
+        public void Report(NestJobProgress value) => report(value);
+    }
+
+    private sealed class CancellableNester : IPlateNester
+    {
+        private readonly Func<PlatePlacementRequest, CancellationToken, PlateCandidate> place;
+
+        public CancellableNester(Func<PlatePlacementRequest, PlateCandidate> place)
+        {
+            this.place = (request, _) => place(request);
+        }
+
+        public CancellableNester(Func<PlatePlacementRequest, CancellationToken, PlateCandidate> place)
+        {
+            this.place = place;
+        }
+
+        public int Calls { get; private set; }
+
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default)
+        {
+            Calls++;
+            return place(request, token);
+        }
+    }
+
+    private sealed class ReportingEngine(Plate plate) : NestEngineBase(plate)
+    {
+        public override string Name => "reporting";
+        public override string Description => "reports progress";
+
+        public override List<Part> Nest(List<NestItem> items, IProgress<NestProgress>? progress,
+            CancellationToken token)
+        {
+            progress?.Report(new NestProgress { Description = "legacy detail" });
+            return new List<Part>();
+        }
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobEngineSelectionTests.cs

@@ -0,0 +1,86 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+/// <summary>
+/// Strategy selection must be instance-scoped: explicit engine choices work without touching the
+/// process-global NestEngineRegistry.ActiveEngineName, and unknown strategies are rejected.
+/// </summary>
+public class NestJobEngineSelectionTests
+{
+    [Fact]
+    public void ExplicitDefaultAndStripSelectionsDoNotTouchGlobalRegistry()
+    {
+        var original = NestEngineRegistry.ActiveEngineName;
+        var job = FiniteStockJobTests.Job(1);
+
+        var defaultResult = new NestJobRunner(PlateNesterFactory.Create).Solve(job);
+        Assert.Equal(NestJobStatus.Complete, defaultResult.Status);
+
+        var stripResult = new NestJobRunner(PlateNesterFactory.Create)
+            .Solve(new NestJob(job.Parts, job.Plates, new NestJobOptions("Strip")));
+        Assert.Equal(NestJobStatus.Complete, stripResult.Status);
+
+        Assert.Equal(original, NestEngineRegistry.ActiveEngineName);
+    }
+
+    [Fact]
+    public void FactoryResolvesNamedEnginesWithoutGlobalState()
+    {
+        var original = NestEngineRegistry.ActiveEngineName;
+        var defaultNester = PlateNesterFactory.Create("Default");
+        var stripNester = PlateNesterFactory.Create("Strip");
+        var verticalNester = PlateNesterFactory.Create("Vertical Remnant");
+        var horizontalNester = PlateNesterFactory.Create("Horizontal Remnant");
+
+        Assert.NotNull(defaultNester);
+        Assert.NotNull(stripNester);
+        Assert.NotNull(verticalNester);
+        Assert.NotNull(horizontalNester);
+        Assert.NotSame(defaultNester, stripNester);
+        Assert.Equal(original, NestEngineRegistry.ActiveEngineName);
+    }
+
+    [Fact]
+    public void UnknownStrategyIsRejected()
+    {
+        Assert.Throws<NotSupportedException>(() => PlateNesterFactory.Create("Not A Real Engine"));
+        var job = FiniteStockJobTests.Job(1);
+        Assert.Throws<NotSupportedException>(() =>
+            new NestJobRunner(key => throw new NotSupportedException($"Unknown placement strategy: {key}"))
+                .Solve(new NestJob(job.Parts, job.Plates, new NestJobOptions("Bogus"))));
+    }
+
+    [Fact]
+    public void LegacyRegistryPluginsDoNotLeakIntoJobSelection()
+    {
+        // A plugin engine registered through the legacy registry must not become selectable
+        // through the job factory; the new boundary is independent of registry state.
+        NestEngineRegistry.Register("ProbePlugin", "test plugin", plate => new PluginShapeEngine(plate));
+        Assert.Contains(NestEngineRegistry.AvailableEngines, e => e.Name == "ProbePlugin");
+
+        Assert.Throws<NotSupportedException>(() => PlateNesterFactory.Create("ProbePlugin"));
+        Assert.NotNull(PlateNesterFactory.Create("Default"));
+    }
+
+    [Fact]
+    public void StripEngineEndToEndPlacesAndAccounts()
+    {
+        var drawing = new Drawing("strip part", TestDrawingFactory.Rectangle(30, 30));
+        var job = new NestJob(new[] { DrawingJobMapper.FromDrawing("part", drawing, 2) },
+            new[] { new NestPlateStock("s", new Size(90, 90), 1) });
+        var result = new NestJobRunner(PlateNesterFactory.Create)
+            .Solve(new NestJob(job.Parts, job.Plates, new NestJobOptions("Strip")));
+
+        Assert.True(result.Plates.SelectMany(p => p.Placements).Count() >= 1);
+        foreach (var f in result.Fulfillment)
+            Assert.Equal(f.Requested, f.Placed + f.Unplaced);
+    }
+
+    private sealed class PluginShapeEngine(Plate plate) : NestEngineBase(plate)
+    {
+        public override string Name => "ProbePlugin";
+        public override string Description => "registered via legacy registry only";
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobGeometryTests.cs

@@ -0,0 +1,159 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestJobGeometryTests
+{
+    [Fact]
+    public void CandidateOutsideUsableWorkAreaFailsWithoutMutatingInput()
+    {
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 3)), 1);
+        var sourceGeometry = part.Geometry.Motions.ToArray();
+        var stock = new NestPlateStock("stock", new Size(20, 30), 1,
+            edgeSpacing: new Spacing(2, 1, 3, 4));
+        var job = new NestJob(new[] { part }, new[] { stock });
+        var runner = new NestJobRunner(_ => new CandidateNester(new[] { new NestJobPlacement("part", 0, 26, 1, 0) }));
+
+        Assert.Throws<InvalidOperationException>(() => runner.Solve(job));
+
+        Assert.Equal(sourceGeometry, job.Parts[0].Geometry.Motions);
+        Assert.Equal(1, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+    }
+
+    [Theory]
+    [InlineData(1, 0, 0)]
+    [InlineData(2, -11, 0)]
+    [InlineData(3, -11, -7)]
+    [InlineData(4, 0, -7)]
+    public void UnequalRectanglesFitAtEachQuadrantsUsableOrigin(int quadrant, double x, double y)
+    {
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 3)), 1);
+        var stock = new NestPlateStock("stock", new Size(7, 11), 1, quadrant: quadrant);
+        var job = new NestJob(new[] { part }, new[] { stock });
+
+        var result = Solve(job, new NestJobPlacement("part", 0, x, y, 0));
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(new NestJobPlacement("part", 0, x, y, 0), Assert.Single(result.Plates[0].Placements));
+    }
+
+    [Fact]
+    public void FixedAndBoundedRotationPoliciesRejectDisallowedAngles()
+    {
+        var fixedPart = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 2)), 1,
+            rotation: RotationPolicy.Fixed(System.Math.PI / 2));
+        var fixedJob = new NestJob(new[] { fixedPart }, new[] { new NestPlateStock("stock", new Size(10, 10), 1) });
+        Assert.Throws<InvalidOperationException>(() => Solve(fixedJob, new NestJobPlacement("part", 0, 0, 0, 0)));
+
+        var fixedResult = Solve(fixedJob, new NestJobPlacement("part", 0, 2, 0, System.Math.PI / 2));
+        Assert.Equal(NestJobStatus.Complete, fixedResult.Status);
+
+        var boundedPart = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 2)), 1,
+            rotation: RotationPolicy.BoundedSweep(0, System.Math.PI / 2, System.Math.PI / 4));
+        var boundedJob = new NestJob(new[] { boundedPart }, new[] { new NestPlateStock("stock", new Size(10, 10), 1) });
+        Assert.Throws<InvalidOperationException>(() => Solve(boundedJob,
+            new NestJobPlacement("part", 0, 2, 0, System.Math.PI / 3)));
+
+        var boundedResult = Solve(boundedJob, new NestJobPlacement("part", 0, 2, 0, System.Math.PI / 4));
+        Assert.Equal(NestJobStatus.Complete, boundedResult.Status);
+    }
+
+    [Fact]
+    public void EdgeTouchingIsAllowedAtZeroSpacingAndRejectedAtPositiveSpacing()
+    {
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 2);
+        var touching = new[]
+        {
+            new NestJobPlacement("part", 0, 0, 0, 0),
+            new NestJobPlacement("part", 1, 2, 0, 0)
+        };
+        var zeroSpacing = new NestJob(new[] { part }, new[] { new NestPlateStock("stock", new Size(10, 10), 1) });
+        var positiveSpacing = new NestJob(new[] { part }, new[] { new NestPlateStock("stock", new Size(10, 10), 1, 0.1) });
+
+        Assert.Equal(NestJobStatus.Complete, Solve(zeroSpacing, touching).Status);
+        Assert.Throws<InvalidOperationException>(() => Solve(positiveSpacing, touching));
+    }
+
+    [Fact]
+    public void OverlapAndContainmentAreRejected()
+    {
+        var outer = new NestJobPart("outer", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(6, 6)), 1);
+        var inner = new NestJobPart("inner", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 1);
+        var job = new NestJob(new[] { outer, inner }, new[] { new NestPlateStock("stock", new Size(20, 20), 1) });
+
+        Assert.Throws<InvalidOperationException>(() => Solve(job,
+            new NestJobPlacement("outer", 0, 0, 0, 0),
+            new NestJobPlacement("inner", 0, 2, 2, 0)));
+    }
+
+    [Fact]
+    public void EmptyStockStopsWithoutCallingCandidateNester()
+    {
+        var nester = new CountingNester();
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 1);
+        var job = new NestJob(new[] { part }, Array.Empty<NestPlateStock>());
+
+        var result = new NestJobRunner(_ => nester).Solve(job);
+
+        Assert.Equal(NestJobStopReason.StockExhausted, result.StopReason);
+        Assert.Equal(0, nester.Calls);
+    }
+
+    [Theory]
+    [InlineData("Default")]
+    [InlineData("Strip")]
+    public void RealEngineSmokeCasesPreserveInputAndProduceSafeAccounting(string strategy)
+    {
+        var drawing = new Drawing("generated rectangle", TestDrawingFactory.Rectangle(6, 4));
+        var part = DrawingJobMapper.FromDrawing("part", drawing, 3);
+        var sourceGeometry = part.Geometry.Motions.ToArray();
+        var stock = new NestPlateStock("stock", new Size(30, 50), 1, 1, new Spacing(1, 1, 1, 1));
+        var job = new NestJob(new[] { part }, new[] { stock }, new NestJobOptions(strategy));
+
+        var result = new NestJobRunner(PlateNesterFactory.Create).Solve(job);
+        var materialized = NestResultMaterializer.Materialize(job, result);
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.All(result.Fulfillment, fulfillment => Assert.Equal(fulfillment.Requested,
+            fulfillment.Placed + fulfillment.Unplaced));
+        Assert.Equal(sourceGeometry, job.Parts[0].Geometry.Motions);
+        Assert.Equal(3, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+        Assert.All(materialized.Nest.Plates, plate =>
+        {
+            var workArea = plate.WorkArea();
+            Assert.All(plate.Parts, placed =>
+            {
+                Assert.True(placed.BoundingBox.Left >= workArea.Left - 1e-6);
+                Assert.True(placed.BoundingBox.Right <= workArea.Right + 1e-6);
+                Assert.True(placed.BoundingBox.Bottom >= workArea.Bottom - 1e-6);
+                Assert.True(placed.BoundingBox.Top <= workArea.Top + 1e-6);
+            });
+            for (var left = 0; left < plate.Parts.Count; left++)
+                for (var right = left + 1; right < plate.Parts.Count; right++)
+                    Assert.False(plate.Parts[left].Intersects(plate.Parts[right], out _));
+        });
+    }
+
+    private static NestJobResult Solve(NestJob job, params NestJobPlacement[] placements) =>
+        new NestJobRunner(_ => new CandidateNester(placements)).Solve(job);
+
+    private sealed class CandidateNester(IEnumerable<NestJobPlacement> placements) : IPlateNester
+    {
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default) => new(placements);
+    }
+
+    private sealed class CountingNester : IPlateNester
+    {
+        public int Calls { get; private set; }
+
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default)
+        {
+            Calls++;
+            return new PlateCandidate(Array.Empty<NestJobPlacement>());
+        }
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobIdentityTests.cs

@@ -0,0 +1,149 @@
+using OpenNest.CNC;
+using OpenNest.Engine.Fill;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+/// <summary>
+/// Names are never identity: two distinct drawings that share a display name must keep
+/// independent quantities, and two requirements that share one source drawing must not
+/// cross-count each other's placements through the legacy engine paths.
+/// </summary>
+public class NestJobIdentityTests
+{
+    [Fact]
+    public void DistinctDrawingsWithSameNameKeepIndependentQuantitiesInRealEngine()
+    {
+        var a = new Drawing("identical", TestDrawingFactory.Rectangle(40, 40));
+        var b = new Drawing("identical", TestDrawingFactory.Rectangle(40, 40));
+        var job = new NestJob(new[]
+        {
+            DrawingJobMapper.FromDrawing("a", a, 2),
+            DrawingJobMapper.FromDrawing("b", b, 2)
+        }, new[] { new NestPlateStock("s", new Size(90, 90), 1) });
+
+        var result = new NestJobRunner(LegacyPlateNesterAdapter.Create).Solve(job);
+
+        // Every placed part maps to a known requirement ID; no part is invented or cross-counted.
+        Assert.True(result.Plates.SelectMany(p => p.Placements).All(p => p.PartId is "a" or "b"));
+        var counts = result.Plates.SelectMany(p => p.Placements).GroupBy(p => p.PartId)
+            .ToDictionary(g => g.Key, g => g.Count());
+        foreach (var (id, placed) in counts)
+            Assert.True(placed <= 2, $"Requirement {id} placed {placed} > requested 2");
+
+        // Fulfillment conservation for both IDs.
+        foreach (var f in result.Fulfillment)
+            Assert.Equal(f.Requested, f.Placed + f.Unplaced);
+    }
+
+    [Fact]
+    public void TwoRequirementsOnSameSourceDrawingKeepIndependentQuantities()
+    {
+        var source = new Drawing("shared", TestDrawingFactory.Rectangle(30, 30));
+        var job = new NestJob(new[]
+        {
+            DrawingJobMapper.FromDrawing("first", source, 2),
+            DrawingJobMapper.FromDrawing("second", source, 2)
+        }, new[] { new NestPlateStock("s", new Size(90, 90), 1) });
+
+        var result = new NestJobRunner(LegacyPlateNesterAdapter.Create).Solve(job);
+
+        Assert.Equal(new[] { "first", "second" }, result.Fulfillment.Select(f => f.PartId));
+        foreach (var f in result.Fulfillment)
+            Assert.Equal(f.Requested, f.Placed + f.Unplaced);
+
+        // Output drawings are distinct even though the input is the same Drawing instance.
+        var output = NestResultMaterializer.Materialize(job, result);
+        Assert.NotSame(output.DrawingsByPartId["first"], output.DrawingsByPartId["second"]);
+        // Caller source is untouched.
+        Assert.Equal(0, source.Quantity.Nested);
+    }
+
+    [Fact]
+    public void EngineDeductionCountsByDrawingReferenceNotName()
+    {
+        // Plate 90x40 fits exactly two 40x40 parts. The engine fills item A with both and
+        // starves item B. Name-based deduction would then zero BOTH items (the two placed
+        // parts carry the shared name, so each item counts 2 as "its own"). Reference-based
+        // deduction leaves B at 2.
+        var a = new Drawing("dup", TestDrawingFactory.Rectangle(40, 40));
+        var b = new Drawing("dup", TestDrawingFactory.Rectangle(40, 40));
+        var plate = new Plate(new Size(90, 40));
+        var items = new List<NestItem>
+        {
+            new() { Drawing = a, Quantity = 2 },
+            new() { Drawing = b, Quantity = 2 }
+        };
+        // Place exactly 2 parts from item A and none from item B, then run the base-class
+        // deduction. Deterministic regardless of any fill heuristic.
+        var placed = new StarvingProbe(plate).Nest(items, null, default);
+
+        var aPlaced = placed.Count(p => ReferenceEquals(p.BaseDrawing, a));
+        var bPlaced = placed.Count(p => ReferenceEquals(p.BaseDrawing, b));
+        Assert.Equal(2, placed.Count);
+        Assert.Equal(2, aPlaced);
+        Assert.Equal(0, bPlaced);
+
+        // Invariant: remaining = requested - own placements. Under name-based counting,
+        // both items would read 0 here because the two placed parts match the shared name.
+        Assert.Equal(0, items[0].Quantity);
+        Assert.Equal(2, items[1].Quantity);
+    }
+
+    [Fact]
+    public void SameNameSinglesAreBothReturnedByPackPhase()
+    {
+        var a = new Drawing("samesingle", TestDrawingFactory.Rectangle(30, 30));
+        var b = new Drawing("samesingle", TestDrawingFactory.Rectangle(30, 30));
+        var plate = new Plate(new Size(100, 100));
+        var items = new List<NestItem>
+        {
+            new() { Drawing = a, Quantity = 1 },
+            new() { Drawing = b, Quantity = 1 }
+        };
+        var placed = new BaseNestEngineProbe(plate).Nest(items, null, default);
+        Assert.Equal(2, placed.Count);
+        Assert.Equal(new[] { 0, 0 }, new[] { items[0].Quantity, items[1].Quantity });
+    }
+
+    private sealed class BaseNestEngineProbe(Plate plate) : NestEngineBase(plate)
+    {
+        public override string Name => "probe";
+        public override string Description => "probe";
+        public override List<Part> Fill(NestItem item, Box workArea,
+            IProgress<NestProgress> progress, CancellationToken token)
+            => new DefaultNestEngine(Plate).Fill(item, workArea, progress, token);
+        public override List<Part> Fill(List<Part> groupParts, Box workArea,
+            IProgress<NestProgress> progress, CancellationToken token)
+            => new DefaultNestEngine(Plate).Fill(groupParts, workArea, progress, token);
+        public override List<Part> PackArea(Box box, List<NestItem> items,
+            IProgress<NestProgress> progress, CancellationToken token)
+            => new DefaultNestEngine(Plate).PackArea(box, items, progress, token);
+    }
+
+    /// <summary>Places exactly 2 parts from the first multi-quantity item and none from the
+    /// rest, forcing the base-class deduction to run on an asymmetric placement result.</summary>
+    private sealed class StarvingProbe(Plate plate) : NestEngineBase(plate)
+    {
+        private int _first = -1;
+        public override string Name => "starving";
+        public override string Description => "starves all but the first fill item";
+        public override List<Part> Fill(NestItem item, Box workArea,
+            IProgress<NestProgress> progress, CancellationToken token)
+        {
+            if (_first < 0) _first = 1;
+            if (_first++ != 1)
+                return new List<Part>();
+            var parts = new List<Part>();
+            var x = 0.0;
+            for (var i = 0; i < 2; i++)
+            {
+                var p = new Part(item.Drawing);
+                p.Offset(new Vector(x, 0));
+                x += item.Drawing.Program.BoundingBox().Width + Plate.PartSpacing;
+                parts.Add(p);
+            }
+            return parts;
+        }
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobRunnerTests.cs

@@ -0,0 +1,102 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestJobRunnerTests
+{
+    [Fact]
+    public void EmptyJobCompletesWithoutPlatesOrPlacementWork()
+    {
+        var fake = new FakePlateNester();
+        var factoryCalls = 0;
+        var runner = new NestJobRunner(_ => { factoryCalls++; return fake; });
+        var job = new NestJob(Array.Empty<NestJobPart>(), new[]
+        {
+            new NestPlateStock("finite", new Size(100, 200), 2),
+            new NestPlateStock("unlimited", new Size(100, 200))
+        });
+
+        var result = runner.Solve(job);
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(NestJobStopReason.Completed, result.StopReason);
+        Assert.Empty(result.Plates);
+        Assert.Empty(result.Fulfillment);
+        Assert.Collection(result.StockUsage,
+            usage => { Assert.Equal(0, usage.Used); Assert.Equal(2, usage.Remaining); },
+            usage => { Assert.Equal(0, usage.Used); Assert.Null(usage.Remaining); });
+        Assert.Equal(0, factoryCalls);
+        Assert.Equal(0, fake.Calls);
+    }
+
+    [Fact]
+    public void PreCancelledEmptyJobThrows()
+    {
+        using var cancellation = new CancellationTokenSource();
+        cancellation.Cancel();
+        var runner = new NestJobRunner(_ => new FakePlateNester());
+        var job = new NestJob(Array.Empty<NestJobPart>(), Array.Empty<NestPlateStock>());
+        Assert.Throws<OperationCanceledException>(() => runner.Solve(job, token: cancellation.Token));
+    }
+
+    [Fact]
+    public void EmptyStockReturnsIncomplete()
+    {
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle()), 1);
+        var job = new NestJob(new[] { part }, Array.Empty<NestPlateStock>());
+        var runner = new NestJobRunner(_ => new FakePlateNester());
+        var result = runner.Solve(job);
+        Assert.Equal(NestJobStatus.Incomplete, result.Status);
+        Assert.Equal(NestJobStopReason.StockExhausted, result.StopReason);
+        Assert.Equal(1, Assert.Single(result.Fulfillment).Unplaced);
+    }
+
+    [Fact]
+    public void JobOwnsCollectionsSettingsAndExactGeometryIncludingHoleArc()
+    {
+        var program = TestDrawingFactory.Rectangle();
+        program.MoveTo(3.123456789, 4);
+        program.ArcTo(3.123456789, 4, 4, 4, RotationType.CW);
+        var geometry = PartGeometrySnapshot.FromProgram(program);
+        var parts = new List<NestJobPart> { new("p", geometry, 3) };
+        var size = new Size(100, 200);
+        var edges = new Spacing(1, 2, 3, 4);
+        var stocks = new List<NestPlateStock> { new("s", size, 0, 2, edges, 3) };
+        var job = new NestJob(parts, stocks);
+        parts.Clear(); stocks.Clear(); program.Codes.Clear(); size.Width = 0; edges.Left = 999;
+
+        Assert.Single(job.Parts);
+        Assert.Equal(3, job.Parts[0].Quantity);
+        Assert.Equal(7, geometry.Motions.Count);
+        Assert.Equal(CodeType.RapidMove, geometry.Motions[5].Type);
+        Assert.Equal(CodeType.ArcMove, geometry.Motions[6].Type);
+        Assert.Equal(3.123456789, geometry.Motions[6].X);
+        Assert.Equal(4, geometry.Motions[6].CenterX);
+        Assert.Equal(RotationType.CW, geometry.Motions[6].Rotation);
+        Assert.Equal(100, job.Plates[0].Size.Width);
+        Assert.Equal(1, job.Plates[0].EdgeSpacing.Left);
+        Assert.Equal(0, job.Plates[0].Quantity);
+        Assert.Equal("Default", job.Options.PlacementStrategy);
+        Assert.Throws<NotSupportedException>(() => ((IList<NestJobPart>)job.Parts).Clear());
+    }
+
+    [Fact]
+    public void LegacyZeroStepMeansAutomaticNotFixed()
+    {
+        Assert.Equal(RotationPolicyKind.Automatic, RotationPolicy.FromLegacy(0, 1, 2).Kind);
+        Assert.Equal(RotationPolicyKind.Fixed, RotationPolicy.Fixed(1).Kind);
+        Assert.Equal(RotationPolicyKind.BoundedSweep, RotationPolicy.BoundedSweep(0, 1, 0.5).Kind);
+    }
+
+    private sealed class FakePlateNester : IPlateNester
+    {
+        public int Calls { get; private set; }
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default)
+        {
+            Calls++;
+            return new PlateCandidate(Array.Empty<NestJobPlacement>());
+        }
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobStockSelectionTests.cs

@@ -0,0 +1,119 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestJobStockSelectionTests
+{
+    [Fact]
+    public void LaterFittingStockWinsWhenFirstStockCannotPlace()
+    {
+        var result = Solve(new[] { Part("p", 1) }, new[] { Stock("small", 10, 10, 1), Stock("large", 20, 20, 1) },
+            request => request.Stock.Id == "large" ? Candidate(request, "p") : Empty());
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal("large", Assert.Single(result.Plates).StockId);
+    }
+
+    [Fact]
+    public void ExhaustedLargeStockIsNotRecreatedWhileSmallerStockServesSmallParts()
+    {
+        var result = Solve(new[] { Part("large", 1, 0), Part("small", 2, 1) },
+            new[] { Stock("large", 20, 20, 1), Stock("small", 10, 10, 2) }, request => request.Stock.Id switch
+            {
+                "large" when request.Parts.Any(part => part.Id == "large") => Candidate(request, "large"),
+                "small" when request.Parts.Any(part => part.Id == "small") => Candidate(request, "small"),
+                _ => Empty()
+            });
+
+        Assert.Equal(new[] { "large", "small", "small" }, result.Plates.Select(plate => plate.StockId));
+        Assert.Collection(result.StockUsage,
+            usage => Assert.Equal(new StockUsage("large", 1, 0), usage),
+            usage => Assert.Equal(new StockUsage("small", 2, 0), usage));
+    }
+
+    [Fact]
+    public void EqualDimensionsWithDifferentStockIdsRemainIndependent()
+    {
+        var result = Solve(new[] { Part("p", 2) }, new[] { Stock("first", 10, 10, 1), Stock("second", 10, 10, 1) },
+            request => Candidate(request, "p"));
+
+        Assert.Equal(new[] { "first", "second" }, result.Plates.Select(plate => plate.StockId));
+        Assert.Equal(new[] { new StockUsage("first", 1, 0), new StockUsage("second", 1, 0) }, result.StockUsage);
+    }
+
+    [Fact]
+    public void LosingTrialsDoNotConsumeStockPartsOrDrawingCounters()
+    {
+        var calls = new List<(string Stock, int Quantity)>();
+        var result = Solve(new[] { Part("p", 2) }, new[] { Stock("wide", 20, 20, 2), Stock("narrow", 10, 10, 2) }, request =>
+        {
+            calls.Add((request.Stock.Id, request.Parts.Single().Quantity));
+            return request.Stock.Id == "wide" ? Candidate(request, "p", 0, 100) : Candidate(request, "p", 0, 0);
+        });
+
+        Assert.Equal(new[] { "narrow", "narrow" }, result.Plates.Select(plate => plate.StockId));
+        Assert.Equal(new[] { ("wide", 2), ("narrow", 2), ("wide", 1), ("narrow", 1) }, calls);
+        Assert.Equal(new StockUsage("wide", 0, 2), result.StockUsage[0]);
+        Assert.Equal(new StockUsage("narrow", 2, 0), result.StockUsage[1]);
+        Assert.Equal(new[] { 0, 1 }, result.Plates.SelectMany(plate => plate.Placements).Select(placement => placement.InstanceIndex));
+    }
+
+    [Fact]
+    public void CandidatePriorityAreaEnvelopeAndInputOrderAreComparedInDocumentedOrder()
+    {
+        var priority = Solve(new[] { Part("high", 1, 0), Part("low", 1, 1) }, new[] { Stock("a", 10, 10, 1), Stock("b", 10, 10, 1) },
+            request => request.Stock.Id == "a" ? Candidate(request, "low") : Candidate(request, "high"));
+        var area = Solve(new[] { Part("p", 1) }, new[] { Stock("large", 20, 20, 1), Stock("small", 10, 10, 1) },
+            request => Candidate(request, "p"));
+        var envelope = Solve(new[] { Part("p", 2) }, new[] { Stock("a", 10, 10, 1), Stock("b", 10, 10, 1) },
+            request => request.Stock.Id == "a" ? CandidatePair("p", 4, 5) : CandidatePair("p", 4, 0));
+        var inputOrder = Solve(new[] { Part("p", 1) }, new[] { Stock("first", 10, 10, 1), Stock("second", 10, 10, 1) },
+            request => Candidate(request, "p"));
+
+        Assert.Equal("b", priority.Plates[0].StockId);
+        Assert.Equal("small", area.Plates[0].StockId);
+        Assert.Equal("b", envelope.Plates[0].StockId);
+        Assert.Equal("first", inputOrder.Plates[0].StockId);
+    }
+
+    [Fact]
+    public void UnlimitedStockStopsWhenDemandIsFulfilledAndPlateLimitLeavesLeftovers()
+    {
+        var unlimited = Solve(new[] { Part("p", 2) }, new[] { Stock("u", 10, 10, null) }, request => Candidate(request, "p"));
+        var limited = Solve(new[] { Part("p", 3) }, new[] { Stock("u", 10, 10, null) }, request => Candidate(request, "p"), new NestJobOptions(maxPlates: 2));
+
+        Assert.Equal(NestJobStopReason.Completed, unlimited.StopReason);
+        Assert.Equal(2, unlimited.Plates.Count);
+        Assert.Equal(NestJobStopReason.PlateLimitReached, limited.StopReason);
+        Assert.Equal(new PartFulfillment("p", 3, 2, 1), Assert.Single(limited.Fulfillment));
+    }
+
+    private static NestJobResult Solve(IEnumerable<NestJobPart> parts, IEnumerable<NestPlateStock> stock,
+        Func<PlatePlacementRequest, PlateCandidate> place, NestJobOptions? options = null) =>
+        new NestJobRunner(_ => new Nester(place)).Solve(new NestJob(parts, stock, options));
+
+    private static NestJobPart Part(string id, int quantity, int priority = 0) =>
+        new(id, PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(4, 5)), quantity, priority);
+
+    private static NestPlateStock Stock(string id, double width, double length, int? quantity) =>
+        new(id, new Size(width, length), quantity);
+
+    private static PlateCandidate Candidate(PlatePlacementRequest request, string id, double firstX = 0, double secondX = 0)
+    {
+        return new PlateCandidate(new[] { new NestJobPlacement(id, 0, firstX, 0, 0) });
+    }
+
+    private static PlateCandidate CandidatePair(string id, double secondX, double secondY) => new(new[]
+    {
+        new NestJobPlacement(id, 0, 0, 0, 0),
+        new NestJobPlacement(id, 1, secondX, secondY, 0)
+    });
+
+    private static PlateCandidate Empty() => new(Array.Empty<NestJobPlacement>());
+
+    private sealed class Nester(Func<PlatePlacementRequest, PlateCandidate> place) : IPlateNester
+    {
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default) => place(request);
+    }
+}

OpenNest.Engine.Tests/Jobs/NestJobValidationTests.cs

@@ -0,0 +1,120 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+public class NestJobValidationTests
+{
+    [Fact]
+    public void IncrementalContoursUseAccumulatedCoordinates()
+    {
+        var program = new Program(Mode.Incremental);
+        program.MoveTo(0, 0);
+        program.LineTo(4, 0);
+        program.LineTo(0, 3);
+        program.LineTo(-4, 0);
+        program.LineTo(0, -3);
+        var job = new NestJob(new[]
+        {
+            new NestJobPart("part", PartGeometrySnapshot.FromProgram(program), 1)
+        }, new[] { new NestPlateStock("stock", new Size(10, 10), 1) });
+
+        var result = Solve(job, new NestJobPlacement("part", 0, 0, 0, 0));
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(new PartFulfillment("part", 1, 1, 0), Assert.Single(result.Fulfillment));
+    }
+
+    [Fact]
+    public void CandidateInsideAnotherRequirementsHoleDoesNotOverlapMaterial()
+    {
+        var outer = new NestJobPart("outer", PartGeometrySnapshot.FromProgram(RectangleWithHole()), 1);
+        var inner = new NestJobPart("inner", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 1);
+        var job = new NestJob(new[] { outer, inner }, new[] { new NestPlateStock("stock", new Size(20, 20), 1) });
+
+        var result = Solve(job,
+            new NestJobPlacement("outer", 0, 0, 0, 0),
+            new NestJobPlacement("inner", 0, 4, 4, 0));
+
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Single(result.Plates);
+        Assert.Equal(2, result.Plates[0].Placements.Count);
+    }
+
+    [Fact]
+    public void UnknownOrOverproducingCandidateFailsBeforeCommitWithoutChangingInput()
+    {
+        var reports = new List<NestJobProgress>();
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 1);
+        var stock = new NestPlateStock("stock", new Size(20, 20), 1);
+        var job = new NestJob(new[] { part }, new[] { stock });
+        var runner = new NestJobRunner(_ => new CandidateNester(new[]
+        {
+            new NestJobPlacement("part", 0, 0, 0, 0),
+            new NestJobPlacement("unknown", 0, 4, 0, 0)
+        }));
+
+        Assert.Throws<InvalidOperationException>(() => runner.Solve(job, new InlineProgress(reports.Add)));
+
+        Assert.Equal(1, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+        Assert.DoesNotContain(reports, report => report.Stage == NestJobStage.PlateCommitted);
+    }
+
+    [Fact]
+    public void CandidateThatOverproducesIsRejectedRatherThanClamped()
+    {
+        var part = new NestJobPart("part", PartGeometrySnapshot.FromProgram(TestDrawingFactory.Rectangle(2, 2)), 1);
+        var job = new NestJob(new[] { part }, new[] { new NestPlateStock("stock", new Size(20, 20), 1) });
+
+        Assert.Throws<InvalidOperationException>(() => Solve(job,
+            new NestJobPlacement("part", 0, 0, 0, 0),
+            new NestJobPlacement("part", 1, 4, 0, 0)));
+
+        Assert.Equal(1, job.Parts[0].Quantity);
+        Assert.Equal(1, job.Plates[0].Quantity);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void OpenOrZeroLengthContoursAreRejected(bool zeroLength)
+    {
+        var program = new Program();
+        program.MoveTo(0, 0);
+        program.LineTo(4, 0);
+        if (zeroLength) program.LineTo(4, 0);
+        program.LineTo(4, 3);
+        program.LineTo(0, 3);
+        if (zeroLength) program.LineTo(0, 0);
+        var job = new NestJob(new[] { new NestJobPart("part", PartGeometrySnapshot.FromProgram(program), 1) },
+            new[] { new NestPlateStock("stock", new Size(20, 20), 1) });
+
+        Assert.Throws<ArgumentException>(() => new NestJobRunner(_ => new CandidateNester(Array.Empty<NestJobPlacement>())).Solve(job));
+    }
+
+    private static NestJobResult Solve(NestJob job, params NestJobPlacement[] placements) =>
+        new NestJobRunner(_ => new CandidateNester(placements)).Solve(job);
+
+    private static Program RectangleWithHole()
+    {
+        var program = TestDrawingFactory.Rectangle(10, 10);
+        program.MoveTo(3, 3);
+        program.LineTo(3, 7);
+        program.LineTo(7, 7);
+        program.LineTo(7, 3);
+        program.LineTo(3, 3);
+        return program;
+    }
+
+    private sealed class CandidateNester(IEnumerable<NestJobPlacement> placements) : IPlateNester
+    {
+        public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress>? progress = null,
+            CancellationToken token = default) => new(placements);
+    }
+
+    private sealed class InlineProgress(Action<NestJobProgress> report) : IProgress<NestJobProgress>
+    {
+        public void Report(NestJobProgress value) => report(value);
+    }
+}

OpenNest.Engine.Tests/Jobs/TestDrawingFactory.cs

@@ -0,0 +1,17 @@
+using OpenNest.CNC;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+internal static class TestDrawingFactory
+{
+    public static Program Rectangle(double width = 10, double length = 20)
+    {
+        var program = new Program();
+        program.MoveTo(0, 0);
+        program.LineTo(width, 0);
+        program.LineTo(width, length);
+        program.LineTo(0, length);
+        program.LineTo(0, 0);
+        return program;
+    }
+}

OpenNest.Engine.Tests/OpenNest.Engine.Tests.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="xunit" Version="2.5.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" />
+  </ItemGroup>
+  <ItemGroup>
+    <Using Include="Xunit" />
+    <ProjectReference Include="../OpenNest.Engine/OpenNest.Engine.csproj" />
+  </ItemGroup>
+</Project>

OpenNest.Engine/Fill/IterativeShrinkFiller.cs

@@ -1,6 +1,7 @@
 using OpenNest.Geometry;
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -130,17 +131,13 @@ namespace OpenNest.Engine.Fill
 
             var placed = filler.FillItems(workItems, shrinkWrapper, token);
 
-            // Build leftovers: compare placed count to original quantities.
-            // RemnantFiller.FillItems does NOT mutate NestItem.Quantity.
+            // Build leftovers: compare placed count to original quantities by drawing
+            // reference. RemnantFiller.FillItems does NOT mutate NestItem.Quantity.
             var leftovers = new List<NestItem>();
             foreach (var item in items)
             {
-                var placedCount = 0;
-                foreach (var p in placed)
-                {
-                    if (p.BaseDrawing.Name == item.Drawing.Name)
-                        placedCount++;
-                }
+                var placedCount = placed.Count(p =>
+                    ReferenceEquals(p.BaseDrawing, item.Drawing));
 
                 if (item.Quantity <= 0)
                     continue; // unlimited items are always "satisfied" — no leftover

OpenNest.Engine/Fill/RemnantFiller.cs

@@ -58,20 +58,20 @@ namespace OpenNest.Engine.Fill
             return allParts;
         }
 
-        private static Dictionary<string, int> BuildLocalQuantities(List<NestItem> items)
+        private static Dictionary<Drawing, int> BuildLocalQuantities(List<NestItem> items)
         {
-            var localQty = new Dictionary<string, int>(items.Count);
+            var localQty = new Dictionary<Drawing, int>(items.Count, ReferenceEqualityComparer.Instance);
             foreach (var item in items)
-                localQty[item.Drawing.Name] = item.Quantity;
+                localQty[item.Drawing] = item.Quantity;
             return localQty;
         }
 
-        private static double FindMinItemDimension(List<NestItem> items, Dictionary<string, int> localQty)
+        private static double FindMinItemDimension(List<NestItem> items, Dictionary<Drawing, int> localQty)
         {
             var minDim = double.MaxValue;
             foreach (var item in items)
             {
-                if (localQty[item.Drawing.Name] <= 0)
+                if (localQty[item.Drawing] <= 0)
                     continue;
                 var bb = item.Drawing.Program.BoundingBox();
                 var dim = System.Math.Min(bb.Width, bb.Length);
@@ -84,7 +84,7 @@ namespace OpenNest.Engine.Fill
         private bool TryFillOneItem(
             List<NestItem> items,
             List<Box> freeBoxes,
-            Dictionary<string, int> localQty,
+            Dictionary<Drawing, int> localQty,
             Func<NestItem, Box, List<Part>> fillFunc,
             List<Part> allParts,
             CancellationToken token)
@@ -94,7 +94,7 @@ namespace OpenNest.Engine.Fill
                 if (token.IsCancellationRequested)
                     return false;
 
-                var qty = localQty[item.Drawing.Name];
+                var qty = localQty[item.Drawing];
                 if (qty <= 0)
                     continue;
 
@@ -110,7 +110,7 @@ namespace OpenNest.Engine.Fill
                     RemoveTopmostPart(placed);
 
                 allParts.AddRange(placed);
-                localQty[item.Drawing.Name] = System.Math.Max(0, qty - placed.Count);
+                localQty[item.Drawing] = System.Math.Max(0, qty - placed.Count);
 
                 // Add the envelope of all placed parts as a single obstacle
                 // rather than individual bounding boxes, preventing the

OpenNest.Engine/Jobs/Adapters/DrawingJobMapper.cs

@@ -0,0 +1,77 @@
+using System;
+using OpenNest.CNC;
+
+namespace OpenNest;
+
+/// <summary>Explicit-ID input mapping and exact supported-geometry reconstruction. Never retains caller objects.</summary>
+public static class DrawingJobMapper
+{
+    public static NestJobPart FromDrawing(string partId, Drawing drawing, int quantity)
+    {
+        ArgumentNullException.ThrowIfNull(drawing);
+        var constraints = drawing.Constraints;
+        return new NestJobPart(partId, PartGeometrySnapshot.FromProgram(drawing.Program), quantity, drawing.Priority,
+            constraints == null ? RotationPolicy.Automatic :
+                RotationPolicy.FromLegacy(constraints.StepAngle, constraints.StartAngle, constraints.EndAngle));
+    }
+
+    public static NestJobPart FromItem(string partId, NestItem item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        ArgumentNullException.ThrowIfNull(item.Drawing);
+        return new NestJobPart(partId, PartGeometrySnapshot.FromProgram(item.Drawing.Program), item.Quantity,
+            item.Priority, RotationPolicy.FromLegacy(item.StepAngle, item.RotationStart, item.RotationEnd));
+    }
+
+    /// <summary>Available stock is explicit; the legacy plate repeat count is not inventory.</summary>
+    public static NestPlateStock FromPlate(string stockId, Plate plate, int? quantity)
+    {
+        ArgumentNullException.ThrowIfNull(plate);
+        return new NestPlateStock(stockId, plate.Size, quantity, plate.PartSpacing, plate.EdgeSpacing, plate.Quadrant);
+    }
+
+    public static Program ToProgram(PartGeometrySnapshot geometry)
+    {
+        ArgumentNullException.ThrowIfNull(geometry);
+        var program = new Program(geometry.Mode);
+        foreach (var motion in geometry.Motions)
+        {
+            var code = motion.Type switch
+            {
+                CodeType.RapidMove => (Motion)new RapidMove(motion.X, motion.Y),
+                CodeType.LinearMove => new LinearMove(motion.X, motion.Y) { Layer = motion.Layer },
+                CodeType.ArcMove => new ArcMove(motion.X, motion.Y, motion.CenterX, motion.CenterY, motion.Rotation)
+                    { Layer = motion.Layer },
+                _ => throw new NotSupportedException("Unsupported snapshot motion.")
+            };
+            code.Suppressed = motion.Suppressed;
+            program.Codes.Add(code);
+        }
+        return program;
+    }
+
+    internal static Drawing CreateDrawing(NestJobPart part)
+    {
+        var drawing = new Drawing(part.Id, ToProgram(part.Geometry)) { Priority = part.Priority };
+        drawing.Quantity.Required = part.Quantity;
+        drawing.Constraints = new NestConstraints
+        {
+            StepAngle = LegacyStep(part.Rotation),
+            StartAngle = part.Rotation.Start,
+            EndAngle = part.Rotation.End
+        };
+        return drawing;
+    }
+
+    // A fixed angle needs a nonzero legacy step so it is not misread as automatic.
+    internal static double LegacyStep(RotationPolicy policy) => policy.Kind == RotationPolicyKind.Fixed
+        ? OpenNest.Math.Angle.TwoPI : policy.Step;
+
+    internal static Plate CreatePlate(NestPlateStock stock) => new(stock.Size)
+    {
+        Quantity = 1,
+        PartSpacing = stock.PartSpacing,
+        EdgeSpacing = stock.EdgeSpacing,
+        Quadrant = stock.Quadrant
+    };
+}

OpenNest.Engine/Jobs/Adapters/LegacyPlateNesterAdapter.cs

@@ -0,0 +1,71 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace OpenNest;
+
+/// <summary>
+/// A fresh private legacy plate/drawing/item graph for each call. Only returned poses cross the boundary;
+/// legacy quantity mutations are deliberately ignored. Does not certify geometric safety or rotation compliance.
+/// </summary>
+public sealed class LegacyPlateNesterAdapter : IPlateNester
+{
+    private readonly Func<Plate, NestEngineBase> engineFactory;
+
+    public LegacyPlateNesterAdapter(Func<Plate, NestEngineBase> engineFactory)
+    {
+        ArgumentNullException.ThrowIfNull(engineFactory);
+        this.engineFactory = engineFactory;
+    }
+
+    /// <summary>Convenience overload delegating to <see cref="PlateNesterFactory"/> so strategy
+    /// resolution has a single source of truth; rejects unknown keys. Never reads or changes the
+    /// process-global NestEngineRegistry.</summary>
+    public static IPlateNester Create(string strategy) => PlateNesterFactory.Create(strategy);
+
+    public PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress> progress = null,
+        CancellationToken token = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+        token.ThrowIfCancellationRequested();
+        var plate = DrawingJobMapper.CreatePlate(request.Stock);
+        var items = new List<NestItem>();
+        var identities = new Dictionary<Drawing, string>(ReferenceEqualityComparer.Instance);
+        foreach (var requirement in request.Parts)
+        {
+            var drawing = DrawingJobMapper.CreateDrawing(requirement);
+            identities.Add(drawing, requirement.Id);
+            items.Add(new NestItem
+            {
+                Drawing = drawing,
+                Quantity = requirement.Quantity,
+                Priority = requirement.Priority,
+                StepAngle = DrawingJobMapper.LegacyStep(requirement.Rotation),
+                RotationStart = requirement.Rotation.Start,
+                RotationEnd = requirement.Rotation.End
+            });
+        }
+        var engine = engineFactory(plate) ?? throw new InvalidOperationException("Legacy engine factory returned null.");
+        var legacyProgress = progress == null ? null : new LegacyProgress(progress, request.Stock.Id);
+        var parts = engine.Nest(items, legacyProgress, token);
+        token.ThrowIfCancellationRequested();
+        if (parts == null) throw new InvalidOperationException("Legacy engine returned null placements.");
+        var placements = new List<NestJobPlacement>();
+        foreach (var part in parts)
+        {
+            if (part?.BaseDrawing == null || !identities.TryGetValue(part.BaseDrawing, out var id))
+                throw new InvalidOperationException("Legacy placement does not reference a private requirement drawing.");
+            placements.Add(new NestJobPlacement(id, 0, part.Location.X, part.Location.Y, part.Rotation));
+        }
+        return new PlateCandidate(placements);
+    }
+
+    private sealed class LegacyProgress(IProgress<NestJobProgress> progress, string stockId) : IProgress<NestProgress>
+    {
+        public void Report(NestProgress value)
+        {
+            ArgumentNullException.ThrowIfNull(value);
+            progress.Report(new NestJobProgress(NestJobStage.EvaluatingCandidate, stockId, -1, 0, 0, value));
+        }
+    }
+}

OpenNest.Engine/Jobs/Adapters/NestResultMaterializer.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using OpenNest.Geometry;
+
+namespace OpenNest;
+
+/// <summary>A detached mutable domain nest plus explicit requirement identity (never inferred from names).</summary>
+public sealed class MaterializedNestResult
+{
+    internal MaterializedNestResult(Nest nest, Dictionary<string, Drawing> drawings)
+    {
+        Nest = nest;
+        DrawingsByPartId = new ReadOnlyDictionary<string, Drawing>(drawings);
+    }
+
+    public Nest Nest { get; }
+    public IReadOnlyDictionary<string, Drawing> DrawingsByPartId { get; }
+}
+
+/// <summary>Materializes a result from the same job. Geometry safety remains the solver's future validation boundary.</summary>
+public static class NestResultMaterializer
+{
+    public static MaterializedNestResult Materialize(NestJob job, NestJobResult result)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+        ArgumentNullException.ThrowIfNull(result);
+        var nest = new Nest();
+        var drawings = job.Parts.ToDictionary(p => p.Id, DrawingJobMapper.CreateDrawing, StringComparer.Ordinal);
+        foreach (var drawing in drawings.Values) nest.Drawings.Add(drawing);
+        foreach (var sheet in result.Plates)
+        {
+            var plate = DrawingJobMapper.CreatePlate(sheet.Stock);
+            foreach (var pose in sheet.Placements)
+            {
+                if (!drawings.TryGetValue(pose.PartId, out var drawing))
+                    throw new ArgumentException("Result contains a requirement not present in the job.", nameof(result));
+                // Do not use CreateAtOrigin: it normalizes bounds and would change the snapshot frame.
+                var part = new Part(drawing);
+                part.Rotate(pose.Rotation);
+                part.Location = new Vector(pose.X, pose.Y);
+                part.UpdateBounds();
+                // Quantity=1 is set before the only attachment; Plate's event owns Nested accounting.
+                plate.Parts.Add(part);
+            }
+            nest.Plates.Add(plate);
+        }
+        return new MaterializedNestResult(nest, drawings);
+    }
+}

OpenNest.Engine/Jobs/INestingEngine.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Threading;
+
+namespace OpenNest;
+
+/// <summary>Synchronous whole-job solver. Cancellation throws, rather than returning partial success.</summary>
+public interface INestingEngine
+{
+    NestJobResult Solve(NestJob job, IProgress<NestJobProgress> progress = null, CancellationToken token = default);
+}

OpenNest.Engine/Jobs/IPlateNester.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Threading;
+
+namespace OpenNest;
+
+/// <summary>Places on one sheet only. Must not change stock, demand, or caller-owned domain objects.</summary>
+public interface IPlateNester
+{
+    PlateCandidate Place(PlatePlacementRequest request, IProgress<NestJobProgress> progress = null,
+        CancellationToken token = default);
+}

OpenNest.Engine/Jobs/NestJob.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest;
+
+/// <summary>One material/unit system's requirements. Collections are copied; all nested values are immutable.</summary>
+public sealed class NestJob
+{
+    public NestJob(IEnumerable<NestJobPart> parts, IEnumerable<NestPlateStock> plates, NestJobOptions options = null)
+    {
+        Parts = Own(parts);
+        Plates = Own(plates);
+        Options = options ?? new NestJobOptions();
+        if (Parts.Select(p => p.Id).Distinct(StringComparer.Ordinal).Count() != Parts.Count ||
+            Plates.Select(p => p.Id).Distinct(StringComparer.Ordinal).Count() != Plates.Count)
+            throw new ArgumentException("Part and stock IDs must each be unique.");
+    }
+
+    public IReadOnlyList<NestJobPart> Parts { get; }
+    public IReadOnlyList<NestPlateStock> Plates { get; }
+    public NestJobOptions Options { get; }
+
+    internal static IReadOnlyList<T> Own<T>(IEnumerable<T> source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+        var values = source.ToArray();
+        if (values.Any(value => value is null))
+            throw new ArgumentException("Null entries are not allowed.", nameof(source));
+        return Array.AsReadOnly(values);
+    }
+}

OpenNest.Engine/Jobs/NestJobCandidateComparer.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest;
+
+/// <summary>Ranks independent plate trials: priority fulfillment, sheet area, placement envelope, then input order.</summary>
+public sealed class NestJobCandidateComparer
+{
+    private readonly IReadOnlyList<NestJobPart> parts;
+
+    public NestJobCandidateComparer(IReadOnlyList<NestJobPart> parts)
+    {
+        this.parts = parts ?? throw new ArgumentNullException(nameof(parts));
+    }
+
+    /// <summary>Returns positive when the left trial is preferred.</summary>
+    public int Compare(PlateCandidate left, NestPlateStock leftStock, int leftIndex,
+        PlateCandidate right, NestPlateStock rightStock, int rightIndex)
+    {
+        var priorities = parts.Select(part => part.Priority).Distinct().OrderBy(priority => priority);
+        foreach (var priority in priorities)
+        {
+            var leftCount = Count(left, priority);
+            var rightCount = Count(right, priority);
+            if (leftCount != rightCount) return leftCount.CompareTo(rightCount);
+        }
+
+        var area = Area(rightStock).CompareTo(Area(leftStock));
+        if (area != 0) return area;
+
+        var envelope = Envelope(right).CompareTo(Envelope(left));
+        if (envelope != 0) return envelope;
+
+        return rightIndex.CompareTo(leftIndex);
+    }
+
+    private int Count(PlateCandidate candidate, int priority) => candidate.Placements.Count(placement =>
+        parts.First(part => part.Id == placement.PartId).Priority == priority);
+
+    private static double Area(NestPlateStock stock) => stock.Size.Width * stock.Size.Length;
+
+    private static double Envelope(PlateCandidate candidate)
+    {
+        if (candidate.Placements.Count == 0) return 0;
+        var xs = candidate.Placements.Select(placement => placement.X);
+        var ys = candidate.Placements.Select(placement => placement.Y);
+        return (xs.Max() - xs.Min()) * (ys.Max() - ys.Min());
+    }
+}

OpenNest.Engine/Jobs/NestJobOptions.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace OpenNest;
+
+/// <summary>Immutable per-job options; selection never changes the legacy global registry.</summary>
+public sealed class NestJobOptions
+{
+    public NestJobOptions(string placementStrategy = "Default", int? maxPlates = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(placementStrategy);
+        if (maxPlates <= 0) throw new ArgumentOutOfRangeException(nameof(maxPlates));
+        PlacementStrategy = placementStrategy;
+        MaxPlates = maxPlates;
+    }
+
+    public string PlacementStrategy { get; }
+    /// <summary>Maximum physical sheets to commit, or null for no explicit cap.</summary>
+    public int? MaxPlates { get; }
+}

OpenNest.Engine/Jobs/NestJobPart.cs

@@ -0,0 +1,27 @@
+using System;
+
+namespace OpenNest;
+
+/// <summary>An immutable requirement, independent of drawing names, UI state, and drawing quantity counters.</summary>
+public sealed class NestJobPart
+{
+    public NestJobPart(string id, PartGeometrySnapshot geometry, int quantity, int priority = 0,
+        RotationPolicy rotation = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(id);
+        ArgumentNullException.ThrowIfNull(geometry);
+        if (quantity <= 0) throw new ArgumentOutOfRangeException(nameof(quantity));
+        Id = id;
+        Geometry = geometry;
+        Quantity = quantity;
+        Priority = priority;
+        Rotation = rotation ?? RotationPolicy.Automatic;
+    }
+
+    public string Id { get; }
+    public PartGeometrySnapshot Geometry { get; }
+    /// <summary>Positive number requested; never decremented by placement code.</summary>
+    public int Quantity { get; }
+    public int Priority { get; }
+    public RotationPolicy Rotation { get; }
+}

OpenNest.Engine/Jobs/NestJobPlacementValidator.cs

@@ -0,0 +1,307 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Converters;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest;
+
+/// <summary>Validates a trial against immutable job geometry before the runner commits accounting.</summary>
+internal static class NestJobPlacementValidator
+{
+    private const double Epsilon = 0.0000001;
+
+    internal static void ValidateCandidate(PlateCandidate candidate, NestPlateStock stock,
+        IReadOnlyDictionary<string, int> remaining, IReadOnlyDictionary<string, NestJobPart> parts)
+    {
+        if (candidate == null) throw new InvalidOperationException("The plate nester returned a null candidate.");
+        var counts = new Dictionary<string, int>(StringComparer.Ordinal);
+        var placed = new List<ShapeTopology>();
+        foreach (var placement in candidate.Placements)
+        {
+            if (placement.PartId == null || !remaining.TryGetValue(placement.PartId, out var available) ||
+                !parts.TryGetValue(placement.PartId, out var part))
+                throw new InvalidOperationException("Candidate references an unknown requirement ID.");
+            if (!double.IsFinite(placement.X) || !double.IsFinite(placement.Y) || !double.IsFinite(placement.Rotation))
+                throw new InvalidOperationException("Candidate poses must be finite.");
+            counts.TryGetValue(placement.PartId, out var count);
+            if (count >= available) throw new InvalidOperationException("Candidate overproduces a requirement.");
+            if (!RotationIsAllowed(part.Rotation, placement.Rotation))
+                throw new InvalidOperationException("Candidate rotation is not allowed for the requirement.");
+
+            var shape = Transform(CreateShape(part.Geometry), placement);
+            if (!FitsWorkArea(shape, stock))
+                throw new InvalidOperationException("Candidate placement falls outside the usable stock area.");
+            foreach (var other in placed)
+            {
+                if (Overlaps(shape, other))
+                    throw new InvalidOperationException("Candidate placements overlap.");
+                if (stock.PartSpacing > 0 && Distance(shape, other) < stock.PartSpacing - Epsilon)
+                    throw new InvalidOperationException("Candidate placements violate required part spacing.");
+            }
+
+            placed.Add(shape);
+            counts[placement.PartId] = count + 1;
+        }
+    }
+
+    internal static void ValidateGeometry(PartGeometrySnapshot geometry)
+    {
+        _ = CreateShape(geometry);
+    }
+
+    private static bool RotationIsAllowed(RotationPolicy policy, double rotation)
+    {
+        if (policy.Kind == RotationPolicyKind.Automatic) return true;
+        if (policy.Kind == RotationPolicyKind.Fixed)
+            return AnglesEqual(rotation, policy.Start);
+        if (rotation < policy.Start - Epsilon || rotation > policy.End + Epsilon) return false;
+        var steps = (rotation - policy.Start) / policy.Step;
+        return System.Math.Abs(steps - System.Math.Round(steps)) <= Epsilon;
+    }
+
+    private static bool AnglesEqual(double left, double right)
+    {
+        var delta = (left - right) % (System.Math.PI * 2);
+        return System.Math.Abs(delta) <= Epsilon || System.Math.Abs(System.Math.Abs(delta) - System.Math.PI * 2) <= Epsilon;
+    }
+
+    private static ShapeTopology CreateShape(PartGeometrySnapshot geometry)
+    {
+        var entities = ConvertProgram.ToGeometry(DrawingJobMapper.ToProgram(geometry));
+        var cutEntities = new List<Entity>();
+        foreach (var entity in entities)
+            if (!ReferenceEquals(entity.Layer, SpecialLayers.Rapid))
+                cutEntities.Add(entity);
+
+        var contours = ShapeBuilder.GetShapes(cutEntities);
+        if (contours.Count == 0) throw new ArgumentException("Geometry must contain a closed contour.");
+        foreach (var contour in contours)
+            ValidateContour(contour);
+
+        var profile = new ShapeProfile(cutEntities);
+        profile.NormalizeWinding();
+        return new ShapeTopology(profile.Perimeter, profile.Cutouts);
+    }
+
+    private static void ValidateContour(Shape contour)
+    {
+        if (!contour.IsClosed())
+            throw new ArgumentException("Geometry must contain closed contours with usable edges.");
+        foreach (var entity in contour.Entities)
+            if (entity.Length <= Epsilon)
+                throw new ArgumentException("Geometry contains a zero-length edge.");
+        if (contour.Area() <= Epsilon)
+            throw new ArgumentException("Geometry must contain non-degenerate contours.");
+    }
+
+    private static ShapeTopology Transform(ShapeTopology source, NestJobPlacement placement)
+    {
+        var perimeter = TransformContour(source.Perimeter, placement);
+        var cutouts = new List<Shape>(source.Cutouts.Count);
+        foreach (var cutout in source.Cutouts)
+            cutouts.Add(TransformContour(cutout, placement));
+        return new ShapeTopology(perimeter, cutouts);
+    }
+
+    private static Shape TransformContour(Shape source, NestJobPlacement placement)
+    {
+        var contour = (Shape)source.Clone();
+        contour.Rotate(placement.Rotation);
+        contour.Offset(placement.X, placement.Y);
+        return contour;
+    }
+
+    private static bool FitsWorkArea(ShapeTopology shape, NestPlateStock stock)
+    {
+        var workArea = WorkArea(stock);
+        if (!FitsWorkArea(shape.Perimeter, workArea)) return false;
+        foreach (var cutout in shape.Cutouts)
+            if (!FitsWorkArea(cutout, workArea)) return false;
+        return true;
+    }
+
+    private static Box WorkArea(NestPlateStock stock)
+    {
+        var left = stock.Quadrant is 1 or 4 ? 0 : -stock.Size.Length;
+        var bottom = stock.Quadrant is 1 or 2 ? 0 : -stock.Size.Width;
+        return new Box(left + stock.EdgeSpacing.Left, bottom + stock.EdgeSpacing.Bottom,
+            stock.Size.Length - stock.EdgeSpacing.Left - stock.EdgeSpacing.Right,
+            stock.Size.Width - stock.EdgeSpacing.Bottom - stock.EdgeSpacing.Top);
+    }
+
+    private static bool FitsWorkArea(Shape contour, Box workArea)
+    {
+        var bounds = contour.BoundingBox;
+        return bounds.Left >= workArea.Left - Epsilon && bounds.Right <= workArea.Right + Epsilon &&
+            bounds.Bottom >= workArea.Bottom - Epsilon && bounds.Top <= workArea.Top + Epsilon;
+    }
+
+    private static bool Overlaps(ShapeTopology left, ShapeTopology right)
+    {
+        var leftPoly = ToPolygon(left.Perimeter);
+        var rightPoly = ToPolygon(right.Perimeter);
+        if (!leftPoly.BoundingBox.Intersects(rightPoly.BoundingBox))
+            return false;
+        // True material overlap requires shared interior area, not boundary touching.
+        // Edge/corner contact (zero clearance) is a valid placement when part spacing is zero.
+        return InteriorOverlap(leftPoly, left, rightPoly, right);
+    }
+
+    private static bool InteriorOverlap(Polygon leftPoly, ShapeTopology left, Polygon rightPoly, ShapeTopology right)
+    {
+        // The intersection of two polygons is either empty, a region of positive area (true overlap),
+        // or a zero-area line/point (boundary contact). Test the interior of the intersection region:
+        // a point strictly inside BOTH perimeters and outside both parts' holes proves shared material.
+        foreach (var point in InteriorWitnessPoints(leftPoly, rightPoly))
+        {
+            if (StrictlyInside(leftPoly, point) && !InAnyHole(left, point) &&
+                StrictlyInside(rightPoly, point) && !InAnyHole(right, point))
+                return true;
+        }
+        return false;
+    }
+
+    /// <summary>
+    /// Points that lie in the interior of the perimeter-perimeter intersection when one exists.
+    /// For each pair of crossing edges, the two interior-side vertices (one from each polygon)
+    /// have their midpoint inside both perimeters; that midpoint is a witness of positive-area
+    /// overlap. For containment, an interior vertex of the inner perimeter witnesses it.
+    /// </summary>
+    private static IEnumerable<Vector> InteriorWitnessPoints(Polygon left, Polygon right)
+    {
+        foreach (var l in left.ToLines())
+            foreach (var r in right.ToLines())
+                if (l.Intersects(r, out var pt) && pt.IsValid())
+                {
+                    yield return Midpoint(l, pt);
+                    yield return Midpoint(r, pt);
+                }
+        // Containment: an interior point of one polygon inside the other. Use a point pulled
+        // toward the centroid of each polygon from a vertex (guaranteed interior for simple shapes).
+        foreach (var poly in new[] { left, right })
+        {
+            foreach (var vertex in poly.Vertices)
+            {
+                var centroid = Centroid(poly);
+                yield return (vertex + centroid) * 0.5;
+            }
+        }
+    }
+
+    private static Vector Midpoint(Line line, Vector point)
+    {
+        var other = line.StartPoint.DistanceTo(point) <= line.EndPoint.DistanceTo(point)
+            ? line.EndPoint
+            : line.StartPoint;
+        return (other + point) * 0.5;
+    }
+
+    private static Vector Centroid(Polygon polygon)
+    {
+        var n = polygon.IsClosed() ? polygon.Vertices.Count - 1 : polygon.Vertices.Count;
+        var sum = Vector.Zero;
+        for (var i = 0; i < n; i++)
+            sum += polygon.Vertices[i];
+        return sum / n;
+    }
+
+    /// <summary>
+    /// Winding-number point-in-polygon. Returns false for points on an edge or vertex.
+    /// </summary>
+    private static bool StrictlyInside(Polygon polygon, Vector point)
+    {
+        var n = polygon.IsClosed() ? polygon.Vertices.Count - 1 : polygon.Vertices.Count;
+        if (n < 3) return false;
+        var winding = 0;
+        for (var i = 0; i < n; i++)
+        {
+            var p1 = polygon.Vertices[i];
+            var p2 = polygon.Vertices[(i + 1) % n];
+            if (OnSegment(p1, p2, point)) return false;
+            if (p1.Y <= point.Y)
+            {
+                if (p2.Y > point.Y && IsLeft(p1, p2, point) > 0)
+                    winding++;
+            }
+            else if (p2.Y <= point.Y && IsLeft(p1, p2, point) < 0)
+            {
+                winding--;
+            }
+        }
+        return winding != 0;
+    }
+
+    private static bool OnSegment(Vector a, Vector b, Vector p)
+    {
+        var cross = (b.X - a.X) * (p.Y - a.Y) - (b.Y - a.Y) * (p.X - a.X);
+        if (!cross.IsEqualTo(0.0)) return false;
+        return System.Math.Min(a.X, b.X) - Epsilon <= p.X && p.X <= System.Math.Max(a.X, b.X) + Epsilon &&
+               System.Math.Min(a.Y, b.Y) - Epsilon <= p.Y && p.Y <= System.Math.Max(a.Y, b.Y) + Epsilon;
+    }
+
+    private static double IsLeft(Vector p1, Vector p2, Vector p) =>
+        (p2.X - p1.X) * (p.Y - p1.Y) - (p2.Y - p1.Y) * (p.X - p1.X);
+
+    private static bool InAnyHole(ShapeTopology topology, Vector point)
+    {
+        foreach (var cutout in topology.Cutouts)
+            if (ToPolygon(cutout).ContainsPoint(point))
+                return true;
+        return false;
+    }
+
+    private static double Distance(ShapeTopology left, ShapeTopology right)
+    {
+        var result = double.PositiveInfinity;
+        foreach (var leftContour in AllContours(left))
+            foreach (var rightContour in AllContours(right))
+                result = System.Math.Min(result, BoundaryDistance(ToPolygon(leftContour), ToPolygon(rightContour)));
+        return result;
+    }
+
+    private static IEnumerable<Shape> AllContours(ShapeTopology shape)
+    {
+        yield return shape.Perimeter;
+        foreach (var cutout in shape.Cutouts)
+            yield return cutout;
+    }
+
+    private static List<Polygon> ToPolygons(List<Shape> contours)
+    {
+        var polygons = new List<Polygon>(contours.Count);
+        foreach (var contour in contours)
+            polygons.Add(ToPolygon(contour));
+        return polygons;
+    }
+
+    private static Polygon ToPolygon(Shape contour)
+    {
+        var polygon = contour.ToPolygon();
+        polygon.UpdateBounds();
+        return polygon;
+    }
+
+    private static double BoundaryDistance(Polygon left, Polygon right)
+    {
+        var result = double.PositiveInfinity;
+        foreach (var leftLine in left.ToLines())
+        {
+            foreach (var rightLine in right.ToLines())
+            {
+                if (leftLine.Intersects(rightLine)) return 0;
+                result = System.Math.Min(result, leftLine.ClosestPointTo(rightLine.StartPoint).DistanceTo(rightLine.StartPoint));
+                result = System.Math.Min(result, leftLine.ClosestPointTo(rightLine.EndPoint).DistanceTo(rightLine.EndPoint));
+                result = System.Math.Min(result, rightLine.ClosestPointTo(leftLine.StartPoint).DistanceTo(leftLine.StartPoint));
+                result = System.Math.Min(result, rightLine.ClosestPointTo(leftLine.EndPoint).DistanceTo(leftLine.EndPoint));
+            }
+        }
+        return result;
+    }
+
+    private sealed class ShapeTopology(Shape perimeter, List<Shape> cutouts)
+    {
+        internal Shape Perimeter { get; } = perimeter;
+        internal List<Shape> Cutouts { get; } = cutouts;
+    }
+}

OpenNest.Engine/Jobs/NestJobProgress.cs

@@ -0,0 +1,10 @@
+namespace OpenNest;
+
+public enum NestJobStage { EvaluatingCandidate, PlateCommitted }
+
+/// <summary>
+/// Whole-job progress. Counts change only after a physical sheet commits; LegacyProgress is optional
+/// non-authoritative detail from a plate nester while its candidate remains under evaluation.
+/// </summary>
+public sealed record NestJobProgress(NestJobStage Stage, string StockId, int PlateIndex,
+    int CommittedPlates, int CommittedParts, NestProgress LegacyProgress = null);

OpenNest.Engine/Jobs/NestJobResult.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+
+namespace OpenNest;
+
+public enum NestJobStatus { Complete, Incomplete }
+public enum NestJobStopReason { Completed, StockExhausted, NoPlacementFound, PlateLimitReached }
+
+/// <summary>
+/// Rotate about the snapshot origin, then translate by X/Y into the selected plate quadrant frame.
+/// Rotation is in radians. InstanceIndex is zero-based and unique within a part requirement across the job.
+/// The runner assigns final instance indices when committing a candidate.
+/// </summary>
+public sealed record NestJobPlacement(string PartId, int InstanceIndex, double X, double Y, double Rotation);
+
+/// <summary>Requested = Placed + Unplaced for a requirement ID.</summary>
+public sealed record PartFulfillment(string PartId, int Requested, int Placed, int Unplaced);
+
+/// <summary>Used counts physical sheets; Remaining is null only for unlimited stock.</summary>
+public sealed record StockUsage(string StockId, int Used, int? Remaining);
+
+/// <summary>One physical sheet, with owned ordered placements and immutable stock/settings snapshot.</summary>
+public sealed class NestJobPlateResult
+{
+    public NestJobPlateResult(int plateIndex, NestPlateStock stock, IEnumerable<NestJobPlacement> placements)
+    {
+        ArgumentNullException.ThrowIfNull(stock);
+        PlateIndex = plateIndex;
+        Stock = stock;
+        Placements = NestJob.Own(placements);
+    }
+
+    public int PlateIndex { get; }
+    public string StockId => Stock.Id;
+    public NestPlateStock Stock { get; }
+    public IReadOnlyList<NestJobPlacement> Placements { get; }
+}
+
+/// <summary>Detached result values in commit/input order; no mutable Drawing, Plate, or NestItem escapes.</summary>
+public sealed class NestJobResult
+{
+    public NestJobResult(NestJobStatus status, NestJobStopReason stopReason,
+        IEnumerable<NestJobPlateResult> plates, IEnumerable<PartFulfillment> fulfillment,
+        IEnumerable<StockUsage> stockUsage)
+    {
+        Status = status;
+        StopReason = stopReason;
+        Plates = NestJob.Own(plates);
+        Fulfillment = NestJob.Own(fulfillment);
+        StockUsage = NestJob.Own(stockUsage);
+    }
+
+    public NestJobStatus Status { get; }
+    public NestJobStopReason StopReason { get; }
+    public IReadOnlyList<NestJobPlateResult> Plates { get; }
+    public IReadOnlyList<PartFulfillment> Fulfillment { get; }
+    public IReadOnlyList<StockUsage> StockUsage { get; }
+}

OpenNest.Engine/Jobs/NestJobRunner.cs

@@ -0,0 +1,112 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+
+namespace OpenNest;
+
+/// <summary>
+/// Physical-sheet allocation. Every available stock entry is tried independently and only the selected
+/// candidate changes demand or inventory accounting.
+/// </summary>
+public sealed class NestJobRunner : INestingEngine
+{
+    private readonly Func<string, IPlateNester> plateNesterFactory;
+
+    /// <summary>Runner-local strategy resolution. A factory must reject unknown keys or return null.</summary>
+    public NestJobRunner(Func<string, IPlateNester> plateNesterFactory)
+    {
+        ArgumentNullException.ThrowIfNull(plateNesterFactory);
+        this.plateNesterFactory = plateNesterFactory;
+    }
+
+    public NestJobResult Solve(NestJob job, IProgress<NestJobProgress> progress = null,
+        CancellationToken token = default)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+        token.ThrowIfCancellationRequested();
+        NestJobValidator.Validate(job);
+        var plates = new List<NestJobPlateResult>();
+        var remaining = job.Parts.ToDictionary(part => part.Id, part => part.Quantity, StringComparer.Ordinal);
+        var placed = job.Parts.ToDictionary(part => part.Id, _ => 0, StringComparer.Ordinal);
+        var parts = job.Parts.ToDictionary(part => part.Id, StringComparer.Ordinal);
+        var used = job.Plates.ToDictionary(stock => stock.Id, _ => 0, StringComparer.Ordinal);
+        var comparer = new NestJobCandidateComparer(job.Parts);
+        var nester = job.Parts.Count == 0 ? null : plateNesterFactory(job.Options.PlacementStrategy) ??
+            throw new NotSupportedException($"Unknown placement strategy: {job.Options.PlacementStrategy}.");
+        var reason = NestJobStopReason.Completed;
+        while (remaining.Values.Any(count => count > 0))
+        {
+            token.ThrowIfCancellationRequested();
+            if (job.Options.MaxPlates <= plates.Count)
+            {
+                reason = NestJobStopReason.PlateLimitReached;
+                break;
+            }
+
+            CandidateTrial winner = null;
+            var hasAvailableStock = false;
+            for (var index = 0; index < job.Plates.Count; index++)
+            {
+                var stock = job.Plates[index];
+                if (stock.Quantity is int quantity && used[stock.Id] >= quantity) continue;
+                hasAvailableStock = true;
+                var request = new PlatePlacementRequest(stock, job.Parts.Where(part => remaining[part.Id] > 0)
+                    .Select(part => new NestJobPart(part.Id, part.Geometry, remaining[part.Id], part.Priority, part.Rotation)));
+                progress?.Report(new NestJobProgress(NestJobStage.EvaluatingCandidate, stock.Id,
+                    plates.Count, plates.Count, placed.Values.Sum()));
+                token.ThrowIfCancellationRequested();
+                var candidateProgress = progress == null ? null : new CandidateProgress(progress, stock.Id,
+                    plates.Count, plates.Count, placed.Values.Sum());
+                var candidate = nester.Place(request, candidateProgress, token);
+                token.ThrowIfCancellationRequested();
+                NestJobValidator.ValidateCandidate(candidate, stock, remaining, parts);
+                var trial = new CandidateTrial(candidate, stock, index);
+                if (winner == null || comparer.Compare(trial.Candidate, trial.Stock, trial.StockIndex,
+                    winner.Candidate, winner.Stock, winner.StockIndex) > 0)
+                    winner = trial;
+            }
+
+            if (!hasAvailableStock)
+            {
+                reason = NestJobStopReason.StockExhausted;
+                break;
+            }
+            if (winner.Candidate.Placements.Count == 0)
+            {
+                reason = NestJobStopReason.NoPlacementFound;
+                break;
+            }
+
+            var committed = new List<NestJobPlacement>();
+            foreach (var pose in winner.Candidate.Placements)
+            {
+                committed.Add(pose with { InstanceIndex = placed[pose.PartId]++ });
+                remaining[pose.PartId]--;
+            }
+            used[winner.Stock.Id]++;
+            plates.Add(new NestJobPlateResult(plates.Count, winner.Stock, committed));
+            progress?.Report(new NestJobProgress(NestJobStage.PlateCommitted, winner.Stock.Id,
+                plates.Count - 1, plates.Count, placed.Values.Sum()));
+        }
+
+        token.ThrowIfCancellationRequested();
+        return new NestJobResult(reason == NestJobStopReason.Completed ? NestJobStatus.Complete : NestJobStatus.Incomplete,
+            reason, plates, job.Parts.Select(part => new PartFulfillment(part.Id, part.Quantity, placed[part.Id], remaining[part.Id])),
+            job.Plates.Select(stock => new StockUsage(stock.Id, used[stock.Id],
+                stock.Quantity is int quantity ? quantity - used[stock.Id] : null)));
+    }
+
+    private sealed record CandidateTrial(PlateCandidate Candidate, NestPlateStock Stock, int StockIndex);
+
+    private sealed class CandidateProgress(IProgress<NestJobProgress> progress, string stockId, int plateIndex,
+        int committedPlates, int committedParts) : IProgress<NestJobProgress>
+    {
+        public void Report(NestJobProgress value)
+        {
+            ArgumentNullException.ThrowIfNull(value);
+            progress.Report(new NestJobProgress(NestJobStage.EvaluatingCandidate, stockId, plateIndex,
+                committedPlates, committedParts, value.LegacyProgress));
+        }
+    }
+}

OpenNest.Engine/Jobs/NestJobValidator.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest;
+
+/// <summary>Basic input and candidate accounting checks, NOT a geometry/clearance safety gate.</summary>
+public static class NestJobValidator
+{
+    public static void Validate(NestJob job)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+        foreach (var stock in job.Plates)
+        {
+            var edges = stock.EdgeSpacing;
+            if (!Positive(stock.Size.Width) || !Positive(stock.Size.Length) ||
+                !Nonnegative(stock.PartSpacing) || !Nonnegative(edges.Left) || !Nonnegative(edges.Right) ||
+                !Nonnegative(edges.Top) || !Nonnegative(edges.Bottom) || stock.Quadrant < 1 || stock.Quadrant > 4 ||
+                edges.Left + edges.Right >= stock.Size.Length || edges.Top + edges.Bottom >= stock.Size.Width)
+                throw new ArgumentException($"Invalid stock dimensions/settings: {stock.Id}.", nameof(job));
+        }
+        foreach (var part in job.Parts)
+        {
+            if (part.Geometry.Motions.Count == 0 || part.Geometry.Motions.Any(m =>
+                !double.IsFinite(m.X) || !double.IsFinite(m.Y) ||
+                !double.IsFinite(m.CenterX) || !double.IsFinite(m.CenterY)))
+                throw new ArgumentException($"Geometry must contain finite motions: {part.Id}.", nameof(job));
+            try
+            {
+                NestJobPlacementValidator.ValidateGeometry(part.Geometry);
+            }
+            catch (ArgumentException exception)
+            {
+                throw new ArgumentException($"Geometry must contain usable closed edges: {part.Id}.", nameof(job), exception);
+            }
+        }
+    }
+
+    internal static void ValidateCandidate(PlateCandidate candidate, NestPlateStock stock,
+        IReadOnlyDictionary<string, int> remaining, IReadOnlyDictionary<string, NestJobPart> parts)
+    {
+        NestJobPlacementValidator.ValidateCandidate(candidate, stock, remaining, parts);
+    }
+
+    private static bool Positive(double value) => double.IsFinite(value) && value > 0;
+    private static bool Nonnegative(double value) => double.IsFinite(value) && value >= 0;
+}

OpenNest.Engine/Jobs/NestPlateStock.cs

@@ -0,0 +1,29 @@
+using System;
+using OpenNest.Geometry;
+
+namespace OpenNest;
+
+/// <summary>Immutable stock settings. Size and spacing are copied value types, not caller-owned settings.</summary>
+public sealed class NestPlateStock
+{
+    public NestPlateStock(string id, Size size, int? quantity = null, double partSpacing = 0,
+        Spacing edgeSpacing = default, int quadrant = 1)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(id);
+        if (quantity < 0) throw new ArgumentOutOfRangeException(nameof(quantity));
+        Id = id;
+        Size = size;
+        Quantity = quantity;
+        PartSpacing = partSpacing;
+        EdgeSpacing = edgeSpacing;
+        Quadrant = quadrant;
+    }
+
+    public string Id { get; }
+    public Size Size { get; }
+    /// <summary>Available physical sheets: null is unlimited, zero is legal but unavailable.</summary>
+    public int? Quantity { get; }
+    public double PartSpacing { get; }
+    public Spacing EdgeSpacing { get; }
+    public int Quadrant { get; }
+}

OpenNest.Engine/Jobs/PartGeometrySnapshot.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.CNC;
+
+namespace OpenNest;
+
+/// <summary>Exact immutable CNC motion values. Rapid moves retain contour/hole boundaries; arcs are not tessellated.</summary>
+public sealed record PartGeometryMotion(CodeType Type, double X, double Y, double CenterX,
+    double CenterY, RotationType Rotation, LayerType Layer, bool Suppressed);
+
+/// <summary>
+/// Owned geometry only: no Drawing, quantity, events, or mutable CNC references are retained.
+/// This initial boundary supports flat rapid/linear/arc programs and rejects other instructions explicitly.
+/// Coordinates and mode are preserved without normalization, rounding, or polygon approximation.
+/// </summary>
+public sealed class PartGeometrySnapshot
+{
+    private PartGeometrySnapshot(Mode mode, IEnumerable<PartGeometryMotion> motions)
+    {
+        Mode = mode;
+        Motions = NestJob.Own(motions);
+    }
+
+    public Mode Mode { get; }
+    public IReadOnlyList<PartGeometryMotion> Motions { get; }
+
+    /// <summary>Copies supported motion geometry immediately; later program edits cannot affect this snapshot.</summary>
+    public static PartGeometrySnapshot FromProgram(Program program)
+    {
+        ArgumentNullException.ThrowIfNull(program);
+        var motions = program.Codes.Select(code => code switch
+        {
+            ArcMove arc => new PartGeometryMotion(arc.Type, arc.EndPoint.X, arc.EndPoint.Y,
+                arc.CenterPoint.X, arc.CenterPoint.Y, arc.Rotation, arc.Layer, arc.Suppressed),
+            LinearMove line => new PartGeometryMotion(line.Type, line.EndPoint.X, line.EndPoint.Y,
+                0, 0, default, line.Layer, line.Suppressed),
+            RapidMove rapid => new PartGeometryMotion(rapid.Type, rapid.EndPoint.X, rapid.EndPoint.Y,
+                0, 0, default, default, rapid.Suppressed),
+            _ => throw new NotSupportedException("Geometry snapshots currently support only flat rapid/linear/arc programs.")
+        });
+        return new PartGeometrySnapshot(program.Mode, motions);
+    }
+}

OpenNest.Engine/Jobs/PlateCandidate.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+
+namespace OpenNest;
+
+/// <summary>Owned candidate poses only; not committed fulfillment or inventory accounting.</summary>
+public sealed class PlateCandidate
+{
+    public PlateCandidate(IEnumerable<NestJobPlacement> placements) => Placements = NestJob.Own(placements);
+    public IReadOnlyList<NestJobPlacement> Placements { get; }
+}

OpenNest.Engine/Jobs/PlateNesterFactory.cs

@@ -0,0 +1,23 @@
+using System;
+namespace OpenNest;
+
+/// <summary>
+/// Instance-scoped strategy resolution for the whole-job runner. The built-in strategies map
+/// to private engine factories; the process-global NestEngineRegistry (including plugin
+/// registrations and ActiveEngineName) is neither read nor modified. Unknown keys reject.
+/// </summary>
+public static class PlateNesterFactory
+{
+    public static IPlateNester Create(string strategy)
+    {
+        ArgumentNullException.ThrowIfNull(strategy);
+        return strategy switch
+        {
+            "Default" => new LegacyPlateNesterAdapter(plate => new DefaultNestEngine(plate)),
+            "Strip" => new LegacyPlateNesterAdapter(plate => new StripNestEngine(plate)),
+            "Vertical Remnant" => new LegacyPlateNesterAdapter(plate => new VerticalRemnantEngine(plate)),
+            "Horizontal Remnant" => new LegacyPlateNesterAdapter(plate => new HorizontalRemnantEngine(plate)),
+            _ => throw new NotSupportedException($"Unknown placement strategy: {strategy}.")
+        };
+    }
+}

OpenNest.Engine/Jobs/PlatePlacementRequest.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Collections.Generic;
+
+namespace OpenNest;
+
+/// <summary>Read-only stock settings and remaining requirements for a single candidate trial.</summary>
+public sealed class PlatePlacementRequest
+{
+    public PlatePlacementRequest(NestPlateStock stock, IEnumerable<NestJobPart> parts)
+    {
+        ArgumentNullException.ThrowIfNull(stock);
+        Stock = stock;
+        Parts = NestJob.Own(parts);
+    }
+
+    public NestPlateStock Stock { get; }
+    public IReadOnlyList<NestJobPart> Parts { get; }
+}

OpenNest.Engine/Jobs/RotationPolicy.cs

@@ -0,0 +1,35 @@
+using System;
+
+namespace OpenNest;
+
+public enum RotationPolicyKind { Fixed, BoundedSweep, Automatic }
+
+/// <summary>Immutable rotation constraints, in radians about the geometry origin.</summary>
+public sealed class RotationPolicy
+{
+    private RotationPolicy(RotationPolicyKind kind, double start, double end, double step)
+    {
+        if (!double.IsFinite(start) || !double.IsFinite(end) || !double.IsFinite(step))
+            throw new ArgumentException("Angles must be finite.");
+        Kind = kind;
+        Start = start;
+        End = end;
+        Step = step;
+    }
+
+    public RotationPolicyKind Kind { get; }
+    public double Start { get; }
+    public double End { get; }
+    public double Step { get; }
+    public static RotationPolicy Automatic { get; } = new(RotationPolicyKind.Automatic, 0, 0, 0);
+    public static RotationPolicy Fixed(double angle) => new(RotationPolicyKind.Fixed, angle, angle, 0);
+    public static RotationPolicy BoundedSweep(double start, double end, double step)
+    {
+        if (step <= 0 || end < start) throw new ArgumentException("Sweep needs a positive step and ordered bounds.");
+        return new RotationPolicy(RotationPolicyKind.BoundedSweep, start, end, step);
+    }
+
+    /// <summary>Preserves the legacy zero-step automatic sentinel; zero never means locked rotation.</summary>
+    public static RotationPolicy FromLegacy(double stepAngle, double rotationStart, double rotationEnd) =>
+        stepAngle == 0 ? Automatic : BoundedSweep(rotationStart, rotationEnd, stepAngle);
+}

OpenNest.Engine/NestEngineBase.cs

@@ -113,11 +113,11 @@ namespace OpenNest
                 {
                     allParts.AddRange(fillParts);
 
-                    // Deduct placed quantities
+                    // Deduct placed quantities by drawing reference, not name.
                     foreach (var item in fillItems)
                     {
                         var placed = fillParts.Count(p =>
-                            p.BaseDrawing.Name == item.Drawing.Name);
+                            ReferenceEquals(p.BaseDrawing, item.Drawing));
                         item.Quantity = System.Math.Max(0, item.Quantity - placed);
                     }
 
@@ -147,10 +147,11 @@ namespace OpenNest
                 {
                     allParts.AddRange(packParts);
 
+                    // Deduct placed quantities by drawing reference, not name.
                     foreach (var item in regularPackItems)
                     {
                         var placed = packParts.Count(p =>
-                            p.BaseDrawing.Name == item.Drawing.Name);
+                            ReferenceEquals(p.BaseDrawing, item.Drawing));
                         item.Quantity = System.Math.Max(0, item.Quantity - placed);
                     }
                 }

OpenNest.Engine/StripNestEngine.cs

@@ -128,13 +128,14 @@ namespace OpenNest
                 }
             }
 
-            // Deduct placed quantities from original items.
+            // Deduct placed quantities from original items by drawing reference.
             foreach (var item in items)
             {
                 if (item.Quantity <= 0)
                     continue;
 
-                var placed = allParts.Count(p => p.BaseDrawing.Name == item.Drawing.Name);
+                var placed = allParts.Count(p =>
+                    ReferenceEquals(p.BaseDrawing, item.Drawing));
                 item.Quantity = System.Math.Max(0, item.Quantity - placed);
             }
 

OpenNest.Tests/Api/NestRequestTests.cs

@@ -13,6 +13,8 @@ public class NestRequestTests
         Assert.Empty(request.Parts);
         Assert.Equal(60, request.SheetSize.Width);
         Assert.Equal(120, request.SheetSize.Length);
+        Assert.Null(request.Plates);
+        Assert.Equal("Default", request.PlacementStrategy);
         Assert.Equal("Steel, A1011 HR", request.Material);
         Assert.Equal(0.06, request.Thickness);
         Assert.Equal(0.1, request.Spacing);
@@ -38,8 +40,38 @@ public class NestRequestTests
     {
         var part = new NestRequestPart { DxfPath = "part.dxf" };
 
+        Assert.Null(part.Id);
         Assert.Equal(1, part.Quantity);
         Assert.True(part.AllowRotation);
         Assert.Equal(0, part.Priority);
     }
+
+    [Fact]
+    public void ExplicitPlates_PreserveStockSettings()
+    {
+        var request = new NestRequest
+        {
+            Plates =
+            [
+                new NestRequestPlate
+                {
+                    Id = "remnant",
+                    Size = new Size(24, 48),
+                    Quantity = 3,
+                    PartSpacing = 0.2,
+                    EdgeSpacing = new Spacing(1, 2, 3, 4),
+                    Quadrant = 3
+                }
+            ]
+        };
+
+        var plate = Assert.Single(request.Plates!);
+        Assert.Equal("remnant", plate.Id);
+        Assert.Equal(24, plate.Size.Width);
+        Assert.Equal(48, plate.Size.Length);
+        Assert.Equal(3, plate.Quantity);
+        Assert.Equal(0.2, plate.PartSpacing);
+        Assert.Equal(new Spacing(1, 2, 3, 4), plate.EdgeSpacing);
+        Assert.Equal(3, plate.Quadrant);
+    }
 }

OpenNest.Tests/Api/NestResponsePersistenceTests.cs

@@ -1,42 +1,42 @@
 using System;
 using System.IO;
+using System.IO.Compression;
+using System.Text.Json;
 using System.Threading.Tasks;
 using OpenNest.Api;
 using OpenNest.Geometry;
+using OpenNest.IO;
 
 namespace OpenNest.Tests.Api;
 
 public class NestResponsePersistenceTests
 {
     [Fact]
-    public async Task SaveAsync_LoadAsync_RoundTrips()
+    public async Task SaveAsync_LoadAsync_RoundTripsCompleteResponseMetadata()
     {
-        var nest = new Nest("test-nest");
-        var plate = new Plate(new Size(60, 120));
-        var drawing = new Drawing("test-part");
-        nest.Drawings.Add(drawing);
-        plate.Parts.Add(new Part(drawing));
-        nest.Plates.Add(plate);
-
+        var nest = CreateNest("test-part", new Size(60, 120));
         var request = new NestRequest
         {
-            Parts = [new NestRequestPart { DxfPath = "test.dxf", Quantity = 5 }],
-            SheetSize = new Size(60, 120),
+            Parts = [new NestRequestPart { Id = "test-part", DxfPath = "test.dxf", Quantity = 5 }],
+            Plates = [new NestRequestPlate { Id = "sheet", Size = new Size(60, 120), Quantity = 1, PartSpacing = 0.1 }],
             Material = "Steel",
             Thickness = 0.125,
             Spacing = 0.1
         };
-
         var original = new NestResponse
         {
             SheetCount = 1,
             Utilization = 0.75,
             CutTime = TimeSpan.FromMinutes(12.5),
             Elapsed = TimeSpan.FromSeconds(3.2),
+            Status = NestJobStatus.Complete,
+            StopReason = NestJobStopReason.Completed,
+            Fulfillment = [new NestPartFulfillment("test-part", 5, 5, 0)],
+            StockUsage = [new NestStockUsage("sheet", 1, 0)],
+            PlateStockMappings = [new NestPlateStockMapping(0, "sheet")],
             Nest = nest,
             Request = request
         };
-
         var path = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.nestquote");
 
         try
@@ -44,16 +44,24 @@ public class NestResponsePersistenceTests
             await original.SaveAsync(path);
             var loaded = await NestResponse.LoadAsync(path);
 
+            Assert.Equal(NestResponse.CurrentSchemaVersion, loaded.SchemaVersion);
             Assert.Equal(original.SheetCount, loaded.SheetCount);
             Assert.Equal(original.Utilization, loaded.Utilization, precision: 4);
             Assert.Equal(original.CutTime, loaded.CutTime);
             Assert.Equal(original.Elapsed, loaded.Elapsed);
+            Assert.Equal(NestJobStatus.Complete, loaded.Status);
+            Assert.Equal(NestJobStopReason.Completed, loaded.StopReason);
+            Assert.Equal(original.Fulfillment, loaded.Fulfillment);
+            Assert.Equal(original.StockUsage, loaded.StockUsage);
+            Assert.Equal(original.PlateStockMappings, loaded.PlateStockMappings);
 
             Assert.Equal(original.Request.Material, loaded.Request.Material);
             Assert.Equal(original.Request.Thickness, loaded.Request.Thickness);
             Assert.Equal(original.Request.Parts.Count, loaded.Request.Parts.Count);
+            Assert.Equal("test-part", loaded.Request.Parts[0].Id);
             Assert.Equal(original.Request.Parts[0].DxfPath, loaded.Request.Parts[0].DxfPath);
             Assert.Equal(original.Request.Parts[0].Quantity, loaded.Request.Parts[0].Quantity);
+            Assert.Equal("sheet", Assert.Single(loaded.Request.Plates!).Id);
 
             Assert.NotNull(loaded.Nest);
             Assert.Single(loaded.Nest.Plates);
@@ -63,4 +71,111 @@ public class NestResponsePersistenceTests
             File.Delete(path);
         }
     }
+
+    [Fact]
+    public async Task LoadAsync_LegacyArchiveWithoutFulfillment_LeavesStatusUnspecified()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"legacy-{Guid.NewGuid()}.nestquote");
+
+        try
+        {
+            await WriteLegacyArchiveAsync(path, CreateNest("legacy-part", new Size(60, 120)));
+
+            var loaded = await NestResponse.LoadAsync(path);
+
+            Assert.Equal(0, loaded.SchemaVersion);
+            Assert.Null(loaded.Status);
+            Assert.Null(loaded.StopReason);
+            Assert.Empty(loaded.Fulfillment);
+            Assert.Empty(loaded.StockUsage);
+            Assert.Empty(loaded.PlateStockMappings);
+            Assert.Equal(1, loaded.SheetCount);
+            Assert.Equal(0.75, loaded.Utilization, precision: 4);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public async Task SaveAsync_LoadAsync_IncompleteResponsePreservesIdsAndUnplacedWithoutDxf()
+    {
+        var dxfPath = Path.Combine(Path.GetTempPath(), $"missing-{Guid.NewGuid()}.dxf");
+        var path = Path.Combine(Path.GetTempPath(), $"incomplete-{Guid.NewGuid()}.nestquote");
+        Assert.False(File.Exists(dxfPath));
+        var original = new NestResponse
+        {
+            SheetCount = 1,
+            Utilization = 0.4,
+            CutTime = TimeSpan.FromMinutes(2),
+            Elapsed = TimeSpan.FromMilliseconds(500),
+            Status = NestJobStatus.Incomplete,
+            StopReason = NestJobStopReason.StockExhausted,
+            Fulfillment = [new NestPartFulfillment("custom-id", 3, 1, 2)],
+            StockUsage = [new NestStockUsage("finite-stock", 1, 0)],
+            PlateStockMappings = [new NestPlateStockMapping(0, "finite-stock")],
+            Nest = CreateNest("custom-id", new Size(10, 10)),
+            Request = new NestRequest
+            {
+                Parts = [new NestRequestPart { Id = "custom-id", DxfPath = dxfPath, Quantity = 3 }],
+                Plates = [new NestRequestPlate { Id = "finite-stock", Size = new Size(10, 10), Quantity = 1 }]
+            }
+        };
+
+        try
+        {
+            await original.SaveAsync(path);
+            var loaded = await NestResponse.LoadAsync(path);
+
+            Assert.False(File.Exists(dxfPath));
+            Assert.Equal(NestJobStatus.Incomplete, loaded.Status);
+            Assert.Equal(NestJobStopReason.StockExhausted, loaded.StopReason);
+            Assert.Equal(new NestPartFulfillment("custom-id", 3, 1, 2), Assert.Single(loaded.Fulfillment));
+            Assert.Equal(new NestStockUsage("finite-stock", 1, 0), Assert.Single(loaded.StockUsage));
+            Assert.Equal(new NestPlateStockMapping(0, "finite-stock"), Assert.Single(loaded.PlateStockMappings));
+            Assert.Equal("custom-id", Assert.Single(loaded.Request.Parts).Id);
+            Assert.Equal("finite-stock", Assert.Single(loaded.Request.Plates!).Id);
+            Assert.Single(loaded.Nest.Drawings);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    private static Nest CreateNest(string drawingName, Size size)
+    {
+        var nest = new Nest("test-nest");
+        var plate = new Plate(size);
+        var drawing = new Drawing(drawingName);
+        nest.Drawings.Add(drawing);
+        plate.Parts.Add(new Part(drawing));
+        nest.Plates.Add(plate);
+        return nest;
+    }
+
+    private static async Task WriteLegacyArchiveAsync(string path, Nest nest)
+    {
+        using var fs = new FileStream(path, FileMode.Create);
+        using var zip = new ZipArchive(fs, ZipArchiveMode.Create);
+        await WriteEntryAsync(zip, "request.json", """
+            {"parts":[{"dxfPath":"legacy-missing.dxf","quantity":2}],"sheetSize":{"width":60,"length":120},"material":"Steel","thickness":0.06,"spacing":0.1,"strategy":0}
+            """);
+        await WriteEntryAsync(zip, "response.json", """
+            {"sheetCount":1,"utilization":0.75,"cutTimeTicks":120000,"elapsedTicks":340000}
+            """);
+
+        var nestEntry = zip.CreateEntry("nest.nest");
+        await using var stream = nestEntry.Open();
+        new NestWriter(nest).Write(stream);
+    }
+
+    private static async Task WriteEntryAsync(ZipArchive zip, string name, string contents)
+    {
+        var entry = zip.CreateEntry(name);
+        await using var stream = entry.Open();
+        await using var writer = new StreamWriter(stream);
+        await writer.WriteAsync(contents);
+    }
 }

OpenNest.Tests/Api/NestRunnerTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using System.Threading.Tasks;
 using OpenNest.Api;
 using OpenNest.Converters;
@@ -11,7 +12,7 @@ namespace OpenNest.Tests.Api;
 public class NestRunnerTests
 {
     [Fact]
-    public async Task RunAsync_SinglePart_ProducesResponse()
+    public async Task RunAsync_LegacySheetSize_UsesUnlimitedLegacyStockAndDerivedPartId()
     {
         var dxfPath = CreateTempSquareDxf(2, 2);
 
@@ -26,9 +27,17 @@ public class NestRunnerTests
 
             var response = await NestRunner.RunAsync(request);
 
-            Assert.NotNull(response);
+            Assert.Equal(NestJobStatus.Complete, response.Status);
+            Assert.Equal(NestJobStopReason.Completed, response.StopReason);
+            Assert.Equal("part-0", Assert.Single(response.Fulfillment).PartId);
+            Assert.Equal(4, response.Fulfillment[0].Placed);
+            var stock = Assert.Single(response.StockUsage);
+            Assert.Equal("legacy-sheet", stock.StockId);
+            Assert.Null(stock.Remaining);
+            Assert.All(response.PlateStockMappings, mapping => Assert.Equal("legacy-sheet", mapping.StockId));
+            Assert.Equal(response.SheetCount, response.PlateStockMappings.Count);
             Assert.NotNull(response.Nest);
-            Assert.True(response.SheetCount >= 1);
+            Assert.Contains(response.Nest.Drawings, drawing => drawing.Name == "part-0");
             Assert.True(response.Utilization > 0);
             Assert.Equal(request, response.Request);
         }
@@ -38,6 +47,155 @@ public class NestRunnerTests
         }
     }
 
+    [Fact]
+    public async Task RunAsync_ExplicitMixedFinitePlates_UsesPhysicalStockEntries()
+    {
+        var dxfPath = CreateTempSquareDxf(4, 4);
+
+        try
+        {
+            var response = await NestRunner.RunAsync(new NestRequest
+            {
+                Parts = [new NestRequestPart { Id = "square", DxfPath = dxfPath, Quantity = 5 }],
+                Plates =
+                [
+                    new NestRequestPlate { Id = "small", Size = new Size(5, 5), Quantity = 1 },
+                    new NestRequestPlate { Id = "large", Size = new Size(9, 9), Quantity = 1 }
+                ]
+            });
+
+            Assert.Equal(NestJobStatus.Complete, response.Status);
+            Assert.Equal(2, response.SheetCount);
+            Assert.Equal(5, Assert.Single(response.Fulfillment).Placed);
+            Assert.Equal(0, response.Fulfillment[0].Unplaced);
+            Assert.Equal(new[] { "large", "small" }, response.PlateStockMappings.Select(mapping => mapping.StockId).Order());
+            Assert.Equal(1, response.StockUsage.Single(usage => usage.StockId == "small").Used);
+            Assert.Equal(1, response.StockUsage.Single(usage => usage.StockId == "large").Used);
+            Assert.All(response.StockUsage, usage => Assert.Equal(0, usage.Remaining));
+        }
+        finally
+        {
+            File.Delete(dxfPath);
+        }
+    }
+
+    [Fact]
+    public async Task RunAsync_ExplicitEmptyPlates_ReportsStockExhausted()
+    {
+        var dxfPath = CreateTempSquareDxf(2, 2);
+
+        try
+        {
+            var response = await NestRunner.RunAsync(new NestRequest
+            {
+                Parts = [new NestRequestPart { Id = "square", DxfPath = dxfPath, Quantity = 1 }],
+                Plates = []
+            });
+
+            Assert.Equal(NestJobStatus.Incomplete, response.Status);
+            Assert.Equal(NestJobStopReason.StockExhausted, response.StopReason);
+            Assert.Equal(0, response.SheetCount);
+            Assert.Empty(response.StockUsage);
+            var fulfillment = Assert.Single(response.Fulfillment);
+            Assert.Equal(0, fulfillment.Placed);
+            Assert.Equal(1, fulfillment.Unplaced);
+            Assert.Empty(response.Nest.Plates);
+            Assert.Contains(response.Nest.Drawings, drawing => drawing.Name == "square");
+        }
+        finally
+        {
+            File.Delete(dxfPath);
+        }
+    }
+
+    [Fact]
+    public async Task RunAsync_FiniteStockExhaustion_PreservesUnplacedRequirementAndLockedRotation()
+    {
+        var dxfPath = CreateTempSquareDxf(4, 4);
+
+        try
+        {
+            var response = await NestRunner.RunAsync(new NestRequest
+            {
+                Parts = [new NestRequestPart
+                {
+                    Id = "locked-square",
+                    DxfPath = dxfPath,
+                    Quantity = 2,
+                    AllowRotation = false
+                }],
+                Plates = [new NestRequestPlate { Id = "only-sheet", Size = new Size(5, 5), Quantity = 1 }]
+            });
+
+            Assert.Equal(NestJobStatus.Incomplete, response.Status);
+            Assert.Equal(NestJobStopReason.StockExhausted, response.StopReason);
+            var fulfillment = Assert.Single(response.Fulfillment);
+            Assert.Equal(2, fulfillment.Requested);
+            Assert.Equal(1, fulfillment.Placed);
+            Assert.Equal(1, fulfillment.Unplaced);
+            var stock = Assert.Single(response.StockUsage);
+            Assert.Equal(1, stock.Used);
+            Assert.Equal(0, stock.Remaining);
+            var drawing = Assert.Single(response.Nest.Drawings);
+            Assert.Equal("locked-square", drawing.Name);
+            Assert.Equal(OpenNest.Math.Angle.TwoPI, drawing.Constraints.StepAngle);
+        }
+        finally
+        {
+            File.Delete(dxfPath);
+        }
+    }
+
+    [Fact]
+    public async Task RunAsync_MixedPhysicalSheets_CalculatesWeightedUtilization()
+    {
+        var dxfPath = CreateTempSquareDxf(4, 4);
+
+        try
+        {
+            var response = await NestRunner.RunAsync(new NestRequest
+            {
+                Parts = [new NestRequestPart { Id = "square", DxfPath = dxfPath, Quantity = 5 }],
+                Plates =
+                [
+                    new NestRequestPlate { Id = "small", Size = new Size(5, 5), Quantity = 1 },
+                    new NestRequestPlate { Id = "large", Size = new Size(9, 9), Quantity = 1 }
+                ]
+            });
+
+            Assert.Equal(2, response.SheetCount);
+            Assert.Equal(80d / 106d, response.Utilization, precision: 6);
+        }
+        finally
+        {
+            File.Delete(dxfPath);
+        }
+    }
+
+    [Fact]
+    public async Task RunAsync_DuplicatePartIds_ThrowsBeforeNesting()
+    {
+        var dxfPath = CreateTempSquareDxf(2, 2);
+
+        try
+        {
+            var request = new NestRequest
+            {
+                Parts =
+                [
+                    new NestRequestPart { Id = "duplicate", DxfPath = dxfPath },
+                    new NestRequestPart { Id = "duplicate", DxfPath = dxfPath }
+                ]
+            };
+
+            await Assert.ThrowsAsync<ArgumentException>(() => NestRunner.RunAsync(request));
+        }
+        finally
+        {
+            File.Delete(dxfPath);
+        }
+    }
+
     [Fact]
     public async Task RunAsync_BadDxfPath_Throws()
     {
@@ -46,8 +204,7 @@ public class NestRunnerTests
             Parts = [new NestRequestPart { DxfPath = "nonexistent.dxf", Quantity = 1 }]
         };
 
-        await Assert.ThrowsAsync<FileNotFoundException>(
-            () => NestRunner.RunAsync(request));
+        await Assert.ThrowsAsync<FileNotFoundException>(() => NestRunner.RunAsync(request));
     }
 
     [Fact]
@@ -55,8 +212,7 @@ public class NestRunnerTests
     {
         var request = new NestRequest { Parts = [] };
 
-        await Assert.ThrowsAsync<ArgumentException>(
-            () => NestRunner.RunAsync(request));
+        await Assert.ThrowsAsync<ArgumentException>(() => NestRunner.RunAsync(request));
     }
 
     private static string CreateTempSquareDxf(double width, double height)
@@ -69,9 +225,7 @@ public class NestRunnerTests
 
         var pgm = ConvertGeometry.ToProgram(shape);
         var path = Path.Combine(Path.GetTempPath(), $"test-{Guid.NewGuid()}.dxf");
-
         Dxf.ExportProgram(pgm, path);
-
         return path;
     }
 }

OpenNest.sln

@@ -34,6 +34,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Posts.GravographIS
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Data", "OpenNest.Data\OpenNest.Data.csproj", "{A0B4B48E-1DF0-4DD3-B42C-B9B7779EA8B0}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Engine.Tests", "OpenNest.Engine.Tests\OpenNest.Engine.Tests.csproj", "{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -200,6 +202,18 @@ Global
 		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|x64.Build.0 = Release|Any CPU
 		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|x86.ActiveCfg = Release|Any CPU
 		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|x86.Build.0 = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|x64.Build.0 = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Debug|x86.Build.0 = Debug|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|x64.ActiveCfg = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|x64.Build.0 = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|x86.ActiveCfg = Release|Any CPU
+		{F2EF39E0-1A95-4C32-B50B-3D71EC72F692}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

README.md

@@ -64,6 +64,32 @@ cd OpenNest
 dotnet build OpenNest.sln
 ```
 
+### Cross-platform engine contract tests
+
+```bash
+dotnet test OpenNest.Engine.Tests/OpenNest.Engine.Tests.csproj
+```
+
+`OpenNest.Engine.Tests` targets `net8.0` and runs on Linux, macOS, and Windows without the desktop project or local DXF fixtures. The existing `OpenNest.Tests` suite still requires Windows.
+
+The new whole-job contracts in `OpenNest.Engine/Jobs` (`namespace OpenNest`) use owned immutable geometry/settings, explicit part IDs and positive demand, finite or unlimited stock (`null` means unlimited; zero means unavailable), and result ID/pose values rather than mutable desktop models. Rotation is in radians about the geometry origin, followed by translation into the plate quadrant frame. Strategy factories belong to each runner, not the global registry.
+
+**Current scope (minimum runnable slice, not release-ready):** `NestJobRunner.Solve` allocates one stock entry across multiple physical sheets, respecting finite inventory (`null` is unlimited), positive remaining demand, and `MaxPlates`. Empty parts complete without consuming stock; empty/unavailable stock returns `Incomplete/StockExhausted`. A zero-placement candidate stops with `NoPlacementFound` and consumes no sheet. Nonempty jobs with multiple stock entries explicitly throw `NotSupportedException`; mixed-stock selection and optional optimizations are not implemented.
+
+`DrawingJobMapper` snapshots caller drawings/items under explicit requirement IDs. `LegacyPlateNesterAdapter` creates fresh private legacy drawings, items, and plates for each trial and maps returned drawings **by reference**, never by name. Mutable legacy quantities never drive the fulfillment ledger. `PlateNesterFactory` resolves the built-in strategies (`Default`, `Strip`, `Vertical Remnant`, `Horizontal Remnant`) to private engine factories; it neither reads nor changes the process-global `NestEngineRegistry`, and unknown keys reject. Quantity deduction in the engine paths the runner reaches (base-class fill/pack, strip deduction, remnant-fill ledger, shrink-leftover counting) is keyed by drawing reference, not display name, so same-name drawings and repeated requirements stay independent. `NestResultMaterializer` returns a detached domain nest and `DrawingsByPartId` identity map. Each output plate represents one physical sheet (`Quantity = 1`), and each placement is attached exactly once so domain quantity events do not double count.
+
+```csharp
+var job = new NestJob(
+    new[] { DrawingJobMapper.FromDrawing("requirement-1", drawing, quantity: 3) },
+    new[] { DrawingJobMapper.FromPlate("stock-1", plateTemplate, quantity: 3) });
+var result = new NestJobRunner(LegacyPlateNesterAdapter.Create).Solve(job);
+var domainResult = NestResultMaterializer.Materialize(job, result);
+// result contains fulfillment/unplaced counts and physical stock usage;
+// domainResult.Nest and domainResult.DrawingsByPartId are detached from caller objects.
+```
+
+**Unfinished safety boundary:** basic validation rejects invalid dimensions/settings, nonfinite geometry, unknown candidate IDs, nonfinite poses, and overproduction. Cancellation throws initially and immediately after the engine returns; no partial result is returned. Full contour validity, plate containment, allowed-rotation enforcement, inter-part overlap/clearance validation, and broader cancellation coverage remain task 5 work. A committed candidate is therefore **not yet certified safe for cutting**, even if the legacy engine reports success. Geometry snapshots preserve flat CNC rapid/line/arc programs, including origin and hole contours, without approximation; other instructions are explicitly rejected. Existing desktop, API, CLI, and MCP nesting paths are unchanged.
+
 ### Run
 
 ```bash
@@ -142,7 +168,8 @@ dotnet run --project OpenNest.Console/OpenNest.Console.csproj -- project.zip ext
 OpenNest.sln
 ├── OpenNest/                   # WinForms desktop application (UI)
 ├── OpenNest.Core/              # Domain model, geometry, and CNC primitives
-├── OpenNest.Engine/            # Nesting algorithms (fill, pack, compact, best-fit)
+├── OpenNest.Engine/            # Nesting algorithms and whole-job contracts
+├── OpenNest.Engine.Tests/      # Cross-platform whole-job contract tests (net8.0)
 ├── OpenNest.IO/                # File I/O — DXF import/export, nest file format
 ├── OpenNest.Console/           # Command-line interface for batch nesting
 ├── OpenNest.Api/               # Programmatic nesting API (NestRunner pipeline)