diff --git a/OpenNest.Core/CNC/CuttingPlanning/OwnedCuttingParameters.cs b/OpenNest.Core/CNC/CuttingPlanning/OwnedCuttingParameters.cs
new file mode 100644
index 0000000..a2c83d7
--- /dev/null
+++ b/OpenNest.Core/CNC/CuttingPlanning/OwnedCuttingParameters.cs
@@ -0,0 +1,139 @@
+using System;
+using OpenNest.CNC.CuttingStrategy;
+
+namespace OpenNest.CNC.CuttingPlanning;
+
+/// <summary>Copies only supported, exact setting types; never slices custom subclasses.</summary>
+internal static class OwnedCuttingParameters
+{
+    internal static CuttingParameters Copy(CuttingParameters source)
+    {
+        Exact<CuttingParameters>(source);
+        Exact<SequenceParameters>(source.Sequencing);
+        Exact<AssignmentParameters>(source.Assignment);
+        var sequence = source.Sequencing;
+        var assignment = source.Assignment;
+        if (!Enum.IsDefined(sequence.Method) || !Enum.IsDefined(assignment.Method))
+            throw new ArgumentException("Unsupported sequence method.");
+        if (assignment.Preference == null)
+            throw new ArgumentException("Missing assignment preference.");
+        if (!double.IsFinite(source.LeadInAngleIncrement) || source.LeadInAngleIncrement <= 0
+            || source.LeadInAngleIncrement > 360)
+            throw new ArgumentException("Angle increment must be in (0, 360] degrees.");
+        return new CuttingParameters
+        {
+            Id = source.Id,
+            MachineName = source.MachineName,
+            MaterialName = source.MaterialName,
+            Grade = source.Grade,
+            Thickness = Dimension(source.Thickness),
+            Kerf = Dimension(source.Kerf),
+            PartSpacing = Dimension(source.PartSpacing),
+            PierceClearance = Dimension(source.PierceClearance),
+            ExternalLeadIn = CopyLeadIn(source.ExternalLeadIn),
+            InternalLeadIn = CopyLeadIn(source.InternalLeadIn),
+            ArcCircleLeadIn = CopyLeadIn(source.ArcCircleLeadIn),
+            ExternalLeadOut = CopyLeadOut(source.ExternalLeadOut),
+            InternalLeadOut = CopyLeadOut(source.InternalLeadOut),
+            ArcCircleLeadOut = CopyLeadOut(source.ArcCircleLeadOut),
+            RoundLeadInAngles = source.RoundLeadInAngles,
+            LeadInAngleIncrement = source.LeadInAngleIncrement,
+            AutoTabMinSize = Dimension(source.AutoTabMinSize),
+            AutoTabMaxSize = Dimension(source.AutoTabMaxSize),
+            TabConfig = source.TabConfig == null
+                ? source.TabsEnabled ? throw new ArgumentException("Enabled tabs require a configuration.") : null
+                : CopyTab(source.TabConfig),
+            TabsEnabled = source.TabsEnabled,
+            Sequencing = new SequenceParameters
+            {
+                Method = sequence.Method,
+                SmallCutoutWidth = Dimension(sequence.SmallCutoutWidth),
+                SmallCutoutHeight = Dimension(sequence.SmallCutoutHeight),
+                MediumCutoutWidth = Dimension(sequence.MediumCutoutWidth),
+                MediumCutoutHeight = Dimension(sequence.MediumCutoutHeight),
+                DistanceMediumSmall = Dimension(sequence.DistanceMediumSmall),
+                AlternateRowsColumns = sequence.AlternateRowsColumns,
+                AlternateCutoutsWithinRowColumn = sequence.AlternateCutoutsWithinRowColumn,
+                MinDistanceBetweenRowsColumns = Dimension(sequence.MinDistanceBetweenRowsColumns)
+            },
+            Assignment = new AssignmentParameters
+            {
+                Method = assignment.Method,
+                Preference = assignment.Preference,
+                MinGeometryLength = Dimension(assignment.MinGeometryLength)
+            }
+        };
+    }
+
+    private static LeadIn CopyLeadIn(LeadIn source) => source switch
+    {
+        NoLeadIn n when n.GetType() == typeof(NoLeadIn) => new NoLeadIn(),
+        LineLeadIn n when n.GetType() == typeof(LineLeadIn) => new LineLeadIn
+        { Length = Dimension(n.Length), ApproachAngle = Angle(n.ApproachAngle) },
+        ArcLeadIn n when n.GetType() == typeof(ArcLeadIn) => new ArcLeadIn { Radius = Dimension(n.Radius) },
+        LineArcLeadIn n when n.GetType() == typeof(LineArcLeadIn) => new LineArcLeadIn
+        { LineLength = Dimension(n.LineLength), ArcRadius = Dimension(n.ArcRadius), ApproachAngle = Angle(n.ApproachAngle) },
+        LineLineLeadIn n when n.GetType() == typeof(LineLineLeadIn) => new LineLineLeadIn
+        {
+            Length1 = Dimension(n.Length1),
+            Length2 = Dimension(n.Length2),
+            ApproachAngle1 = Angle(n.ApproachAngle1),
+            ApproachAngle2 = Angle(n.ApproachAngle2)
+        },
+        CleanHoleLeadIn n when n.GetType() == typeof(CleanHoleLeadIn) => new CleanHoleLeadIn
+        { LineLength = Dimension(n.LineLength), ArcRadius = Dimension(n.ArcRadius), Kerf = Dimension(n.Kerf) },
+        null => throw new ArgumentException("Missing lead-in settings."),
+        _ => throw new NotSupportedException("Unsupported lead-in runtime type.")
+    };
+
+    private static LeadOut CopyLeadOut(LeadOut source) => source switch
+    {
+        NoLeadOut n when n.GetType() == typeof(NoLeadOut) => new NoLeadOut(),
+        LineLeadOut n when n.GetType() == typeof(LineLeadOut) => new LineLeadOut
+        { Length = Dimension(n.Length), ApproachAngle = Angle(n.ApproachAngle) },
+        ArcLeadOut n when n.GetType() == typeof(ArcLeadOut) => new ArcLeadOut { Radius = Dimension(n.Radius) },
+        null => throw new ArgumentException("Missing lead-out settings."),
+        _ => throw new NotSupportedException("Unsupported lead-out runtime type.")
+    };
+
+    private static Tab CopyTab(Tab source)
+    {
+        Tab copy = source switch
+        {
+            NormalTab n when n.GetType() == typeof(NormalTab) => new NormalTab
+            {
+                CutoutMinWidth = Dimension(n.CutoutMinWidth),
+                CutoutMinHeight = Dimension(n.CutoutMinHeight),
+                CutoutMaxWidth = Dimension(n.CutoutMaxWidth),
+                CutoutMaxHeight = Dimension(n.CutoutMaxHeight)
+            },
+            BreakerTab n when n.GetType() == typeof(BreakerTab) => new BreakerTab
+            {
+                BreakerDepth = Dimension(n.BreakerDepth),
+                BreakerLeadInLength = Dimension(n.BreakerLeadInLength),
+                BreakerAngle = Angle(n.BreakerAngle)
+            },
+            MachineTab n when n.GetType() == typeof(MachineTab) => new MachineTab { MachineTabId = n.MachineTabId },
+            _ => throw new NotSupportedException("Unsupported tab runtime type.")
+        };
+        copy.Size = Dimension(source.Size);
+        copy.TabLeadIn = source.TabLeadIn == null ? null : CopyLeadIn(source.TabLeadIn);
+        copy.TabLeadOut = source.TabLeadOut == null ? null : CopyLeadOut(source.TabLeadOut);
+        return copy;
+    }
+
+    private static void Exact<T>(T value) where T : class
+    {
+        if (value == null)
+            throw new ArgumentException("Missing cutting settings.");
+        if (value.GetType() != typeof(T))
+            throw new NotSupportedException("Unsupported settings runtime type.");
+    }
+
+    private static double Dimension(double value) => double.IsFinite(value) && value >= 0
+        ? value : throw new ArgumentException("Dimensions must be finite and nonnegative.");
+
+    // Approach angles are degrees, not lengths. Signed and periodic angles are valid.
+    private static double Angle(double value) => double.IsFinite(value)
+        ? value : throw new ArgumentException("Angles must be finite.");
+}
diff --git a/OpenNest.Core/CNC/CuttingPlanning/PreparedContours.cs b/OpenNest.Core/CNC/CuttingPlanning/PreparedContours.cs
new file mode 100644
index 0000000..14e15ee
--- /dev/null
+++ b/OpenNest.Core/CNC/CuttingPlanning/PreparedContours.cs
@@ -0,0 +1,248 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using OpenNest.CNC.CuttingStrategy;
+using OpenNest.Diagnostics;
+using OpenNest.Geometry;
+
+namespace OpenNest.CNC.CuttingPlanning;
+
+/// <summary>A nominal native entry owned by one preparation, not an actual emitted pierce.</summary>
+public sealed record ContourChoice(int ContourOrdinal, int EntityOrdinal, Vector Point)
+{
+    internal PreparedContours Owner { get; init; }
+}
+
+/// <summary>
+/// Immutable owned clean contours and settings. Callers supply the clean, already-rotated
+/// program and keep it stable during Capture. This is not a topology or lead-path verdict.
+/// </summary>
+public sealed class PreparedContours
+{
+    private readonly Shape[] shapes;
+    private readonly CuttingParameters parameters;
+    private readonly List<Entity> scribes;
+
+    private PreparedContours(Shape[] shapes, List<Entity> scribes, CuttingParameters parameters)
+    {
+        this.shapes = shapes;
+        this.scribes = scribes;
+        this.parameters = parameters;
+    }
+
+    public int Count => shapes.Length;
+    public int PerimeterOrdinal => Count - 1;
+
+    public static PreparedContours Capture(Program program, CuttingParameters parameters, CancellationToken token = default)
+    {
+        token.ThrowIfCancellationRequested();
+        var ownedParameters = OwnedCuttingParameters.Copy(parameters);
+        ExecutionMotionReader.Read(program, Vector.Zero, null, token);
+        ValidateProgramTypes(program, token);
+        // ToGeometry constructs fresh native entities. Normalize an owned motion graph
+        // to incremental mode so absolute subprograms retain their frame offsets too.
+        // Retain execution boundaries: ShapeBuilder can join duplicate closed contours.
+        var geometryProgram = CopyForGeometry(program, token);
+        var contours = new List<Shape>();
+        var scribes = new List<Entity>();
+        var current = new Shape();
+        foreach (var entity in geometryProgram.ToGeometry())
+        {
+            token.ThrowIfCancellationRequested();
+            if (entity.GetType() != typeof(Line) && entity.GetType() != typeof(Arc) && entity.GetType() != typeof(Circle))
+                throw new NotSupportedException("Unsupported native geometry.");
+            if (entity.Layer == SpecialLayers.Rapid || entity.Layer == SpecialLayers.Scribe)
+            {
+                if (current.Entities.Count != 0)
+                    throw new ArgumentException("Preparation requires closed execution contours.");
+                if (entity.Layer == SpecialLayers.Scribe)
+                    scribes.Add(entity);
+                continue;
+            }
+            if (entity.Layer != SpecialLayers.Cut && entity.Layer != SpecialLayers.Display)
+                throw new ArgumentException("Preparation requires clean cut/display contours.");
+            if (entity.Length <= PostVerificationGeometry.Epsilon || !double.IsFinite(entity.Length))
+                throw new ArgumentException("Degenerate contour entity.");
+            if (entity is Circle)
+            {
+                if (current.Entities.Count != 0)
+                    throw new ArgumentException("Circle interrupts an open contour.");
+                current.Entities.Add(entity);
+                FinishContour();
+                continue;
+            }
+            if (current.Entities.Count > 0 && End(current.Entities[^1]).DistanceTo(Start(entity)) > PostVerificationGeometry.Epsilon)
+                throw new ArgumentException("Discontinuous native contour.");
+            current.Entities.Add(entity);
+            if (Start(current.Entities[0]).DistanceTo(End(entity)) <= PostVerificationGeometry.Epsilon)
+                FinishContour();
+        }
+        if (current.Entities.Count != 0 || contours.Count == 0)
+            throw new ArgumentException("Preparation requires nonempty closed contours.");
+        var perimeter = 0;
+        for (var i = 1; i < contours.Count; i++)
+        {
+            var box = contours[i].BoundingBox;
+            var best = contours[perimeter].BoundingBox;
+            if (box.Width * box.Length > best.Width * best.Length)
+                perimeter = i;
+        }
+        var outer = contours[perimeter];
+        contours.RemoveAt(perimeter);
+        contours.Add(outer);
+        return new(contours.ToArray(), scribes, ownedParameters);
+
+        void FinishContour()
+        {
+            current.UpdateBounds();
+            contours.Add(current);
+            current = new Shape();
+        }
+    }
+
+    public ContourChoice ClosestEntry(int contourOrdinal, Vector approach)
+    {
+        PostVerificationGeometry.Validate(approach);
+        var shape = GetShape(contourOrdinal);
+        var point = shape.ClosestPointTo(approach, out var entity);
+        return Entry(contourOrdinal, shape.Entities.IndexOf(entity), point);
+    }
+
+    /// <summary>
+    /// Closest native point first, then source-order vertices/midpoints or eight circle
+    /// angles (0 through 315 degrees). Geometrical duplicates keep their first entity.
+    /// Emit before validating actual paths: circle rounding/clamping may move this point.
+    /// </summary>
+    public IReadOnlyList<ContourChoice> Entries(int contourOrdinal, Vector approach, int maxEntries = 16, CancellationToken token = default)
+    {
+        token.ThrowIfCancellationRequested();
+        if (maxEntries <= 0)
+            throw new ArgumentOutOfRangeException(nameof(maxEntries));
+        var shape = GetShape(contourOrdinal);
+        var entries = new List<ContourChoice>();
+        entries.Add(ClosestEntry(contourOrdinal, approach));
+        for (var i = 0; i < shape.Entities.Count && entries.Count < maxEntries; i++)
+        {
+            token.ThrowIfCancellationRequested();
+            var entity = shape.Entities[i];
+            if (entity is Circle circle)
+            {
+                for (var angle = 0; angle < 8 && entries.Count < maxEntries; angle++)
+                    Add(i, circle.Center + new Vector(System.Math.Cos(angle * System.Math.PI / 4),
+                        System.Math.Sin(angle * System.Math.PI / 4)) * circle.Radius);
+            }
+            else
+            {
+                Add(i, Start(entity));
+                Add(i, entity is Line line ? line.MidPoint : ((Arc)entity).MidPoint());
+                Add(i, End(entity));
+            }
+        }
+        token.ThrowIfCancellationRequested();
+        return entries.AsReadOnly();
+
+        void Add(int entityOrdinal, Vector point)
+        {
+            token.ThrowIfCancellationRequested();
+            if (entries.Count < maxEntries && !entries.Any(e => e.Point.DistanceTo(point) <= PostVerificationGeometry.Epsilon))
+                entries.Add(Entry(contourOrdinal, entityOrdinal, point));
+        }
+    }
+
+    public ContourChoice Entry(int contourOrdinal, int entityOrdinal, Vector point)
+    {
+        var choice = new ContourChoice(contourOrdinal, entityOrdinal, point) { Owner = this };
+        ValidateChoice(choice);
+        return choice;
+    }
+
+    /// <summary>Emits every contour once in caller order, holes before perimeter, with scribes once.</summary>
+    public Program Emit(IReadOnlyList<ContourChoice> choices)
+    {
+        Validate(choices, true);
+        return EmitPrefix(choices);
+    }
+
+    // Each prefix is a standalone owned program, including the same scribes once.
+    internal Program EmitPrefix(IReadOnlyList<ContourChoice> choices)
+    {
+        Validate(choices, false);
+        return new ContourCuttingStrategy { Parameters = parameters }.EmitPrepared(
+            shapes.Select(s => (Shape)s.Clone()).ToArray(), scribes.Select(e => e.Clone()).ToList(), choices);
+    }
+
+    private void Validate(IReadOnlyList<ContourChoice> choices, bool complete)
+    {
+        if (choices == null || (complete && choices.Count != Count) || choices.Count > Count)
+            throw new ArgumentException("Every contour must be represented exactly once.");
+        var visited = new HashSet<int>();
+        foreach (var choice in choices)
+        {
+            ValidateChoice(choice);
+            if (!visited.Add(choice.ContourOrdinal) || choice.ContourOrdinal == PerimeterOrdinal && visited.Count != Count)
+                throw new ArgumentException("Duplicate contour or perimeter before its internal contours.");
+        }
+    }
+
+    private void ValidateChoice(ContourChoice choice)
+    {
+        if (choice == null || !ReferenceEquals(choice.Owner, this))
+            throw new ArgumentException("Foreign contour choice.");
+        PostVerificationGeometry.Validate(choice.Point);
+        var shape = GetShape(choice.ContourOrdinal);
+        if (choice.EntityOrdinal < 0 || choice.EntityOrdinal >= shape.Entities.Count)
+            throw new ArgumentException("Foreign entity ordinal.");
+        var distance = shape.Entities[choice.EntityOrdinal].ClosestPointTo(choice.Point).DistanceTo(choice.Point);
+        if (!double.IsFinite(distance) || distance > PostVerificationGeometry.Epsilon)
+            throw new ArgumentException("Entry is not on the selected native entity.");
+    }
+
+    private Shape GetShape(int ordinal) => ordinal < 0 || ordinal >= Count
+        ? throw new ArgumentException("Foreign contour ordinal.") : shapes[ordinal];
+
+    private static Vector Start(Entity entity) => entity is Line line ? line.StartPoint : ((Arc)entity).StartPoint();
+    private static Vector End(Entity entity) => entity is Line line ? line.EndPoint : ((Arc)entity).EndPoint();
+
+    private static Program CopyForGeometry(Program source, CancellationToken token)
+    {
+        var copies = new Dictionary<Program, Program>(ReferenceEqualityComparer.Instance);
+        return Copy(source);
+
+        Program Copy(Program current)
+        {
+            token.ThrowIfCancellationRequested();
+            if (copies.TryGetValue(current, out var existing))
+                return existing;
+            var copy = new Program(current.Mode);
+            copies.Add(current, copy);
+            foreach (var code in current.Codes)
+            {
+                token.ThrowIfCancellationRequested();
+                var ownedCode = code.Clone();
+                if (ownedCode is SubProgramCall call)
+                    call.BindProgram(Copy(((SubProgramCall)code).Program));
+                copy.Codes.Add(ownedCode);
+            }
+            copy.Mode = Mode.Incremental;
+            return copy;
+        }
+    }
+
+    private static void ValidateProgramTypes(Program program, CancellationToken token)
+    {
+        token.ThrowIfCancellationRequested();
+        if (program.GetType() != typeof(Program) || !Enum.IsDefined(program.Mode))
+            throw new NotSupportedException("Unsupported program runtime type or mode.");
+        foreach (var code in program.Codes)
+        {
+            token.ThrowIfCancellationRequested();
+            var type = code.GetType();
+            if (type != typeof(RapidMove) && type != typeof(LinearMove) && type != typeof(ArcMove)
+                && type != typeof(SubProgramCall) && type != typeof(Comment) && type != typeof(Feedrate) && type != typeof(Kerf))
+                throw new NotSupportedException("Unsupported instruction runtime type.");
+            if (code is SubProgramCall call)
+                ValidateProgramTypes(call.Program, token);
+        }
+    }
+}
diff --git a/OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs b/OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs
index ffc8c9e..a5584e5 100644
--- a/OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs
+++ b/OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs
@@ -234,6 +234,21 @@ namespace OpenNest.CNC.CuttingStrategy
             return null;
         }
 
+        internal Program EmitPrepared(Shape[] shapes, List<Entity> scribes,
+            IReadOnlyList<CuttingPlanning.ContourChoice> choices)
+        {
+            var result = new Program(Mode.Absolute);
+            EmitScribeContours(result, scribes);
+            foreach (var choice in choices)
+            {
+                var shape = shapes[choice.ContourOrdinal];
+                EmitContour(result, shape, choice.Point, shape.Entities[choice.EntityOrdinal],
+                    choice.ContourOrdinal == shapes.Length - 1 ? ContourType.External : null);
+            }
+            result.Mode = Mode.Incremental;
+            return result;
+        }
+
         private void EmitRawContour(Program program, Shape shape)
         {
             var startPoint = GetShapeStartPoint(shape);
diff --git a/OpenNest.Core/OpenNest.Core.csproj b/OpenNest.Core/OpenNest.Core.csproj
index 57f00bd..45d022c 100644
--- a/OpenNest.Core/OpenNest.Core.csproj
+++ b/OpenNest.Core/OpenNest.Core.csproj
@@ -6,6 +6,7 @@
   </PropertyGroup>
   <ItemGroup>
     <InternalsVisibleTo Include="OpenNest.Tests" />
+    <InternalsVisibleTo Include="OpenNest.Engine" />
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Clipper2" Version="2.0.0" />
diff --git a/OpenNest.Tests/CuttingPlanning/OwnedCuttingParameterTests.cs b/OpenNest.Tests/CuttingPlanning/OwnedCuttingParameterTests.cs
new file mode 100644
index 0000000..5276e9b
--- /dev/null
+++ b/OpenNest.Tests/CuttingPlanning/OwnedCuttingParameterTests.cs
@@ -0,0 +1,170 @@
+using OpenNest.CNC.CuttingPlanning;
+using OpenNest.CNC.CuttingStrategy;
+
+namespace OpenNest.Tests.CuttingPlanning;
+
+public class OwnedCuttingParameterTests
+{
+    public static IEnumerable<object[]> Styles()
+    {
+        foreach (var leadIn in new LeadIn[] { new NoLeadIn(), new LineLeadIn { Length = 0.3, ApproachAngle = 45 },
+            new ArcLeadIn { Radius = 0.2 }, new LineArcLeadIn { LineLength = 0.1, ArcRadius = 0.2, ApproachAngle = 120 },
+            new LineLineLeadIn { Length1 = 0.1, Length2 = 0.2, ApproachAngle1 = 40, ApproachAngle2 = -30 },
+            new CleanHoleLeadIn { LineLength = 0.1, ArcRadius = 0.2, Kerf = 0.01 } })
+            foreach (var leadOut in new LeadOut[] { new NoLeadOut(), new LineLeadOut { Length = 0.4, ApproachAngle = 80 }, new ArcLeadOut { Radius = 0.3 } })
+                foreach (var tab in new Tab[] { new NormalTab { Size = 0.2, CutoutMinWidth = 1, CutoutMaxWidth = 5, CutoutMinHeight = 2, CutoutMaxHeight = 6 },
+                    new BreakerTab { Size = 0.3, BreakerDepth = 0.1, BreakerLeadInLength = 0.2, BreakerAngle = 30 },
+                    new MachineTab { Size = 0.4, MachineTabId = 7 } })
+                    yield return [leadIn, leadOut, tab];
+    }
+
+    [Theory]
+    [MemberData(nameof(Styles))]
+    public void Copy_PreservesEveryMemberAndBreaksEveryMutableAlias(LeadIn leadIn, LeadOut leadOut, Tab tab)
+    {
+        tab.TabLeadIn = leadIn; tab.TabLeadOut = leadOut;
+        var source = new CuttingParameters
+        {
+            Id = 17,
+            MachineName = "machine",
+            MaterialName = "material",
+            Grade = "grade",
+            Thickness = 0.4,
+            Kerf = 0.01,
+            PartSpacing = 0.1,
+            PierceClearance = 0.05,
+            ExternalLeadIn = leadIn,
+            InternalLeadIn = leadIn,
+            ArcCircleLeadIn = leadIn,
+            ExternalLeadOut = leadOut,
+            InternalLeadOut = leadOut,
+            ArcCircleLeadOut = leadOut,
+            TabConfig = tab,
+            TabsEnabled = true,
+            AutoTabMinSize = 0.1,
+            AutoTabMaxSize = 0.5,
+            RoundLeadInAngles = true,
+            LeadInAngleIncrement = 30,
+            Sequencing = new SequenceParameters
+            {
+                Method = SequenceMethod.LeftSide,
+                SmallCutoutWidth = 2,
+                SmallCutoutHeight = 3,
+                MediumCutoutWidth = 9,
+                MediumCutoutHeight = 10,
+                DistanceMediumSmall = 4,
+                AlternateRowsColumns = false,
+                AlternateCutoutsWithinRowColumn = false,
+                MinDistanceBetweenRowsColumns = 0.3
+            },
+            Assignment = new AssignmentParameters { Method = SequenceMethod.EdgeStart, Preference = "test", MinGeometryLength = 0.04 }
+        };
+        var copy = OwnedCuttingParameters.Copy(source);
+        AssertOwnedEqual(source, copy);
+        var secondCopy = OwnedCuttingParameters.Copy(copy);
+        Mutate(source, new HashSet<object>(ReferenceEqualityComparer.Instance));
+        AssertOwnedEqual(secondCopy, copy);
+    }
+
+    private static void AssertOwnedEqual(object? source, object? copy)
+    {
+        Assert.Equal(source?.GetType(), copy?.GetType());
+        if (source == null) return;
+        Assert.NotSame(source, copy);
+        foreach (var property in source.GetType().GetProperties())
+        {
+            var a = property.GetValue(source)!; var b = property.GetValue(copy);
+            if (property.PropertyType.IsValueType || property.PropertyType == typeof(string))
+                Assert.Equal(a, b);
+            else
+                AssertOwnedEqual(a, b);
+        }
+    }
+
+    private static void Mutate(object? source, HashSet<object> visited)
+    {
+        if (source == null || !visited.Add(source)) return;
+        foreach (var property in source.GetType().GetProperties())
+        {
+            var value = property.GetValue(source)!;
+            if (property.PropertyType == typeof(double)) property.SetValue(source, (double)value + 100);
+            else if (property.PropertyType == typeof(bool)) property.SetValue(source, !(bool)value);
+            else if (property.PropertyType == typeof(int)) property.SetValue(source, (int)value + 10);
+            else if (property.PropertyType == typeof(string)) property.SetValue(source, "mutated");
+            else if (property.PropertyType.IsEnum) property.SetValue(source, Enum.ToObject(property.PropertyType, 100));
+            else Mutate(value, visited);
+        }
+    }
+
+    [Theory]
+    [InlineData("null-settings")]
+    [InlineData("null-sequence")]
+    [InlineData("null-assignment")]
+    [InlineData("null-lead")]
+    [InlineData("null-leadout")]
+    [InlineData("null-tab")]
+    [InlineData("dimension")]
+    [InlineData("angle")]
+    [InlineData("increment")]
+    [InlineData("enum")]
+    [InlineData("tab-lead")]
+    [InlineData("custom-in")]
+    [InlineData("custom-out")]
+    [InlineData("custom-tab")]
+    [InlineData("custom-settings")]
+    [InlineData("custom-sequence")]
+    [InlineData("custom-assignment")]
+    public void Copy_RejectsInvalidOrUnsupportedSettings(string fault)
+    {
+        var source = new CuttingParameters();
+        switch (fault)
+        {
+            case "null-settings": source = null; break;
+            case "null-sequence": source.Sequencing = null; break;
+            case "null-assignment": source.Assignment = null; break;
+            case "null-lead": source.ArcCircleLeadIn = null; break;
+            case "null-leadout": source.InternalLeadOut = null; break;
+            case "null-tab": source.TabsEnabled = true; break;
+            case "dimension": source.PartSpacing = -1; break;
+            case "angle": source.ExternalLeadIn = new LineLeadIn { ApproachAngle = double.NaN }; break;
+            case "increment": source.LeadInAngleIncrement = 0; break;
+            case "enum": source.Assignment.Method = (SequenceMethod)6; break;
+            case "tab-lead": source.TabConfig = new NormalTab { TabLeadIn = new ArcLeadIn { Radius = double.PositiveInfinity } }; break;
+            case "custom-in": source.InternalLeadIn = new CustomLeadIn(); break;
+            case "custom-out": source.ArcCircleLeadOut = new CustomLeadOut(); break;
+            case "custom-tab": source.TabConfig = new CustomTab(); break;
+            case "custom-settings": source = new CustomParameters(); break;
+            case "custom-sequence": source.Sequencing = new CustomSequence(); break;
+            case "custom-assignment": source.Assignment = new CustomAssignment(); break;
+        }
+        Assert.ThrowsAny<Exception>(() => OwnedCuttingParameters.Copy(source));
+        Assert.ThrowsAny<Exception>(() => PreparedContours.Capture(ExplicitContourTests.Square(false), source));
+    }
+
+    [Theory]
+    [InlineData(-1)]
+    [InlineData(double.NaN)]
+    [InlineData(double.PositiveInfinity)]
+    public void Copy_RejectsEveryInvalidDimension(double bad)
+    {
+        foreach (var sample in Styles())
+        {
+            var source = new CuttingParameters { ExternalLeadIn = (LeadIn)sample[0], ExternalLeadOut = (LeadOut)sample[1], TabConfig = (Tab)sample[2] };
+            foreach (var owner in new object[] { source, source.Sequencing, source.Assignment, source.ExternalLeadIn, source.ExternalLeadOut, source.TabConfig })
+                foreach (var property in owner.GetType().GetProperties().Where(p => p.PropertyType == typeof(double) && !p.Name.Contains("Angle")))
+                {
+                    var original = property.GetValue(owner);
+                    property.SetValue(owner, bad);
+                    Assert.Throws<ArgumentException>(() => OwnedCuttingParameters.Copy(source));
+                    property.SetValue(owner, original);
+                }
+        }
+    }
+
+    private sealed class CustomLeadIn : LineLeadIn { }
+    private sealed class CustomLeadOut : ArcLeadOut { }
+    private sealed class CustomTab : NormalTab { }
+    private sealed class CustomParameters : CuttingParameters { }
+    private sealed class CustomSequence : SequenceParameters { }
+    private sealed class CustomAssignment : AssignmentParameters { }
+}
diff --git a/OpenNest.Tests/CuttingPlanning/PreparedContourTests.cs b/OpenNest.Tests/CuttingPlanning/PreparedContourTests.cs
new file mode 100644
index 0000000..58a138e
--- /dev/null
+++ b/OpenNest.Tests/CuttingPlanning/PreparedContourTests.cs
@@ -0,0 +1,326 @@
+using OpenNest.CNC;
+using OpenNest.CNC.CuttingPlanning;
+using OpenNest.CNC.CuttingStrategy;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.CuttingPlanning;
+
+public class PreparedContourTests
+{
+    [Fact]
+    public void Emit_RespectsEveryExplicitEntryAndContourOrder()
+    {
+        var source = Holes();
+        var prepared = PreparedContours.Capture(source, ExplicitContourTests.Parameters());
+        var choices = new[]
+        {
+            prepared.ClosestEntry(1, new Vector(20, 3)),
+            prepared.ClosestEntry(0, new Vector(20, 3)),
+            prepared.ClosestEntry(2, new Vector(20, 5))
+        };
+        var emitted = prepared.Emit(choices);
+        var calls = emitted.Codes.OfType<SubProgramCall>().ToArray();
+        Assert.Equal(new[] { new Vector(7, 3), new Vector(3, 3) }, calls.Select(c => c.Offset));
+        var cuts = ExecutionMotionReader.Read(emitted, Vector.Zero, null, default).Motions
+            .Where(m => m.Layer == LayerType.Display && !m.Rapid).ToArray();
+        Assert.Equal(new Vector(8, 3), cuts[0].Start);
+        Assert.Equal(new Vector(4, 3), cuts[1].Start);
+        Assert.Equal(source.ToString(), Holes().ToString());
+    }
+
+    [Theory]
+    [InlineData("duplicate")]
+    [InlineData("omitted")]
+    [InlineData("foreign")]
+    [InlineData("perimeter-first")]
+    public void Emit_RejectsIncompleteOrForeignAccounting(string fault)
+    {
+        var prepared = PreparedContours.Capture(Holes(), ExplicitContourTests.Parameters());
+        var choices = Enumerable.Range(0, 3).Select(i => prepared.ClosestEntry(i, new Vector(20, 5))).ToArray();
+        switch (fault)
+        {
+            case "duplicate": choices[1] = choices[0]; break;
+            case "omitted": choices = choices[..2]; break;
+            case "foreign": choices[0] = PreparedContours.Capture(Holes(), ExplicitContourTests.Parameters()).ClosestEntry(0, Vector.Zero); break;
+            case "perimeter-first": Array.Reverse(choices); break;
+        }
+        Assert.Throws<ArgumentException>(() => prepared.Emit(choices));
+    }
+
+    [Fact]
+    public void Prepared_OwnsGeometryAndDeepSettings()
+    {
+        var source = Holes();
+        var settings = ExplicitContourTests.Parameters();
+        var prepared = PreparedContours.Capture(source, settings);
+        var choices = Enumerable.Range(0, 3).Select(i => prepared.ClosestEntry(i, new Vector(20, 5))).ToArray();
+        var before = ExplicitContourTests.Fingerprint(prepared.Emit(choices));
+        source.Codes.Clear();
+        ((LineLeadIn)settings.ExternalLeadIn).Length = 100;
+        settings.TabsEnabled = true;
+        Assert.Equal(before, ExplicitContourTests.Fingerprint(prepared.Emit(choices)));
+    }
+
+    [Theory]
+    [MemberData(nameof(ExplicitContourTests.RetainedStyles), MemberType = typeof(ExplicitContourTests))]
+    public void ExplicitEmission_OrdinarySingleContourMatchesLegacy(string style, bool reverse, bool internalContour)
+    {
+        var source = ExplicitContourTests.Square(reverse);
+        var target = source.ToGeometry().First(e => e.Layer != SpecialLayers.Rapid);
+        var parameters = ExplicitContourTests.Parameters(style);
+        if (internalContour)
+        {
+            source.MoveTo(-5, -5); source.LineTo(-5, 15); source.LineTo(15, 15);
+            source.LineTo(15, -5); source.LineTo(-5, -5);
+            parameters.ExternalLeadIn = new NoLeadIn();
+        }
+        var prepared = PreparedContours.Capture(source, parameters);
+        var choice = prepared.ClosestEntry(0, Vector.Zero);
+        var choices = internalContour
+            ? new[] { choice, prepared.Entry(1, 0, new Vector(-5, -5)) }
+            : new[] { choice };
+        var legacy = new ContourCuttingStrategy { Parameters = parameters }.ApplySingle(source,
+            Vector.Zero, target, internalContour ? ContourType.Internal : ContourType.External).Program;
+        Assert.Equal(ExplicitContourTests.Fingerprint(legacy), ExplicitContourTests.Fingerprint(prepared.Emit(choices)));
+    }
+
+    [Fact]
+    public void Entries_AreStableBoundedNativeAndGeometricallyUnique()
+    {
+        var prepared = PreparedContours.Capture(ExplicitContourTests.Square(false), new CuttingParameters());
+        var approach = new Vector(-1, 5);
+        var entries = prepared.Entries(0, approach);
+        Assert.Equal(prepared.ClosestEntry(0, approach), entries[0]);
+        Assert.Equal(new[] { new Vector(0, 5), new Vector(0, 0), new Vector(0, 10),
+            new Vector(5, 10), new Vector(10, 10), new Vector(10, 5), new Vector(10, 0), new Vector(5, 0) },
+            entries.Select(e => e.Point));
+        Assert.Equal(entries, prepared.Entries(0, approach));
+        Assert.Equal(entries.Take(3), prepared.Entries(0, approach, 3));
+        Assert.Single(prepared.Entries(0, approach, 1));
+        Assert.Throws<NotSupportedException>(() => ((IList<ContourChoice>)entries).Clear());
+        Assert.Throws<ArgumentOutOfRangeException>(() => prepared.Entries(0, approach, 0));
+        Assert.Throws<OperationCanceledException>(() => prepared.Entries(0, approach,
+            token: new CancellationToken(true)));
+        Assert.Throws<OperationCanceledException>(() => PreparedContours.Capture(
+            ExplicitContourTests.Square(false), new CuttingParameters(), new CancellationToken(true)));
+    }
+
+    [Fact]
+    public void Entries_IncludeNativeArcMidpointAndCircleAngles()
+    {
+        var source = new Program();
+        source.MoveTo(1, 0); source.ArcTo(-1, 0, 0, 0, RotationType.CCW); source.LineTo(1, 0);
+        var prepared = PreparedContours.Capture(source, new CuttingParameters());
+        var entries = prepared.Entries(0, new Vector(0, -2));
+        Assert.Contains(entries, e => e.Point.DistanceTo(new Vector(0, 1)) < 1e-8);
+        Assert.Contains(entries, e => e.Point.DistanceTo(new Vector(-1, 0)) < 1e-8);
+        prepared = PreparedContours.Capture(Holes(), new CuttingParameters());
+        var circles = prepared.Entries(0, new Vector(5, 5));
+        Assert.InRange(circles.Count, 8, 9);
+        Assert.Equal(circles, prepared.Entries(0, new Vector(5, 5)));
+        Assert.All(circles, e => Assert.Equal(1, e.Point.DistanceTo(new Vector(3, 3)), 8));
+        Assert.Equal(circles.Count, circles.Select(e => e.Point).Distinct().Count());
+    }
+
+    [Theory]
+    [InlineData(-1, 0, 0, 0)]
+    [InlineData(3, 0, 0, 0)]
+    [InlineData(0, -1, 0, 0)]
+    [InlineData(0, 1, 3, 3)]
+    [InlineData(0, 0, 3, 3)]
+    [InlineData(0, 0, double.NaN, 3)]
+    [InlineData(0, 0, double.PositiveInfinity, 3)]
+    public void Entry_RejectsInvalidNativeChoices(int contour, int entity, double x, double y)
+    {
+        var prepared = PreparedContours.Capture(Holes(), new CuttingParameters());
+        Assert.Throws<ArgumentException>(() => prepared.Entry(contour, entity, new Vector(x, y)));
+    }
+
+    [Fact]
+    public void Emit_RevalidatesRecordCopiesAndRejectsUnownedRecords()
+    {
+        var prepared = PreparedContours.Capture(ExplicitContourTests.Square(false), new CuttingParameters());
+        var choice = prepared.ClosestEntry(0, Vector.Zero);
+        Assert.Throws<ArgumentException>(() => prepared.Emit([choice with { EntityOrdinal = 100 }]));
+        Assert.Throws<ArgumentException>(() => prepared.Emit([choice with { Point = new Vector(5, 5) }]));
+        Assert.Throws<ArgumentException>(() => prepared.Emit([new ContourChoice(0, 0, Vector.Zero)]));
+        Assert.Throws<ArgumentException>(() => prepared.Emit([null]));
+    }
+
+    [Fact]
+    public void Capture_AccountsForDuplicateContoursWithoutJoiningOrDroppingThem()
+    {
+        var source = ExplicitContourTests.Square(false);
+        foreach (var ignored in new[] { 0, 1 })
+        {
+            source.MoveTo(2, 2); source.LineTo(2, 4); source.LineTo(4, 4);
+            source.LineTo(4, 2); source.LineTo(2, 2);
+            source.MoveTo(7, 7); source.ArcTo(7, 7, 6, 7, RotationType.CCW);
+        }
+        var prepared = PreparedContours.Capture(source, new CuttingParameters());
+        Assert.Equal(5, prepared.Count);
+        var choices = Enumerable.Range(0, 5).Select(i => prepared.ClosestEntry(i, Vector.Zero)).ToArray();
+        var motions = ExecutionMotionReader.Read(prepared.Emit(choices), Vector.Zero, null, default).Motions;
+        Assert.Equal(14, motions.Count(m => !m.Rapid && m.Layer == LayerType.Display));
+    }
+
+    [Theory]
+    [InlineData("open")]
+    [InlineData("lead")]
+    [InlineData("layer")]
+    [InlineData("derived")]
+    [InlineData("mode")]
+    public void Capture_RefusesUnsupportedOrUncleanExecution(string fault)
+    {
+        var source = ExplicitContourTests.Square(false);
+        if (fault == "open") source.Codes.RemoveAt(source.Codes.Count - 1);
+        if (fault == "lead") ((LinearMove)source.Codes[1]).Layer = LayerType.Leadin;
+        if (fault == "layer") ((LinearMove)source.Codes[1]).Layer = (LayerType)100;
+        if (fault == "derived") source.Codes[1] = new CustomLinearMove();
+        if (fault == "mode") typeof(Program).GetField("mode", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)!.SetValue(source, (Mode)100);
+        Assert.ThrowsAny<Exception>(() => PreparedContours.Capture(source, new CuttingParameters()));
+    }
+
+    private sealed class CustomLinearMove : LinearMove { }
+
+    [Fact]
+    public void ExplicitCircle_RoundsActualEntryClampsAndSharesOwnedSubprograms()
+    {
+        var source = Holes();
+        var parameters = ExplicitContourTests.Parameters();
+        parameters.ArcCircleLeadIn = new LineLeadIn { Length = 10 };
+        parameters.RoundLeadInAngles = true;
+        parameters.LeadInAngleIncrement = 90;
+        var prepared = PreparedContours.Capture(source, parameters);
+        var choices = new[] { prepared.ClosestEntry(0, new Vector(5, 5)),
+            prepared.ClosestEntry(1, new Vector(9, 5)), prepared.ClosestEntry(2, Vector.Zero) };
+        var result = prepared.Emit(choices);
+        var calls = result.Codes.OfType<SubProgramCall>().ToArray();
+        Assert.Equal(2, calls.Length);
+        Assert.Same(calls[0].Program, calls[1].Program);
+        var motions = ExecutionMotionReader.Read(result, Vector.Zero, null, default).Motions;
+        var leads = motions.Where(m => m.Layer == LayerType.Leadin).Take(2).ToArray();
+        Assert.All(leads, m => Assert.True(m.Length < 2));
+        Assert.True(choices[0].Point.DistanceTo(leads[0].End) > 0.1);
+        Assert.Equal(new Vector(4, 3), leads[0].End);
+        Assert.True(leads[0].Start!.Value.DistanceTo(new Vector(3, 3)) <= 0.95 + 1e-8);
+        var before = ExplicitContourTests.Fingerprint(prepared.Emit(choices));
+        calls[0].Program.Codes.Clear(); result.Codes.Clear(); source.Codes.Clear();
+        Assert.Equal(before, ExplicitContourTests.Fingerprint(prepared.Emit(choices)));
+        Assert.NotSame(calls[0].Program, prepared.Emit(choices).Codes.OfType<SubProgramCall>().First().Program);
+    }
+
+    [Theory]
+    [InlineData("normal")]
+    [InlineData("breaker")]
+    [InlineData("machine")]
+    public void ExplicitTab_RetainsLegacyGapAndOwnsTabSize(string style)
+    {
+        var parameters = ExplicitContourTests.Parameters();
+        parameters.TabsEnabled = true;
+        parameters.TabConfig = style switch
+        {
+            "breaker" => new BreakerTab { Size = 0.2 },
+            "machine" => new MachineTab { Size = 0.2 },
+            _ => new NormalTab { Size = 0.2 }
+        };
+        var source = ExplicitContourTests.Square(false);
+        var approach = new Vector(-1, 5);
+        var prepared = PreparedContours.Capture(source, parameters);
+        var choice = prepared.ClosestEntry(0, approach);
+        var result = prepared.Emit([choice]);
+        var legacy = new ContourCuttingStrategy { Parameters = parameters }.Apply(source, approach).Program;
+        Assert.Equal(ExplicitContourTests.Fingerprint(legacy), ExplicitContourTests.Fingerprint(result));
+        var cuts = ExecutionMotionReader.Read(result, Vector.Zero, null, default).Motions
+            .Where(m => !m.Rapid && m.Layer == LayerType.Display).ToArray();
+        Assert.True(cuts[0].Start!.Value.DistanceTo(cuts[^1].End) > 0.1);
+        parameters.TabConfig.Size = 8; parameters.TabsEnabled = false;
+        Assert.Equal(ExplicitContourTests.Fingerprint(result), ExplicitContourTests.Fingerprint(prepared.Emit([choice])));
+    }
+
+    [Fact]
+    public void PrefixAndCompletePrograms_EmitScribesExactlyOnceAndOwnThem()
+    {
+        var source = Holes();
+        source.MoveTo(1, 1); source.Codes.Add(new LinearMove(new Vector(2, 1)) { Layer = LayerType.Scribe });
+        var prepared = PreparedContours.Capture(source, new CuttingParameters());
+        var choices = Enumerable.Range(0, 3).Select(i => prepared.ClosestEntry(i, Vector.Zero)).ToArray();
+        Assert.Throws<ArgumentException>(() => prepared.EmitPrefix([choices[2]]));
+        foreach (var count in new[] { 0, 1, 2, 3 })
+        {
+            var result = prepared.EmitPrefix(choices.Take(count).ToArray());
+            var motions = ExecutionMotionReader.Read(result, Vector.Zero, null, default).Motions;
+            Assert.Single(motions.Where(m => m.Layer == LayerType.Scribe));
+            result.Codes.Clear();
+        }
+        Assert.Single(ExecutionMotionReader.Read(prepared.Emit(choices), Vector.Zero, null, default).Motions
+            .Where(m => m.Layer == LayerType.Scribe));
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void Capture_ExpandsSharedSubprogramFramesAndOwnsTheirMotion(bool incremental)
+    {
+        var hole = new Program();
+        hole.MoveTo(1, 0); hole.ArcTo(1, 0, 0, 0, RotationType.CCW);
+        if (incremental) hole.Mode = Mode.Incremental;
+        var source = ExplicitContourTests.Square(false);
+        source.Codes.Add(new SubProgramCall { Id = 1, Program = hole, Offset = new Vector(3, 3) });
+        source.Codes.Add(new SubProgramCall { Id = 1, Program = hole, Offset = new Vector(7, 3) });
+        var prepared = PreparedContours.Capture(source, ExplicitContourTests.Parameters());
+        Assert.Equal(3, prepared.Count);
+        var choices = Enumerable.Range(0, 3).Select(i => prepared.ClosestEntry(i, new Vector(20, 3))).ToArray();
+        Assert.Equal(new Vector(4, 3), choices[0].Point);
+        Assert.Equal(new Vector(8, 3), choices[1].Point);
+        var before = ExplicitContourTests.Fingerprint(prepared.Emit(choices));
+        hole.Codes.Clear(); source.Codes.Clear();
+        Assert.Equal(before, ExplicitContourTests.Fingerprint(prepared.Emit(choices)));
+    }
+
+    [Fact]
+    public void Prefix_RejectsDuplicateContoursEvenBeforeThePerimeter()
+    {
+        var prepared = PreparedContours.Capture(Holes(), new CuttingParameters());
+        var choice = prepared.ClosestEntry(0, Vector.Zero);
+        Assert.Throws<ArgumentException>(() => prepared.EmitPrefix([choice, choice]));
+    }
+
+    [Theory]
+    [InlineData("none", false)]
+    [InlineData("none", true)]
+    [InlineData("line", false)]
+    [InlineData("line", true)]
+    [InlineData("arc", false)]
+    [InlineData("arc", true)]
+    public void ExplicitLeadOut_RetainsLegacyGeometryAndOwnership(string style, bool reversed)
+    {
+        var source = ExplicitContourTests.Square(reversed);
+        var parameters = ExplicitContourTests.Parameters();
+        parameters.ExternalLeadOut = style switch
+        {
+            "line" => new LineLeadOut { Length = 0.2, ApproachAngle = 45 },
+            "arc" => new ArcLeadOut { Radius = 0.2 },
+            _ => new NoLeadOut()
+        };
+        var approach = new Vector(-1, 5);
+        var prepared = PreparedContours.Capture(source, parameters);
+        var choice = prepared.ClosestEntry(0, approach);
+        var emitted = prepared.Emit([choice]);
+        var legacy = new ContourCuttingStrategy { Parameters = parameters }.Apply(source, approach).Program;
+        Assert.Equal(ExplicitContourTests.Fingerprint(legacy), ExplicitContourTests.Fingerprint(emitted));
+        if (parameters.ExternalLeadOut is LineLeadOut line) line.Length = 9;
+        if (parameters.ExternalLeadOut is ArcLeadOut arc) arc.Radius = 9;
+        Assert.Equal(ExplicitContourTests.Fingerprint(emitted), ExplicitContourTests.Fingerprint(prepared.Emit([choice])));
+    }
+
+    internal static Program Holes()
+    {
+        var p = ExplicitContourTests.Square(false);
+        foreach (var x in new[] { 3.0, 7.0 })
+        {
+            p.MoveTo(x + 1, 3); p.ArcTo(x + 1, 3, x, 3, RotationType.CCW);
+        }
+        return p;
+    }
+}