refactor: two-pass lead-in placement in ContourCuttingStrategy

Resolve lead-in points by walking backward through cutting order (from
perimeter outward) so each lead-in faces the next cutout to be cut
rather than pointing back at the previous lead-out. Extract EmitContour
and EmitScribeContours to eliminate duplicated cutout/perimeter logic.

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

OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs

@@ -8,113 +8,101 @@ namespace OpenNest.CNC.CuttingStrategy
     {
         public CuttingParameters Parameters { get; set; }
 
+        private record ContourEntry(Shape Shape, Vector Point, Entity Entity);
+
         public CuttingResult Apply(Program partProgram, Vector approachPoint)
         {
-            var exitPoint = approachPoint;
             var entities = partProgram.ToGeometry();
             entities.RemoveAll(e => e.Layer == SpecialLayers.Rapid);
 
-            // Separate scribe/etch entities — they don't get lead-ins or kerf
             var scribeEntities = entities.FindAll(e => e.Layer == SpecialLayers.Scribe);
             entities.RemoveAll(e => e.Layer == SpecialLayers.Scribe);
 
             var profile = new ShapeProfile(entities);
 
-            // Find closest point on perimeter from exit point
+            // Forward pass: sequence cutouts nearest-neighbor from perimeter
-            var perimeterPoint = profile.Perimeter.ClosestPointTo(exitPoint, out var perimeterEntity);
+            var perimeterPoint = profile.Perimeter.ClosestPointTo(approachPoint, out _);
-
-            // Chain cutouts by nearest-neighbor from perimeter point, then reverse
-            // so farthest cutouts are cut first, nearest-to-perimeter cut last
             var orderedCutouts = SequenceCutouts(profile.Cutouts, perimeterPoint);
             orderedCutouts.Reverse();
 
-            // Build output program: scribe first, cutouts second, perimeter last
+            // Backward pass: walk from perimeter back through cutting order
+            // so each lead-in faces the next cutout to be cut, not the previous
+            var cutoutEntries = ResolveLeadInPoints(orderedCutouts, perimeterPoint);
+
             var result = new Program(Mode.Absolute);
-            var currentPoint = exitPoint;
 
-            // Emit scribe/etch contours first (no lead-ins, no kerf)
+            EmitScribeContours(result, scribeEntities);
-            if (scribeEntities.Count > 0)
-            {
-                var scribeShapes = ShapeBuilder.GetShapes(scribeEntities);
-                foreach (var scribe in scribeShapes)
-                {
-                    var startPt = GetShapeStartPoint(scribe);
-                    result.Codes.Add(new RapidMove(startPt));
-                    result.Codes.AddRange(ConvertShapeToMoves(scribe, startPt, LayerType.Scribe));
-                    currentPoint = startPt;
-                }
-            }
 
-            foreach (var cutout in orderedCutouts)
+            foreach (var entry in cutoutEntries)
-            {
+                EmitContour(result, entry.Shape, entry.Point, entry.Entity);
-                var contourType = DetectContourType(cutout);
-                var closestPt = cutout.ClosestPointTo(currentPoint, out var entity);
-                var normal = ComputeNormal(closestPt, entity, contourType);
-                var winding = DetermineWinding(cutout);
-
-                var leadIn = SelectLeadIn(contourType);
-                var leadOut = SelectLeadOut(contourType);
-
-                if (contourType == ContourType.ArcCircle && entity is Circle circle)
-                    leadIn = ClampLeadInForCircle(leadIn, circle, closestPt, normal);
-
-                result.Codes.AddRange(leadIn.Generate(closestPt, normal, winding));
-                var reindexed = cutout.ReindexAt(closestPt, entity);
-
-                if (Parameters.TabsEnabled && Parameters.TabConfig != null)
-                {
-                    var trimmed = TrimShapeForTab(reindexed, closestPt, Parameters.TabConfig.Size);
-                    result.Codes.AddRange(ConvertShapeToMoves(trimmed, closestPt));
-                    result.Codes.AddRange(leadOut.Generate(closestPt, normal, winding));
-                }
-                else
-                {
-                    result.Codes.AddRange(ConvertShapeToMoves(reindexed, closestPt));
-                    result.Codes.AddRange(leadOut.Generate(closestPt, normal, winding));
-                }
-
-                currentPoint = closestPt;
-            }
-
-            var lastCutPoint = exitPoint;
 
             // Perimeter last
-            {
+            var lastRefPoint = cutoutEntries.Count > 0 ? cutoutEntries[cutoutEntries.Count - 1].Point : approachPoint;
-                var perimeterPt = profile.Perimeter.ClosestPointTo(currentPoint, out perimeterEntity);
+            var perimeterPt = profile.Perimeter.ClosestPointTo(lastRefPoint, out var perimeterEntity);
-                lastCutPoint = perimeterPt;
+            EmitContour(result, profile.Perimeter, perimeterPt, perimeterEntity, ContourType.External);
-                var normal = ComputeNormal(perimeterPt, perimeterEntity, ContourType.External);
-                var winding = DetermineWinding(profile.Perimeter);
 
-                var leadIn = SelectLeadIn(ContourType.External);
-                var leadOut = SelectLeadOut(ContourType.External);
-
-                result.Codes.AddRange(leadIn.Generate(perimeterPt, normal, winding));
-                var reindexed = profile.Perimeter.ReindexAt(perimeterPt, perimeterEntity);
-
-                if (Parameters.TabsEnabled && Parameters.TabConfig != null)
-                {
-                    var trimmed = TrimShapeForTab(reindexed, perimeterPt, Parameters.TabConfig.Size);
-                    result.Codes.AddRange(ConvertShapeToMoves(trimmed, perimeterPt));
-                    result.Codes.AddRange(leadOut.Generate(perimeterPt, normal, winding));
-                }
-                else
-                {
-                    result.Codes.AddRange(ConvertShapeToMoves(reindexed, perimeterPt));
-                    result.Codes.AddRange(leadOut.Generate(perimeterPt, normal, winding));
-                }
-            }
-
-            // Convert to incremental mode to match the convention used by
-            // the rest of the system (rendering, bounding box, drag, etc.).
             result.Mode = Mode.Incremental;
 
             return new CuttingResult
             {
                 Program = result,
-                LastCutPoint = lastCutPoint
+                LastCutPoint = perimeterPt
             };
         }
 
+        private static List<ContourEntry> ResolveLeadInPoints(List<Shape> cutouts, Vector startPoint)
+        {
+            var entries = new ContourEntry[cutouts.Count];
+            var currentPoint = startPoint;
+
+            // Walk backward through cutting order (from perimeter outward)
+            // so each cutout's lead-in point faces the next cutout to be cut
+            for (var i = cutouts.Count - 1; i >= 0; i--)
+            {
+                var closestPt = cutouts[i].ClosestPointTo(currentPoint, out var entity);
+                entries[i] = new ContourEntry(cutouts[i], closestPt, entity);
+                currentPoint = closestPt;
+            }
+
+            return new List<ContourEntry>(entries);
+        }
+
+        private void EmitContour(Program program, Shape shape, Vector point, Entity entity, ContourType? forceType = null)
+        {
+            var contourType = forceType ?? DetectContourType(shape);
+            var normal = ComputeNormal(point, entity, contourType);
+            var winding = DetermineWinding(shape);
+
+            var leadIn = SelectLeadIn(contourType);
+            var leadOut = SelectLeadOut(contourType);
+
+            if (contourType == ContourType.ArcCircle && entity is Circle circle)
+                leadIn = ClampLeadInForCircle(leadIn, circle, point, normal);
+
+            program.Codes.AddRange(leadIn.Generate(point, normal, winding));
+
+            var reindexed = shape.ReindexAt(point, entity);
+
+            if (Parameters.TabsEnabled && Parameters.TabConfig != null)
+                reindexed = TrimShapeForTab(reindexed, point, Parameters.TabConfig.Size);
+
+            program.Codes.AddRange(ConvertShapeToMoves(reindexed, point));
+            program.Codes.AddRange(leadOut.Generate(point, normal, winding));
+        }
+
+        private void EmitScribeContours(Program program, List<Entity> scribeEntities)
+        {
+            if (scribeEntities.Count == 0) return;
+
+            var shapes = ShapeBuilder.GetShapes(scribeEntities);
+            foreach (var shape in shapes)
+            {
+                var startPt = GetShapeStartPoint(shape);
+                program.Codes.Add(new RapidMove(startPt));
+                program.Codes.AddRange(ConvertShapeToMoves(shape, startPt, LayerType.Scribe));
+            }
+        }
+
         private List<Shape> SequenceCutouts(List<Shape> cutouts, Vector startPoint)
         {
             var remaining = new List<Shape>(cutouts);

OpenNest.Core/Geometry/Arc.cs

@@ -155,6 +155,17 @@ namespace OpenNest.Geometry
                 Center.Y + Radius * System.Math.Sin(EndAngle));
         }
 
+        /// <summary>
+        /// Mid point of the arc (point at the angle midway between start and end).
+        /// </summary>
+        public Vector MidPoint()
+        {
+            var midAngle = StartAngle + (IsReversed ? -SweepAngle() / 2 : SweepAngle() / 2);
+            return new Vector(
+                Center.X + Radius * System.Math.Cos(midAngle),
+                Center.Y + Radius * System.Math.Sin(midAngle));
+        }
+
         /// <summary>
         /// Splits the arc at the given point, returning two sub-arcs.
         /// Either half may be null if the split point coincides with an endpoint.

OpenNest.Posts.Cincinnati/CincinnatiPartSubprogramWriter.cs

@@ -70,6 +70,26 @@ public sealed class CincinnatiPartSubprogramWriter
         w.WriteLine($"M99 (END OF {drawingName})");
     }
 
+    /// <summary>
+    /// If the program has no leading rapid, inserts a synthetic rapid at the
+    /// last motion endpoint (the contour return point). This ensures the feature
+    /// writer knows the true pierce location and preserves the first contour segment.
+    /// </summary>
+    internal static void EnsureLeadingRapid(Program pgm)
+    {
+        if (pgm.Codes.Count == 0 || pgm.Codes[0] is RapidMove)
+            return;
+
+        for (var i = pgm.Codes.Count - 1; i >= 0; i--)
+        {
+            if (pgm.Codes[i] is Motion lastMotion)
+            {
+                pgm.Codes.Insert(0, new RapidMove(lastMotion.EndPoint));
+                return;
+            }
+        }
+    }
+
     /// <summary>
     /// Creates a sub-program key for matching parts to their sub-programs.
     /// </summary>
@@ -99,9 +119,17 @@ public sealed class CincinnatiPartSubprogramWriter
                     mapping[key] = subNum;
 
                     var pgm = part.Program.Clone() as Program;
+                    pgm.Mode = Mode.Absolute;
                     var bbox = pgm.BoundingBox();
                     pgm.Offset(-bbox.Location.X, -bbox.Location.Y);
 
+                    // If the program has no leading rapid, the feature writer
+                    // will use the first motion endpoint as the pierce point,
+                    // losing the first contour segment. Insert a synthetic rapid
+                    // at the contour's return point (last motion endpoint) so
+                    // the full contour is preserved.
+                    EnsureLeadingRapid(pgm);
+
                     entries.Add((subNum, part.BaseDrawing.Name, pgm));
                 }
             }

OpenNest.Posts.Cincinnati/FeatureUtils.cs

@@ -69,8 +69,31 @@ public static class FeatureUtils
     /// Splits a part's program into features by rapids, classifies each as etch or cut,
     /// and orders etch features before cut features.
     /// </summary>
-    public static List<(List<ICode> codes, bool isEtch)> SplitAndClassify(Part part) =>
+    public static List<(List<ICode> codes, bool isEtch)> SplitAndClassify(Part part)
-        ClassifyAndOrder(SplitByRapids(part.Program.Codes));
+    {
+        part.Program.Mode = Mode.Absolute;
+        var codes = part.Program.Codes;
+
+        // If no leading rapid, the first contour segment would be lost because
+        // the feature writer pierces at the first motion endpoint. Insert a
+        // synthetic rapid at the contour's return point to preserve closure.
+        if (codes.Count > 0 && codes[0] is not RapidMove)
+        {
+            for (var i = codes.Count - 1; i >= 0; i--)
+            {
+                if (codes[i] is Motion lastMotion)
+                {
+                    var withRapid = new List<ICode>(codes.Count + 1);
+                    withRapid.Add(new RapidMove(lastMotion.EndPoint));
+                    withRapid.AddRange(codes);
+                    codes = withRapid;
+                    break;
+                }
+            }
+        }
+
+        return ClassifyAndOrder(SplitByRapids(codes));
+    }
 
     /// <summary>
     /// Returns true if any non-rapid move in the feature has LayerType.Scribe.

OpenNest.Posts.Cincinnati/MaterialLibraryResolver.cs

@@ -24,7 +24,7 @@ public sealed class MaterialLibraryResolver
             System.Math.Abs(e.Thickness - thickness) <= ThicknessTolerance &&
             string.Equals(e.Gas, gas, StringComparison.OrdinalIgnoreCase));
 
-        return entry?.Library ?? "";
+        return EnsureLibExtension(entry?.Library ?? "");
     }
 
     public string ResolveEtchLibrary(string gas)
@@ -32,7 +32,18 @@ public sealed class MaterialLibraryResolver
         var entry = _etchLibraries.FirstOrDefault(e =>
             string.Equals(e.Gas, gas, StringComparison.OrdinalIgnoreCase));
 
-        return entry?.Library ?? "";
+        return EnsureLibExtension(entry?.Library ?? "");
+    }
+
+    private static string EnsureLibExtension(string library)
+    {
+        if (string.IsNullOrEmpty(library))
+            return library;
+
+        if (!library.EndsWith(".lib", StringComparison.OrdinalIgnoreCase))
+            return library + ".lib";
+
+        return library;
     }
 
     public static string ResolveGas(Nest nest, CincinnatiPostConfig config)

OpenNest.Tests/Cincinnati/CincinnatiPostProcessorTests.cs

@@ -388,6 +388,57 @@ public class CincinnatiPostProcessorTests
         Assert.Equal(300, deserialized.PartSubprogramStart);
     }
 
+    [Fact]
+    public void Post_ClosedContourWithoutRapid_OutputsAllSegments()
+    {
+        // Reproduce bug: a closed contour with no leading rapid loses its
+        // first segment in the CNC output because the feature writer uses
+        // the first LinearMove endpoint as the pierce point.
+        var pgm = new Program(Mode.Incremental);
+        pgm.Codes.Add(new LinearMove(0, 2));    // (0,0) → (0,2)
+        pgm.Codes.Add(new LinearMove(2, 0));    // (0,2) → (2,2)
+        pgm.Codes.Add(new LinearMove(0, -2));   // (2,2) → (2,0)
+        pgm.Codes.Add(new LinearMove(-2, 0));   // (2,0) → (0,0)
+
+        var drawing = new Drawing("ClosedSquare", pgm);
+        var nest = new Nest("TestClosure");
+        nest.Drawings.Add(drawing);
+        var plate = new Plate(24, 24);
+        plate.Parts.Add(new Part(drawing, new Vector(1, 1)));
+        nest.Plates.Add(plate);
+
+        var config = new CincinnatiPostConfig
+        {
+            UsePartSubprograms = true,
+            PostedAccuracy = 4
+        };
+        var post = new CincinnatiPostProcessor(config);
+
+        using var ms = new MemoryStream();
+        post.Post(nest, ms);
+        var output = Encoding.UTF8.GetString(ms.ToArray());
+
+        // The subprogram should contain all 4 segments of the square.
+        // Without the fix, the first segment (0,0)→(0,2) was lost
+        // because the feature writer pierced at (0,2) making it zero-length.
+        var lines = output.Split('\n').Select(l => l.Trim()).ToArray();
+
+        // Count G1 moves in the subprogram (should be 4 for a square)
+        var subStart = Array.FindIndex(lines, l => l.StartsWith(":200") || l.StartsWith(":300"));
+        Assert.True(subStart >= 0, "Expected a part subprogram");
+
+        var g1Count = 0;
+        for (var i = subStart; i < lines.Length; i++)
+        {
+            if (lines[i].StartsWith("M99"))
+                break;
+            if (lines[i].Contains("G1 "))
+                g1Count++;
+        }
+
+        Assert.Equal(4, g1Count);
+    }
+
     private static Nest CreateTestNest()
     {
         var nest = new Nest("TestNest");

OpenNest/Actions/ActionLeadIn.cs

@@ -14,6 +14,10 @@ namespace OpenNest.Actions
     [DisplayName("Place Lead-in")]
     public class ActionLeadIn : Action
     {
+        private enum SnapType { None, Endpoint, Midpoint }
+
+        private const double SnapCapturePixels = 10.0;
+
         private LayoutPart selectedLayoutPart;
         private Part selectedPart;
         private ShapeProfile profile;
@@ -23,6 +27,7 @@ namespace OpenNest.Actions
         private ContourType snapContourType;
         private double snapNormal;
         private bool hasSnap;
+        private SnapType activeSnapType;
         private ShapeInfo hoveredContour;
         private ContextMenuStrip contextMenu;
         private static readonly Brush grayOverlay = new SolidBrush(Color.FromArgb(160, 180, 180, 180));
@@ -57,6 +62,7 @@ namespace OpenNest.Actions
             profile = null;
             contours = null;
             hasSnap = false;
+            activeSnapType = SnapType.None;
             hoveredContour = null;
             plateView.Invalidate();
         }
@@ -81,6 +87,7 @@ namespace OpenNest.Actions
             // Find closest contour and point
             var bestDist = double.MaxValue;
             hasSnap = false;
+            activeSnapType = SnapType.None;
             hoveredContour = null;
 
             foreach (var info in contours)
@@ -100,6 +107,10 @@ namespace OpenNest.Actions
                 }
             }
 
+            // Check endpoint/midpoint snaps on the hovered contour
+            if (hoveredContour != null)
+                TrySnapToEntityPoints(localPt);
+
             plateView.Invalidate();
         }
 
@@ -142,33 +153,39 @@ namespace OpenNest.Actions
         {
             var g = e.Graphics;
 
-            // Gray overlay on all parts except the selected one
+            DrawOverlay(g);
+            DrawHoveredContour(g);
+            DrawLeadInPreview(g);
+        }
+
+        private void DrawOverlay(Graphics g)
+        {
             foreach (var lp in plateView.LayoutParts)
             {
-                if (lp == selectedLayoutPart)
+                if (lp != selectedLayoutPart && lp.Path != null)
-                    continue;
-
-                if (lp.Path != null)
                     g.FillPath(grayOverlay, lp.Path);
             }
+        }
 
-            // Highlight the hovered contour
+        private void DrawHoveredContour(Graphics g)
-            if (hoveredContour != null && selectedPart != null)
+        {
-            {
+            if (hoveredContour == null || selectedPart == null)
-                using var contourPath = hoveredContour.Shape.GetGraphicsPath();
+                return;
 
-                // Translate from local part space to world space, then apply view transform
+            using var contourPath = hoveredContour.Shape.GetGraphicsPath();
-                using var contourMatrix = new Matrix();
+            using var contourMatrix = new Matrix();
-                contourMatrix.Translate((float)selectedPart.Location.X, (float)selectedPart.Location.Y);
+            contourMatrix.Translate((float)selectedPart.Location.X, (float)selectedPart.Location.Y);
-                contourMatrix.Multiply(plateView.Matrix, MatrixOrder.Append);
+            contourMatrix.Multiply(plateView.Matrix, MatrixOrder.Append);
-                contourPath.Transform(contourMatrix);
+            contourPath.Transform(contourMatrix);
 
-                var prevSmooth = g.SmoothingMode;
+            var prevSmooth = g.SmoothingMode;
-                g.SmoothingMode = SmoothingMode.AntiAlias;
+            g.SmoothingMode = SmoothingMode.AntiAlias;
-                g.DrawPath(highlightPen, contourPath);
+            g.DrawPath(highlightPen, contourPath);
-                g.SmoothingMode = prevSmooth;
+            g.SmoothingMode = prevSmooth;
-            }
+        }
 
+        private void DrawLeadInPreview(Graphics g)
+        {
             if (!hasSnap || selectedPart == null)
                 return;
 
@@ -176,67 +193,113 @@ namespace OpenNest.Actions
             if (parameters == null)
                 return;
 
-            // Transform snap point from local part space to world space
-            var worldSnap = TransformToWorld(snapPoint);
-
-            // Get the appropriate lead-in for this contour type
             var leadIn = SelectLeadIn(parameters, snapContourType);
             if (leadIn == null)
                 return;
 
-            // Clamp lead-in for circle contours so it stays inside the hole
+            leadIn = ClampLeadInForCircle(leadIn, parameters);
-            if (snapContourType == ContourType.ArcCircle && snapEntity is Circle snapCircle
-                && parameters.PierceClearance > 0)
-            {
-                var pierceCheck = leadIn.GetPiercePoint(snapPoint, snapNormal);
-                var distFromCenter = pierceCheck.DistanceTo(snapCircle.Center);
-                var maxRadius = snapCircle.Radius - parameters.PierceClearance;
-                if (maxRadius > 0 && distFromCenter > maxRadius)
-                {
-                    var currentDist = snapPoint.DistanceTo(pierceCheck);
-                    if (currentDist > Tolerance.Epsilon)
-                    {
-                        var dx = (pierceCheck.X - snapPoint.X) / currentDist;
-                        var dy = (pierceCheck.Y - snapPoint.Y) / currentDist;
-                        var vx = snapPoint.X - snapCircle.Center.X;
-                        var vy = snapPoint.Y - snapCircle.Center.Y;
-                        var b = 2.0 * (vx * dx + vy * dy);
-                        var c = vx * vx + vy * vy - maxRadius * maxRadius;
-                        var disc = b * b - 4.0 * c;
-                        if (disc >= 0)
-                        {
-                            var t = (-b + System.Math.Sqrt(disc)) / 2.0;
-                            if (t > 0 && t < currentDist)
-                                leadIn = leadIn.Scale(t / currentDist);
-                        }
-                    }
-                }
-            }
 
-            // Get the pierce point (in local space)
             var piercePoint = leadIn.GetPiercePoint(snapPoint, snapNormal);
-            var worldPierce = TransformToWorld(piercePoint);
+            var pt1 = plateView.PointWorldToGraph(TransformToWorld(piercePoint));
+            var pt2 = plateView.PointWorldToGraph(TransformToWorld(snapPoint));
 
             var oldSmooth = g.SmoothingMode;
             g.SmoothingMode = SmoothingMode.AntiAlias;
 
-            // Draw the lead-in preview as a line from pierce point to contour point
-            var pt1 = plateView.PointWorldToGraph(worldPierce);
-            var pt2 = plateView.PointWorldToGraph(worldSnap);
-
             using var previewPen = new Pen(Color.Magenta, 2.0f / plateView.ViewScale);
             g.DrawLine(previewPen, pt1, pt2);
 
-            // Draw a small circle at the pierce point
             var radius = 3.0f / plateView.ViewScale;
             g.FillEllipse(Brushes.Magenta, pt1.X - radius, pt1.Y - radius, radius * 2, radius * 2);
 
-            // Draw a small circle at the contour start point
+            if (activeSnapType != SnapType.None)
-            g.FillEllipse(Brushes.Lime, pt2.X - radius, pt2.Y - radius, radius * 2, radius * 2);
+                DrawSnapMarker(g, pt2, activeSnapType);
+            else
+                g.FillEllipse(Brushes.Lime, pt2.X - radius, pt2.Y - radius, radius * 2, radius * 2);
 
             g.SmoothingMode = oldSmooth;
         }
 
+        private LeadIn ClampLeadInForCircle(LeadIn leadIn, CuttingParameters parameters)
+        {
+            if (snapContourType != ContourType.ArcCircle
+                || !(snapEntity is Circle snapCircle)
+                || parameters.PierceClearance <= 0)
+                return leadIn;
+
+            var pierceCheck = leadIn.GetPiercePoint(snapPoint, snapNormal);
+            var maxRadius = snapCircle.Radius - parameters.PierceClearance;
+
+            if (maxRadius <= 0 || pierceCheck.DistanceTo(snapCircle.Center) <= maxRadius)
+                return leadIn;
+
+            var currentDist = snapPoint.DistanceTo(pierceCheck);
+            if (currentDist <= Tolerance.Epsilon)
+                return leadIn;
+
+            var dx = (pierceCheck.X - snapPoint.X) / currentDist;
+            var dy = (pierceCheck.Y - snapPoint.Y) / currentDist;
+            var vx = snapPoint.X - snapCircle.Center.X;
+            var vy = snapPoint.Y - snapCircle.Center.Y;
+            var b = 2.0 * (vx * dx + vy * dy);
+            var c = vx * vx + vy * vy - maxRadius * maxRadius;
+            var disc = b * b - 4.0 * c;
+
+            if (disc < 0)
+                return leadIn;
+
+            var t = (-b + System.Math.Sqrt(disc)) / 2.0;
+            return (t > 0 && t < currentDist) ? leadIn.Scale(t / currentDist) : leadIn;
+        }
+
+        private void TrySnapToEntityPoints(Vector localPt)
+        {
+            var captureRadius = SnapCapturePixels / plateView.ViewScale;
+            var bestDist = captureRadius;
+            var bestPoint = default(Vector);
+            var bestEntity = default(Entity);
+            var bestType = SnapType.None;
+
+            foreach (var entity in hoveredContour.Shape.Entities)
+            {
+                switch (entity)
+                {
+                    case Line line:
+                        TryCandidate(line.StartPoint, line, SnapType.Endpoint);
+                        TryCandidate(line.EndPoint, line, SnapType.Endpoint);
+                        TryCandidate(line.MidPoint, line, SnapType.Midpoint);
+                        break;
+                    case Arc arc:
+                        TryCandidate(arc.StartPoint(), arc, SnapType.Endpoint);
+                        TryCandidate(arc.EndPoint(), arc, SnapType.Endpoint);
+                        TryCandidate(arc.MidPoint(), arc, SnapType.Midpoint);
+                        break;
+                }
+            }
+
+            if (bestType != SnapType.None)
+            {
+                snapPoint = bestPoint;
+                snapEntity = bestEntity;
+                snapNormal = ContourCuttingStrategy.ComputeNormal(bestPoint, bestEntity, snapContourType);
+                activeSnapType = bestType;
+            }
+
+            return;
+
+            void TryCandidate(Vector pt, Entity ent, SnapType type)
+            {
+                var dist = pt.DistanceTo(localPt);
+                if (dist < bestDist)
+                {
+                    bestDist = dist;
+                    bestPoint = pt;
+                    bestEntity = ent;
+                    bestType = type;
+                }
+            }
+        }
+
         private void SelectPartAtCursor()
         {
             var layoutPart = plateView.GetPartAtPoint(plateView.CurrentPoint);
@@ -342,6 +405,7 @@ namespace OpenNest.Actions
             profile = null;
             contours = null;
             hasSnap = false;
+            activeSnapType = SnapType.None;
             hoveredContour = null;
             plateView.Invalidate();
         }
@@ -365,6 +429,35 @@ namespace OpenNest.Actions
             contextMenu.Show(plateView, location);
         }
 
+        private void DrawSnapMarker(Graphics g, PointF pt, SnapType type)
+        {
+            var size = 5f;
+
+            if (type == SnapType.Endpoint)
+            {
+                // Diamond
+                var points = new[]
+                {
+                    new PointF(pt.X, pt.Y - size),
+                    new PointF(pt.X + size, pt.Y),
+                    new PointF(pt.X, pt.Y + size),
+                    new PointF(pt.X - size, pt.Y)
+                };
+                g.FillPolygon(Brushes.Red, points);
+            }
+            else if (type == SnapType.Midpoint)
+            {
+                // Triangle
+                var points = new[]
+                {
+                    new PointF(pt.X, pt.Y - size),
+                    new PointF(pt.X + size, pt.Y + size),
+                    new PointF(pt.X - size, pt.Y + size)
+                };
+                g.FillPolygon(Brushes.Red, points);
+            }
+        }
+
         private Vector TransformToWorld(Vector localPt)
         {
             // The contours are already in rotated local space (we rotated the program

OpenNest/Forms/BomImportForm.cs

@@ -432,7 +432,6 @@ namespace OpenNest.Forms
                             var rapid = (RapidMove)pgm[0];
                             drawing.Source.Offset = rapid.EndPoint;
                             pgm.Offset(-rapid.EndPoint);
-                            pgm.Codes.RemoveAt(0);
                         }
 
                         drawing.Program = pgm;

OpenNest/Forms/CadConverterForm.cs

@@ -362,7 +362,6 @@ namespace OpenNest.Forms
                 var rapid = (RapidMove)pgm[0];
                 originOffset = rapid.EndPoint;
                 pgm.Offset(-originOffset);
-                pgm.Codes.RemoveAt(0);
             }
 
             var drawing = new Drawing(item.Name, pgm);
@@ -660,7 +659,8 @@ namespace OpenNest.Forms
                     var rapid = (RapidMove)firstCode;
                     drawing.Source.Offset = rapid.EndPoint;
                     pgm.Offset(-rapid.EndPoint);
-                    pgm.Codes.RemoveAt(0);
+                    // Keep the rapid (now at origin) — it marks the contour
+                    // start and is needed by the post for correct pierce placement.
                 }
 
                 if (item == CurrentItem && programEditor.IsDirty && programEditor.Program != null)