fix: improve arc-tangency fitting and add layered engrave/cut passes for GravographIS

GeometrySimplifier/ArcFit now fit arcs that pass exactly through run
endpoints while balancing tangency error between trusted and estimated
directions, fixing arcs that previously bulged or broke tangent
continuity at fillet/compound-curve junctions.

GravographIS post processor gains per-layer (engrave/cut) tool passes
via a new GravographISPostConfig, so ENGRAVE/ETCH-tagged geometry runs
as a separate scribe pass with its own feed/depth and an operator
pause before the cut pass (spring-floated spindle needs a tool swap).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -213,3 +213,6 @@ docs/superpowers/
 
 # Launch settings
 **/Properties/launchSettings.json
+
+# Local test config (contains user-specific paths to proprietary test assets)
+OpenNest.Tests/test-config.json

CLAUDE.md

@@ -120,3 +120,4 @@ Always keep `README.md` and `CLAUDE.md` up to date when making changes that affe
 - **Cut-off materialization lifecycle**: `CutOff` objects live on `Plate.CutOffs`. Each generates a `Drawing` (with `IsCutOff = true`) whose `Program` contains trimmed line segments. `Plate.RegenerateCutOffs(settings)` removes old cut-off Parts, recomputes programs, and re-adds them to `Plate.Parts`. Regeneration triggers: cut-off add/remove/move, part drag complete, fill complete, plate transform. Cut-off Parts are excluded from quantity tracking, utilization, overlap detection, and nest file serialization (programs are regenerated from definitions on load).
 - **User-defined G-code variables**: Programs can contain named variable definitions (`name = expression [inline] [global]`) referenced in coordinates with `$name`. Variables resolve to doubles at parse time for geometry/nesting. `VariableRefs` on `Motion`/`Feedrate` track the symbolic link so post processors can emit machine variable references. Cincinnati post maps non-inline variables to numbered machine variables (`#200+`) with descriptive comments. Global variables share a number across programs; local variables get per-drawing numbers. `ProgramReader` uses a two-pass parse (collect definitions, then parse G-code with substitution). `NestWriter` serializes definitions and `$references` back to text for round-trip fidelity.
 - **CAD import pipeline**: All "DXF → Drawing" conversion goes through `OpenNest.IO.CadImporter`. The UI form uses `Import` on file load (storing the mutable result in a `FileListItem`) and `BuildDrawing` on save (passing the user's current visible entities and bends). Console, MCP, API, and Training projects use `ImportDrawing` for headless conversion. This guarantees all callers produce drawings with the same shape: pierce-point `Source.Offset`, stable `SourceEntities` with GUIDs, `SuppressedEntityIds`, detected bends, and metadata.
+- **GravographIS engrave/cut passes**: The `OpenNest.Posts.GravographIS` post splits geometry by `LayerType` into ordered tool passes — engrave (`Scribe`) then cut (`Cut`/`Leadin`/`Leadout`); `Display` is skipped. `ConvertGeometry` tags DXF layers `ENGRAVE`/`ETCH` (lines, arcs, circles) as `Scribe`; the layer round-trips through `.nest` via `NestWriter`/`ProgramReader`. `NestPolylineExtractor.ExtractLayered` carries `LayerType` per polyline (splitting a continuous chain at any layer change); `GravographISPostProcessor.BuildPasses` groups them and `GravographISWriter.Write(IReadOnlyList<GravographPass>, …)` emits each pass at its own feed/depth, parking to origin and emitting an operator pause (motor off → aux off → `LB` console message → motor on) before any pass whose config has `PauseBefore`. Per-pass parameters live in `GravographISPostConfig` (an `IConfigurablePostProcessor` config with `Engrave`/`Cut` `LayerCutConfig` blocks), edited in the shared `PostProcessorConfigForm` PropertyGrid and persisted to JSON. The cut block pauses by default so the operator can swap/adjust the tool (the spring-floated spindle means programmed `DZ` depth is not the real cut depth).

OpenNest.Console/Program.cs

@@ -41,7 +41,6 @@ static class NestConsole
             }
         }
 
-        using var log = SetUpLog(options);
         var nest = LoadOrCreateNest(options);
 
         if (nest == null)
@@ -68,10 +67,6 @@ static class NestConsole
 
         var overlapCount = CheckOverlaps(plate, options);
 
-        // Flush and close the log before printing results.
-        Trace.Flush();
-        log?.Dispose();
-
         PrintResults(success, plate, elapsed);
         Save(nest, options);
         PostProcess(nest, options);
@@ -112,9 +107,6 @@ static class NestConsole
                 case "--no-save":
                     o.NoSave = true;
                     break;
-                case "--no-log":
-                    o.NoLog = true;
-                    break;
                 case "--keep-parts":
                     o.KeepParts = true;
                     break;
@@ -153,28 +145,14 @@ static class NestConsole
         return o;
     }
 
-    static StreamWriter SetUpLog(Options options)
-    {
-        if (options.NoLog)
-            return null;
-
-        var baseDir = Path.GetDirectoryName(options.InputFiles[0]);
-        var logDir = Path.Combine(baseDir, "test-harness-logs");
-        Directory.CreateDirectory(logDir);
-        var logFile = Path.Combine(logDir, $"debug-{DateTime.Now:yyyyMMdd-HHmmss}.log");
-        var writer = new StreamWriter(logFile) { AutoFlush = true };
-        Trace.Listeners.Add(new TextWriterTraceListener(writer));
-        Console.WriteLine($"Debug log: {logFile}");
-        return writer;
-    }
-
     static Nest LoadOrCreateNest(Options options)
     {
         var nestFile = options.InputFiles.FirstOrDefault(f =>
             f.EndsWith(NestFormat.FileExtension, StringComparison.OrdinalIgnoreCase)
             || f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
         var dxfFiles = options.InputFiles.Where(f =>
-            f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)).ToList();
+            f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase) ||
+            f.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase)).ToList();
 
         // If we have a nest file, load it and optionally add DXFs.
         if (nestFile != null)
@@ -210,7 +188,7 @@ static class NestConsole
         // DXF-only mode: create a fresh nest.
         if (dxfFiles.Count == 0)
         {
-            Console.Error.WriteLine("Error: no nest (.nest) or DXF (.dxf) files specified");
+            Console.Error.WriteLine("Error: no nest (.nest) or CAD (.dxf/.dwg) files specified");
             return null;
         }
 
@@ -484,7 +462,7 @@ static class NestConsole
         Console.Error.WriteLine("Usage: OpenNest.Console <input-files...> [options]");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Arguments:");
-        Console.Error.WriteLine("  input-files            One or more .nest nest files or .dxf drawing files");
+        Console.Error.WriteLine("  input-files            One or more .nest nest files or .dxf/.dwg drawing files");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Modes:");
         Console.Error.WriteLine("  <nest.nest>             Load nest and fill (existing behavior)");
@@ -503,7 +481,6 @@ static class NestConsole
         Console.Error.WriteLine("  --keep-parts           Don't clear existing parts before filling");
         Console.Error.WriteLine("  --check-overlaps       Run overlap detection after fill (exit code 1 if found)");
         Console.Error.WriteLine("  --no-save              Skip saving output file");
-        Console.Error.WriteLine("  --no-log               Skip writing debug log file");
         Console.Error.WriteLine("  --post <name>          Run a post processor after nesting");
         Console.Error.WriteLine("  --post-output <path>   Output file for post processor (default: <input>.cnc)");
         Console.Error.WriteLine("  --posts-dir <path>     Directory containing post processor DLLs (default: Posts/)");
@@ -522,7 +499,6 @@ static class NestConsole
         public Size? PlateSize;
         public bool CheckOverlaps;
         public bool NoSave;
-        public bool NoLog;
         public bool KeepParts;
         public bool AutoNest;
         public string TemplateFile;

OpenNest.Core/CanonicalAngle.cs

@@ -0,0 +1,78 @@
+using OpenNest.Converters;
+using OpenNest.Geometry;
+using System.Linq;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// Computes the rotation that maps a drawing to its canonical (MBR-axis-aligned) frame.
+    /// Lives in OpenNest.Core so Drawing.Program setter can invoke it directly without
+    /// a circular dependency on OpenNest.Engine.
+    /// </summary>
+    public static class CanonicalAngle
+    {
+        /// <summary>Angles with |v| below this (radians) are snapped to 0.</summary>
+        public const double SnapToZero = 0.001;
+
+        /// <summary>
+        /// Derives the canonical angle from a pre-computed MBR. Used both by Compute (which
+        /// computes the MBR itself) and by PartClassifier (which already has one). Single formula
+        /// across both callers.
+        /// </summary>
+        public static double FromMbr(BoundingRectangleResult mbr)
+        {
+            if (mbr.Area <= OpenNest.Math.Tolerance.Epsilon)
+                return 0.0;
+
+            // The MBR edge angle can represent any of four equivalent orientations
+            // (edge-i, edge-i + π/2, edge-i + π, edge-i - π/2) depending on which hull
+            // edge the algorithm happened to pick. Normalize -mbr.Angle to the
+            // representative in [-π/4, π/4] so snap-to-zero works for inputs near
+            // ANY of the equivalent orientations.
+            var angle = -mbr.Angle;
+            const double halfPi = System.Math.PI / 2.0;
+            angle -= halfPi * System.Math.Round(angle / halfPi);
+
+            if (System.Math.Abs(angle) < SnapToZero)
+                return 0.0;
+
+            return angle;
+        }
+
+        public static double Compute(Drawing drawing)
+        {
+            if (drawing?.Program == null)
+                return 0.0;
+
+            var entities = ConvertProgram.ToGeometry(drawing.Program)
+                .Where(e => e.Layer != SpecialLayers.Rapid);
+
+            var shapes = ShapeBuilder.GetShapes(entities);
+            if (shapes.Count == 0)
+                return 0.0;
+
+            var perimeter = shapes[0];
+            var perimeterArea = perimeter.Area();
+            for (var i = 1; i < shapes.Count; i++)
+            {
+                var area = shapes[i].Area();
+                if (area > perimeterArea)
+                {
+                    perimeter = shapes[i];
+                    perimeterArea = area;
+                }
+            }
+
+            var polygon = perimeter.ToPolygonWithTolerance(0.1);
+            if (polygon == null || polygon.Vertices.Count < 3)
+                return 0.0;
+
+            var hull = ConvexHull.Compute(polygon.Vertices);
+            if (hull.Vertices.Count < 3)
+                return 0.0;
+
+            var mbr = RotatingCalipers.MinimumBoundingRectangle(hull);
+            return FromMbr(mbr);
+        }
+    }
+}

OpenNest.Core/Converters/ConvertGeometry.cs

@@ -1,5 +1,6 @@
 using OpenNest.CNC;
 using OpenNest.Geometry;
+using OpenNest.Math;
 using System.Collections.Generic;
 
 namespace OpenNest.Converters
@@ -81,12 +82,22 @@ namespace OpenNest.Converters
             var startpt = arc.StartPoint();
             var endpt = arc.EndPoint();
 
-            if (startpt != lastpt)
+            if (startpt.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(startpt);
 
             lastpt = endpt;
 
-            pgm.ArcTo(endpt, arc.Center, arc.IsReversed ? RotationType.CW : RotationType.CCW);
+            var layer = ClassifyLayer(arc);
+            var sweep = System.Math.Abs(arc.SweepAngle());
+            if (sweep < Tolerance.Epsilon || sweep.IsEqualTo(Angle.TwoPI))
+            {
+                pgm.Codes.Add(new LinearMove(endpt) { Layer = layer });
+            }
+            else
+            {
+                pgm.Codes.Add(new ArcMove(endpt, arc.Center, arc.IsReversed ? RotationType.CW : RotationType.CCW) { Layer = layer });
+            }
+
             return lastpt;
         }
 
@@ -94,10 +105,10 @@ namespace OpenNest.Converters
         {
             var startpt = new Vector(circle.Center.X + circle.Radius, circle.Center.Y);
 
-            if (startpt != lastpt)
+            if (startpt.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(startpt);
 
-            pgm.ArcTo(startpt, circle.Center, circle.Rotation);
+            pgm.Codes.Add(new ArcMove(startpt, circle.Center, circle.Rotation) { Layer = ClassifyLayer(circle) });
 
             lastpt = startpt;
             return lastpt;
@@ -105,16 +116,25 @@ namespace OpenNest.Converters
 
         private static Vector AddLine(Program pgm, Vector lastpt, Line line)
         {
-            if (line.StartPoint != lastpt)
+            if (line.StartPoint.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(line.StartPoint);
 
-            var move = new LinearMove(line.EndPoint);
-            if (string.Equals(line.Layer?.Name, "ETCH", System.StringComparison.OrdinalIgnoreCase))
-                move.Layer = LayerType.Scribe;
-            pgm.Codes.Add(move);
+            pgm.Codes.Add(new LinearMove(line.EndPoint) { Layer = ClassifyLayer(line) });
 
             lastpt = line.EndPoint;
             return lastpt;
         }
+
+        // Engrave/etch geometry maps to Scribe so the post processor can treat it as a
+        // separate tool pass; everything else keeps the move's default Cut layer.
+        private static LayerType ClassifyLayer(Entity geo)
+        {
+            var name = geo.Layer?.Name;
+            if (string.Equals(name, "ENGRAVE", System.StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(name, "ETCH", System.StringComparison.OrdinalIgnoreCase))
+                return LayerType.Scribe;
+
+            return LayerType.Cut;
+        }
     }
 }

OpenNest.Core/Drawing.cs

@@ -54,9 +54,9 @@ namespace OpenNest
             Id = Interlocked.Increment(ref nextId);
             Name = name;
             Material = new Material();
-            Program = pgm;
             Constraints = new NestConstraints();
             Source = new SourceInfo();
+            Program = pgm;
         }
 
         public int Id { get; }
@@ -78,9 +78,29 @@ namespace OpenNest
             {
                 program = value;
                 UpdateArea();
+                RecomputeCanonicalAngle();
             }
         }
 
+        /// <summary>
+        /// Recomputes and stores the canonical angle from the current Program.
+        /// Callers that mutate Program in place (rather than reassigning it) must invoke this explicitly.
+        /// Cut-off drawings are left with Angle=0.
+        /// </summary>
+        public void RecomputeCanonicalAngle()
+        {
+            if (Source == null)
+                Source = new SourceInfo();
+
+            if (program == null || IsCutOff)
+            {
+                Source.Angle = 0.0;
+                return;
+            }
+
+            Source.Angle = CanonicalAngle.Compute(this);
+        }
+
         public Color Color { get; set; }
 
         public bool IsCutOff { get; set; }
@@ -163,5 +183,15 @@ namespace OpenNest
         /// Offset distances to the original location.
         /// </summary>
         public Vector Offset { get; set; }
+
+        /// <summary>
+        /// Rotation (radians) that maps the source program geometry to its canonical
+        /// (MBR-axis-aligned) frame. Populated automatically by the <see cref="Drawing.Program"/>
+        /// setter via <see cref="CanonicalAngle.Compute"/>. A value of 0 means the drawing is
+        /// already canonical or <see cref="Drawing.IsCutOff"/> is true. Callers that mutate
+        /// <see cref="Drawing.Program"/> in place must invoke
+        /// <see cref="Drawing.RecomputeCanonicalAngle"/> to refresh.
+        /// </summary>
+        public double Angle { get; set; }
     }
 }

OpenNest.Core/Geometry/Arc.cs

@@ -93,6 +93,9 @@ namespace OpenNest.Geometry
             }
         }
 
+        public bool IsFullCircle() =>
+            SweepAngle() >= Angle.TwoPI - Tolerance.Epsilon;
+
         /// <summary>
         /// Angle in radians between start and end angles.
         /// </summary>
@@ -404,10 +407,12 @@ namespace OpenNest.Geometry
                 maxY = startpt.Y;
             }
 
+            var sweep = SweepAngle();
+            if (sweep > Tolerance.Epsilon)
+            {
                 var angle1 = StartAngle;
                 var angle2 = EndAngle;
 
-            // switch the angle to counter clockwise.
                 if (IsReversed)
                     Generic.Swap(ref angle1, ref angle2);
 
@@ -424,6 +429,7 @@ namespace OpenNest.Geometry
 
                 if (Angle.IsBetweenRad(Angle.TwoPI, angle1, angle2))
                     maxX = Center.X + Radius;
+            }
 
             boundingBox.X = minX;
             boundingBox.Y = minY;

OpenNest.Core/Geometry/ArcFit.cs

@@ -57,13 +57,14 @@ namespace OpenNest.Geometry
         }
 
         /// <summary>
-        /// Fits a circular arc constrained to be tangent to the given directions at both
-        /// the first and last points. The center lies at the intersection of the normals
-        /// at P1 and Pn, guaranteeing the arc departs P1 in the start direction and arrives
-        /// at Pn in the end direction. Uses the radius from P1 (exact start tangent);
-        /// deviation includes any endpoint gap at Pn.
+        /// Fits a circular arc that passes exactly through both the first and last points
+        /// while matching the given endpoint tangents as closely as possible. For any
+        /// circle through two points, the tangents at those points make equal mirrored
+        /// angles with the chord, so the achievable inscribed angle is the average of the
+        /// two requested ones — when the requested tangents are consistent with a single
+        /// circular arc, both are matched exactly.
         /// </summary>
-        internal static (Vector center, double radius, double deviation) FitWithDualTangent(
+        internal static (Vector center, double radius, double deviation) FitThroughEndpointsWithTangents(
             List<Vector> points, Vector startTangent, Vector endTangent)
         {
             if (points.Count < 3)
@@ -72,42 +73,39 @@ namespace OpenNest.Geometry
             var p1 = points[0];
             var pn = points[^1];
 
-            var stLen = System.Math.Sqrt(startTangent.X * startTangent.X + startTangent.Y * startTangent.Y);
-            var etLen = System.Math.Sqrt(endTangent.X * endTangent.X + endTangent.Y * endTangent.Y);
-            if (stLen < 1e-10 || etLen < 1e-10)
-                return (Vector.Invalid, 0, double.MaxValue);
-
-            // Normal to start tangent at P1 (perpendicular)
-            var n1x = -startTangent.Y / stLen;
-            var n1y = startTangent.X / stLen;
-
-            // Normal to end tangent at Pn
-            var n2x = -endTangent.Y / etLen;
-            var n2y = endTangent.X / etLen;
-
-            // Solve: P1 + t1*N1 = Pn + t2*N2
-            var det = n1x * (-n2y) - (-n2x) * n1y;
-            if (System.Math.Abs(det) < 1e-10)
-                return (Vector.Invalid, 0, double.MaxValue);
-
             var dx = pn.X - p1.X;
             var dy = pn.Y - p1.Y;
-            var t1 = (dx * (-n2y) - (-n2x) * dy) / det;
-
-            var cx = p1.X + t1 * n1x;
-            var cy = p1.Y + t1 * n1y;
-
-            // Use radius from P1 (guarantees exact start tangent and passes through P1)
-            var r1 = System.Math.Sqrt((cx - p1.X) * (cx - p1.X) + (cy - p1.Y) * (cy - p1.Y));
-            if (r1 < 1e-10)
+            var chordLen = System.Math.Sqrt(dx * dx + dy * dy);
+            if (chordLen < 1e-10)
                 return (Vector.Invalid, 0, double.MaxValue);
 
-            // Measure endpoint gap at Pn
-            var r2 = System.Math.Sqrt((cx - pn.X) * (cx - pn.X) + (cy - pn.Y) * (cy - pn.Y));
-            var endpointDev = System.Math.Abs(r2 - r1);
+            var ux = dx / chordLen;
+            var uy = dy / chordLen;
 
-            var interiorDev = MaxRadialDeviation(points, cx, cy, r1);
-            return (new Vector(cx, cy), r1, System.Math.Max(endpointDev, interiorDev));
+            // Inscribed angle between chord and tangent at each endpoint (mirrored at Pn)
+            var theta1 = SignedAngle(ux, uy, startTangent);
+            var theta2 = -SignedAngle(ux, uy, endTangent);
+            var theta = (theta1 + theta2) / 2;
+
+            // Nearly straight or degenerate (sweep would exceed ~356 degrees)
+            if (System.Math.Abs(theta) < 1e-3 || System.Math.Abs(theta) > System.Math.PI * 0.99)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var halfChord = chordLen / 2;
+            var radius = halfChord / System.Math.Abs(System.Math.Sin(theta));
+            var d = -halfChord / System.Math.Tan(theta);
+
+            var cx = (p1.X + pn.X) / 2 + d * -uy;
+            var cy = (p1.Y + pn.Y) / 2 + d * ux;
+
+            return (new Vector(cx, cy), radius, MaxRadialDeviation(points, cx, cy, radius));
+        }
+
+        private static double SignedAngle(double ux, double uy, Vector to)
+        {
+            var len = System.Math.Sqrt(to.X * to.X + to.Y * to.Y);
+            if (len < 1e-10) return 0;
+            return System.Math.Atan2(ux * to.Y - uy * to.X, ux * to.X + uy * to.Y);
         }
 
         /// <summary>

OpenNest.Core/Geometry/Box.cs

@@ -1,8 +1,9 @@
-using OpenNest.Math;
+using System;
+using OpenNest.Math;
 
 namespace OpenNest.Geometry
 {
-    public class Box
+    public class Box : IComparable<Box>
     {
         public static readonly Box Empty = new Box();
 
@@ -214,5 +215,19 @@ namespace OpenNest.Geometry
         {
             return string.Format("[Box: X={0}, Y={1}, Width={2}, Length={3}]", X, Y, Width, Length);
         }
+
+        public int CompareTo(Box other)
+        {
+            var cmp = Width.CompareTo(other.Width);
+            return cmp != 0 ? cmp : Length.CompareTo(other.Length);
+        }
+
+        public static bool operator >(Box a, Box b) => a.CompareTo(b) > 0;
+
+        public static bool operator <(Box a, Box b) => a.CompareTo(b) < 0;
+
+        public static bool operator >=(Box a, Box b) => a.CompareTo(b) >= 0;
+
+        public static bool operator <=(Box a, Box b) => a.CompareTo(b) <= 0;
     }
 }

OpenNest.Core/Geometry/EllipseConverter.cs

@@ -173,7 +173,11 @@ namespace OpenNest.Geometry
 
             if (maxDev <= tolerance)
             {
-                results.Add(CreateArc(arcCenter, radius, center, semiMajor, semiMinor, rotation, t0, t1));
+                var arc = CreateArc(arcCenter, radius, center, semiMajor, semiMinor, rotation, t0, t1);
+                if (arc.SweepAngle() < Tolerance.Epsilon)
+                    results.Add(new Line(p0, p1));
+                else
+                    results.Add(arc);
             }
             else
             {

OpenNest.Core/Geometry/GeometryOptimizer.cs

@@ -17,6 +17,38 @@ namespace OpenNest.Geometry
                 (list, item, i) => list.GetCollinearLines(item, i),
                 (Line a, Line b, out Line joined) => TryJoinLines(a, b, out joined));
 
+        public static void Deduplicate(IList<Circle> circles)
+        {
+            for (var i = circles.Count - 1; i >= 1; i--)
+            {
+                for (var j = i - 1; j >= 0; j--)
+                {
+                    if (circles[i].Center.DistanceTo(circles[j].Center) <= Tolerance.Epsilon
+                        && circles[i].Radius.IsEqualTo(circles[j].Radius))
+                    {
+                        circles.RemoveAt(i);
+                        break;
+                    }
+                }
+            }
+        }
+
+        public static void Deduplicate(IList<Circle> circles, IList<Arc> arcs)
+        {
+            for (var i = circles.Count - 1; i >= 0; i--)
+            {
+                for (var j = arcs.Count - 1; j >= 0; j--)
+                {
+                    if (arcs[j].Center.DistanceTo(circles[i].Center) <= Tolerance.Epsilon
+                        && arcs[j].Radius.IsEqualTo(circles[i].Radius)
+                        && arcs[j].IsFullCircle())
+                    {
+                        arcs.RemoveAt(j);
+                    }
+                }
+            }
+        }
+
         private delegate bool TryJoin<T>(T a, T b, out T joined);
 
         private static void MergePass<T>(IList<T> items,

OpenNest.Core/Geometry/GeometrySimplifier.cs

@@ -374,11 +374,8 @@ public class GeometrySimplifier
         var points = CollectPoints(entities, start, k);
         if (points.Count < 3) return null;
 
-        var startTangent = chainedTangent.IsValid()
-            ? chainedTangent
-            : new Vector(points[1].X - points[0].X, points[1].Y - points[0].Y);
-
-        var endTangent = GetExitDirection(entities[k]);
+        var startTangent = EstimateStartTangent(entities, start, points, chainedTangent);
+        var endTangent = EstimateEndTangent(entities, k, points);
         var (center, radius, dev) = TryFit(points, startTangent, endTangent);
         if (!center.IsValid()) return null;
 
@@ -386,8 +383,10 @@ public class GeometrySimplifier
         while (k + 1 <= runEnd)
         {
             var extPoints = CollectPoints(entities, start, k + 1);
-            var extEndTangent = GetExitDirection(entities[k + 1]);
-            var (nc, nr, nd) = extPoints.Count >= 3 ? TryFit(extPoints, startTangent, extEndTangent) : (Vector.Invalid, 0, 0d);
+            if (extPoints.Count < 3) break;
+
+            var extEndTangent = EstimateEndTangent(entities, k + 1, extPoints);
+            var (nc, nr, nd) = TryFit(extPoints, startTangent, extEndTangent);
             if (!nc.IsValid()) break;
 
             k++;
@@ -407,37 +406,172 @@ public class GeometrySimplifier
         return new ArcFitResult(center, radius, dev, points, k);
     }
 
-    private (Vector center, double radius, double deviation) TryFit(List<Vector> points, Vector startTangent, Vector endTangent)
+    private (Vector center, double radius, double deviation) TryFit(
+        List<Vector> points, TangentEstimate start, TangentEstimate end)
     {
-        // Try dual-tangent fit first (matches direction at both endpoints)
-        if (endTangent.IsValid())
+        foreach (var (center, radius, dev) in FitAttempts(points, start, end))
         {
-            var (dc, dr, dd) = ArcFit.FitWithDualTangent(points, startTangent, endTangent);
-            if (dc.IsValid() && dd <= Tolerance)
-            {
-                var isRev = SumSignedAngles(dc, points) < 0;
-                var aDev = MaxArcToSegmentDeviation(points, dc, dr, isRev);
-                if (aDev <= Tolerance)
-                    return (dc, dr, System.Math.Max(dd, aDev));
-            }
-        }
-
-        // Fall back to start-tangent-only, then mirror axis
-        var (center, radius, dev) = ArcFit.FitWithStartTangent(points, startTangent);
             if (!center.IsValid() || dev > Tolerance)
-            (center, radius, dev) = FitMirrorAxis(points);
-        if (!center.IsValid() || dev > Tolerance)
-            return (Vector.Invalid, 0, 0);
+                continue;
 
             // Check that the arc doesn't bulge away from the original line segments
             var isReversed = SumSignedAngles(center, points) < 0;
             var arcDev = MaxArcToSegmentDeviation(points, center, radius, isReversed);
             if (arcDev > Tolerance)
-            return (Vector.Invalid, 0, 0);
+                continue;
 
             return (center, radius, System.Math.Max(dev, arcDev));
         }
 
+        return (Vector.Invalid, 0, 0);
+    }
+
+    /// <summary>
+    /// Yields fit attempts in preference order. A trusted tangent (chained from the
+    /// previous arc, an adjacent original arc, or a long straight edge) is enforced
+    /// exactly on its side; otherwise the tangency error is balanced between both
+    /// endpoints. The unconstrained mirror-axis fit is the last resort. Every attempt
+    /// passes exactly through both endpoints, so no gaps are introduced.
+    /// </summary>
+    private IEnumerable<(Vector center, double radius, double deviation)> FitAttempts(
+        List<Vector> points, TangentEstimate start, TangentEstimate end)
+    {
+        if (start.Trusted && !end.Trusted)
+        {
+            yield return ArcFit.FitWithStartTangent(points, start.Direction);
+            yield return ArcFit.FitThroughEndpointsWithTangents(points, start.Direction, end.Direction);
+            yield return FitWithEndTangent(points, end.Direction);
+        }
+        else if (end.Trusted && !start.Trusted)
+        {
+            yield return FitWithEndTangent(points, end.Direction);
+            yield return ArcFit.FitThroughEndpointsWithTangents(points, start.Direction, end.Direction);
+            yield return ArcFit.FitWithStartTangent(points, start.Direction);
+        }
+        else
+        {
+            yield return ArcFit.FitThroughEndpointsWithTangents(points, start.Direction, end.Direction);
+            yield return ArcFit.FitWithStartTangent(points, start.Direction);
+            yield return FitWithEndTangent(points, end.Direction);
+        }
+
+        yield return FitMirrorAxis(points);
+    }
+
+    /// <summary>
+    /// Fits an arc through both endpoints with an exact tangent at the last point,
+    /// by running the start-tangent fit on the reversed point sequence.
+    /// </summary>
+    private static (Vector center, double radius, double deviation) FitWithEndTangent(
+        List<Vector> points, Vector endTangent)
+    {
+        var reversed = new List<Vector>(points);
+        reversed.Reverse();
+        return ArcFit.FitWithStartTangent(reversed, new Vector(-endTangent.X, -endTangent.Y));
+    }
+
+    /// <summary>
+    /// An estimated tangent direction at a fit endpoint. Trusted estimates come from
+    /// exact geometry (a chained arc, an adjacent original arc, or a long straight
+    /// edge) and are enforced exactly; untrusted ones are derived from the polyline
+    /// vertices and only guide the fit.
+    /// </summary>
+    private readonly record struct TangentEstimate(Vector Direction, bool Trusted);
+
+    /// <summary>Segment-length ratio above which a neighboring line counts as a true
+    /// straight edge (rather than another chord of the tessellated curve).</summary>
+    private const double NeighborEdgeFactor = 3.0;
+
+    private static TangentEstimate EstimateStartTangent(
+        List<Entity> entities, int start, List<Vector> points, Vector chainedTangent)
+    {
+        if (chainedTangent.IsValid())
+            return new TangentEstimate(chainedTangent, true);
+
+        if (entities[start] is Arc startArc)
+            return new TangentEstimate(GetEntryDirection(startArc), true);
+
+        var firstChordLen = points[0].DistanceTo(points[1]);
+        if (start > 0)
+        {
+            var prev = entities[start - 1];
+            var prevEnd = prev switch { Line l => l.EndPoint, Arc a => a.EndPoint(), _ => Vector.Invalid };
+            if (prevEnd.IsValid() && prevEnd.DistanceTo(points[0]) < 1e-6)
+            {
+                if (prev is Arc)
+                    return new TangentEstimate(GetExitDirection(prev), true);
+                if (prev is Line prevLine && prevLine.StartPoint.DistanceTo(prevLine.EndPoint) >= NeighborEdgeFactor * firstChordLen)
+                    return new TangentEstimate(GetExitDirection(prevLine), true);
+            }
+        }
+
+        var chord = new Vector(points[1].X - points[0].X, points[1].Y - points[0].Y);
+        if (points.Count >= 3)
+            return new TangentEstimate(EstimateVertexTangent(points[0], points[1], points[2], chord), false);
+        return new TangentEstimate(chord, false);
+    }
+
+    private static TangentEstimate EstimateEndTangent(List<Entity> entities, int k, List<Vector> points)
+    {
+        if (entities[k] is Arc endArc)
+            return new TangentEstimate(GetExitDirection(endArc), true);
+
+        var lastChordLen = points[^1].DistanceTo(points[^2]);
+        if (k + 1 < entities.Count)
+        {
+            var next = entities[k + 1];
+            var nextStart = next switch { Line l => l.StartPoint, Arc a => a.StartPoint(), _ => Vector.Invalid };
+            if (nextStart.IsValid() && nextStart.DistanceTo(points[^1]) < 1e-6)
+            {
+                if (next is Arc nextArc)
+                    return new TangentEstimate(GetEntryDirection(nextArc), true);
+                if (next is Line nextLine && nextLine.StartPoint.DistanceTo(nextLine.EndPoint) >= NeighborEdgeFactor * lastChordLen)
+                    return new TangentEstimate(GetExitDirection(nextLine), true);
+            }
+        }
+
+        var chord = new Vector(points[^1].X - points[^2].X, points[^1].Y - points[^2].Y);
+        if (points.Count >= 3)
+            return new TangentEstimate(EstimateVertexTangent(points[^1], points[^2], points[^3], chord), false);
+        return new TangentEstimate(chord, false);
+    }
+
+    /// <summary>
+    /// Estimates the curve tangent at a polyline vertex from the circle through it and
+    /// its two nearest neighbors. A raw chord direction is off from the true tangent by
+    /// half the chord's subtended angle; the circumcircle estimate removes that bias.
+    /// Falls back to the travel direction when the three points are collinear.
+    /// </summary>
+    private static Vector EstimateVertexTangent(Vector at, Vector b, Vector c, Vector travel)
+    {
+        var d = 2 * (at.X * (b.Y - c.Y) + b.X * (c.Y - at.Y) + c.X * (at.Y - b.Y));
+        if (System.Math.Abs(d) < 1e-14)
+            return travel;
+
+        var sqA = at.X * at.X + at.Y * at.Y;
+        var sqB = b.X * b.X + b.Y * b.Y;
+        var sqC = c.X * c.X + c.Y * c.Y;
+        var cx = (sqA * (b.Y - c.Y) + sqB * (c.Y - at.Y) + sqC * (at.Y - b.Y)) / d;
+        var cy = (sqA * (c.X - b.X) + sqB * (at.X - c.X) + sqC * (b.X - at.X)) / d;
+
+        var tangent = new Vector(-(at.Y - cy), at.X - cx);
+        if (tangent.X * travel.X + tangent.Y * travel.Y < 0)
+            tangent = new Vector(-tangent.X, -tangent.Y);
+        return tangent;
+    }
+
+    /// <summary>
+    /// Returns the entry direction (tangent at start point) of an entity.
+    /// </summary>
+    private static Vector GetEntryDirection(Entity entity) => entity switch
+    {
+        Line line => new Vector(line.EndPoint.X - line.StartPoint.X, line.EndPoint.Y - line.StartPoint.Y),
+        Arc arc => arc.IsReversed
+            ? new Vector(System.Math.Sin(arc.StartAngle), -System.Math.Cos(arc.StartAngle))
+            : new Vector(-System.Math.Sin(arc.StartAngle), System.Math.Cos(arc.StartAngle)),
+        _ => Vector.Invalid,
+    };
+
     /// <summary>
     /// Computes the tangent direction at the last point of a fitted arc,
     /// used to chain tangent continuity to the next arc.

OpenNest.Core/Geometry/ShapeBuilder.cs

@@ -1,12 +1,13 @@
 using OpenNest.Math;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 
 namespace OpenNest.Geometry
 {
     public static class ShapeBuilder
     {
-        public static List<Shape> GetShapes(IEnumerable<Entity> entities)
+        public static List<Shape> GetShapes(IEnumerable<Entity> entities, double? weldTolerance = null)
         {
             var lines = new List<Line>();
             var arcs = new List<Arc>();
@@ -57,6 +58,9 @@ namespace OpenNest.Geometry
             entityList.AddRange(lines);
             entityList.AddRange(arcs);
 
+            if (weldTolerance.HasValue)
+                WeldEndpoints(entityList, weldTolerance.Value);
+
             while (entityList.Count > 0)
             {
                 var next = entityList[0];
@@ -107,6 +111,93 @@ namespace OpenNest.Geometry
             return shapes;
         }
 
+        public static void WeldEndpoints(List<Entity> entities, double tolerance)
+        {
+            var endpointGroups = new List<List<(Entity entity, bool isStart, Vector point)>>();
+
+            foreach (var entity in entities)
+            {
+                var (start, end) = GetEndpoints(entity);
+                if (!start.IsValid() || !end.IsValid())
+                    continue;
+
+                AddToGroup(endpointGroups, entity, true, start, tolerance);
+                AddToGroup(endpointGroups, entity, false, end, tolerance);
+            }
+
+            foreach (var group in endpointGroups)
+            {
+                if (group.Count <= 1)
+                    continue;
+
+                var avgX = group.Average(g => g.point.X);
+                var avgY = group.Average(g => g.point.Y);
+                var weldedPoint = new Vector(avgX, avgY);
+
+                foreach (var (entity, isStart, _) in group)
+                    ApplyWeld(entity, isStart, weldedPoint);
+            }
+        }
+
+        private static void AddToGroup(
+            List<List<(Entity entity, bool isStart, Vector point)>> groups,
+            Entity entity, bool isStart, Vector point, double tolerance)
+        {
+            foreach (var group in groups)
+            {
+                if (group[0].point.DistanceTo(point) <= tolerance)
+                {
+                    group.Add((entity, isStart, point));
+                    return;
+                }
+            }
+
+            groups.Add(new List<(Entity, bool, Vector)> { (entity, isStart, point) });
+        }
+
+        private static (Vector start, Vector end) GetEndpoints(Entity entity)
+        {
+            switch (entity.Type)
+            {
+                case EntityType.Arc:
+                    var arc = (Arc)entity;
+                    return (arc.StartPoint(), arc.EndPoint());
+
+                case EntityType.Line:
+                    var line = (Line)entity;
+                    return (line.StartPoint, line.EndPoint);
+
+                default:
+                    return (Vector.Invalid, Vector.Invalid);
+            }
+        }
+
+        private static void ApplyWeld(Entity entity, bool isStart, Vector weldedPoint)
+        {
+            switch (entity.Type)
+            {
+                case EntityType.Line:
+                    var line = (Line)entity;
+                    if (isStart)
+                        line.StartPoint = weldedPoint;
+                    else
+                        line.EndPoint = weldedPoint;
+                    break;
+
+                case EntityType.Arc:
+                    var arc = (Arc)entity;
+                    var deltaX = weldedPoint.X - arc.Center.X;
+                    var deltaY = weldedPoint.Y - arc.Center.Y;
+                    var angle = System.Math.Atan2(deltaY, deltaX);
+
+                    if (isStart)
+                        arc.StartAngle = angle;
+                    else
+                        arc.EndAngle = angle;
+                    break;
+            }
+        }
+
         internal static Entity GetConnected(Vector pt, IEnumerable<Entity> geometry)
         {
             var tol = Tolerance.ChainTolerance;

OpenNest.Core/Math/Fraction.cs

@@ -3,7 +3,7 @@ using System.Linq;
 using System.Text;
 using System.Text.RegularExpressions;
 
-namespace OpenNest.IO.Bom
+namespace OpenNest.Math
 {
     public static class Fraction
     {

OpenNest.Engine/BestFit/BestFitCache.cs

@@ -24,6 +24,9 @@ namespace OpenNest.Engine.BestFit
             if (_cache.TryGetValue(key, out var cached))
                 return cached;
 
+            // Operate on the canonical frame so cached pair positions are orientation-invariant.
+            var canonical = CanonicalFrame.AsCanonicalCopy(drawing);
+
             IPairEvaluator evaluator = null;
             ISlideComputer slideComputer = null;
 
@@ -31,7 +34,7 @@ namespace OpenNest.Engine.BestFit
             {
                 if (CreateEvaluator != null)
                 {
-                    try { evaluator = CreateEvaluator(drawing, spacing); }
+                    try { evaluator = CreateEvaluator(canonical, spacing); }
                     catch { /* fall back to default evaluator */ }
                 }
 
@@ -42,7 +45,7 @@ namespace OpenNest.Engine.BestFit
                 }
 
                 var finder = new BestFitFinder(plateWidth, plateHeight, evaluator, slideComputer);
-                var results = finder.FindBestFits(drawing, spacing, StepSize);
+                var results = finder.FindBestFits(canonical, spacing, StepSize);
 
                 _cache.TryAdd(key, results);
                 return results;
@@ -86,9 +89,12 @@ namespace OpenNest.Engine.BestFit
 
             try
             {
+                // Operate on the canonical frame so cached pair positions are orientation-invariant.
+                var canonical = CanonicalFrame.AsCanonicalCopy(drawing);
+
                 if (CreateEvaluator != null)
                 {
-                    try { evaluator = CreateEvaluator(drawing, spacing); }
+                    try { evaluator = CreateEvaluator(canonical, spacing); }
                     catch { /* fall back to default evaluator */ }
                 }
 
@@ -100,7 +106,7 @@ namespace OpenNest.Engine.BestFit
 
                 // Compute candidates and evaluate once with the largest plate.
                 var finder = new BestFitFinder(maxWidth, maxHeight, evaluator, slideComputer);
-                var baseResults = finder.FindBestFits(drawing, spacing, StepSize);
+                var baseResults = finder.FindBestFits(canonical, spacing, StepSize);
 
                 // Cache a filtered copy for each plate size.
                 foreach (var size in needed)

OpenNest.Engine/BestFit/BestFitResult.cs

@@ -1,6 +1,9 @@
+using OpenNest.Engine;
+using OpenNest.Converters;
 using OpenNest.Geometry;
 using OpenNest.Math;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace OpenNest.Engine.BestFit
 {
@@ -54,6 +57,68 @@ namespace OpenNest.Engine.BestFit
 
             return new List<Part> { part1, part2 };
         }
+
+        public List<Part> BuildCanonicalParts()
+        {
+            return NormalizeToCutOrigin(BuildParts(Candidate.Drawing));
+        }
+
+        public List<Part> BuildSourceParts(Drawing drawing)
+        {
+            var parts = BuildCanonicalParts();
+            var sourceAngle = drawing?.Source?.Angle ?? 0.0;
+
+            for (var i = 0; i < parts.Count; i++)
+            {
+                var p = parts[i];
+                var rebound = Part.CreateAtOrigin(drawing, p.Rotation);
+                var delta = p.BoundingBox.Location - rebound.BoundingBox.Location;
+                rebound.Offset(delta);
+                rebound.UpdateBounds();
+                parts[i] = rebound;
+            }
+
+            return NormalizeToCutOrigin(CanonicalFrame.FromCanonical(parts, sourceAngle));
+        }
+
+        public Box GetCutBounds(List<Part> parts)
+        {
+            return GetCutBoundingBox(parts);
+        }
+
+        private static List<Part> NormalizeToCutOrigin(List<Part> parts)
+        {
+            if (parts == null || parts.Count == 0)
+                return parts;
+
+            var bounds = GetCutBoundingBox(parts);
+            var offset = new Vector(-bounds.Left, -bounds.Bottom);
+
+            foreach (var part in parts)
+                part.Offset(offset);
+
+            return parts;
+        }
+
+        private static Box GetCutBoundingBox(List<Part> parts)
+        {
+            var entities = new List<IBoundable>();
+
+            foreach (var part in parts)
+            {
+                var partEntities = ConvertProgram.ToGeometry(part.Program)
+                    .Where(e => e.Layer != SpecialLayers.Rapid)
+                    .ToList();
+
+                foreach (var entity in partEntities)
+                {
+                    entity.Offset(part.Location);
+                    entities.Add(entity);
+                }
+            }
+
+            return entities.GetBoundingBox();
+        }
     }
 
     public enum BestFitSortField

OpenNest.Engine/BestFit/NfpSlideStrategy.cs

@@ -1,18 +1,10 @@
 using OpenNest.Geometry;
-using OpenNest.Math;
 using System.Collections.Generic;
-using System.IO;
 
 namespace OpenNest.Engine.BestFit
 {
     public class NfpSlideStrategy : IBestFitStrategy
     {
-        private static readonly string LogPath = Path.Combine(
-            System.Environment.GetFolderPath(System.Environment.SpecialFolder.Desktop),
-            "nfp-slide-debug.log");
-
-        private static readonly object LogLock = new object();
-
         private readonly double _part2Rotation;
         private readonly Polygon _stationaryPerimeter;
         private readonly Polygon _stationaryHull;
@@ -46,12 +38,6 @@ namespace OpenNest.Engine.BestFit
 
             var hull = ConvexHull.Compute(result.Polygon.Vertices);
 
-            Log($"=== Create: drawing={drawing.Name}, rotation={Angle.ToDegrees(part2Rotation):F1}deg ===");
-            Log($"  Perimeter: {result.Polygon.Vertices.Count} verts, bounds={FormatBounds(result.Polygon)}");
-            Log($"  Hull: {hull.Vertices.Count} verts, bounds={FormatBounds(hull)}");
-            Log($"  Correction: ({result.Correction.X:F4}, {result.Correction.Y:F4})");
-            Log($"  ProgramBBox: {drawing.Program.BoundingBox()}");
-
             return new NfpSlideStrategy(part2Rotation, type, description,
                 result.Polygon, hull, result.Correction);
         }
@@ -63,40 +49,17 @@ namespace OpenNest.Engine.BestFit
             if (stepSize <= 0)
                 return candidates;
 
-            Log($"--- GenerateCandidates: drawing={drawing.Name}, part2Rot={Angle.ToDegrees(_part2Rotation):F1}deg, spacing={spacing}, stepSize={stepSize} ---");
-
-            // Orbiting polygon: same shape rotated to Part2's angle.
             var orbitingPerimeter = PolygonHelper.RotatePolygon(_stationaryPerimeter, _part2Rotation, reNormalize: true);
             var orbitingPoly = ConvexHull.Compute(orbitingPerimeter.Vertices);
 
-            Log($"  Stationary hull: {_stationaryHull.Vertices.Count} verts, bounds={FormatBounds(_stationaryHull)}");
-            Log($"  Orbiting perimeter (rotated): {orbitingPerimeter.Vertices.Count} verts, bounds={FormatBounds(orbitingPerimeter)}");
-            Log($"  Orbiting hull: {orbitingPoly.Vertices.Count} verts, bounds={FormatBounds(orbitingPoly)}");
-
             var nfp = NoFitPolygon.ComputeConvex(_stationaryHull, orbitingPoly);
 
             if (nfp == null || nfp.Vertices.Count < 3)
-            {
-                Log($"  NFP failed or degenerate (verts={nfp?.Vertices.Count ?? 0})");
                 return candidates;
-            }
 
             var verts = nfp.Vertices;
             var vertCount = nfp.IsClosed() ? verts.Count - 1 : verts.Count;
 
-            Log($"  NFP: {verts.Count} verts (closed={nfp.IsClosed()}, walking {vertCount}), bounds={FormatBounds(nfp)}");
-            Log($"  Correction: ({_correction.X:F4}, {_correction.Y:F4})");
-
-            // Log NFP vertices
-            for (var v = 0; v < vertCount; v++)
-                Log($"    NFP vert[{v}]: ({verts[v].X:F4}, {verts[v].Y:F4}) -> corrected: ({verts[v].X - _correction.X:F4}, {verts[v].Y - _correction.Y:F4})");
-
-            // Compare with what RotationSlideStrategy would produce
-            var part1 = Part.CreateAtOrigin(drawing);
-            var part2 = Part.CreateAtOrigin(drawing, _part2Rotation);
-            Log($"  Part1 (rot=0): loc=({part1.Location.X:F4}, {part1.Location.Y:F4}), bbox={part1.BoundingBox}");
-            Log($"  Part2 (rot={Angle.ToDegrees(_part2Rotation):F1}): loc=({part2.Location.X:F4}, {part2.Location.Y:F4}), bbox={part2.BoundingBox}");
-
             var testNumber = 0;
 
             for (var i = 0; i < vertCount; i++)
@@ -125,20 +88,6 @@ namespace OpenNest.Engine.BestFit
                 }
             }
 
-            // Log overlap check for vertex candidates (first few)
-            var checkCount = System.Math.Min(vertCount, 8);
-            for (var c = 0; c < checkCount; c++)
-            {
-                var cand = candidates[c];
-                var p2 = Part.CreateAtOrigin(drawing, cand.Part2Rotation);
-                p2.Location = cand.Part2Offset;
-                var overlaps = part1.Intersects(p2, out _);
-                Log($"  Candidate[{c}]: offset=({cand.Part2Offset.X:F4}, {cand.Part2Offset.Y:F4}), overlaps={overlaps}");
-            }
-
-            Log($"  Total candidates: {candidates.Count}");
-            Log("");
-
             return candidates;
         }
 
@@ -160,20 +109,5 @@ namespace OpenNest.Engine.BestFit
                 Spacing = spacing
             };
         }
-
-        private static string FormatBounds(Polygon polygon)
-        {
-            polygon.UpdateBounds();
-            var bb = polygon.BoundingBox;
-            return $"[({bb.Left:F4}, {bb.Bottom:F4})-({bb.Right:F4}, {bb.Top:F4}), {bb.Width:F2}x{bb.Length:F2}]";
-        }
-
-        private static void Log(string message)
-        {
-            lock (LogLock)
-            {
-                File.AppendAllText(LogPath, message + "\n");
-            }
-        }
     }
 }

OpenNest.Engine/CanonicalFrame.cs

@@ -0,0 +1,76 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using System.Collections.Generic;
+
+namespace OpenNest.Engine
+{
+    /// <summary>
+    /// Produces transient canonical (MBR-axis-aligned) copies of drawings for engine consumption
+    /// and un-rotates placed parts back to the drawing's original frame.
+    /// </summary>
+    public static class CanonicalFrame
+    {
+        /// <summary>
+        /// Returns a new Drawing whose Program geometry is rotated to the canonical frame.
+        /// The source drawing is not mutated.
+        /// </summary>
+        public static Drawing AsCanonicalCopy(Drawing drawing)
+        {
+            if (drawing == null)
+                return null;
+
+            var angle = drawing.Source?.Angle ?? 0.0;
+
+            // Clone program (never mutate the source).
+            var pgm = (drawing.Program.Clone() as OpenNest.CNC.Program)
+                      ?? new OpenNest.CNC.Program();
+
+            if (!Tolerance.IsEqualTo(angle, 0))
+                pgm.Rotate(angle, pgm.BoundingBox().Center);
+
+            var copy = new Drawing(drawing.Name ?? string.Empty, pgm)
+            {
+                Color = drawing.Color,
+                Constraints = drawing.Constraints,
+                Material = drawing.Material,
+                Priority = drawing.Priority,
+                Customer = drawing.Customer,
+                IsCutOff = drawing.IsCutOff,
+                Source = new SourceInfo
+                {
+                    Path = drawing.Source?.Path,
+                    Offset = drawing.Source?.Offset ?? new Vector(0, 0),
+                    Angle = 0.0,
+                },
+            };
+            return copy;
+        }
+
+        /// <summary>
+        /// Composes the source drawing's canonical angle onto each placed part so the
+        /// returned list is in the drawing's original (visible) frame.
+        ///
+        /// Derivation: let sourceAngle = S (rotation mapping source -> canonical).
+        /// Canonical part at rotation R shows visible orientation R.
+        /// Source part at rotation R' shows visible orientation R' + (-S), because the
+        /// source geometry is already rotated by -S relative to canonical.
+        /// Setting equal gives R' = R + S, so we ADD sourceAngle to each placed part.
+        ///
+        /// Rotation is performed around the part's Location so its placement position is preserved;
+        /// only the orientation composes.
+        /// </summary>
+        public static List<Part> FromCanonical(List<Part> placed, double sourceAngle)
+        {
+            if (placed == null || placed.Count == 0)
+                return placed;
+            if (Tolerance.IsEqualTo(sourceAngle, 0))
+                return placed;
+
+            foreach (var p in placed)
+                p.Rotate(sourceAngle, p.Location);
+
+            return placed;
+        }
+    }
+}

OpenNest.Engine/DefaultNestEngine.cs

@@ -47,14 +47,29 @@ namespace OpenNest
             PhaseResults.Clear();
             AngleResults.Clear();
 
-            // Fast path: for very small quantities, skip the full strategy pipeline.
-            if (item.Quantity > 0 && item.Quantity <= 2)
+            // Replace the item's Drawing with a canonical copy for the duration of this fill.
+            // All internal methods see canonical geometry; this wrapper un-canonicalizes the final result.
+            var sourceAngle = item.Drawing?.Source?.Angle ?? 0.0;
+            var originalDrawing = item.Drawing;
+            var canonicalItem = new NestItem
             {
-                var fast = TryFillSmallQuantity(item, workArea);
-                if (fast != null && fast.Count >= item.Quantity)
+                Drawing = CanonicalFrame.AsCanonicalCopy(item.Drawing),
+                Quantity = item.Quantity,
+                Priority = item.Priority,
+                RotationStart = item.RotationStart,
+                RotationEnd = item.RotationEnd,
+                StepAngle = item.StepAngle,
+            };
+
+            // Fast path for qty 1-2.
+            if (canonicalItem.Quantity > 0 && canonicalItem.Quantity <= 2)
             {
-                    Debug.WriteLine($"[Fill] Fast path: placed {fast.Count} parts for qty={item.Quantity}");
+                var fast = TryFillSmallQuantity(canonicalItem, workArea);
+                if (fast != null && fast.Count >= canonicalItem.Quantity)
+                {
+                    Debug.WriteLine($"[Fill] Fast path: placed {fast.Count} parts for qty={canonicalItem.Quantity}");
                     WinnerPhase = NestPhase.Pairs;
+                    fast = RebindAndUnCanonicalize(fast, originalDrawing, sourceAngle);
                     ReportProgress(progress, new ProgressReport
                     {
                         Phase = WinnerPhase,
@@ -68,32 +83,30 @@ namespace OpenNest
                 }
             }
 
-            // For low quantities, shrink the work area in both dimensions to avoid
-            // running expensive strategies against the full plate.
             var effectiveWorkArea = workArea;
-            if (item.Quantity > 0)
+            if (canonicalItem.Quantity > 0)
             {
-                effectiveWorkArea = ShrinkWorkArea(item, workArea, Plate.PartSpacing);
-
+                effectiveWorkArea = ShrinkWorkArea(canonicalItem, workArea, Plate.PartSpacing);
                 if (effectiveWorkArea != workArea)
-                    Debug.WriteLine($"[Fill] Low-qty shrink: {item.Quantity} requested, " +
+                    Debug.WriteLine($"[Fill] Low-qty shrink: {canonicalItem.Quantity} requested, " +
                         $"from {workArea.Width:F1}x{workArea.Length:F1} " +
                         $"to {effectiveWorkArea.Width:F1}x{effectiveWorkArea.Length:F1}");
             }
 
-            var best = RunFillPipeline(item, effectiveWorkArea, progress, token);
+            var best = RunFillPipeline(canonicalItem, effectiveWorkArea, progress, token);
 
-            // Fallback: if the reduced area didn't yield enough, retry with full area.
-            if (item.Quantity > 0 && best.Count < item.Quantity && effectiveWorkArea != workArea)
+            if (canonicalItem.Quantity > 0 && best.Count < canonicalItem.Quantity && effectiveWorkArea != workArea)
             {
-                Debug.WriteLine($"[Fill] Low-qty fallback: got {best.Count}, need {item.Quantity}, retrying full area");
+                Debug.WriteLine($"[Fill] Low-qty fallback: got {best.Count}, need {canonicalItem.Quantity}, retrying full area");
                 PhaseResults.Clear();
                 AngleResults.Clear();
-                best = RunFillPipeline(item, workArea, progress, token);
+                best = RunFillPipeline(canonicalItem, workArea, progress, token);
             }
 
-            if (item.Quantity > 0 && best.Count > item.Quantity)
-                best = ShrinkFiller.TrimToCount(best, item.Quantity, TrimAxis);
+            if (canonicalItem.Quantity > 0 && best.Count > canonicalItem.Quantity)
+                best = ShrinkFiller.TrimToCount(best, canonicalItem.Quantity, TrimAxis);
+
+            best = RebindAndUnCanonicalize(best, originalDrawing, sourceAngle);
 
             ReportProgress(progress, new ProgressReport
             {
@@ -108,6 +121,31 @@ namespace OpenNest
             return best;
         }
 
+        /// <summary>
+        /// Single exit point for canonical -> source frame conversion. Rebinds every Part to the
+        /// original Drawing (so consumers see the user's drawing identity, not the transient canonical copy)
+        /// and composes sourceAngle onto each Part's rotation via CanonicalFrame.FromCanonical.
+        /// </summary>
+        private static List<Part> RebindAndUnCanonicalize(List<Part> parts, Drawing original, double sourceAngle)
+        {
+            if (parts == null || parts.Count == 0)
+                return parts;
+
+            for (var i = 0; i < parts.Count; i++)
+            {
+                var p = parts[i];
+                // Rebind to `original` while preserving world pose. CreateAtOrigin rotates
+                // at the origin (keeping bbox at world (0,0)) then we offset to match p's bbox.
+                var rebound = Part.CreateAtOrigin(original, p.Rotation);
+                var delta = p.BoundingBox.Location - rebound.BoundingBox.Location;
+                rebound.Offset(delta);
+                rebound.UpdateBounds();
+                parts[i] = rebound;
+            }
+
+            return CanonicalFrame.FromCanonical(parts, sourceAngle);
+        }
+
         /// <summary>
         /// Fast path for qty 1-2: place a single part or a best-fit pair
         /// without running the full strategy pipeline.
@@ -139,6 +177,10 @@ namespace OpenNest
             var bestFits = BestFitCache.GetOrCompute(
                 drawing, Plate.Size.Length, Plate.Size.Width, Plate.PartSpacing);
 
+            // Build pair candidates with a canonical drawing so their geometry matches
+            // the coordinate frame of the cached fit results.
+            var canonicalDrawing = CanonicalFrame.AsCanonicalCopy(drawing);
+
             List<Part> bestPlacement = null;
 
             foreach (var fit in bestFits)
@@ -152,7 +194,7 @@ namespace OpenNest
                 if (fit.LongestSide > System.Math.Max(workArea.Width, workArea.Length) + Tolerance.Epsilon)
                     continue;
 
-                var landscape = fit.BuildParts(drawing);
+                var landscape = fit.BuildParts(canonicalDrawing);
                 var portrait = RotatePair90(landscape);
 
                 var lFits = TryOffsetToWorkArea(landscape, workArea);
@@ -174,6 +216,8 @@ namespace OpenNest
                     bestPlacement = candidate;
             }
 
+            // Parts are returned in canonical frame, bound to the canonical drawing.
+            // The outer Fill wrapper (Task 7) rebinds to `drawing` and composes sourceAngle onto rotation.
             return bestPlacement;
         }
 

OpenNest.Engine/Fill/Compactor.cs

@@ -1,6 +1,7 @@
 using OpenNest.Geometry;
 using System.Collections.Generic;
 using System.Linq;
+using OpenNest.Math;
 
 namespace OpenNest.Engine.Fill
 {
@@ -14,7 +15,7 @@ namespace OpenNest.Engine.Fill
         public static double Push(List<Part> movingParts, Plate plate, PushDirection direction)
         {
             var obstacleParts = plate.Parts
-                .Where(p => !movingParts.Contains(p))
+                .Where(p => !movingParts.Contains(p) && !IntersectsAny(p, movingParts))
                 .ToList();
 
             return Push(movingParts, obstacleParts, plate.WorkArea(), plate.PartSpacing, direction);
@@ -26,7 +27,7 @@ namespace OpenNest.Engine.Fill
         public static double Push(List<Part> movingParts, Plate plate, double angle)
         {
             var obstacleParts = plate.Parts
-                .Where(p => !movingParts.Contains(p))
+                .Where(p => !movingParts.Contains(p) && !IntersectsAny(p, movingParts))
                 .ToList();
 
             var direction = new Vector(System.Math.Cos(angle), System.Math.Sin(angle));
@@ -99,6 +100,13 @@ namespace OpenNest.Engine.Fill
                         : PartGeometry.GetPerimeterEntities(obstacleParts[i]);
 
                     var d = SpatialQuery.DirectionalDistance(movingEntities, obstacleEntities[i], direction);
+                    if (d <= Tolerance.Epsilon
+                        && partSpacing <= Tolerance.Epsilon
+                        && CanNudgeWithoutOverlap(moving, obstacleParts[i], direction))
+                    {
+                        continue;
+                    }
+
                     if (d < distance)
                         distance = d;
                 }
@@ -115,6 +123,31 @@ namespace OpenNest.Engine.Fill
             return 0;
         }
 
+        private static bool IntersectsAny(Part candidate, List<Part> parts)
+        {
+            for (var i = 0; i < parts.Count; i++)
+            {
+                if (candidate.Intersects(parts[i], out _))
+                    return true;
+            }
+            return false;
+        }
+
+        private static bool CanNudgeWithoutOverlap(Part moving, Part obstacle, Vector direction)
+        {
+            var nudge = direction * (Tolerance.Epsilon * 10);
+
+            moving.Offset(nudge);
+            try
+            {
+                return !moving.Intersects(obstacle, out _);
+            }
+            finally
+            {
+                moving.Offset(-nudge);
+            }
+        }
+
         public static double Push(List<Part> movingParts, List<Part> obstacleParts,
             Box workArea, double partSpacing, PushDirection direction)
         {
@@ -130,7 +163,7 @@ namespace OpenNest.Engine.Fill
         public static double PushBoundingBox(List<Part> movingParts, Plate plate, PushDirection direction)
         {
             var obstacleParts = plate.Parts
-                .Where(p => !movingParts.Contains(p))
+                .Where(p => !movingParts.Contains(p) && !IntersectsAny(p, movingParts))
                 .ToList();
 
             return PushBoundingBox(movingParts, obstacleParts, plate.WorkArea(), plate.PartSpacing, direction);

OpenNest.Engine/Fill/FillLinear.cs

@@ -61,92 +61,91 @@ namespace OpenNest.Engine.Fill
                 : NestDirection.Horizontal;
         }
 
-        /// <summary>
-        /// Computes the slide distance for the push algorithm, returning the
-        /// geometry-aware copy distance along the given axis.
-        /// </summary>
-        private double ComputeCopyDistance(double bboxDim, double slideDistance)
-        {
-            if (slideDistance >= double.MaxValue || slideDistance < 0)
-                return bboxDim + PartSpacing;
-
-            // The geometry-aware slide can produce a copy distance smaller than
-            // the part itself when inflated corner/arc vertices interact spuriously.
-            // Clamp to bboxDim + PartSpacing to prevent bounding box overlap.
-            return System.Math.Max(bboxDim - slideDistance, bboxDim + PartSpacing);
-        }
-
         /// <summary>
         /// Finds the geometry-aware copy distance between two identical parts along an axis.
-        /// Both parts are inflated by half-spacing for symmetric spacing.
+        /// Uses native Line/Arc entities (inflated by half-spacing) so curves are handled
+        /// exactly without polygon sampling error.
         /// </summary>
-        private double FindCopyDistance(Part partA, NestDirection direction, PartBoundary boundary)
+        private double FindCopyDistance(Part partA, NestDirection direction)
         {
             var bboxDim = GetDimension(partA.BoundingBox, direction);
             var pushDir = GetPushDirection(direction);
+            var startOffset = bboxDim + PartSpacing + Tolerance.Epsilon;
+            var offset = MakeOffset(direction, startOffset);
 
-            var locationBOffset = MakeOffset(direction, bboxDim);
+            var stationaryEntities = PartGeometry.GetOffsetPerimeterEntities(partA, HalfSpacing);
+            var movingEntities = PartGeometry.GetOffsetPerimeterEntities(
+                partA.CloneAtOffset(offset), HalfSpacing);
 
-            // Use the most efficient array-based overload to avoid all allocations.
             var slideDistance = SpatialQuery.DirectionalDistance(
-                boundary.GetEdges(pushDir), partA.Location + locationBOffset,
-                boundary.GetEdges(SpatialQuery.OppositeDirection(pushDir)), partA.Location,
-                pushDir);
+                movingEntities, stationaryEntities, pushDir);
 
-            return ComputeCopyDistance(bboxDim, slideDistance);
+            if (slideDistance >= double.MaxValue || slideDistance < 0)
+                return bboxDim + PartSpacing;
+
+            return startOffset - slideDistance;
         }
 
         /// <summary>
         /// Finds the geometry-aware copy distance between two identical patterns along an axis.
-        /// Checks every pair of parts across adjacent patterns so that multi-part
-        /// patterns (e.g. interlocking pairs) maintain spacing between ALL parts.
-        /// Both sides are inflated by half-spacing for symmetric spacing.
+        /// Checks every pair of parts across adjacent pattern copies so multi-part patterns
+        /// (e.g. interlocking pairs) maintain spacing between ALL parts. Uses native entity
+        /// geometry inflated by half-spacing — same primitive the Compactor uses — so arcs
+        /// are exact and no bbox clamp is needed.
         /// </summary>
-        private double FindPatternCopyDistance(Pattern patternA, NestDirection direction, PartBoundary[] boundaries)
+        private double FindPatternCopyDistance(Pattern patternA, NestDirection direction)
         {
-            if (patternA.Parts.Count <= 1)
-                return FindSinglePartPatternCopyDistance(patternA, direction, boundaries[0]);
+            if (patternA.Parts.Count == 1)
+                return FindCopyDistance(patternA.Parts[0], direction);
 
             var bboxDim = GetDimension(patternA.BoundingBox, direction);
             var pushDir = GetPushDirection(direction);
             var opposite = SpatialQuery.OppositeDirection(pushDir);
+            var dirVec = SpatialQuery.DirectionToOffset(pushDir, 1.0);
 
             // bboxDim already spans max(upper) - min(lower) across all parts,
             // so the start offset just needs to push beyond that plus spacing.
             var startOffset = bboxDim + PartSpacing + Tolerance.Epsilon;
             var offset = MakeOffset(direction, startOffset);
 
-            var maxCopyDistance = FindMaxPairDistance(
-                patternA.Parts, boundaries, offset, pushDir, opposite, startOffset);
+            var parts = patternA.Parts;
+            var stationaryBoxes = new Box[parts.Count];
+            var movingBoxes = new Box[parts.Count];
+            var stationaryEntities = new List<Entity>[parts.Count];
+            var movingEntities = new List<Entity>[parts.Count];
 
-            // The copy distance must be at least bboxDim + PartSpacing to prevent
-            // bounding box overlap. Cross-pair slides can underestimate when the
-            // circumscribed polygon boundary overshoots the true arc, creating
-            // spurious contacts between diagonal parts in adjacent copies.
-            return System.Math.Max(maxCopyDistance, bboxDim + PartSpacing);
+            for (var i = 0; i < parts.Count; i++)
+            {
+                stationaryBoxes[i] = parts[i].BoundingBox;
+                movingBoxes[i] = stationaryBoxes[i].Translate(offset);
             }
 
-        /// <summary>
-        /// Tests every pair of parts across adjacent pattern copies and returns the
-        /// maximum copy distance found. Returns 0 if no valid slide was found.
-        /// </summary>
-        private static double FindMaxPairDistance(
-            List<Part> parts, PartBoundary[] boundaries, Vector offset,
-            PushDirection pushDir, PushDirection opposite, double startOffset)
-        {
             var maxCopyDistance = 0.0;
 
             for (var j = 0; j < parts.Count; j++)
             {
-                var movingEdges = boundaries[j].GetEdges(pushDir);
-                var locationB = parts[j].Location + offset;
+                var movingBox = movingBoxes[j];
 
                 for (var i = 0; i < parts.Count; i++)
                 {
+                    var stationaryBox = stationaryBoxes[i];
+
+                    // Skip if stationary is already ahead of moving in the push direction
+                    // (sliding forward would take them further apart).
+                    if (SpatialQuery.DirectionalGap(movingBox, stationaryBox, opposite) > 0)
+                        continue;
+
+                    // Skip if bboxes can't overlap along the axis perpendicular to the push.
+                    if (!SpatialQuery.PerpendicularOverlap(movingBox, stationaryBox, dirVec))
+                        continue;
+
+                    stationaryEntities[i] ??= PartGeometry.GetOffsetPerimeterEntities(
+                        parts[i], HalfSpacing);
+                    movingEntities[j] ??= PartGeometry.GetOffsetPerimeterEntities(
+                        parts[j].CloneAtOffset(offset), HalfSpacing);
+
                     var slideDistance = SpatialQuery.DirectionalDistance(
-                        movingEdges, locationB,
-                        boundaries[i].GetEdges(opposite), parts[i].Location,
-                        pushDir);
+                        movingEntities[j], stationaryEntities[i], pushDir);
 
                     if (slideDistance >= double.MaxValue || slideDistance < 0)
                         continue;
@@ -161,86 +160,15 @@ namespace OpenNest.Engine.Fill
             return maxCopyDistance;
         }
 
-        /// <summary>
-        /// Fast path for single-part patterns — no cross-part conflicts possible.
-        /// </summary>
-        private double FindSinglePartPatternCopyDistance(Pattern patternA, NestDirection direction, PartBoundary boundary)
-        {
-            var template = patternA.Parts[0];
-            return FindCopyDistance(template, direction, boundary);
-        }
-
-        /// <summary>
-        /// Gets offset boundary lines for all parts in a pattern using a shared boundary.
-        /// </summary>
-        private static List<Line> GetPatternLines(Pattern pattern, PartBoundary boundary, PushDirection direction)
-        {
-            var lines = new List<Line>();
-
-            foreach (var part in pattern.Parts)
-                lines.AddRange(boundary.GetLines(part.Location, direction));
-
-            return lines;
-        }
-
-        /// <summary>
-        /// Gets boundary lines for all parts in a pattern, with an additional
-        /// location offset applied. Avoids cloning the pattern.
-        /// </summary>
-        private static List<Line> GetOffsetPatternLines(Pattern pattern, Vector offset, PartBoundary boundary, PushDirection direction)
-        {
-            var lines = new List<Line>();
-
-            foreach (var part in pattern.Parts)
-                lines.AddRange(boundary.GetLines(part.Location + offset, direction));
-
-            return lines;
-        }
-
-        /// <summary>
-        /// Creates boundaries for all parts in a pattern. Parts that share the same
-        /// program geometry (same drawing and rotation) reuse the same boundary instance.
-        /// </summary>
-        private PartBoundary[] CreateBoundaries(Pattern pattern)
-        {
-            var boundaries = new PartBoundary[pattern.Parts.Count];
-            var cache = new List<(Drawing drawing, double rotation, PartBoundary boundary)>();
-
-            for (var i = 0; i < pattern.Parts.Count; i++)
-            {
-                var part = pattern.Parts[i];
-                PartBoundary found = null;
-
-                foreach (var entry in cache)
-                {
-                    if (entry.drawing == part.BaseDrawing && entry.rotation.IsEqualTo(part.Rotation))
-                    {
-                        found = entry.boundary;
-                        break;
-                    }
-                }
-
-                if (found == null)
-                {
-                    found = new PartBoundary(part, HalfSpacing);
-                    cache.Add((part.BaseDrawing, part.Rotation, found));
-                }
-
-                boundaries[i] = found;
-            }
-
-            return boundaries;
-        }
-
         /// <summary>
         /// Tiles a pattern along the given axis, returning the cloned parts
         /// (does not include the original pattern's parts). For multi-part
         /// patterns, also adds individual parts from the next incomplete copy
         /// that still fit within the work area.
         /// </summary>
-        private List<Part> TilePattern(Pattern basePattern, NestDirection direction, PartBoundary[] boundaries)
+        private List<Part> TilePattern(Pattern basePattern, NestDirection direction)
         {
-            var copyDistance = FindPatternCopyDistance(basePattern, direction, boundaries);
+            var copyDistance = FindPatternCopyDistance(basePattern, direction);
 
             if (copyDistance <= 0)
                 return new List<Part>();
@@ -394,11 +322,10 @@ namespace OpenNest.Engine.Fill
         private List<Part> FillGrid(Pattern pattern, NestDirection direction)
         {
             var perpAxis = PerpendicularAxis(direction);
-            var boundaries = CreateBoundaries(pattern);
 
             // Step 1: Tile along primary axis
             var row = new List<Part>(pattern.Parts);
-            row.AddRange(TilePattern(pattern, direction, boundaries));
+            row.AddRange(TilePattern(pattern, direction));
 
             if (pattern.Parts.Count > 1 && HasOverlappingParts(row, out var a1, out var b1))
             {
@@ -410,7 +337,7 @@ namespace OpenNest.Engine.Fill
             // If primary tiling didn't produce copies, just tile along perpendicular
             if (row.Count <= pattern.Parts.Count)
             {
-                row.AddRange(TilePattern(pattern, perpAxis, boundaries));
+                row.AddRange(TilePattern(pattern, perpAxis));
 
                 if (pattern.Parts.Count > 1 && HasOverlappingParts(row, out var a2, out var b2))
                 {
@@ -427,9 +354,8 @@ namespace OpenNest.Engine.Fill
             rowPattern.Parts.AddRange(row);
             rowPattern.UpdateBounds();
 
-            var rowBoundaries = CreateBoundaries(rowPattern);
             var gridResult = new List<Part>(rowPattern.Parts);
-            gridResult.AddRange(TilePattern(rowPattern, perpAxis, rowBoundaries));
+            gridResult.AddRange(TilePattern(rowPattern, perpAxis));
 
             if (HasOverlappingParts(gridResult, out var a3, out var b3))
             {
@@ -481,9 +407,8 @@ namespace OpenNest.Engine.Fill
                 return seed;
 
             var template = seed.Parts[0];
-            var boundary = new PartBoundary(template, HalfSpacing);
 
-            var copyDistance = FindCopyDistance(template, direction, boundary);
+            var copyDistance = FindCopyDistance(template, direction);
 
             if (copyDistance <= 0)
                 return seed;

OpenNest.Engine/ML/FeatureExtractor.cs

@@ -27,7 +27,10 @@ namespace OpenNest.Engine.ML
     {
         public static PartFeatures Extract(Drawing drawing)
         {
-            var entities = OpenNest.Converters.ConvertProgram.ToGeometry(drawing.Program)
+            // Normalize to canonical frame so features are invariant to import orientation.
+            var canonical = CanonicalFrame.AsCanonicalCopy(drawing);
+
+            var entities = OpenNest.Converters.ConvertProgram.ToGeometry(canonical.Program)
                 .Where(e => e.Layer != SpecialLayers.Rapid)
                 .ToList();
 
@@ -45,18 +48,18 @@ namespace OpenNest.Engine.ML
 
             var features = new PartFeatures
             {
-                Area = drawing.Area,
-                Convexity = drawing.Area / (hullArea > 0 ? hullArea : 1.0),
+                Area = canonical.Area,
+                Convexity = canonical.Area / (hullArea > 0 ? hullArea : 1.0),
                 AspectRatio = bb.Length / (bb.Width > 0 ? bb.Width : 1.0),
-                BoundingBoxFill = drawing.Area / (bb.Area() > 0 ? bb.Area() : 1.0),
+                BoundingBoxFill = canonical.Area / (bb.Area() > 0 ? bb.Area() : 1.0),
                 VertexCount = polygon.Vertices.Count,
                 Bitmask = GenerateBitmask(polygon, 32)
             };
 
             // Circularity = 4 * PI * Area / Perimeter^2
             var perimeterLen = polygon.Perimeter();
-            features.Circularity = (4 * System.Math.PI * drawing.Area) / (perimeterLen * perimeterLen);
-            features.PerimeterToAreaRatio = drawing.Area > 0 ? perimeterLen / drawing.Area : 0;
+            features.Circularity = (4 * System.Math.PI * canonical.Area) / (perimeterLen * perimeterLen);
+            features.PerimeterToAreaRatio = canonical.Area > 0 ? perimeterLen / canonical.Area : 0;
 
             return features;
         }

OpenNest.Engine/NestEngineBase.cs

@@ -334,6 +334,12 @@ namespace OpenNest
                 var bestFits = BestFitCache.GetOrCompute(
                     item.Drawing, Plate.Size.Length, Plate.Size.Width, Plate.PartSpacing);
 
+                // BestFitCache stores pair coordinates in canonical frame. Build candidates
+                // from a canonical drawing copy so geometry and coords share a frame; rebind
+                // + un-rotate winning pair to the original drawing's frame before returning.
+                var canonicalDrawing = CanonicalFrame.AsCanonicalCopy(item.Drawing);
+                var sourceAngle = item.Drawing?.Source?.Angle ?? 0.0;
+
                 List<Part> bestPlacement = null;
                 Box bestTarget = null;
 
@@ -342,7 +348,7 @@ namespace OpenNest
                     if (!fit.Keep)
                         continue;
 
-                    var parts = fit.BuildParts(item.Drawing);
+                    var parts = fit.BuildParts(canonicalDrawing);
                     var pairBbox = ((IEnumerable<IBoundable>)parts).GetBoundingBox();
                     var pairW = pairBbox.Width;
                     var pairL = pairBbox.Length;
@@ -374,6 +380,10 @@ namespace OpenNest
 
                 if (bestPlacement == null) continue;
 
+                // Rebind to the original drawing and compose sourceAngle onto rotation so the
+                // final placed parts sit in the user's visible frame.
+                bestPlacement = RebindPairToOriginal(bestPlacement, item.Drawing, sourceAngle);
+
                 result.AddRange(bestPlacement);
                 item.Quantity = 0;
 
@@ -388,6 +398,30 @@ namespace OpenNest
             return result;
         }
 
+        /// <summary>
+        /// Rebinds each canonical-frame Part in the pair to the original Drawing at its current
+        /// world pose, then composes sourceAngle onto each via CanonicalFrame.FromCanonical so
+        /// the returned list is in the original drawing's visible frame. Mirrors
+        /// DefaultNestEngine.RebindAndUnCanonicalize.
+        /// </summary>
+        private static List<Part> RebindPairToOriginal(List<Part> parts, Drawing original, double sourceAngle)
+        {
+            if (parts == null || parts.Count == 0)
+                return parts;
+
+            for (var i = 0; i < parts.Count; i++)
+            {
+                var p = parts[i];
+                var rebound = Part.CreateAtOrigin(original, p.Rotation);
+                var delta = p.BoundingBox.Location - rebound.BoundingBox.Location;
+                rebound.Offset(delta);
+                rebound.UpdateBounds();
+                parts[i] = rebound;
+            }
+
+            return CanonicalFrame.FromCanonical(parts, sourceAngle);
+        }
+
         /// <summary>
         /// Determines whether a drawing should use grid-fill (true) or bin-pack (false).
         /// Low-quantity items whose total area is a small fraction of the plate are

OpenNest.Engine/PartClassifier.cs

@@ -64,8 +64,8 @@ namespace OpenNest.Engine
             var mbrArea = mbr.Area;
             var mbrPerimeter = 2 * (mbr.Width + mbr.Height);
 
-            // Store primary angle (negated to align MBR with axes, same as RotationAnalysis).
-            result.PrimaryAngle = -mbr.Angle;
+            // Share the single angle formula with CanonicalAngle (no duplicate MBR compute).
+            result.PrimaryAngle = CanonicalAngle.FromMbr(mbr);
 
             // Drawing perimeter for circularity and perimeter ratio.
             var drawingPerimeter = polygon.Perimeter();

OpenNest.IO/Bom/BomAnalyzer.cs

@@ -42,6 +42,11 @@ namespace OpenNest.IO.Bom
                     var nameWithoutExt = Path.GetFileNameWithoutExtension(file);
                     dxfFiles[nameWithoutExt] = file;
                 }
+                foreach (var file in Directory.GetFiles(dxfFolder, "*.dwg"))
+                {
+                    var nameWithoutExt = Path.GetFileNameWithoutExtension(file);
+                    dxfFiles.TryAdd(nameWithoutExt, file);
+                }
             }
 
             // Partition items into: skipped, unmatched, or matched (grouped)
@@ -57,8 +62,8 @@ namespace OpenNest.IO.Bom
 
                 var lookupName = item.FileName;
 
-                // Strip .dxf extension if the BOM includes it
-                if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase))
+                if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)
+                    || lookupName.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase))
                     lookupName = Path.GetFileNameWithoutExtension(lookupName);
 
                 if (!folderExists)

OpenNest.IO/CadImportResult.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using ACadSharp;
 using OpenNest.Bending;
 using OpenNest.Geometry;
 
@@ -38,5 +39,11 @@ namespace OpenNest.IO
         /// Default drawing name (filename without extension, unless overridden).
         /// </summary>
         public string Name { get; set; }
+
+        /// <summary>
+        /// The raw CAD document from the source file. Available for callers
+        /// that need access to non-geometry entities (e.g., text annotations).
+        /// </summary>
+        public CadDocument Document { get; set; }
     }
 }

OpenNest.IO/CadImporter.cs

@@ -5,6 +5,7 @@ using OpenNest.Bending;
 using OpenNest.Converters;
 using OpenNest.Geometry;
 using OpenNest.IO.Bending;
+using OpenNest.Math;
 
 namespace OpenNest.IO
 {
@@ -25,6 +26,9 @@ namespace OpenNest.IO
 
             var dxf = Dxf.Import(path);
 
+            RemoveDuplicateArcs(dxf.Entities);
+            RemoveZeroSweepArcs(dxf.Entities);
+
             var bends = new List<Bend>();
             if (options.DetectBends && dxf.Document != null)
             {
@@ -44,6 +48,7 @@ namespace OpenNest.IO
                 Bounds = dxf.Entities.GetBoundingBox(),
                 SourcePath = path,
                 Name = options.Name ?? Path.GetFileNameWithoutExtension(path),
+                Document = dxf.Document,
             };
         }
 
@@ -136,5 +141,39 @@ namespace OpenNest.IO
 
             return drawing;
         }
+
+        internal static void RemoveZeroSweepArcs(List<Entity> entities)
+        {
+            entities.RemoveAll(e =>
+                e is Arc arc && arc.StartAngle.IsEqualTo(arc.EndAngle, Tolerance.ChainTolerance));
+        }
+
+        internal static void RemoveDuplicateArcs(List<Entity> entities)
+        {
+            var circles = entities.OfType<Circle>().ToList();
+            var arcs = entities.OfType<Arc>().ToList();
+            var arcsToRemove = new List<Arc>();
+
+            foreach (var arc in arcs)
+            {
+                foreach (var circle in circles)
+                {
+                    if (arc.Layer?.Name != circle.Layer?.Name)
+                        continue;
+
+                    if (!arc.Center.DistanceTo(circle.Center).IsEqualTo(0))
+                        continue;
+
+                    if (!arc.Radius.IsEqualTo(circle.Radius))
+                        continue;
+
+                    arcsToRemove.Add(arc);
+                    break;
+                }
+            }
+
+            foreach (var arc in arcsToRemove)
+                entities.Remove(arc);
+        }
     }
 }

OpenNest.IO/ChrFont.cs

@@ -0,0 +1,369 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using OpenNest.Geometry;
+
+namespace OpenNest.IO
+{
+    public class ChrFont
+    {
+        private readonly Dictionary<int, ChrGlyph> glyphs = new();
+
+        public string Name { get; internal set; }
+        public string Version { get; internal set; }
+        public double CapHeight { get; internal set; } = 5000;
+
+        internal void AddGlyph(int charCode, ChrGlyph glyph)
+        {
+            glyphs[charCode] = glyph;
+        }
+
+        public bool HasGlyph(int charCode) => glyphs.ContainsKey(charCode);
+
+        public ChrGlyph GetGlyph(int charCode) =>
+            glyphs.TryGetValue(charCode, out var g) ? g : null;
+
+        public double MeasureTextWidth(string text, double height)
+        {
+            var scale = height / CapHeight;
+            double width = 0;
+            foreach (var ch in text)
+            {
+                var glyph = GetGlyph(ch);
+                if (glyph == null)
+                {
+                    var space = GetGlyph(' ');
+                    width += (space?.AdvanceWidth ?? CapHeight * 0.6) * scale;
+                    continue;
+                }
+                width += glyph.AdvanceWidth * scale;
+            }
+            return width;
+        }
+
+        public List<Entity> RenderText(string text, double height, Vector position, Layer layer = null)
+        {
+            var scale = height / CapHeight;
+            var entities = new List<Entity>();
+            var cursorX = position.X;
+
+            foreach (var ch in text)
+            {
+                var glyph = GetGlyph(ch);
+                if (glyph == null)
+                {
+                    var space = GetGlyph(' ');
+                    cursorX += (space?.AdvanceWidth ?? CapHeight * 0.6) * scale;
+                    continue;
+                }
+
+                var glyphEntities = glyph.ToEntities(scale, cursorX, position.Y, layer);
+                entities.AddRange(glyphEntities);
+                cursorX += glyph.AdvanceWidth * scale;
+            }
+
+            return entities;
+        }
+
+        public static ChrFont Read(string path, byte? xorKey = null)
+        {
+            var raw = File.ReadAllBytes(path);
+
+            // The whole file is obfuscated with a single-byte XOR. Different
+            // GravoStyle versions use different keys (0x2F in older releases,
+            // 0xCF in 7000-series). The font name at offset 0 is ASCII stored
+            // as UTF-16LE, so the high byte of its first character is 0x00 in
+            // plaintext — which means raw[1] is exactly the XOR key. Detect it
+            // from the file unless the caller forces a specific key.
+            var key = xorKey ?? (raw.Length > 1 ? raw[1] : (byte)0x2F);
+
+            var data = new byte[raw.Length];
+            for (var i = 0; i < raw.Length; i++)
+                data[i] = (byte)(raw[i] ^ key);
+
+            return Parse(data);
+        }
+
+        private static ChrFont Parse(byte[] data)
+        {
+            var font = new ChrFont();
+
+            font.Name = Encoding.Unicode.GetString(data, 0, 26).TrimEnd('\0').Trim();
+            font.Version = Encoding.ASCII.GetString(data, 26, 12).TrimEnd('\0').Trim();
+
+            var charTable = new List<(int charCode, int offset)>();
+            var i = 0x40;
+            while (i + 5 < data.Length)
+            {
+                var charCode = data[i] | (data[i + 1] << 8);
+                var offset = data[i + 2] | (data[i + 3] << 8) | (data[i + 4] << 16) | (data[i + 5] << 24);
+
+                if (charCode < 0x20 || offset == 0 || offset >= data.Length)
+                    break;
+
+                charTable.Add((charCode, offset));
+                i += 6;
+            }
+
+            for (var c = 0; c < charTable.Count; c++)
+            {
+                var (charCode, offset) = charTable[c];
+
+                var nextOffset = c + 1 < charTable.Count
+                    ? FindNextOffset(charTable, offset, data.Length)
+                    : data.Length;
+
+                var glyph = ParseGlyph(data, offset, nextOffset);
+                if (glyph != null)
+                    font.AddGlyph(charCode, glyph);
+            }
+
+            if (font.glyphs.Count > 0)
+            {
+                foreach (var g in font.glyphs.Values)
+                {
+                    if (g.CapHeight > 0)
+                    {
+                        font.CapHeight = g.CapHeight;
+                        break;
+                    }
+                }
+            }
+
+            return font;
+        }
+
+        private static int FindNextOffset(List<(int charCode, int offset)> table, int currentOffset, int fileLength)
+        {
+            var best = fileLength;
+            foreach (var (_, off) in table)
+            {
+                if (off > currentOffset && off < best)
+                    best = off;
+            }
+            return best;
+        }
+
+        private static ChrGlyph ParseGlyph(byte[] data, int offset, int endOffset)
+        {
+            if (offset + 92 > data.Length)
+                return null;
+
+            var glyph = new ChrGlyph();
+            glyph.CapHeight = ReadBE16(data, offset + 15 * 2);
+            var bearing = System.Math.Abs(ReadBE16(data, offset + 18 * 2));
+            glyph.AdvanceWidth = ReadBE16(data, offset + 22 * 2) + bearing;
+
+            var strokeStart = offset + 92;
+            var pos = strokeStart;
+            var currentStroke = new List<ChrStrokePoint>();
+
+            while (pos + 5 < endOffset)
+            {
+                var cmd = ReadBE16(data, pos);
+                var x = ReadBE16(data, pos + 2);
+                var y = ReadBE16(data, pos + 4);
+                pos += 6;
+
+                if (System.Math.Abs(x) > 15000 || System.Math.Abs(y) > 15000)
+                    break;
+
+                if (cmd < -1000)
+                    break;
+
+                var type = cmd switch
+                {
+                    1 => ChrPointType.Vertex,
+                    4 => ChrPointType.Control,
+                    5 => ChrPointType.EndPoint,
+                    _ => ChrPointType.Vertex,
+                };
+
+                currentStroke.Add(new ChrStrokePoint(type, x, y));
+
+                if (type == ChrPointType.EndPoint)
+                {
+                    if (currentStroke.Count > 0)
+                        glyph.Strokes.Add(currentStroke);
+                    currentStroke = new List<ChrStrokePoint>();
+                }
+            }
+
+            if (currentStroke.Count > 0)
+                glyph.Strokes.Add(currentStroke);
+
+            return glyph;
+        }
+
+        private static int ReadBE16(byte[] data, int offset)
+        {
+            var val = (data[offset] << 8) | data[offset + 1];
+            if (val > 32767) val -= 65536;
+            return val;
+        }
+    }
+
+    internal enum ChrPointType
+    {
+        Vertex,
+        Control,
+        EndPoint,
+    }
+
+    internal struct ChrStrokePoint
+    {
+        public ChrPointType Type;
+        public double X;
+        public double Y;
+
+        public ChrStrokePoint(ChrPointType type, double x, double y)
+        {
+            Type = type;
+            X = x;
+            Y = y;
+        }
+    }
+
+    public class ChrGlyph
+    {
+        internal readonly List<List<ChrStrokePoint>> Strokes = new();
+
+        public double AdvanceWidth { get; internal set; }
+        public double CapHeight { get; internal set; }
+
+        private const int ArcSamples = 16;
+
+        public List<Entity> ToEntities(double scale, double offsetX, double offsetY, Layer layer = null)
+        {
+            var entities = new List<Entity>();
+            layer ??= Layer.Default;
+
+            foreach (var stroke in Strokes)
+            {
+                if (stroke.Count < 2) continue;
+
+                var segments = BuildSegments(stroke);
+                foreach (var seg in segments)
+                {
+                    if (seg.Points.Count < 2) continue;
+
+                    var scaled = new List<Vector>(seg.Points.Count);
+                    foreach (var pt in seg.Points)
+                        scaled.Add(new Vector(pt.X * scale + offsetX, pt.Y * scale + offsetY));
+
+                    var converted = PointsToLines(scaled);
+
+                    foreach (var e in converted)
+                    {
+                        e.Layer = layer;
+                        entities.Add(e);
+                    }
+                }
+            }
+
+            return entities;
+        }
+
+        private static List<Entity> PointsToLines(List<Vector> points)
+        {
+            var entities = new List<Entity>();
+            for (var i = 0; i < points.Count - 1; i++)
+            {
+                if (points[i].DistanceTo(points[i + 1]) < 0.001)
+                    continue;
+                entities.Add(new Line(points[i], points[i + 1]));
+            }
+            return entities;
+        }
+
+        private static List<StrokeSegment> BuildSegments(List<ChrStrokePoint> stroke)
+        {
+            var segments = new List<StrokeSegment>();
+            var current = new StrokeSegment();
+
+            var i = 0;
+            while (i < stroke.Count)
+            {
+                var pt = stroke[i];
+
+                if (pt.Type == ChrPointType.Vertex || pt.Type == ChrPointType.EndPoint)
+                {
+                    if (i + 1 < stroke.Count && stroke[i + 1].Type == ChrPointType.Control)
+                    {
+                        var p0 = new Vector(pt.X, pt.Y);
+                        var pMid = new Vector(stroke[i + 1].X, stroke[i + 1].Y);
+                        var p2End = i + 2 < stroke.Count ? stroke[i + 2] : stroke[i + 1];
+                        var p1 = new Vector(p2End.X, p2End.Y);
+
+                        SampleCircularArc(current.Points, p0, pMid, p1, ArcSamples);
+                        current.HasCurves = true;
+                        i += 2;
+                    }
+                    else
+                    {
+                        current.Points.Add(new Vector(pt.X, pt.Y));
+                        i++;
+                    }
+                }
+                else
+                {
+                    i++;
+                }
+            }
+
+            if (current.Points.Count >= 2)
+                segments.Add(current);
+
+            return segments;
+        }
+
+        private class StrokeSegment
+        {
+            public readonly List<Vector> Points = new();
+            public bool HasCurves;
+        }
+
+        private static void SampleCircularArc(List<Vector> output, Vector p0, Vector pMid, Vector p1, int samples)
+        {
+            if (output.Count == 0 || output[^1].DistanceTo(p0) > 0.01)
+                output.Add(p0);
+
+            double ax = p0.X, ay = p0.Y;
+            double bx = pMid.X, by = pMid.Y;
+            double cx = p1.X, cy = p1.Y;
+
+            var d = 2 * (ax * (by - cy) + bx * (cy - ay) + cx * (ay - by));
+
+            if (System.Math.Abs(d) < 1e-6)
+            {
+                output.Add(pMid);
+                output.Add(p1);
+                return;
+            }
+
+            var ux = ((ax * ax + ay * ay) * (by - cy) + (bx * bx + by * by) * (cy - ay) + (cx * cx + cy * cy) * (ay - by)) / d;
+            var uy = ((ax * ax + ay * ay) * (cx - bx) + (bx * bx + by * by) * (ax - cx) + (cx * cx + cy * cy) * (bx - ax)) / d;
+            var radius = System.Math.Sqrt((ax - ux) * (ax - ux) + (ay - uy) * (ay - uy));
+
+            var a0 = System.Math.Atan2(ay - uy, ax - ux);
+            var am = System.Math.Atan2(by - uy, bx - ux);
+            var a1 = System.Math.Atan2(cy - uy, cx - ux);
+
+            var ccwSweep = a1 - a0;
+            while (ccwSweep <= 0) ccwSweep += 2 * System.Math.PI;
+
+            var midRel = am - a0;
+            while (midRel < 0) midRel += 2 * System.Math.PI;
+
+            var sweep = midRel < ccwSweep ? ccwSweep : ccwSweep - 2 * System.Math.PI;
+
+            for (var i = 1; i <= samples; i++)
+            {
+                var t = (double)i / samples;
+                var angle = a0 + sweep * t;
+                output.Add(new Vector(ux + radius * System.Math.Cos(angle), uy + radius * System.Math.Sin(angle)));
+            }
+        }
+    }
+}

OpenNest.IO/Dxf.cs

@@ -27,8 +27,7 @@ namespace OpenNest.IO
         /// </summary>
         public static DxfImportResult Import(string path)
         {
-            using var reader = new DxfReader(path);
-            var doc = reader.Read();
+            var doc = ReadDocument(path);
 
             return new DxfImportResult
             {
@@ -41,8 +40,7 @@ namespace OpenNest.IO
         {
             try
             {
-                using var reader = new DxfReader(path);
-                var doc = reader.Read();
+                var doc = ReadDocument(path);
                 return ConvertEntities(doc);
             }
             catch (Exception ex)
@@ -67,6 +65,36 @@ namespace OpenNest.IO
             }
         }
 
+        public static List<Entity> GetGeometry(string path, Func<string, bool> layerFilter)
+        {
+            try
+            {
+                using var reader = new DxfReader(path);
+                var doc = reader.Read();
+                return ConvertEntities(doc, layerFilter);
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine(ex.Message);
+                return new List<Entity>();
+            }
+        }
+
+        public static List<Entity> GetGeometry(Stream stream, Func<string, bool> layerFilter)
+        {
+            try
+            {
+                using var reader = new DxfReader(stream);
+                var doc = reader.Read();
+                return ConvertEntities(doc, layerFilter);
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine(ex.Message);
+                return new List<Entity>();
+            }
+        }
+
         #endregion
 
         #region Export
@@ -113,15 +141,34 @@ namespace OpenNest.IO
 
         #region Private
 
-        private static List<Entity> ConvertEntities(CadDocument doc)
+        private static bool IsDwg(string path) =>
+            Path.GetExtension(path).Equals(".dwg", StringComparison.OrdinalIgnoreCase);
+
+        private static CadDocument ReadDocument(string path)
+        {
+            if (IsDwg(path))
+            {
+                using var reader = new DwgReader(path);
+                return reader.Read();
+            }
+            else
+            {
+                using var reader = new DxfReader(path);
+                return reader.Read();
+            }
+        }
+
+        private static List<Entity> ConvertEntities(CadDocument doc, Func<string, bool> layerFilter = null)
         {
             var entities = new List<Entity>();
             var lines = new List<Line>();
             var arcs = new List<Arc>();
+            var circles = new List<Circle>();
+            var filter = layerFilter ?? IsNonCutLayer;
 
             foreach (var entity in doc.Entities)
             {
-                if (IsNonCutLayer(entity.Layer?.Name))
+                if (filter(entity.Layer?.Name))
                     continue;
 
                 switch (entity)
@@ -135,7 +182,7 @@ namespace OpenNest.IO
                         break;
 
                     case ACadSharp.Entities.Circle circle:
-                        entities.Add(circle.ToOpenNest());
+                        circles.Add(circle.ToOpenNest());
                         break;
 
                     case ACadSharp.Entities.Spline spline:
@@ -166,7 +213,10 @@ namespace OpenNest.IO
 
             GeometryOptimizer.Optimize(lines);
             GeometryOptimizer.Optimize(arcs);
+            GeometryOptimizer.Deduplicate(circles);
+            GeometryOptimizer.Deduplicate(circles, arcs);
 
+            entities.AddRange(circles);
             entities.AddRange(lines);
             entities.AddRange(arcs);
 
@@ -192,6 +242,7 @@ namespace OpenNest.IO
             public ExportContext()
             {
                 Document = new CadDocument();
+                Document.Header.Version = ACadVersion.AC1018;
 
                 CutLayer = new Layer("Cut") { Color = new Color(1) };
                 RapidLayer = new Layer("Rapid") { Color = new Color(5) };

OpenNest.IO/Extensions.cs

@@ -181,13 +181,22 @@ namespace OpenNest.IO
         {
             var center = new Vector(ellipse.Center.X, ellipse.Center.Y);
             var majorAxis = new Vector(ellipse.MajorAxisEndPoint.X, ellipse.MajorAxisEndPoint.Y);
-            var semiMajor = System.Math.Sqrt(majorAxis.X * majorAxis.X + majorAxis.Y * majorAxis.Y);
-            var semiMinor = semiMajor * ellipse.RadiusRatio;
-            var rotation = System.Math.Atan2(majorAxis.Y, majorAxis.X);
 
             var startParam = ellipse.StartParameter;
             var endParam = ellipse.EndParameter;
 
+            if (ellipse.Normal.Z < 0)
+            {
+                var newStart = OpenNest.Math.Angle.TwoPI - endParam;
+                var newEnd = OpenNest.Math.Angle.TwoPI - startParam;
+                startParam = newStart;
+                endParam = newEnd;
+            }
+
+            var semiMajor = System.Math.Sqrt(majorAxis.X * majorAxis.X + majorAxis.Y * majorAxis.Y);
+            var semiMinor = semiMajor * ellipse.RadiusRatio;
+            var rotation = System.Math.Atan2(majorAxis.Y, majorAxis.X);
+
             var layer = ellipse.Layer.ToOpenNest();
             var color = ellipse.ResolveColor();
             var lineTypeName = ellipse.ResolveLineTypeName();

OpenNest.IO/OpenNest.IO.csproj

@@ -4,6 +4,9 @@
     <RootNamespace>OpenNest.IO</RootNamespace>
     <AssemblyName>OpenNest.IO</AssemblyName>
   </PropertyGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="OpenNest.Tests" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />
     <ProjectReference Include="..\OpenNest.Engine\OpenNest.Engine.csproj" />

OpenNest.Posts.GravographIS/GravographISPort.cs

@@ -0,0 +1,99 @@
+using System;
+using System.IO.Ports;
+using System.Threading;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// Serial streamer for the Gravograph IS8000. 9600 8-N-1; flow control is
+    /// configurable and defaults to RTS/CTS (the controller is buffered and drops
+    /// CTS to apply backpressure). The job is sent in modest chunks rather than as
+    /// one giant write so the handshake can pause the write mid-stream.
+    /// </summary>
+    public sealed class GravographISPort : IDisposable
+    {
+        private SerialPort port;
+
+        public const int DefaultBaudRate = 9600;
+        public const int DefaultChunkSize = 256;
+        public const int DefaultWriteTimeoutMs = 30000;
+
+        public int ChunkSize { get; set; } = DefaultChunkSize;
+        public int WriteTimeoutMs { get; set; } = DefaultWriteTimeoutMs;
+
+        public bool IsOpen => port != null && port.IsOpen;
+
+        /// <summary>
+        /// Opens the port at the controller's required line settings (9600 8-N-1)
+        /// with the given <paramref name="handshake"/>. Throws if the port is
+        /// already open or if opening fails.
+        /// </summary>
+        public void Open(string portName, Handshake handshake = Handshake.RequestToSend)
+        {
+            if (string.IsNullOrWhiteSpace(portName))
+                throw new ArgumentException("Port name is required.", nameof(portName));
+            if (port != null)
+                throw new InvalidOperationException("Port is already open.");
+
+            port = new SerialPort(portName, DefaultBaudRate, Parity.None, 8, StopBits.One)
+            {
+                Handshake = handshake,
+                WriteTimeout = WriteTimeoutMs,
+                ReadTimeout = WriteTimeoutMs,
+                // DTR/RTS are needed for some USB-serial bridges and for RTS/CTS flow:
+                DtrEnable = true,
+                RtsEnable = handshake != Handshake.RequestToSend &&
+                            handshake != Handshake.RequestToSendXOnXOff,
+            };
+
+            port.Open();
+        }
+
+        /// <summary>
+        /// Streams the encoded job to the port in chunks. Cancellable. The chunked
+        /// write is intentional — Write() blocks until the OS accepts the bytes,
+        /// which with RTS/CTS or XOn/XOff yields cleanly when the controller's
+        /// buffer is full.
+        /// </summary>
+        public void StreamJob(byte[] data, CancellationToken cancellationToken = default)
+        {
+            if (data == null) throw new ArgumentNullException(nameof(data));
+            if (port == null || !port.IsOpen)
+                throw new InvalidOperationException("Port is not open.");
+
+            var chunk = ChunkSize > 0 ? ChunkSize : DefaultChunkSize;
+            var offset = 0;
+
+            while (offset < data.Length)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                var count = System.Math.Min(chunk, data.Length - offset);
+                port.Write(data, offset, count);
+                offset += count;
+            }
+
+            // Block until the OS has handed the last bytes to the line. SerialPort
+            // doesn't expose flush-and-drain directly; BaseStream.Flush is a no-op
+            // on Windows, so this is best-effort.
+            try { port.BaseStream.Flush(); }
+            catch { /* ignored — Flush is advisory on SerialPort */ }
+        }
+
+        public void Close()
+        {
+            if (port == null) return;
+            try
+            {
+                if (port.IsOpen) port.Close();
+            }
+            finally
+            {
+                port.Dispose();
+                port = null;
+            }
+        }
+
+        public void Dispose() => Close();
+    }
+}

OpenNest.Posts.GravographIS/GravographISPostConfig.cs

@@ -0,0 +1,81 @@
+using System.ComponentModel;
+using OpenNest.CNC;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// Cut parameters for one kind of pass (engrave or cut). Edited in the post
+    /// configuration PropertyGrid and persisted to JSON.
+    /// </summary>
+    [TypeConverter(typeof(ExpandableObjectConverter))]
+    public sealed class LayerCutConfig
+    {
+        [DisplayName("Feed (mm/sec)")]
+        [Description("XY and Z feed for this pass. Patches the VS and VZ wire commands.")]
+        public int FeedMmPerSec { get; set; } = 10;
+
+        [DisplayName("Depth (inches)")]
+        [Description("Programmed Z plunge (DZ). Note: the spring-floated spindle means this does not set actual cut depth — tool protrusion does.")]
+        public double Depth { get; set; } = 0.25;
+
+        [DisplayName("Pause Before")]
+        [Description("Stop the spindle and prompt the operator before this pass begins, so the tool can be swapped/adjusted.")]
+        public bool PauseBefore { get; set; }
+
+        [DisplayName("Pause Message")]
+        [Description("Message shown on the controller during the pause.")]
+        public string PauseMessage { get; set; } = "";
+
+        public override string ToString() => $"{FeedMmPerSec} mm/s, {Depth:0.###}\"" + (PauseBefore ? ", pause" : "");
+    }
+
+    /// <summary>
+    /// Configuration for the Gravograph IS post processor: one <see cref="LayerCutConfig"/>
+    /// per cut kind. The engrave block applies to <see cref="LayerType.Scribe"/> paths,
+    /// the cut block to <see cref="LayerType.Cut"/>/<see cref="LayerType.Leadin"/>/<see cref="LayerType.Leadout"/>.
+    /// The cut block carries the tool-change pause by default.
+    /// </summary>
+    public sealed class GravographISPostConfig
+    {
+        [Category("Engrave (Scribe)")]
+        [DisplayName("Engrave")]
+        [Description("Parameters for engrave/scribe geometry (text).")]
+        public LayerCutConfig Engrave { get; set; } = new LayerCutConfig
+        {
+            FeedMmPerSec = 10,
+            Depth = 0.25,
+            PauseBefore = false,
+            PauseMessage = "",
+        };
+
+        [Category("Cut")]
+        [DisplayName("Cut")]
+        [Description("Parameters for cut geometry (outlines). Pauses for a tool change by default.")]
+        public LayerCutConfig Cut { get; set; } = new LayerCutConfig
+        {
+            FeedMmPerSec = 3,
+            Depth = 0.25,
+            PauseBefore = true,
+            PauseMessage = "Change tool",
+        };
+
+        /// <summary>
+        /// Returns the cut config a polyline of the given layer should use, or null
+        /// if the layer is non-cutting (<see cref="LayerType.Display"/>) and should be skipped.
+        /// </summary>
+        public LayerCutConfig ConfigFor(LayerType layer)
+        {
+            switch (layer)
+            {
+                case LayerType.Scribe:
+                    return Engrave;
+                case LayerType.Cut:
+                case LayerType.Leadin:
+                case LayerType.Leadout:
+                    return Cut;
+                default:
+                    return null;
+            }
+        }
+    }
+}

OpenNest.Posts.GravographIS/GravographISPostProcessor.cs

@@ -0,0 +1,160 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.IO.Ports;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Threading;
+using OpenNest.Geometry;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// IPostProcessor implementation for the Gravograph IS8000. <see cref="Post(Nest, Stream)"/>
+    /// writes the binary HPGL bytes. For serial streaming, use <see cref="Stream(Nest, string, Handshake, CancellationToken)"/>.
+    ///
+    /// Geometry is split by <see cref="OpenNest.CNC.LayerType"/> into an engrave pass
+    /// (Scribe) and a cut pass (Cut), each with its own feed/depth from <see cref="Config"/>.
+    /// The cut pass pauses by default so the operator can swap/adjust the tool.
+    /// </summary>
+    public sealed class GravographISPostProcessor : IConfigurablePostProcessor
+    {
+        private static readonly JsonSerializerOptions JsonOptions = new()
+        {
+            WriteIndented = true,
+            Converters = { new JsonStringEnumConverter() }
+        };
+
+        public string Name => "Gravograph IS8000";
+        public string Author => "OpenNest";
+        public string Description => "Gravograph IS8000 mechanical engraver (binary HPGL over serial)";
+
+        public GravographISWriterOptions WriterOptions { get; } = new GravographISWriterOptions();
+
+        public NestPolylineExtractor Extractor { get; } = new NestPolylineExtractor();
+
+        public double StitchTolerance { get; set; } = PolylinePrePass.DefaultStitchTolerance;
+
+        public bool AllowReverse { get; set; } = true;
+
+        public GravographISPostConfig Config { get; }
+
+        object IConfigurablePostProcessor.Config => Config;
+
+        public GravographISPostProcessor()
+        {
+            var configPath = GetConfigPath();
+            if (File.Exists(configPath))
+            {
+                var json = File.ReadAllText(configPath);
+                Config = JsonSerializer.Deserialize<GravographISPostConfig>(json, JsonOptions)
+                    ?? new GravographISPostConfig();
+            }
+            else
+            {
+                Config = new GravographISPostConfig();
+                SaveConfig();
+            }
+        }
+
+        public GravographISPostProcessor(GravographISPostConfig config)
+        {
+            Config = config ?? throw new ArgumentNullException(nameof(config));
+        }
+
+        public void SaveConfig()
+        {
+            var configPath = GetConfigPath();
+            var json = JsonSerializer.Serialize(Config, JsonOptions);
+            File.WriteAllText(configPath, json);
+        }
+
+        private static string GetConfigPath()
+        {
+            var assemblyPath = typeof(GravographISPostProcessor).Assembly.Location;
+            var dir = Path.GetDirectoryName(assemblyPath);
+            var name = Path.GetFileNameWithoutExtension(assemblyPath);
+            return Path.Combine(dir, name + ".json");
+        }
+
+        public void Post(Nest nest, Stream outputStream)
+        {
+            if (nest == null) throw new ArgumentNullException(nameof(nest));
+            if (outputStream == null) throw new ArgumentNullException(nameof(outputStream));
+
+            var passes = BuildPasses(Extractor.ExtractLayered(nest));
+            new GravographISWriter(WriterOptions).Write(passes, outputStream);
+        }
+
+        public void Post(Nest nest, string outputFile)
+        {
+            using var fs = new FileStream(outputFile, FileMode.Create, FileAccess.Write);
+            Post(nest, fs);
+        }
+
+        /// <summary>
+        /// Groups layer-tagged polylines into ordered tool passes: engrave (Scribe)
+        /// first, then cut. Each group is stitch/reverse-optimized independently.
+        /// Geometry whose layer maps to no config (Display) is skipped. When only one
+        /// group is present, a single pass is returned (and so the writer emits no pause).
+        /// </summary>
+        public IReadOnlyList<GravographPass> BuildPasses(IEnumerable<LayeredPolyline> polylines)
+        {
+            if (polylines == null) throw new ArgumentNullException(nameof(polylines));
+
+            var engrave = new List<IReadOnlyList<Vector>>();
+            var cut = new List<IReadOnlyList<Vector>>();
+
+            foreach (var poly in polylines)
+            {
+                if (poly == null) continue;
+                var block = Config.ConfigFor(poly.Layer);
+                if (block == null)
+                    continue; // non-cutting (Display) geometry
+                if (ReferenceEquals(block, Config.Engrave))
+                    engrave.Add(poly.Points);
+                else
+                    cut.Add(poly.Points);
+            }
+
+            var passes = new List<GravographPass>();
+            if (engrave.Count > 0)
+                passes.Add(MakePass(Config.Engrave, engrave));
+            if (cut.Count > 0)
+                passes.Add(MakePass(Config.Cut, cut));
+
+            return passes;
+        }
+
+        private GravographPass MakePass(LayerCutConfig block, List<IReadOnlyList<Vector>> polylines)
+        {
+            return new GravographPass
+            {
+                Polylines = PolylinePrePass.Prepare(polylines, StitchTolerance, AllowReverse),
+                FeedMmPerSec = block.FeedMmPerSec,
+                DepthInches = block.Depth,
+                PauseBefore = block.PauseBefore,
+                PauseMessage = block.PauseMessage ?? "",
+            };
+        }
+
+        /// <summary>
+        /// Buffers the encoded job in memory, then streams it to the named COM port.
+        /// </summary>
+        public void Stream(Nest nest, string portName,
+            Handshake handshake = Handshake.RequestToSend,
+            CancellationToken cancellationToken = default)
+        {
+            byte[] bytes;
+            using (var ms = new MemoryStream())
+            {
+                Post(nest, ms);
+                bytes = ms.ToArray();
+            }
+
+            using var port = new GravographISPort();
+            port.Open(portName, handshake);
+            port.StreamJob(bytes, cancellationToken);
+        }
+    }
+}

OpenNest.Posts.GravographIS/GravographISWriter.cs

@@ -0,0 +1,464 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using OpenNest.Geometry;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// One tool pass: a run of polylines cut at a single feed/depth, optionally
+    /// preceded by an operator pause (to swap or adjust the tool). The Gravograph
+    /// post builds one pass for engrave and one for cut.
+    /// </summary>
+    public sealed class GravographPass
+    {
+        public IEnumerable<IReadOnlyList<Vector>> Polylines { get; set; }
+
+        public int FeedMmPerSec { get; set; }
+
+        public double DepthInches { get; set; }
+
+        /// <summary>When true, park to origin and prompt the operator before this pass.</summary>
+        public bool PauseBefore { get; set; }
+
+        public string PauseMessage { get; set; } = "";
+    }
+
+    /// <summary>
+    /// Encodes polylines (in inches) into the Gravograph IS8000 native "binary HPGL"
+    /// wire format. The byte stream is byte-exact against captures from GravoStyle'98.
+    ///
+    /// Scale: 80 steps/mm = 2032 steps/inch. Y (and Z) are negated on the wire.
+    /// Deltas are signed big-endian int16 (max ±32767 steps ≈ ±16 inches per move).
+    /// </summary>
+    public sealed class GravographISWriter
+    {
+        // 93-byte preamble — captured from GravoStyle'98 with the trailing
+        // job-specific travel block stripped. The VS, VZ and DZ operands are
+        // patched by the writer to reflect feed and depth options.
+        //
+        // The original capture ended with a DR command (FF FD 44 52 00 00)
+        // followed by three 8-byte int16 records — same format as PU/PD —
+        // that carried a chunked travel from the head's parked position to
+        // the original job's first vertex (cumulative ΔX ≈ 1", ΔY ≈ 47").
+        // Those frozen deltas have nothing to do with our job geometry, so
+        // replaying them sends the head to a fixed point regardless of where
+        // the operator set zero. Stripped for the same reason as the captured
+        // fixed return-to-home block.
+        private static readonly byte[] PreambleTemplate = new byte[]
+        {
+            0x21, 0x41, 0x53, 0x20, 0x33, 0x38, 0x3b, 0x01, 0x90, 0x01,
+            0xf4, 0x01, 0x90, 0x01, 0xf4, 0x01, 0x90, 0x01, 0xf4, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00, 0x09, 0x00, 0x00, 0x03, 0xe8, 0x05, 0x06, 0x00,
+            0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xfd, 0x32, 0x44, 0x00,
+            0x00, 0xff, 0xfd, 0x4d, 0x43, 0x00, 0x01, 0xff, 0xfd, 0x4f,
+            0x55, 0xff, 0xfb, 0xff, 0xfd, 0x4f, 0x55, 0xff, 0xfa, 0xff,
+            0xfd, 0x50, 0x5a, 0x00, 0x00, 0xff, 0xfd, 0x56, 0x53, 0x00,
+            0x23, 0xff, 0xfd, 0x56, 0x5a, 0x00, 0x23, 0xff, 0xfd, 0x44,
+            0x5a, 0x01, 0xfc,
+        };
+
+        // Stripped 36-byte postamble: lift, aux off, motor off, operator beep,
+        // job-finish. The 24-byte return-to-home block that appears in GravoStyle's
+        // captured postamble between MC and OP is intentionally OMITTED — those
+        // three 8-byte int16 records carry chunked job-specific return deltas
+        // (each record is [word1:int16][param:int16][ΔX:int16][ΔY:int16], same
+        // format as PU/PD records; the original capture chunked the long Y return
+        // across three records because each delta has to fit in int16). Reusing
+        // GravoStyle's frozen deltas on different geometry overshoots the X-axis
+        // limit. We emit calculated return deltas for the current job instead.
+        // The writer now replaces the captured fixed return block with a calculated
+        // lift + PU travel to the operator-set origin before these final commands.
+        private static readonly byte[] EndJobBytes = new byte[]
+        {
+            0xff, 0xfd, 0x4f, 0x55, 0xff, 0xfa, // OU 0xFFFA  aux off
+            0xff, 0xfd, 0x4f, 0x55, 0xff, 0xfb, // OU 0xFFFB  aux off
+            0xff, 0xfd, 0x4d, 0x43, 0x00, 0x00, // MC 0x0000  motor off
+            0xff, 0xfd, 0x4f, 0x50, 0x00, 0x00, // OP 0x0000  operator beep
+            0xff, 0xfd, 0x4a, 0x46, 0x00, 0x00, // JF 0x0000  job finish
+        };
+
+        // 80 steps/mm × 25.4 mm/in
+        internal const int StepsPerInch = 2032;
+
+        public GravographISWriterOptions Options { get; }
+
+        public GravographISWriter()
+            : this(new GravographISWriterOptions())
+        {
+        }
+
+        public GravographISWriter(GravographISWriterOptions options)
+        {
+            Options = options ?? throw new ArgumentNullException(nameof(options));
+        }
+
+        /// <summary>
+        /// Writes the full byte stream (preamble + geometry + postamble) for the given
+        /// polylines. Polyline coordinates are in inches, relative to the operator-set
+        /// work origin. The writer emits a leading DR travel to the first polyline
+        /// start before lowering for the first cut.
+        /// </summary>
+        public void Write(IEnumerable<IReadOnlyList<Vector>> polylines, Stream output)
+        {
+            if (polylines == null) throw new ArgumentNullException(nameof(polylines));
+
+            // A single pass at the configured feed/depth — byte-identical to the
+            // original single-group output (no transitions, no pause).
+            Write(new[]
+            {
+                new GravographPass
+                {
+                    Polylines = polylines,
+                    FeedMmPerSec = Options.FeedMmPerSec,
+                    DepthInches = Options.DepthInches,
+                    PauseBefore = false,
+                    PauseMessage = "",
+                },
+            }, output);
+        }
+
+        /// <summary>
+        /// Writes the full byte stream for an ordered list of tool passes. The preamble
+        /// carries the first pass's feed/depth; each later pass emits an inline feed
+        /// (and depth, if changed) and, when <see cref="GravographPass.PauseBefore"/> is
+        /// set, parks to the operator origin and emits an operator pause before cutting.
+        /// </summary>
+        public void Write(IReadOnlyList<GravographPass> passes, Stream output)
+        {
+            if (passes == null) throw new ArgumentNullException(nameof(passes));
+            if (output == null) throw new ArgumentNullException(nameof(output));
+
+            var firstFeed = passes.Count > 0 ? passes[0].FeedMmPerSec : Options.FeedMmPerSec;
+            var firstDepth = passes.Count > 0 ? passes[0].DepthInches : Options.DepthInches;
+
+            var preamble = (byte[])PreambleTemplate.Clone();
+            PatchOperand(preamble, (byte)'V', (byte)'S', (short)firstFeed);
+            PatchOperand(preamble, (byte)'V', (byte)'Z', (short)firstFeed);
+            PatchOperand(preamble, (byte)'D', (byte)'Z', DepthInStepsAsInt16(firstDepth));
+            output.Write(preamble, 0, preamble.Length);
+
+            // Cumulative head position from the operator-set upper-left origin, in
+            // wire steps. The first polyline gets a leading DR travel from this
+            // origin before PD lowers for cutting. Used by the envelope guard to
+            // catch bad records before they ship to the engraver.
+            var headX = 0;
+            var headY = 0;
+            var envelopeXSteps = (int)System.Math.Round(Options.WorkEnvelopeXMm * StepsPerMm,
+                MidpointRounding.AwayFromZero);
+            var envelopeYSteps = (int)System.Math.Round(Options.WorkEnvelopeYMm * StepsPerMm,
+                MidpointRounding.AwayFromZero);
+
+            var firstPolyline = true;
+            var polyIndex = 0;
+            var currentFeed = firstFeed;
+            var currentDepth = firstDepth;
+
+            for (var p = 0; p < passes.Count; p++)
+            {
+                var pass = passes[p];
+
+                if (p > 0)
+                {
+                    if (pass.PauseBefore)
+                    {
+                        // Park: lift Z, then rapid (pen-up) back to the operator origin so
+                        // the head is clear of the work while the tool is swapped.
+                        WriteLiftOnly(output);
+                        WriteTravel(output, (byte)'P', (byte)'U',
+                            checked(-headX), checked(-headY),
+                            ref headX, ref headY, envelopeXSteps, envelopeYSteps, polyIndex);
+                        WritePauseCore(output, pass.PauseMessage);
+                    }
+
+                    if (pass.FeedMmPerSec != currentFeed)
+                    {
+                        WriteCommand(output, (byte)'V', (byte)'S', (short)pass.FeedMmPerSec);
+                        WriteCommand(output, (byte)'V', (byte)'Z', (short)pass.FeedMmPerSec);
+                        currentFeed = pass.FeedMmPerSec;
+                    }
+
+                    if (pass.DepthInches != currentDepth)
+                    {
+                        WriteCommand(output, (byte)'D', (byte)'Z', DepthInStepsAsInt16(pass.DepthInches));
+                        currentDepth = pass.DepthInches;
+                    }
+                }
+
+                if (pass.Polylines == null) continue;
+
+                foreach (var poly in pass.Polylines)
+                {
+                    polyIndex++;
+                    if (poly == null || poly.Count < 2)
+                        continue;
+
+                    WritePolyline(output, poly, ref firstPolyline, ref headX, ref headY,
+                        envelopeXSteps, envelopeYSteps, polyIndex);
+                }
+            }
+
+            WriteLiftOnly(output);
+            if (Options.ReturnToOriginAtEnd && !firstPolyline)
+            {
+                WriteTravel(output, (byte)'P', (byte)'U',
+                    checked(-headX), checked(-headY),
+                    ref headX, ref headY, envelopeXSteps, envelopeYSteps, polyIndex);
+            }
+            output.Write(EndJobBytes, 0, EndJobBytes.Length);
+        }
+
+        private void WritePolyline(Stream output, IReadOnlyList<Vector> poly,
+            ref bool firstPolyline, ref int headX, ref int headY,
+            int envelopeXSteps, int envelopeYSteps, int polyIndex)
+        {
+            var (startX, startY) = ToWire(poly[0]);
+            WriteTravel(output,
+                firstPolyline ? (byte)'D' : (byte)'P',
+                firstPolyline ? (byte)'R' : (byte)'U',
+                checked(startX - headX), checked(startY - headY),
+                ref headX, ref headY, envelopeXSteps, envelopeYSteps, polyIndex);
+
+            // PD command + single records-follow flag, then one record per segment.
+            output.WriteByte(0xFF);
+            output.WriteByte(0xFD);
+            output.WriteByte((byte)'P');
+            output.WriteByte((byte)'D');
+            output.WriteByte(0x00);
+            output.WriteByte(0x00);
+
+            var prevX = startX;
+            var prevY = startY;
+            for (int i = 1; i < poly.Count; i++)
+            {
+                var (cx, cy) = ToWire(poly[i]);
+                var dx = checked(cx - prevX);
+                var dy = checked(cy - prevY);
+                EnsureEnvelope(headX + dx, headY + dy, envelopeXSteps, envelopeYSteps,
+                    polyIndex, segment: i, isTravel: false);
+                WriteRecord(output, dx, dy);
+                prevX = cx;
+                prevY = cy;
+                headX += dx;
+                headY += dy;
+            }
+
+            firstPolyline = false;
+        }
+
+        // The operator pause, minus the leading lift/park which the caller emits.
+        // Stops the spindle (MC off), turns off aux, writes the console message, then
+        // restarts the spindle (MC on) so the job resumes when the operator presses start.
+        private static void WritePauseCore(Stream s, string message)
+        {
+            WriteCommandRaw(s, (byte)'M', (byte)'C', 0x00, 0x00); // motor off
+            WriteCommandRaw(s, (byte)'O', (byte)'U', 0xFF, 0xFB); // aux off
+            WriteCommandRaw(s, (byte)'O', (byte)'U', 0xFF, 0xFA); // aux off
+            WriteCommandRaw(s, (byte)'L', (byte)'B', 0x00, 0x00); // begin message
+            WriteMessagePackets(s, message);
+            WriteCommandRaw(s, (byte)'N', (byte)'R', 0x00, 0x01); // line terminator
+            WriteCommandRaw(s, (byte)'L', (byte)'B', 0x00, 0x01); // end message
+            WriteCommandRaw(s, (byte)'M', (byte)'C', 0x00, 0x01); // motor on
+        }
+
+        // Console label packets carry two ASCII chars each; an odd-length message is
+        // space-padded to a whole number of packets so widths stay 2 bytes.
+        private static void WriteMessagePackets(Stream s, string message)
+        {
+            if (string.IsNullOrEmpty(message)) return;
+
+            var chars = Encoding.ASCII.GetBytes(message);
+            for (var i = 0; i < chars.Length; i += 2)
+            {
+                var c0 = chars[i];
+                var c1 = (i + 1 < chars.Length) ? chars[i + 1] : (byte)0x20;
+                WriteCommandRaw(s, (byte)'L', (byte)'B', c0, c1);
+            }
+        }
+
+        private static void WriteCommand(Stream s, byte c0, byte c1, short value)
+        {
+            WriteCommandRaw(s, c0, c1, (byte)((value >> 8) & 0xFF), (byte)(value & 0xFF));
+        }
+
+        private static void WriteCommandRaw(Stream s, byte c0, byte c1, byte hi, byte lo)
+        {
+            s.WriteByte(0xFF);
+            s.WriteByte(0xFD);
+            s.WriteByte(c0);
+            s.WriteByte(c1);
+            s.WriteByte(hi);
+            s.WriteByte(lo);
+        }
+
+        private const double StepsPerMm = 80.0;
+
+        private void EnsureEnvelope(int wireX, int wireY,
+            int envXSteps, int envYSteps,
+            int polyIndex, int segment, bool isTravel)
+        {
+            if (!Options.EnvelopeGuardEnabled) return;
+
+            // Wire frame: X is identity to input; Y is negated. With the operator
+            // origin set at the upper-left of the work envelope and an OpenNest
+            // quadrant-4 plate, valid part coordinates are +X/right and -Y/down:
+            //   wireX ∈ [0, +envXSteps]
+            //   wireY ∈ [0, +envYSteps]
+            if (wireX >= 0 && wireX <= envXSteps && wireY >= 0 && wireY <= envYSteps)
+                return;
+
+            var inputX = wireX / (double)StepsPerInch;
+            var inputY = -wireY / (double)StepsPerInch;
+            var kind = isTravel ? "pen-up travel" : "cut segment";
+            throw new InvalidOperationException(
+                $"Polyline {polyIndex} {kind} (segment {segment}) would place the head at " +
+                $"({inputX:F3}\", {inputY:F3}\"), outside the {Options.WorkEnvelopeXMm}×{Options.WorkEnvelopeYMm} mm " +
+                $"work envelope from upper-left origin. Refusing to emit the record.");
+        }
+
+        private static short DepthInStepsAsInt16(double depthInches)
+        {
+            var steps = (long)System.Math.Round(depthInches * StepsPerInch, MidpointRounding.AwayFromZero);
+            if (steps < short.MinValue || steps > short.MaxValue)
+                throw new ArgumentOutOfRangeException(nameof(depthInches), $"Depth {depthInches} in. → {steps} steps overflows int16.");
+            return (short)steps;
+        }
+
+        private static (int x, int y) ToWire(Vector v)
+        {
+            // Inches -> steps. With upper-left origin in OpenNest quadrant 4,
+            // negative input Y is down; Y is negated on the wire.
+            var x = (int)System.Math.Round(v.X * StepsPerInch, MidpointRounding.AwayFromZero);
+            var y = (int)System.Math.Round(-v.Y * StepsPerInch, MidpointRounding.AwayFromZero);
+            return (x, y);
+        }
+
+        private void WriteTravel(Stream s, byte c0, byte c1, int dx, int dy,
+            ref int headX, ref int headY,
+            int envelopeXSteps, int envelopeYSteps,
+            int polyIndex)
+        {
+            if (dx == 0 && dy == 0)
+                return;
+
+            s.WriteByte(0xFF);
+            s.WriteByte(0xFD);
+            s.WriteByte(c0);
+            s.WriteByte(c1);
+            s.WriteByte(0x00);
+            s.WriteByte(0x00);
+
+            var chunks = System.Math.Max(
+                (int)System.Math.Ceiling(System.Math.Abs(dx) / (double)short.MaxValue),
+                (int)System.Math.Ceiling(System.Math.Abs(dy) / (double)short.MaxValue));
+            if (chunks < 1) chunks = 1;
+
+            var emittedX = 0;
+            var emittedY = 0;
+            for (var i = 1; i <= chunks; i++)
+            {
+                var targetX = (int)System.Math.Round(dx * (i / (double)chunks), MidpointRounding.AwayFromZero);
+                var targetY = (int)System.Math.Round(dy * (i / (double)chunks), MidpointRounding.AwayFromZero);
+                var chunkX = checked(targetX - emittedX);
+                var chunkY = checked(targetY - emittedY);
+
+                EnsureEnvelope(headX + chunkX, headY + chunkY, envelopeXSteps, envelopeYSteps,
+                    polyIndex, segment: 0, isTravel: true);
+                WriteRecord(s, chunkX, chunkY);
+
+                emittedX = targetX;
+                emittedY = targetY;
+                headX += chunkX;
+                headY += chunkY;
+            }
+        }
+
+        private static void WriteLiftOnly(Stream s)
+        {
+            s.WriteByte(0xFF);
+            s.WriteByte(0xFD);
+            s.WriteByte((byte)'P');
+            s.WriteByte((byte)'U');
+            s.WriteByte(0x00);
+            s.WriteByte(0x01);
+        }
+
+        private static void WriteCommandWithRecord(Stream s, byte c0, byte c1, int dx, int dy)
+        {
+            s.WriteByte(0xFF);
+            s.WriteByte(0xFD);
+            s.WriteByte(c0);
+            s.WriteByte(c1);
+            // Records-follow flag (0x0000) emitted once per PU/PD packet.
+            s.WriteByte(0x00);
+            s.WriteByte(0x00);
+            WriteRecord(s, dx, dy);
+        }
+
+        private static void WriteRecord(Stream s, int dx, int dy)
+        {
+            if (dx < short.MinValue || dx > short.MaxValue ||
+                dy < short.MinValue || dy > short.MaxValue)
+            {
+                throw new InvalidOperationException(
+                    $"Move delta ({dx}, {dy}) steps overflows signed int16 — split moves upstream.");
+            }
+
+            int word1;
+            int param;
+
+            var absDx = (double)System.Math.Abs(dx);
+            var absDy = (double)System.Math.Abs(dy);
+            var len = System.Math.Sqrt(absDx * absDx + absDy * absDy);
+
+            if (len < 1.0)
+            {
+                // Zero-length lift (PU 00 01) is the dedicated form; for a record-carrying
+                // packet a true zero-length move shouldn't occur, but stay numerically safe.
+                word1 = 16384;
+                param = 1;
+            }
+            else
+            {
+                var maxAbs = System.Math.Max(absDx, absDy);
+                word1 = (int)System.Math.Round(16384.0 * maxAbs / len, MidpointRounding.AwayFromZero);
+                param = (int)System.Math.Round(len / 22.4, MidpointRounding.AwayFromZero);
+                if (param < 1) param = 1;
+                if (param > 180) param = 180;
+                if (word1 > 16384) word1 = 16384;
+            }
+
+            WriteBigEndianInt16(s, (short)word1);
+            WriteBigEndianInt16(s, (short)param);
+            WriteBigEndianInt16(s, (short)dx);
+            WriteBigEndianInt16(s, (short)dy);
+        }
+
+        private static void WriteBigEndianInt16(Stream s, short value)
+        {
+            s.WriteByte((byte)((value >> 8) & 0xFF));
+            s.WriteByte((byte)(value & 0xFF));
+        }
+
+        // Locates the operand of a command (FF FD <c0> <c1> <hi> <lo>) and overwrites it.
+        // Throws if the command isn't present — that would mean the preamble was mis-edited.
+        private static void PatchOperand(byte[] buffer, byte c0, byte c1, short value)
+        {
+            for (int i = 0; i <= buffer.Length - 6; i++)
+            {
+                if (buffer[i] == 0xFF && buffer[i + 1] == 0xFD &&
+                    buffer[i + 2] == c0 && buffer[i + 3] == c1)
+                {
+                    buffer[i + 4] = (byte)((value >> 8) & 0xFF);
+                    buffer[i + 5] = (byte)(value & 0xFF);
+                    return;
+                }
+            }
+
+            throw new InvalidOperationException(
+                $"Command '{(char)c0}{(char)c1}' not found in preamble template.");
+        }
+    }
+}

OpenNest.Posts.GravographIS/GravographISWriterOptions.cs

@@ -0,0 +1,24 @@
+namespace OpenNest.Posts.GravographIS
+{
+    public sealed class GravographISWriterOptions
+    {
+        public double DepthInches { get; set; } = 0.25;
+
+        public int FeedMmPerSec { get; set; } = 35;
+
+        // IS8000 work envelope in millimeters, from the operator-set upper-left
+        // work origin. Defaults to the catalog 0.610 m x 1.220 m bed. With an
+        // OpenNest quadrant-4 plate, motion is allowed right (+X) and down (-Y).
+        public double WorkEnvelopeXMm { get; set; } = 610.0;
+        public double WorkEnvelopeYMm { get; set; } = 1220.0;
+
+        // When true, the writer throws an InvalidOperationException naming the
+        // offending polyline and segment before any out-of-envelope record is
+        // emitted. Disable only for off-machine encoding tests.
+        public bool EnvelopeGuardEnabled { get; set; } = true;
+
+        // When true, lift at the end of the last cut and return to the
+        // operator-set origin before shutting the job down.
+        public bool ReturnToOriginAtEnd { get; set; } = true;
+    }
+}

OpenNest.Posts.GravographIS/NestPolylineExtractor.cs

@@ -0,0 +1,232 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// A polyline together with the <see cref="LayerType"/> of the moves that
+    /// produced it. The Gravograph post groups by layer to emit separate engrave
+    /// and cut passes (with a tool-change pause between them).
+    /// </summary>
+    public sealed class LayeredPolyline
+    {
+        public LayeredPolyline(List<Vector> points, LayerType layer)
+        {
+            Points = points;
+            Layer = layer;
+        }
+
+        public List<Vector> Points { get; }
+
+        public LayerType Layer { get; }
+    }
+
+    /// <summary>
+    /// Lifts polylines out of an OpenNest <see cref="Nest"/> for the Gravograph
+    /// backend. Walks each <see cref="Part"/>'s <see cref="Program"/>, breaks
+    /// polylines at rapid moves and at <see cref="LayerType"/> changes, and
+    /// tessellates arcs to a chord-deviation tolerance (the wire format takes
+    /// line segments only).
+    /// </summary>
+    public sealed class NestPolylineExtractor
+    {
+        public double ArcChordToleranceInches { get; set; } = 0.001;
+
+        /// <summary>
+        /// Extracts polylines from every non-cutoff part in every plate of the nest,
+        /// returning them in plate coordinates (inches). Layer information is dropped;
+        /// use <see cref="ExtractLayered(Nest)"/> to keep it.
+        /// </summary>
+        public List<List<Vector>> Extract(Nest nest)
+        {
+            return ExtractLayered(nest).Select(p => p.Points).ToList();
+        }
+
+        /// <summary>
+        /// Extracts polylines for a single part without layer information.
+        /// </summary>
+        public List<List<Vector>> ExtractPart(Part part)
+        {
+            return ExtractPartLayered(part).Select(p => p.Points).ToList();
+        }
+
+        /// <summary>
+        /// Extracts layer-tagged polylines from every non-cutoff part in every plate,
+        /// in plate coordinates (inches). Each polyline is layer-uniform.
+        /// </summary>
+        public List<LayeredPolyline> ExtractLayered(Nest nest)
+        {
+            if (nest == null) throw new ArgumentNullException(nameof(nest));
+
+            var result = new List<LayeredPolyline>();
+
+            foreach (var plate in nest.Plates)
+            {
+                foreach (var part in plate.Parts)
+                {
+                    if (part.BaseDrawing != null && part.BaseDrawing.IsCutOff)
+                        continue;
+
+                    ExtractPart(part, result);
+                }
+            }
+
+            return result;
+        }
+
+        /// <summary>
+        /// Extracts layer-tagged polylines for a single part. Public so callers
+        /// driving the writer directly (e.g. from a console one-off) can use it.
+        /// </summary>
+        public List<LayeredPolyline> ExtractPartLayered(Part part)
+        {
+            var list = new List<LayeredPolyline>();
+            ExtractPart(part, list);
+            return list;
+        }
+
+        private void ExtractPart(Part part, List<LayeredPolyline> sink)
+        {
+            var program = part.Program;
+            if (program == null) return;
+
+            // The walk below treats Motion.EndPoint as absolute. Convert a working
+            // copy to absolute mode so G91 programs (the form OpenNest's UI writes)
+            // produce correct geometry. Cloning keeps part.Program untouched.
+            if (program.Mode == Mode.Incremental)
+            {
+                program = (Program)program.Clone();
+                program.Mode = Mode.Absolute;
+            }
+
+            var offset = part.Location;
+            var pos = new Vector(0, 0);
+            List<Vector> current = null;
+            var currentLayer = LayerType.Cut;
+
+            foreach (var code in program.Codes)
+            {
+                if (code is Motion m && m.Suppressed)
+                    continue;
+
+                switch (code)
+                {
+                    case RapidMove rapid:
+                    {
+                        FlushCurrent(sink, ref current, currentLayer);
+                        pos = rapid.EndPoint;
+                        break;
+                    }
+
+                    case LinearMove linear:
+                    {
+                        StartOrSplit(sink, ref current, ref currentLayer, linear.Layer, pos + offset);
+                        var end = linear.EndPoint;
+                        current.Add(end + offset);
+                        pos = end;
+                        break;
+                    }
+
+                    case ArcMove arc:
+                    {
+                        StartOrSplit(sink, ref current, ref currentLayer, arc.Layer, pos + offset);
+                        TessellateArc(pos, arc, offset, ArcChordToleranceInches, current);
+                        pos = arc.EndPoint;
+                        break;
+                    }
+                }
+            }
+
+            FlushCurrent(sink, ref current, currentLayer);
+        }
+
+        // Ensures `current` is an open polyline whose layer matches `moveLayer`,
+        // seeded at `seed` (the current pen position). When the layer changes
+        // mid-chain the previous polyline is flushed and a new one begins at the
+        // shared seam vertex so engrave and cut passes stay geometrically continuous.
+        private static void StartOrSplit(List<LayeredPolyline> sink, ref List<Vector> current,
+            ref LayerType currentLayer, LayerType moveLayer, Vector seed)
+        {
+            if (current == null)
+            {
+                current = new List<Vector> { seed };
+                currentLayer = moveLayer;
+            }
+            else if (moveLayer != currentLayer)
+            {
+                FlushCurrent(sink, ref current, currentLayer);
+                current = new List<Vector> { seed };
+                currentLayer = moveLayer;
+            }
+        }
+
+        private static void FlushCurrent(List<LayeredPolyline> sink, ref List<Vector> current, LayerType layer)
+        {
+            if (current != null && current.Count >= 2)
+                sink.Add(new LayeredPolyline(current, layer));
+            current = null;
+        }
+
+        // Sample points along an arc to within chordTol of the true curve. start is
+        // the arc's start point (current pen position), arc.CenterPoint is absolute
+        // (G-code I/J in this codebase are stored as the absolute center), arc.EndPoint
+        // is absolute end. The starting point is assumed to already be in the polyline;
+        // intermediate samples and the endpoint are appended.
+        private static void TessellateArc(Vector start, ArcMove arc, Vector offset,
+            double chordTol, List<Vector> sink)
+        {
+            var c = arc.CenterPoint;
+            var r = c.DistanceTo(start);
+            if (r < 1e-9)
+            {
+                sink.Add(arc.EndPoint + offset);
+                return;
+            }
+
+            var a0 = System.Math.Atan2(start.Y - c.Y, start.X - c.X);
+            var a1 = System.Math.Atan2(arc.EndPoint.Y - c.Y, arc.EndPoint.X - c.X);
+
+            double sweep;
+            if (arc.Rotation == RotationType.CW)
+            {
+                sweep = a0 - a1;
+                if (sweep <= 0) sweep += 2 * System.Math.PI;
+            }
+            else
+            {
+                sweep = a1 - a0;
+                if (sweep <= 0) sweep += 2 * System.Math.PI;
+            }
+
+            // Treat a near-zero sweep with coincident start/end as a full circle.
+            if (sweep < 1e-9 &&
+                System.Math.Abs(start.X - arc.EndPoint.X) < 1e-9 &&
+                System.Math.Abs(start.Y - arc.EndPoint.Y) < 1e-9)
+            {
+                sweep = 2 * System.Math.PI;
+            }
+
+            // Max angle step from chord-deviation tolerance: dev = r * (1 - cos(t/2)).
+            var maxAngleStep = 2.0 * System.Math.Acos(System.Math.Max(0.0, 1.0 - chordTol / r));
+            if (double.IsNaN(maxAngleStep) || maxAngleStep <= 0)
+                maxAngleStep = System.Math.PI / 32;
+
+            var steps = (int)System.Math.Ceiling(sweep / maxAngleStep);
+            if (steps < 1) steps = 1;
+
+            var direction = arc.Rotation == RotationType.CW ? -1.0 : 1.0;
+            for (int i = 1; i < steps; i++)
+            {
+                var t = sweep * (i / (double)steps);
+                var ang = a0 + direction * t;
+                var pt = new Vector(c.X + r * System.Math.Cos(ang), c.Y + r * System.Math.Sin(ang));
+                sink.Add(pt + offset);
+            }
+
+            sink.Add(arc.EndPoint + offset);
+        }
+    }
+}

OpenNest.Posts.GravographIS/OpenNest.Posts.GravographIS.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <RootNamespace>OpenNest.Posts.GravographIS</RootNamespace>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />
+    <PackageReference Include="System.IO.Ports" Version="8.0.0" />
+  </ItemGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="OpenNest.Tests" />
+  </ItemGroup>
+  <Target Name="CopyToPostsDir" AfterTargets="Build">
+    <PropertyGroup>
+      <PostsDir>..\OpenNest\bin\$(Configuration)\$(TargetFramework)\Posts\</PostsDir>
+    </PropertyGroup>
+    <MakeDir Directories="$(PostsDir)" />
+    <Copy SourceFiles="$(TargetPath)" DestinationFolder="$(PostsDir)" SkipUnchangedFiles="true" ContinueOnError="true" />
+  </Target>
+</Project>

OpenNest.Posts.GravographIS/PolylinePrePass.cs

@@ -0,0 +1,196 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest.Posts.GravographIS
+{
+    /// <summary>
+    /// Geometry pre-pass for the Gravograph IS8000 backend. The machine is a dumb
+    /// executor — it never reorders geometry and always lifts between separate
+    /// entities — so we stitch shared-endpoint polylines together and reorder by
+    /// nearest-neighbor before encoding.
+    /// </summary>
+    public static class PolylinePrePass
+    {
+        public const double DefaultStitchTolerance = 1e-6;
+
+        /// <summary>
+        /// Joins polylines whose endpoints coincide (within <paramref name="tolerance"/>)
+        /// into single continuous polylines. Polylines with fewer than two points are
+        /// dropped. Direction is reversed as needed to make a join. Each input polyline
+        /// is copied — the inputs are not mutated.
+        /// </summary>
+        public static List<List<Vector>> Stitch(
+            IEnumerable<IReadOnlyList<Vector>> polylines,
+            double tolerance = DefaultStitchTolerance)
+        {
+            if (polylines == null) throw new ArgumentNullException(nameof(polylines));
+
+            var segs = new List<List<Vector>>();
+            foreach (var p in polylines)
+            {
+                if (p == null || p.Count < 2)
+                    continue;
+                segs.Add(new List<Vector>(p));
+            }
+
+            bool changed;
+            do
+            {
+                changed = false;
+                for (int i = 0; i < segs.Count; i++)
+                {
+                    var a = segs[i];
+
+                    for (int j = 0; j < segs.Count; j++)
+                    {
+                        if (i == j) continue;
+                        var b = segs[j];
+
+                        // a-end ↔ b-start: append b to a (skip duplicated joint)
+                        if (Near(a[a.Count - 1], b[0], tolerance))
+                        {
+                            for (int k = 1; k < b.Count; k++) a.Add(b[k]);
+                            segs.RemoveAt(j);
+                            if (j < i) i--;
+                            changed = true;
+                            break;
+                        }
+
+                        // a-end ↔ b-end: append reversed b to a
+                        if (Near(a[a.Count - 1], b[b.Count - 1], tolerance))
+                        {
+                            for (int k = b.Count - 2; k >= 0; k--) a.Add(b[k]);
+                            segs.RemoveAt(j);
+                            if (j < i) i--;
+                            changed = true;
+                            break;
+                        }
+
+                        // a-start ↔ b-end: prepend b to a
+                        if (Near(a[0], b[b.Count - 1], tolerance))
+                        {
+                            var combined = new List<Vector>(b.Count + a.Count - 1);
+                            combined.AddRange(b);
+                            for (int k = 1; k < a.Count; k++) combined.Add(a[k]);
+                            segs[i] = combined;
+                            segs.RemoveAt(j);
+                            if (j < i) i--;
+                            changed = true;
+                            break;
+                        }
+
+                        // a-start ↔ b-start: prepend reversed b to a
+                        if (Near(a[0], b[0], tolerance))
+                        {
+                            var combined = new List<Vector>(b.Count + a.Count - 1);
+                            for (int k = b.Count - 1; k >= 0; k--) combined.Add(b[k]);
+                            for (int k = 1; k < a.Count; k++) combined.Add(a[k]);
+                            segs[i] = combined;
+                            segs.RemoveAt(j);
+                            if (j < i) i--;
+                            changed = true;
+                            break;
+                        }
+                    }
+
+                    if (changed) break;
+                }
+            }
+            while (changed);
+
+            return segs;
+        }
+
+        /// <summary>
+        /// Greedy nearest-neighbor ordering of polylines starting from
+        /// <paramref name="origin"/> (defaults to 0,0 = the work origin = the first
+        /// polyline's first point on the wire). When <paramref name="allowReverse"/>
+        /// is true a polyline may be reversed if its tail is closer than its head.
+        /// </summary>
+        public static List<List<Vector>> Reorder(
+            IEnumerable<IReadOnlyList<Vector>> polylines,
+            bool allowReverse = true,
+            Vector? origin = null)
+        {
+            if (polylines == null) throw new ArgumentNullException(nameof(polylines));
+
+            var pool = new List<List<Vector>>();
+            foreach (var p in polylines)
+            {
+                if (p == null || p.Count < 2)
+                    continue;
+                pool.Add(new List<Vector>(p));
+            }
+
+            var ordered = new List<List<Vector>>(pool.Count);
+            var current = origin ?? new Vector(0, 0);
+
+            while (pool.Count > 0)
+            {
+                var bestIdx = -1;
+                var bestReverse = false;
+                var bestDistSq = double.PositiveInfinity;
+
+                for (int i = 0; i < pool.Count; i++)
+                {
+                    var p = pool[i];
+                    var dHead = SquaredDistance(current, p[0]);
+                    if (dHead < bestDistSq)
+                    {
+                        bestDistSq = dHead;
+                        bestIdx = i;
+                        bestReverse = false;
+                    }
+
+                    if (allowReverse)
+                    {
+                        var dTail = SquaredDistance(current, p[p.Count - 1]);
+                        if (dTail < bestDistSq)
+                        {
+                            bestDistSq = dTail;
+                            bestIdx = i;
+                            bestReverse = true;
+                        }
+                    }
+                }
+
+                var pick = pool[bestIdx];
+                pool.RemoveAt(bestIdx);
+                if (bestReverse)
+                    pick.Reverse();
+                ordered.Add(pick);
+                current = pick[pick.Count - 1];
+            }
+
+            return ordered;
+        }
+
+        /// <summary>
+        /// Convenience: stitch then reorder.
+        /// </summary>
+        public static List<List<Vector>> Prepare(
+            IEnumerable<IReadOnlyList<Vector>> polylines,
+            double stitchTolerance = DefaultStitchTolerance,
+            bool allowReverse = true,
+            Vector? origin = null)
+        {
+            var stitched = Stitch(polylines, stitchTolerance);
+            return Reorder(stitched, allowReverse, origin);
+        }
+
+        private static bool Near(Vector a, Vector b, double tol)
+        {
+            var dx = a.X - b.X;
+            var dy = a.Y - b.Y;
+            return (dx * dx + dy * dy) <= tol * tol;
+        }
+
+        private static double SquaredDistance(Vector a, Vector b)
+        {
+            var dx = a.X - b.X;
+            var dy = a.Y - b.Y;
+            return dx * dx + dy * dy;
+        }
+    }
+}

OpenNest.Tests/BestFit/BestFitResultFrameTests.cs

@@ -0,0 +1,72 @@
+using OpenNest.Engine;
+using OpenNest.Engine.BestFit;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.BestFit;
+
+public class BestFitResultFrameTests
+{
+    [Fact]
+    public void BuildCanonicalParts_NonAxisAlignedPairNormalizesActualBounds()
+    {
+        var drawing = new TShape { Width = 10, Height = 8 }.GetDrawing();
+        var canonical = CanonicalFrame.AsCanonicalCopy(drawing);
+
+        var result = EvaluateOffsetPair(canonical, new Vector(40, 30));
+
+        Assert.True(IsNonAxisAligned(result.OptimalRotation),
+            $"Expected a non-axis-aligned result, got {Angle.ToDegrees(result.OptimalRotation):F2} degrees.");
+
+        var parts = result.BuildCanonicalParts();
+        var bounds = result.GetCutBounds(parts);
+
+        Assert.Equal(0, bounds.Left, 3);
+        Assert.Equal(0, bounds.Bottom, 3);
+        Assert.Equal(result.BoundingWidth, bounds.Length, 2);
+        Assert.Equal(result.BoundingHeight, bounds.Width, 2);
+    }
+
+    [Fact]
+    public void BuildSourceParts_RebindsCanonicalResultToRotatedSourceDrawing()
+    {
+        var drawing = new TShape { Width = 10, Height = 8 }.GetDrawing();
+        drawing.Program.Rotate(Angle.ToRadians(30), drawing.Program.BoundingBox().Center);
+        drawing.RecomputeCanonicalAngle();
+
+        var canonical = CanonicalFrame.AsCanonicalCopy(drawing);
+        var result = EvaluateOffsetPair(canonical, new Vector(40, 30));
+
+        var parts = result.BuildSourceParts(drawing);
+        var bounds = result.GetCutBounds(parts);
+
+        Assert.All(parts, p => Assert.Same(drawing, p.BaseDrawing));
+        Assert.Equal(0, bounds.Left, 3);
+        Assert.Equal(0, bounds.Bottom, 3);
+        Assert.False(parts[0].Intersects(parts[1], out _));
+    }
+
+    private static BestFitResult EvaluateOffsetPair(Drawing drawing, Vector offset)
+    {
+        var candidate = new PairCandidate
+        {
+            Drawing = drawing,
+            Part1Rotation = 0,
+            Part2Rotation = System.Math.PI,
+            Part2Offset = offset,
+            Spacing = 0.25
+        };
+
+        return new PairEvaluator().Evaluate(candidate);
+    }
+
+    private static bool IsNonAxisAligned(double angle)
+    {
+        var normalized = Angle.NormalizeRad(angle);
+        var nearestQuadrant = Angle.HalfPI * System.Math.Round(normalized / Angle.HalfPI);
+        var delta = System.Math.Abs(normalized - nearestQuadrant);
+        delta = System.Math.Min(delta, Angle.HalfPI - delta);
+        return delta > Angle.ToRadians(1);
+    }
+}

OpenNest.Tests/Converters/ConvertGeometryLayerTests.cs

@@ -0,0 +1,70 @@
+using System.Linq;
+using OpenNest.CNC;
+using OpenNest.Converters;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Converters;
+
+public class ConvertGeometryLayerTests
+{
+    private static Program ProgramFor(Entity entity)
+    {
+        var shape = new Shape();
+        shape.Entities.Add(entity);
+        return ConvertGeometry.ToProgram(shape);
+    }
+
+    [Fact]
+    public void AddLine_EngraveLayer_TagsScribe()
+    {
+        var line = new Line(0, 0, 1, 0) { Layer = new Layer("ENGRAVE") };
+
+        var pgm = ProgramFor(line);
+
+        Assert.All(pgm.Codes.OfType<LinearMove>(), m => Assert.Equal(LayerType.Scribe, m.Layer));
+    }
+
+    [Fact]
+    public void AddLine_EtchLayer_TagsScribe()
+    {
+        var line = new Line(0, 0, 1, 0) { Layer = new Layer("etch") };
+
+        var pgm = ProgramFor(line);
+
+        Assert.All(pgm.Codes.OfType<LinearMove>(), m => Assert.Equal(LayerType.Scribe, m.Layer));
+    }
+
+    [Fact]
+    public void AddArc_EngraveLayer_TagsScribe()
+    {
+        var arc = new Arc(new Vector(0, 0), 1, 0, System.Math.PI / 2) { Layer = new Layer("ENGRAVE") };
+
+        var pgm = ProgramFor(arc);
+
+        var arcs = pgm.Codes.OfType<ArcMove>().ToList();
+        Assert.NotEmpty(arcs);
+        Assert.All(arcs, m => Assert.Equal(LayerType.Scribe, m.Layer));
+    }
+
+    [Fact]
+    public void AddCircle_EngraveLayer_TagsScribe()
+    {
+        var circle = new Circle(0, 0, 1) { Layer = new Layer("ENGRAVE") };
+
+        var pgm = ProgramFor(circle);
+
+        var arcs = pgm.Codes.OfType<ArcMove>().ToList();
+        Assert.NotEmpty(arcs);
+        Assert.All(arcs, m => Assert.Equal(LayerType.Scribe, m.Layer));
+    }
+
+    [Fact]
+    public void AddLine_DefaultLayer_StaysCut()
+    {
+        var line = new Line(0, 0, 1, 0) { Layer = new Layer("0") };
+
+        var pgm = ProgramFor(line);
+
+        Assert.All(pgm.Codes.OfType<LinearMove>(), m => Assert.Equal(LayerType.Cut, m.Layer));
+    }
+}

OpenNest.Tests/Engine/CanonicalAngleTests.cs

@@ -0,0 +1,156 @@
+using System.Linq;
+using OpenNest.CNC;
+using OpenNest.Converters;
+using OpenNest.Engine;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest.Tests.Engine;
+
+public class CanonicalAngleTests
+{
+    private const double AngleTol = 0.002; // ~0.11°
+
+    private static Drawing MakeRect(double w, double h)
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return new Drawing("rect", pgm);
+    }
+
+    private static Drawing RotateCopy(Drawing src, double angle)
+    {
+        var pgm = src.Program.Clone() as OpenNest.CNC.Program;
+        pgm.Rotate(angle, pgm.BoundingBox().Center);
+        return new Drawing("rotated", pgm);
+    }
+
+    [Fact]
+    public void AxisAlignedRectangle_ReturnsZero()
+    {
+        var d = MakeRect(100, 50);
+        Assert.Equal(0.0, CanonicalAngle.Compute(d), precision: 6);
+    }
+
+    // Program.BoundingBox() has a pre-existing bug where minX/minY initialize to 0 and can
+    // only decrease, so programs whose extents stay in the positive half-plane report a
+    // too-large AABB. To validate MBR-axis-alignment without tripping that bug, extract the
+    // outer perimeter polygon and compute its true AABB from vertices.
+    private static (double length, double width) TrueAabb(OpenNest.CNC.Program pgm)
+    {
+        var entities = ConvertProgram.ToGeometry(pgm).Where(e => e.Layer != SpecialLayers.Rapid);
+        var shapes = ShapeBuilder.GetShapes(entities);
+        var outer = shapes.OrderByDescending(s => s.Area()).First();
+        var poly = outer.ToPolygonWithTolerance(0.1);
+        var minX = poly.Vertices.Min(v => v.X);
+        var maxX = poly.Vertices.Max(v => v.X);
+        var minY = poly.Vertices.Min(v => v.Y);
+        var maxY = poly.Vertices.Max(v => v.Y);
+        return (maxX - minX, maxY - minY);
+    }
+
+    [Theory]
+    [InlineData(0.3)]
+    [InlineData(0.7)]
+    [InlineData(1.2)]
+    public void Rectangle_ReturnsNegatedRotation_Modulo90(double theta)
+    {
+        var rotated = RotateCopy(MakeRect(100, 50), theta);
+        var angle = CanonicalAngle.Compute(rotated);
+
+        // Applying the returned angle should leave MBR axis-aligned.
+        var canonical = rotated.Program.Clone() as OpenNest.CNC.Program;
+        canonical.Rotate(angle, canonical.BoundingBox().Center);
+
+        var (length, width) = TrueAabb(canonical);
+        var longer = System.Math.Max(length, width);
+        var shorter = System.Math.Min(length, width);
+        Assert.InRange(longer, 100 - 0.1, 100 + 0.1);
+        Assert.InRange(shorter, 50 - 0.1, 50 + 0.1);
+    }
+
+    [Fact]
+    public void NearZeroInput_SnapsToZero()
+    {
+        var rotated = RotateCopy(MakeRect(100, 50), 0.0005);
+        Assert.Equal(0.0, CanonicalAngle.Compute(rotated), precision: 6);
+    }
+
+    [Fact]
+    public void DegeneratePolygon_ReturnsZero()
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 10)));
+        var d = new Drawing("line", pgm);
+        Assert.Equal(0.0, CanonicalAngle.Compute(d), precision: 6);
+    }
+
+    [Fact]
+    public void EmptyProgram_ReturnsZero()
+    {
+        var d = new Drawing("empty", new OpenNest.CNC.Program());
+        Assert.Equal(0.0, CanonicalAngle.Compute(d), precision: 6);
+    }
+}
+
+public class DrawingCanonicalAngleWiringTests
+{
+    private static OpenNest.CNC.Program RotatedRectProgram(double w, double h, double theta)
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        if (!OpenNest.Math.Tolerance.IsEqualTo(theta, 0))
+            pgm.Rotate(theta, pgm.BoundingBox().Center);
+        return pgm;
+    }
+
+    [Fact]
+    public void Constructor_ComputesAngleOnProgramAssignment()
+    {
+        var pgm = RotatedRectProgram(100, 50, 0.5);
+        var d = new Drawing("r", pgm);
+        Assert.InRange(d.Source.Angle, -0.52, -0.48);
+    }
+
+    [Fact]
+    public void SetProgram_RecomputesAngle()
+    {
+        var d = new Drawing("r", RotatedRectProgram(100, 50, 0.0));
+        Assert.Equal(0.0, d.Source.Angle, precision: 6);
+
+        d.Program = RotatedRectProgram(100, 50, 0.5);
+        Assert.InRange(d.Source.Angle, -0.52, -0.48);
+    }
+
+    [Fact]
+    public void IsCutOff_SkipsAngleComputation()
+    {
+        var d = new Drawing("cut", RotatedRectProgram(100, 50, 0.5)) { IsCutOff = true };
+        // Re-assign after flag is set so the setter observes IsCutOff.
+        d.Program = RotatedRectProgram(100, 50, 0.5);
+        Assert.Equal(0.0, d.Source.Angle, precision: 6);
+    }
+
+    [Fact]
+    public void RecomputeCanonicalAngle_UpdatesAfterMutation()
+    {
+        var d = new Drawing("r", RotatedRectProgram(100, 50, 0.0));
+        Assert.Equal(0.0, d.Source.Angle, precision: 6);
+
+        // Mutate in-place (doesn't trigger setter).
+        d.Program.Rotate(0.5, d.Program.BoundingBox().Center);
+        Assert.Equal(0.0, d.Source.Angle, precision: 6); // still stale
+
+        d.RecomputeCanonicalAngle();
+        Assert.InRange(d.Source.Angle, -0.52, -0.48);
+    }
+}

OpenNest.Tests/Engine/CanonicalFrameTests.cs

@@ -0,0 +1,84 @@
+using OpenNest.CNC;
+using OpenNest.Engine;
+using OpenNest.Geometry;
+using OpenNest.Math;
+
+namespace OpenNest.Tests.Engine;
+
+public class CanonicalFrameTests
+{
+    private static Drawing MakeRect(double w, double h, double rotation)
+    {
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(w, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, h)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        if (!Tolerance.IsEqualTo(rotation, 0))
+            pgm.Rotate(rotation, pgm.BoundingBox().Center);
+        return new Drawing("rect", pgm) { Source = new SourceInfo { Angle = -rotation } };
+    }
+
+    [Fact]
+    public void AsCanonicalCopy_AxisAlignsMbr()
+    {
+        var d = MakeRect(100, 50, 0.6);
+        var canonical = CanonicalFrame.AsCanonicalCopy(d);
+
+        var bb = canonical.Program.BoundingBox();
+        var longer = System.Math.Max(bb.Length, bb.Width);
+        var shorter = System.Math.Min(bb.Length, bb.Width);
+        Assert.InRange(longer, 100 - 0.1, 100 + 0.1);
+        Assert.InRange(shorter, 50 - 0.1, 50 + 0.1);
+        Assert.Equal(0.0, canonical.Source.Angle, precision: 6);
+    }
+
+    [Fact]
+    public void AsCanonicalCopy_DoesNotMutateSource()
+    {
+        var d = MakeRect(100, 50, 0.6);
+        var originalBbox = d.Program.BoundingBox();
+        var originalAngle = d.Source.Angle;
+
+        CanonicalFrame.AsCanonicalCopy(d);
+
+        var afterBbox = d.Program.BoundingBox();
+        Assert.Equal(originalBbox.Width, afterBbox.Width, precision: 6);
+        Assert.Equal(originalBbox.Length, afterBbox.Length, precision: 6);
+        Assert.Equal(originalAngle, d.Source.Angle, precision: 6);
+    }
+
+    [Fact]
+    public void FromCanonical_ComposesSourceAngleOntoRotation()
+    {
+        var d = MakeRect(100, 50, 0.0);
+        var part = new Part(d);
+        part.Rotate(0.2); // engine returned a canonical-frame part at R = 0.2
+
+        var placed = CanonicalFrame.FromCanonical(new List<Part> { part }, sourceAngle: -0.5);
+
+        // R' = R + sourceAngle = 0.2 + (-0.5) = -0.3
+        // Part.Rotation comes from Program.Rotation which is normalized to [0, 2PI),
+        // so compare after normalizing the expected value as well.
+        Assert.Single(placed);
+        Assert.Equal(Angle.NormalizeRad(-0.3), placed[0].Rotation, precision: 4);
+    }
+
+    [Fact]
+    public void RoundTrip_RestoresGeometry()
+    {
+        var d = MakeRect(100, 50, 0.4);
+        var canonical = CanonicalFrame.AsCanonicalCopy(d);
+
+        // Place a part at origin in the canonical frame.
+        var part = Part.CreateAtOrigin(canonical);
+        var canonicalBbox = part.BoundingBox;
+
+        var placed = CanonicalFrame.FromCanonical(new List<Part> { part }, d.Source.Angle);
+
+        var originalBbox = d.Program.BoundingBox();
+        Assert.Equal(originalBbox.Width, placed[0].BoundingBox.Width, precision: 2);
+        Assert.Equal(originalBbox.Length, placed[0].BoundingBox.Length, precision: 2);
+    }
+}

OpenNest.Tests/Engine/NestInvarianceTests.cs

@@ -0,0 +1,84 @@
+using OpenNest.CNC;
+using OpenNest.Engine;
+using OpenNest.Engine.BestFit;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using System.Threading;
+
+namespace OpenNest.Tests.Engine;
+
+public class NestInvarianceTests
+{
+    private static OpenNest.CNC.Program MakeLShapedProgram()
+    {
+        // L-shape: 100x50 outer rect with a 50x30 notch removed from top-right.
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(100, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(100, 20)));
+        pgm.Codes.Add(new LinearMove(new Vector(50, 20)));
+        pgm.Codes.Add(new LinearMove(new Vector(50, 50)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 50)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return pgm;
+    }
+
+    private static Drawing MakeImportedAt(double rotation)
+    {
+        var pgm = MakeLShapedProgram();
+        if (!Tolerance.IsEqualTo(rotation, 0))
+            pgm.Rotate(rotation, pgm.BoundingBox().Center);
+        return new Drawing("L", pgm);
+    }
+
+    private static Plate MakePlate() => new Plate(new Size(500, 500))
+    {
+        Quadrant = 1,
+        PartSpacing = 2,
+    };
+
+    private static int RunFillCount(Drawing drawing, Plate plate)
+    {
+        BestFitCache.Clear();
+        var engine = new DefaultNestEngine(plate);
+        var item = new NestItem { Drawing = drawing };
+        var parts = engine.Fill(item, plate.WorkArea(), progress: null, token: CancellationToken.None);
+        return parts?.Count ?? 0;
+    }
+
+    [Theory]
+    [InlineData(0.0)]
+    [InlineData(0.3)]
+    [InlineData(0.8)]
+    [InlineData(1.2)]
+    public void Fill_SameCount_AcrossImportOrientations(double theta)
+    {
+        var baseline = RunFillCount(MakeImportedAt(0.0), MakePlate());
+        var rotated = RunFillCount(MakeImportedAt(theta), MakePlate());
+
+        // Allow +/-1 tolerance for sweep quantization edge effects near plate boundaries.
+        Assert.InRange(rotated, baseline - 1, baseline + 1);
+    }
+
+    [Fact]
+    public void Fill_PlacedPartsStayWithinWorkArea_AcrossImportOrientations()
+    {
+        var plate = MakePlate();
+        var workArea = plate.WorkArea();
+
+        foreach (var theta in new[] { 0.0, 0.3, 0.8, 1.2 })
+        {
+            BestFitCache.Clear();
+            var engine = new DefaultNestEngine(plate);
+            var item = new NestItem { Drawing = MakeImportedAt(theta) };
+            var parts = engine.Fill(item, workArea, progress: null, token: CancellationToken.None);
+
+            Assert.NotNull(parts);
+            foreach (var p in parts)
+            {
+                Assert.InRange(p.BoundingBox.Left, workArea.Left - 0.5, workArea.Right + 0.5);
+                Assert.InRange(p.BoundingBox.Bottom, workArea.Bottom - 0.5, workArea.Top + 0.5);
+            }
+        }
+    }
+}

OpenNest.Tests/Fill/CompactorTests.cs

@@ -97,6 +97,33 @@ namespace OpenNest.Tests.Fill
             return part;
         }
 
+        private static Drawing MakeTriangleDrawing(params Vector[] points)
+        {
+            var pgm = new OpenNest.CNC.Program();
+            pgm.Codes.Add(new OpenNest.CNC.RapidMove(points[0]));
+
+            for (var i = 1; i < points.Length; i++)
+                pgm.Codes.Add(new OpenNest.CNC.LinearMove(points[i]));
+
+            pgm.Codes.Add(new OpenNest.CNC.LinearMove(points[0]));
+            return new Drawing("triangle", pgm);
+        }
+
+        private static Part MakeTrianglePart(params Vector[] points)
+        {
+            var part = new Part(MakeTriangleDrawing(points));
+            part.UpdateBounds();
+            return part;
+        }
+
+        private static Part MakeTrianglePart(double x, double y, params Vector[] points)
+        {
+            var part = MakeTrianglePart(points);
+            part.Location = new Vector(x, y);
+            part.UpdateBounds();
+            return part;
+        }
+
         [Fact]
         public void Push_Left_MovesPartTowardEdge()
         {
@@ -171,6 +198,86 @@ namespace OpenNest.Tests.Fill
             Assert.NotEqual(distNoSpacing, distWithSpacing);
         }
 
+        [Fact]
+        public void Push_Up_AllowsSharedDiagonalEdgeToSeparate()
+        {
+            var workArea = new Box(0, 0, 20, 20);
+            var obstacle = MakeTrianglePart(
+                new Vector(0, 0),
+                new Vector(10, 0),
+                new Vector(0, 10));
+            var movingPart = MakeTrianglePart(
+                new Vector(0, 10),
+                new Vector(10, 0),
+                new Vector(10, 10));
+
+            var distance = Compactor.Push(
+                new List<Part> { movingPart },
+                new List<Part> { obstacle },
+                workArea,
+                0,
+                PushDirection.Up);
+
+            Assert.True(distance > 0);
+            Assert.True(movingPart.BoundingBox.Top > 19.9);
+            Assert.False(movingPart.Intersects(obstacle, out _));
+        }
+
+        [Fact]
+        public void Push_Up_MovesAfterRightTriangleIsPushedLeftIntoSharedEdge()
+        {
+            var workArea = new Box(0, 0, 24, 24);
+            var leftTriangle = MakeTrianglePart(
+                2, 2,
+                new Vector(0, 0),
+                new Vector(8, 0),
+                new Vector(4, 10));
+            var rightTriangle = MakeTrianglePart(
+                14, 4,
+                new Vector(0, 10),
+                new Vector(8, 10),
+                new Vector(4, 0));
+
+            var moving = new List<Part> { rightTriangle };
+            var obstacles = new List<Part> { leftTriangle };
+
+            var leftDistance = Compactor.Push(moving, obstacles, workArea, 0, PushDirection.Left);
+            var yBeforePushUp = rightTriangle.Location.Y;
+            var bottomBeforePushUp = rightTriangle.BoundingBox.Bottom;
+
+            var upDistance = Compactor.Push(moving, obstacles, workArea, 0, PushDirection.Up);
+
+            Assert.True(leftDistance > 0);
+            Assert.True(upDistance > 0);
+            Assert.True(rightTriangle.Location.Y > yBeforePushUp);
+            Assert.True(rightTriangle.BoundingBox.Bottom > bottomBeforePushUp);
+            Assert.False(rightTriangle.Intersects(leftTriangle, out _));
+        }
+
+        [Fact]
+        public void Push_Left_BlocksWhenSharedDiagonalEdgeWouldOverlap()
+        {
+            var workArea = new Box(0, 0, 20, 20);
+            var obstacle = MakeTrianglePart(
+                new Vector(0, 0),
+                new Vector(10, 0),
+                new Vector(0, 10));
+            var movingPart = MakeTrianglePart(
+                new Vector(0, 10),
+                new Vector(10, 0),
+                new Vector(10, 10));
+
+            var distance = Compactor.Push(
+                new List<Part> { movingPart },
+                new List<Part> { obstacle },
+                workArea,
+                0,
+                PushDirection.Left);
+
+            Assert.Equal(0, distance);
+            Assert.Equal(0, movingPart.BoundingBox.Left);
+        }
+
         [Fact]
         public void Push_AngleLeft_MovesPartTowardEdge()
         {

OpenNest.Tests/Geometry/BoxComparisonTests.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Tests.Geometry;
+
+public class BoxComparisonTests
+{
+    [Fact]
+    public void GreaterThan_TallerBox_ReturnsTrue()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(tall > short_);
+        Assert.False(short_ > tall);
+    }
+
+    [Fact]
+    public void GreaterThan_SameWidthLongerBox_ReturnsTrue()
+    {
+        var longer = new Box(0, 0, 20, 10);
+        var shorter = new Box(0, 0, 10, 10);
+
+        Assert.True(longer > shorter);
+        Assert.False(shorter > longer);
+    }
+
+    [Fact]
+    public void LessThan_ShorterBox_ReturnsTrue()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(short_ < tall);
+        Assert.False(tall < short_);
+    }
+
+    [Fact]
+    public void GreaterThanOrEqual_EqualBoxes_ReturnsTrue()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.True(a >= b);
+        Assert.True(b >= a);
+    }
+
+    [Fact]
+    public void LessThanOrEqual_EqualBoxes_ReturnsTrue()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.True(a <= b);
+        Assert.True(b <= a);
+    }
+
+    [Fact]
+    public void CompareTo_TallerBox_ReturnsPositive()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(tall.CompareTo(short_) > 0);
+        Assert.True(short_.CompareTo(tall) < 0);
+    }
+
+    [Fact]
+    public void CompareTo_EqualBoxes_ReturnsZero()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.Equal(0, a.CompareTo(b));
+    }
+
+    [Fact]
+    public void Sort_OrdersByWidthThenLength()
+    {
+        var boxes = new List<Box>
+        {
+            new Box(0, 0, 20, 10),
+            new Box(0, 0, 5, 30),
+            new Box(0, 0, 10, 10),
+        };
+
+        boxes.Sort();
+
+        Assert.Equal(10, boxes[0].Width);
+        Assert.Equal(10, boxes[0].Length);
+        Assert.Equal(10, boxes[1].Width);
+        Assert.Equal(20, boxes[1].Length);
+        Assert.Equal(30, boxes[2].Width);
+    }
+}

OpenNest.Tests/Geometry/EllipseConverterTests.cs

@@ -1,14 +1,19 @@
 using OpenNest.Geometry;
+using OpenNest.IO;
 using OpenNest.Math;
 using Xunit;
+using Xunit.Abstractions;
 using System.Linq;
 
 namespace OpenNest.Tests.Geometry;
 
 public class EllipseConverterTests
 {
+    private readonly ITestOutputHelper _output;
     private const double Tol = 1e-10;
 
+    public EllipseConverterTests(ITestOutputHelper output) => _output = output;
+
     [Fact]
     public void EvaluatePoint_AtZero_ReturnsMajorAxisEnd()
     {
@@ -244,6 +249,101 @@ public class EllipseConverterTests
         }
     }
 
+    [Fact]
+    public void DxfImport_ArcBoundingBoxes_Diagnostic()
+    {
+        var path = @"C:\Users\aisaacs\Desktop\11ga tab.dxf";
+        if (!System.IO.File.Exists(path)) return;
+
+        var result = Dxf.Import(path);
+        var all = (System.Collections.Generic.IEnumerable<IBoundable>)result.Entities;
+        var bbox = all.GetBoundingBox();
+        _output.WriteLine($"Overall: X={bbox.X:F4} Y={bbox.Y:F4} W={bbox.Length:F4} H={bbox.Width:F4}");
+
+        for (var i = 0; i < result.Entities.Count; i++)
+        {
+            var e = result.Entities[i];
+            var b = e.BoundingBox;
+            var flag = (b.Length > 1 || b.Width > 1) ? " ***" : "";
+            _output.WriteLine($"{i + 1,3}. {e.GetType().Name,-8} X={b.X:F4} Y={b.Y:F4} W={b.Length:F4} H={b.Width:F4}{flag}");
+        }
+    }
+
+    [Fact]
+    public void ToOpenNest_FlippedNormalZ_ProducesCorrectArcs()
+    {
+        var normal = new ACadSharp.Entities.Ellipse
+        {
+            Center = new CSMath.XYZ(-0.275, -0.245, 0),
+            MajorAxisEndPoint = new CSMath.XYZ(0.0001, 1.245, 0),
+            RadiusRatio = 0.28,
+            StartParameter = 0.017,
+            EndParameter = 1.571,
+            Normal = new CSMath.XYZ(0, 0, 1)
+        };
+
+        var flipped = new ACadSharp.Entities.Ellipse
+        {
+            Center = new CSMath.XYZ(0.275, -0.245, 0),
+            MajorAxisEndPoint = new CSMath.XYZ(-0.0001, 1.245, 0),
+            RadiusRatio = 0.28,
+            StartParameter = 0.017,
+            EndParameter = 1.571,
+            Normal = new CSMath.XYZ(0, 0, -1)
+        };
+
+        var normalArcs = normal.ToOpenNest();
+        var flippedArcs = flipped.ToOpenNest();
+
+        Assert.True(normalArcs.Count > 0);
+        Assert.True(flippedArcs.Count > 0);
+        Assert.True(normalArcs.All(e => e is Arc));
+        Assert.True(flippedArcs.All(e => e is Arc));
+
+        var normalFirst = (Arc)normalArcs.First();
+        var flippedFirst = (Arc)flippedArcs.First();
+        var normalStart = GetArcStart(normalFirst);
+        var flippedStart = GetArcStart(flippedFirst);
+
+        Assert.True(normalStart.X < 0, $"Normal ellipse start X should be negative, got {normalStart.X}");
+        Assert.True(flippedStart.X > 0, $"Flipped ellipse should bulge right, got {flippedStart.X}");
+
+        var normalBbox = GetBoundingBox(normalArcs.Cast<Arc>());
+        var flippedBbox = GetBoundingBox(flippedArcs.Cast<Arc>());
+        Assert.True(flippedBbox.minX > 0, $"Flipped ellipse should stay on positive X side, minX={flippedBbox.minX}");
+        Assert.True(normalBbox.maxX < 0, $"Normal ellipse should stay on negative X side, maxX={normalBbox.maxX}");
+    }
+
+    private static (double minX, double maxX) GetBoundingBox(IEnumerable<Arc> arcs)
+    {
+        var minX = double.MaxValue;
+        var maxX = double.MinValue;
+        foreach (var arc in arcs)
+        {
+            var s = GetArcStart(arc);
+            var e = GetArcEnd(arc);
+            minX = System.Math.Min(minX, System.Math.Min(s.X, e.X));
+            maxX = System.Math.Max(maxX, System.Math.Max(s.X, e.X));
+        }
+        return (minX, maxX);
+    }
+
+    private static Vector GetArcStart(Arc arc)
+    {
+        var angle = arc.IsReversed ? arc.EndAngle : arc.StartAngle;
+        return new Vector(
+            arc.Center.X + arc.Radius * System.Math.Cos(angle),
+            arc.Center.Y + arc.Radius * System.Math.Sin(angle));
+    }
+
+    private static Vector GetArcEnd(Arc arc)
+    {
+        var angle = arc.IsReversed ? arc.StartAngle : arc.EndAngle;
+        return new Vector(
+            arc.Center.X + arc.Radius * System.Math.Cos(angle),
+            arc.Center.Y + arc.Radius * System.Math.Sin(angle));
+    }
+
     private static double MaxDeviationFromEllipse(Arc arc, Vector ellipseCenter,
         double semiMajor, double semiMinor, double rotation, int samples)
     {

OpenNest.Tests/Geometry/GeometrySimplifierTests.cs

@@ -131,6 +131,111 @@ public class GeometrySimplifierTests
         Assert.IsType<Arc>(result.Entities[6]);
     }
 
+    [Fact]
+    public void Analyze_FilletBetweenTangentLines_ArcIsTangentToLines()
+    {
+        // A 90-degree fillet (r=0.3, center origin, 270deg..360deg CCW) between two
+        // long tangent lines, approximated by 8 chords whose interior vertices bulge
+        // radially outward within tolerance (simulates real DXF tessellation noise).
+        var r = 0.3;
+        var deltas = new[] { 0.0, 0.002, 0.003, 0.0035, 0.0035, 0.0035, 0.003, 0.002, 0.0 };
+        var pts = new List<Vector>();
+        for (var i = 0; i <= 8; i++)
+        {
+            var ang = OpenNest.Math.Angle.ToRadians(270 + 11.25 * i);
+            var radius = r + deltas[i];
+            pts.Add(new Vector(radius * System.Math.Cos(ang), radius * System.Math.Sin(ang)));
+        }
+
+        var shape = new Shape();
+        shape.Entities.Add(new Line(new Vector(-2, -r), pts[0]));
+        for (var i = 0; i < pts.Count - 1; i++)
+            shape.Entities.Add(new Line(pts[i], pts[i + 1]));
+        shape.Entities.Add(new Line(pts[^1], new Vector(r, 2)));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.004 };
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.Single(candidates);
+        var arc = candidates[0].FittedArc;
+
+        // Arc must pass exactly through the run's boundary vertices (no gaps)
+        Assert.True(arc.StartPoint().DistanceTo(pts[0]) < 1e-6);
+        Assert.True(arc.EndPoint().DistanceTo(pts[^1]) < 1e-6);
+
+        // Arc must be tangent to the adjacent straight edges at its endpoints
+        var startDelta = AngleBetweenDeg(ArcTangentAt(arc, arc.StartPoint()), new Vector(1, 0));
+        var endDelta = AngleBetweenDeg(ArcTangentAt(arc, arc.EndPoint()), new Vector(0, 1));
+        Assert.True(startDelta < 0.3, $"Arc start not tangent to incoming line: off by {startDelta:F3} deg");
+        Assert.True(endDelta < 0.3, $"Arc end not tangent to outgoing line: off by {endDelta:F3} deg");
+    }
+
+    [Fact]
+    public void Analyze_CompoundCurve_AdjacentArcsAreTangentAtJunction()
+    {
+        // Two tangent-continuous arcs of different radii (r=0.2 sweeping 60deg, then
+        // r=0.6 sweeping 40deg), tessellated into chords with slight radial noise.
+        // The fitted arcs must stay tangent-continuous at their junction.
+        var c1 = new Vector(0, 0);
+        var r1 = 0.2;
+        var deltas1 = new[] { 0.0, 0.001, 0.0005, -0.0005, -0.001, -0.0005, 0.0 };
+        var pts = new List<Vector>();
+        for (var i = 0; i <= 6; i++)
+        {
+            var ang = OpenNest.Math.Angle.ToRadians(10 * i);
+            var radius = r1 + deltas1[i];
+            pts.Add(new Vector(c1.X + radius * System.Math.Cos(ang), c1.Y + radius * System.Math.Sin(ang)));
+        }
+
+        // Second arc center along the junction radius so tangents match at the junction
+        var junctionAngle = OpenNest.Math.Angle.ToRadians(60);
+        var u = new Vector(System.Math.Cos(junctionAngle), System.Math.Sin(junctionAngle));
+        var r2 = 0.6;
+        var c2 = new Vector(c1.X + u.X * (r1 - r2), c1.Y + u.Y * (r1 - r2));
+        var deltas2 = new[] { 0.0, 0.001, -0.001, 0.0005, -0.0005, 0.0 };
+        for (var i = 1; i <= 5; i++)
+        {
+            var ang = OpenNest.Math.Angle.ToRadians(60 + 8 * i);
+            var radius = r2 + deltas2[i];
+            pts.Add(new Vector(c2.X + radius * System.Math.Cos(ang), c2.Y + radius * System.Math.Sin(ang)));
+        }
+
+        var shape = new Shape();
+        for (var i = 0; i < pts.Count - 1; i++)
+            shape.Entities.Add(new Line(pts[i], pts[i + 1]));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.004 };
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.Equal(2, candidates.Count);
+        var arcA = candidates[0].FittedArc;
+        var arcB = candidates[1].FittedArc;
+
+        // Arcs must share the junction vertex exactly
+        Assert.True(arcA.EndPoint().DistanceTo(arcB.StartPoint()) < 1e-6);
+
+        // Tangent continuity across the junction
+        var junctionDelta = AngleBetweenDeg(ArcTangentAt(arcA, arcA.EndPoint()), ArcTangentAt(arcB, arcB.StartPoint()));
+        Assert.True(junctionDelta < 0.3, $"Tangent break of {junctionDelta:F3} deg at arc-arc junction");
+    }
+
+    private static Vector ArcTangentAt(Arc arc, Vector pt)
+    {
+        var ang = System.Math.Atan2(pt.Y - arc.Center.Y, pt.X - arc.Center.X);
+        return arc.IsReversed
+            ? new Vector(System.Math.Sin(ang), -System.Math.Cos(ang))
+            : new Vector(-System.Math.Sin(ang), System.Math.Cos(ang));
+    }
+
+    private static double AngleBetweenDeg(Vector v1, Vector v2)
+    {
+        var l1 = System.Math.Sqrt(v1.X * v1.X + v1.Y * v1.Y);
+        var l2 = System.Math.Sqrt(v2.X * v2.X + v2.Y * v2.Y);
+        var dot = (v1.X * v2.X + v1.Y * v2.Y) / (l1 * l2);
+        dot = System.Math.Max(-1, System.Math.Min(1, dot));
+        return System.Math.Acos(dot) * 180.0 / System.Math.PI;
+    }
+
     [Fact]
     public void Apply_DynaPanDxf_NoGapsAfterSimplification()
     {

OpenNest.Tests/Geometry/WeldEndpointsTests.cs

@@ -0,0 +1,72 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.Geometry;
+
+public class WeldEndpointsTests
+{
+    [Fact]
+    public void WeldEndpoints_SnapsNearbyLineEndpoints()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.0000005, 0, 20, 0);
+        var entities = new List<Entity> { line1, line2 };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.000001);
+
+        Assert.True(line1.EndPoint.DistanceTo(line2.StartPoint) <= Tolerance.Epsilon);
+    }
+
+    [Fact]
+    public void WeldEndpoints_SnapsArcEndpointByAdjustingAngle()
+    {
+        var line = new Line(0, 0, 10, 0);
+        var arc = new Arc(15, 0, 5, Angle.ToRadians(180.001), Angle.ToRadians(90));
+        var entities = new List<Entity> { line, arc };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.01);
+
+        var arcStart = arc.StartPoint();
+        Assert.True(line.EndPoint.DistanceTo(arcStart) <= 0.01);
+    }
+
+    [Fact]
+    public void WeldEndpoints_DoesNotWeldDistantEndpoints()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.1, 0, 20, 0);
+        var entities = new List<Entity> { line1, line2 };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.000001);
+
+        Assert.True(line1.EndPoint.DistanceTo(line2.StartPoint) > 0.01);
+    }
+
+    [Fact]
+    public void GetShapes_WithWeldTolerance_WeldsBeforeChaining()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.0000005, 0, 10.0000005, 10);
+        var entities = new List<Entity> { line1, line2 };
+
+        var shapes = ShapeBuilder.GetShapes(entities, weldTolerance: 0.000001);
+
+        Assert.Single(shapes);
+        Assert.Equal(2, shapes[0].Entities.Count);
+    }
+
+    [Fact]
+    public void GetShapes_WithoutWeldTolerance_DefaultBehavior()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10, 0, 10, 10);
+        var entities = new List<Entity> { line1, line2 };
+
+        var shapes = ShapeBuilder.GetShapes(entities);
+
+        Assert.Single(shapes);
+        Assert.Equal(2, shapes[0].Entities.Count);
+    }
+}

OpenNest.Tests/GravographIS/EnvelopeGuardTests.cs

@@ -0,0 +1,165 @@
+using System.Collections.Generic;
+using System.IO;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class EnvelopeGuardTests
+{
+    // 0.610 m / 0.0125 mm/step = 48 800 steps = 24.0157 inches
+    // 1.220 m / 0.0125 mm/step = 97 600 steps = 48.0315 inches
+
+    [Fact]
+    public void NegativeX_FromOrigin_Throws()
+    {
+        // Operator origin is upper-left; quadrant 4 walks right/down. A cut that walks
+        // left of origin in -X must be refused.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(-1, 0) },
+        };
+
+        var ex = Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter().Write(polylines, ms);
+        });
+
+        Assert.Contains("Polyline 1", ex.Message);
+        Assert.Contains("cut segment", ex.Message);
+        Assert.Contains("segment 1", ex.Message);
+    }
+
+    [Fact]
+    public void PositiveY_FromOrigin_Throws()
+    {
+        // Positive input-Y is above the upper-left origin in quadrant 4.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(0, 1) },
+        };
+
+        var ex = Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter().Write(polylines, ms);
+        });
+
+        Assert.Contains("Polyline 1", ex.Message);
+    }
+
+    [Fact]
+    public void XExceedsEnvelope_Throws_AndNamesSegment()
+    {
+        // 25" in X is past the 0.610 m (~24.02") envelope.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(10, 0), new Vector(25, 0) },
+        };
+
+        var ex = Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter().Write(polylines, ms);
+        });
+
+        Assert.Contains("Polyline 1", ex.Message);
+        Assert.Contains("segment 2", ex.Message); // 0→10 ok; 10→25 trips
+        Assert.Contains("25.000\"", ex.Message);
+    }
+
+    [Fact]
+    public void YExceedsEnvelope_Throws()
+    {
+        // -49" in Y is past the 1.220 m (~48.03") envelope.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(0, -49) },
+        };
+
+        Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter().Write(polylines, ms);
+        });
+    }
+
+    [Fact]
+    public void PenUpTravel_OutsideEnvelope_AlsoThrows_AndIsLabeledTravel()
+    {
+        // Polyline 1 ends in-envelope; the PU travel to polyline 2 leaves it.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(30, 0), new Vector(30, -1) },
+        };
+
+        var ex = Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter().Write(polylines, ms);
+        });
+
+        Assert.Contains("Polyline 2", ex.Message);
+        Assert.Contains("pen-up travel", ex.Message);
+    }
+
+    [Fact]
+    public void RightAtEnvelopeCorner_IsAllowed()
+    {
+        // Walk to (24", -48") in int16-sized hops (each delta < 16.1"). The
+        // catalog envelope is 24.02" × 48.03", so this lands just inside.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[]
+            {
+                new Vector(0, 0),
+                new Vector(8, -16),
+                new Vector(16, -32),
+                new Vector(24, -48),
+            },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter().Write(polylines, ms); // no throw
+        Assert.True(ms.Length > 0);
+    }
+
+    [Fact]
+    public void EnvelopeGuard_CanBeDisabled_ForOffMachineEncoding()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(-5, 0) },
+        };
+
+        var opts = new GravographISWriterOptions { EnvelopeGuardEnabled = false };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(opts).Write(polylines, ms); // no throw
+        Assert.True(ms.Length > 0);
+    }
+
+    [Fact]
+    public void CustomEnvelope_TightensTheCheck()
+    {
+        // Restrict to 1" × 1" — a 2" line in -Y now overshoots.
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(0, -2) },
+        };
+
+        var opts = new GravographISWriterOptions
+        {
+            WorkEnvelopeXMm = 25.4,
+            WorkEnvelopeYMm = 25.4,
+        };
+
+        Assert.Throws<System.InvalidOperationException>(() =>
+        {
+            using var ms = new MemoryStream();
+            new GravographISWriter(opts).Write(polylines, ms);
+        });
+    }
+}

OpenNest.Tests/GravographIS/GravographISPostConfigTests.cs

@@ -0,0 +1,51 @@
+using OpenNest.CNC;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class GravographISPostConfigTests
+{
+    [Fact]
+    public void Defaults_EngraveBlock_NoPause_FasterFeed()
+    {
+        var config = new GravographISPostConfig();
+
+        Assert.Equal(10, config.Engrave.FeedMmPerSec);
+        Assert.False(config.Engrave.PauseBefore);
+    }
+
+    [Fact]
+    public void Defaults_CutBlock_PausesToChangeTool()
+    {
+        var config = new GravographISPostConfig();
+
+        Assert.Equal(3, config.Cut.FeedMmPerSec);
+        Assert.True(config.Cut.PauseBefore);
+        Assert.Equal("Change tool", config.Cut.PauseMessage);
+    }
+
+    [Theory]
+    [InlineData(LayerType.Scribe)]
+    public void ConfigFor_Scribe_ReturnsEngraveBlock(LayerType layer)
+    {
+        var config = new GravographISPostConfig();
+        Assert.Same(config.Engrave, config.ConfigFor(layer));
+    }
+
+    [Theory]
+    [InlineData(LayerType.Cut)]
+    [InlineData(LayerType.Leadin)]
+    [InlineData(LayerType.Leadout)]
+    public void ConfigFor_CutLayers_ReturnCutBlock(LayerType layer)
+    {
+        var config = new GravographISPostConfig();
+        Assert.Same(config.Cut, config.ConfigFor(layer));
+    }
+
+    [Fact]
+    public void ConfigFor_Display_ReturnsNull_SoItIsSkipped()
+    {
+        var config = new GravographISPostConfig();
+        Assert.Null(config.ConfigFor(LayerType.Display));
+    }
+}

OpenNest.Tests/GravographIS/GravographISPostProcessorTests.cs

@@ -0,0 +1,70 @@
+using System.Collections.Generic;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class GravographISPostProcessorTests
+{
+    private static LayeredPolyline Poly(LayerType layer, params Vector[] pts)
+        => new LayeredPolyline(new List<Vector>(pts), layer);
+
+    [Fact]
+    public void BuildPasses_EngraveAndCut_OrdersEngraveFirstThenCutWithPause()
+    {
+        var post = new GravographISPostProcessor();
+
+        var passes = post.BuildPasses(new[]
+        {
+            Poly(LayerType.Cut, new Vector(0, 0), new Vector(1, 0)),
+            Poly(LayerType.Scribe, new Vector(0, 0), new Vector(0, 1)),
+        });
+
+        Assert.Equal(2, passes.Count);
+
+        Assert.Equal(post.Config.Engrave.FeedMmPerSec, passes[0].FeedMmPerSec);
+        Assert.False(passes[0].PauseBefore);
+
+        Assert.Equal(post.Config.Cut.FeedMmPerSec, passes[1].FeedMmPerSec);
+        Assert.True(passes[1].PauseBefore);
+        Assert.Equal("Change tool", passes[1].PauseMessage);
+    }
+
+    [Fact]
+    public void BuildPasses_CutOnly_IsSinglePass()
+    {
+        var post = new GravographISPostProcessor();
+
+        var passes = post.BuildPasses(new[]
+        {
+            Poly(LayerType.Cut, new Vector(0, 0), new Vector(1, 0)),
+        });
+
+        Assert.Single(passes);
+        Assert.Equal(post.Config.Cut.FeedMmPerSec, passes[0].FeedMmPerSec);
+    }
+
+    [Fact]
+    public void BuildPasses_SkipsDisplayGeometry()
+    {
+        var post = new GravographISPostProcessor();
+
+        var passes = post.BuildPasses(new[]
+        {
+            Poly(LayerType.Display, new Vector(0, 0), new Vector(1, 0)),
+            Poly(LayerType.Cut, new Vector(0, 0), new Vector(0, 1)),
+        });
+
+        Assert.Single(passes);
+        Assert.Equal(post.Config.Cut.FeedMmPerSec, passes[0].FeedMmPerSec);
+    }
+
+    [Fact]
+    public void Config_IsExposedThroughConfigurableInterface()
+    {
+        var post = new GravographISPostProcessor(new GravographISPostConfig());
+        OpenNest.IConfigurablePostProcessor configurable = post;
+        Assert.Same(post.Config, configurable.Config);
+    }
+}

OpenNest.Tests/GravographIS/GravographISWriterTests.cs

@@ -0,0 +1,318 @@
+using System.Collections.Generic;
+using System.IO;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class GravographISWriterTests
+{
+    // 93-byte preamble captured from GravoStyle'98 (VS/VZ=35, DZ=508 → matches defaults).
+    // The original capture ended with a DR command (FF FD 44 52) followed by three
+    // 8-byte int16 records carrying a chunked job-specific travel (~1" X, ~47" Y).
+    // Stripped from the writer (see GravographISWriter.PreambleTemplate) because
+    // those frozen deltas send the head to a fixed point regardless of the job. The
+    // writer now emits a job-specific leading DR travel from operator zero instead.
+    private const string PreambleHex =
+        "21 41 53 20 33 38 3b 01 90 01 f4 01 90 01 f4 01 90 01 f4 00 00 00 00 00 00 00 00 00 00 " +
+        "00 00 00 09 00 00 03 e8 05 06 00 00 00 00 00 00 ff fd 32 44 00 00 ff fd 4d 43 00 01 ff fd " +
+        "4f 55 ff fb ff fd 4f 55 ff fa ff fd 50 5a 00 00 ff fd 56 53 00 23 ff fd 56 5a 00 23 ff fd " +
+        "44 5a 01 fc";
+
+    // Legacy 36-byte tail with lift, aux off, motor off, operator beep, job finish.
+    // Byte-exact capture tests disable dynamic return-to-origin to preserve this form.
+    private const string PostambleHex =
+        "ff fd 50 55 00 01 ff fd 4f 55 ff fa ff fd 4f 55 ff fb ff fd 4d 43 00 00 " +
+        "ff fd 4f 50 00 00 ff fd 4a 46 00 00";
+
+    [Fact]
+    public void TestA_SingleTwoInchVerticalLine_IsByteExact()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(1, 1), new Vector(1, 3) },
+        };
+
+        var writer = new GravographISWriter(new GravographISWriterOptions
+        {
+            DepthInches = 0.25,
+            FeedMmPerSec = 35,
+            EnvelopeGuardEnabled = false,
+            ReturnToOriginAtEnd = false,
+        });
+
+        using var ms = new MemoryStream();
+        writer.Write(polylines, ms);
+
+        const string GeomHex =
+            "ff fd 44 52 00 00 2d 41 00 80 07 f0 f8 10 " +
+            "ff fd 50 44 00 00 40 00 00 b4 00 00 f0 20";
+        var expected = HexToBytes(PreambleHex + " " + GeomHex + " " + PostambleHex);
+
+        Assert.Equal(expected, ms.ToArray());
+    }
+
+    [Fact]
+    public void TestB_FourLines_IsByteExact()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(1, 1), new Vector(1, 3) },
+            new[] { new Vector(4, 1), new Vector(4, 3) },
+            new[] { new Vector(4, 5), new Vector(4, 7) },
+            new[] { new Vector(1, 5), new Vector(1, 7) },
+        };
+
+        var writer = new GravographISWriter(new GravographISWriterOptions
+        {
+            DepthInches = 0.25,
+            FeedMmPerSec = 35,
+            EnvelopeGuardEnabled = false,
+            ReturnToOriginAtEnd = false,
+        });
+
+        using var ms = new MemoryStream();
+        writer.Write(polylines, ms);
+
+        const string GeomHex =
+            "ff fd 44 52 00 00 2d 41 00 80 07 f0 f8 10 " +
+            "ff fd 50 44 00 00 40 00 00 b4 00 00 f0 20 " +
+            "ff fd 50 55 00 00 35 40 00 b4 17 d0 0f e0 " +
+            "ff fd 50 44 00 00 40 00 00 b4 00 00 f0 20 " +
+            "ff fd 50 55 00 00 40 00 00 b4 00 00 f0 20 " +
+            "ff fd 50 44 00 00 40 00 00 b4 00 00 f0 20 " +
+            "ff fd 50 55 00 00 35 40 00 b4 e8 30 0f e0 " +
+            "ff fd 50 44 00 00 40 00 00 b4 00 00 f0 20";
+        var expected = HexToBytes(PreambleHex + " " + GeomHex + " " + PostambleHex);
+
+        Assert.Equal(expected, ms.ToArray());
+    }
+
+    [Fact]
+    public void LeadingDR_TravelsToFirstPolylineStartBeforePD()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(2, 2), new Vector(3, 2) },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions { EnvelopeGuardEnabled = false }).Write(polylines, ms);
+
+        var bytes = ms.ToArray();
+        // First command after the 93-byte preamble must be DR to the first point,
+        // followed by PD for the first cut.
+        Assert.Equal(0xFF, bytes[93]);
+        Assert.Equal(0xFD, bytes[94]);
+        Assert.Equal((byte)'D', bytes[95]);
+        Assert.Equal((byte)'R', bytes[96]);
+
+        Assert.Equal(0xFF, bytes[107]);
+        Assert.Equal(0xFD, bytes[108]);
+        Assert.Equal((byte)'P', bytes[109]);
+        Assert.Equal((byte)'D', bytes[110]);
+    }
+
+    [Fact]
+    public void LeadingDR_LongTravel_IsChunked()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(1, 47), new Vector(2, 47) },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions { EnvelopeGuardEnabled = false }).Write(polylines, ms);
+
+        var bytes = ms.ToArray();
+        Assert.Equal((byte)'D', bytes[95]);
+        Assert.Equal((byte)'R', bytes[96]);
+        Assert.Equal((byte)'P', bytes[125]);
+        Assert.Equal((byte)'D', bytes[126]);
+    }
+
+    [Fact]
+    public void OptionsPatchVsVzDz()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(0.5, 0) },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions
+        {
+            DepthInches = 0.125,   // 254 steps = 0x00FE
+            FeedMmPerSec = 50,     // 0x0032
+        }).Write(polylines, ms);
+
+        var bytes = ms.ToArray();
+        AssertOperand(bytes, (byte)'V', (byte)'S', 0x00, 0x32);
+        AssertOperand(bytes, (byte)'V', (byte)'Z', 0x00, 0x32);
+        AssertOperand(bytes, (byte)'D', (byte)'Z', 0x00, 0xFE);
+    }
+
+    [Fact]
+    public void ReturnsToOriginAfterFinalLift_ByDefault()
+    {
+        var polylines = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0), new Vector(1, -1) },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter().Write(polylines, ms);
+
+        var bytes = ms.ToArray();
+        var liftIndex = LastIndexOfCommand(bytes, (byte)'P', (byte)'U', 0x00, 0x01);
+        Assert.True(liftIndex >= 0);
+
+        Assert.Equal(0xFF, bytes[liftIndex + 6]);
+        Assert.Equal(0xFD, bytes[liftIndex + 7]);
+        Assert.Equal((byte)'P', bytes[liftIndex + 8]);
+        Assert.Equal((byte)'U', bytes[liftIndex + 9]);
+
+        var dx = ReadInt16(bytes, liftIndex + 16);
+        var dy = ReadInt16(bytes, liftIndex + 18);
+        Assert.Equal(-GravographISWriter.StepsPerInch, dx);
+        Assert.Equal(-GravographISWriter.StepsPerInch, dy);
+    }
+
+    [Fact]
+    public void Passes_PauseBeforeCut_EmitsPauseSequenceBetweenGroups()
+    {
+        var engrave = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(1, 0) } };
+        var cut = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(0, -1) } };
+        var passes = new List<GravographPass>
+        {
+            new GravographPass { Polylines = engrave, FeedMmPerSec = 10, DepthInches = 0.25 },
+            new GravographPass { Polylines = cut, FeedMmPerSec = 3, DepthInches = 0.25, PauseBefore = true, PauseMessage = "Hi" },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions
+        {
+            EnvelopeGuardEnabled = false,
+            ReturnToOriginAtEnd = false,
+        }).Write(passes, ms);
+        var bytes = ms.ToArray();
+
+        var mcOff = IndexOf(bytes, 0, (byte)'M', (byte)'C', 0x00, 0x00);
+        var ouFb = IndexOf(bytes, mcOff, (byte)'O', (byte)'U', 0xFF, 0xFB);
+        var ouFa = IndexOf(bytes, ouFb, (byte)'O', (byte)'U', 0xFF, 0xFA);
+        var lbBegin = IndexOf(bytes, ouFa, (byte)'L', (byte)'B', 0x00, 0x00);
+        var lbMsg = IndexOf(bytes, lbBegin, (byte)'L', (byte)'B', (byte)'H', (byte)'i');
+        var nr = IndexOf(bytes, lbMsg, (byte)'N', (byte)'R', 0x00, 0x01);
+        var lbEnd = IndexOf(bytes, nr, (byte)'L', (byte)'B', 0x00, 0x01);
+        var mcOn = IndexOf(bytes, lbEnd, (byte)'M', (byte)'C', 0x00, 0x01);
+
+        Assert.True(mcOff >= 0, "motor-off (MC 0000) not found");
+        Assert.True(mcOff < ouFb && ouFb < ouFa && ouFa < lbBegin && lbBegin < lbMsg
+            && lbMsg < nr && nr < lbEnd && lbEnd < mcOn,
+            "pause commands out of order");
+
+        // Resume sets the cut feed inline (VS 0x0003) after the motor restarts.
+        var vsCut = IndexOf(bytes, mcOn, (byte)'V', (byte)'S', 0x00, 0x03);
+        Assert.True(vsCut > mcOn, "cut feed not set after resume");
+    }
+
+    [Fact]
+    public void Passes_PauseOddMessage_SpacePadsLastPacket()
+    {
+        var passes = new List<GravographPass>
+        {
+            new GravographPass { Polylines = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(1, 0) } }, FeedMmPerSec = 10 },
+            new GravographPass { Polylines = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(0, -1) } }, FeedMmPerSec = 3, PauseBefore = true, PauseMessage = "abc" },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions { EnvelopeGuardEnabled = false, ReturnToOriginAtEnd = false }).Write(passes, ms);
+        var bytes = ms.ToArray();
+
+        var lbAb = IndexOf(bytes, 0, (byte)'L', (byte)'B', (byte)'a', (byte)'b');
+        var lbCPad = IndexOf(bytes, lbAb, (byte)'L', (byte)'B', (byte)'c', 0x20);
+        Assert.True(lbAb >= 0, "first message packet 'ab' not found");
+        Assert.True(lbCPad > lbAb, "odd packet not space-padded to 'c '");
+    }
+
+    [Fact]
+    public void Passes_DifferentFeeds_NoPause_EmitsInlineFeedChangeNoMessage()
+    {
+        var passes = new List<GravographPass>
+        {
+            new GravographPass { Polylines = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(1, 0) } }, FeedMmPerSec = 10 },
+            new GravographPass { Polylines = new List<IReadOnlyList<Vector>> { new[] { new Vector(0, 0), new Vector(0, -1) } }, FeedMmPerSec = 3, PauseBefore = false },
+        };
+
+        using var ms = new MemoryStream();
+        new GravographISWriter(new GravographISWriterOptions { EnvelopeGuardEnabled = false, ReturnToOriginAtEnd = false }).Write(passes, ms);
+        var bytes = ms.ToArray();
+
+        Assert.True(IndexOf(bytes, 0, (byte)'V', (byte)'S', 0x00, 0x03) >= 0, "inline cut feed change missing");
+        Assert.True(IndexOfCmd(bytes, (byte)'L', (byte)'B') < 0, "no LB message expected without a pause");
+    }
+
+    private static int IndexOf(byte[] bytes, int from, byte c0, byte c1, byte hi, byte lo)
+    {
+        for (var i = System.Math.Max(0, from); i <= bytes.Length - 6; i++)
+        {
+            if (bytes[i] == 0xFF && bytes[i + 1] == 0xFD && bytes[i + 2] == c0 &&
+                bytes[i + 3] == c1 && bytes[i + 4] == hi && bytes[i + 5] == lo)
+                return i;
+        }
+        return -1;
+    }
+
+    private static int IndexOfCmd(byte[] bytes, byte c0, byte c1)
+    {
+        for (var i = 0; i <= bytes.Length - 4; i++)
+        {
+            if (bytes[i] == 0xFF && bytes[i + 1] == 0xFD && bytes[i + 2] == c0 && bytes[i + 3] == c1)
+                return i;
+        }
+        return -1;
+    }
+
+    private static void AssertOperand(byte[] bytes, byte c0, byte c1, byte hi, byte lo)
+    {
+        for (var i = 0; i < bytes.Length - 5; i++)
+        {
+            if (bytes[i] == 0xFF && bytes[i + 1] == 0xFD && bytes[i + 2] == c0 && bytes[i + 3] == c1)
+            {
+                Assert.Equal(hi, bytes[i + 4]);
+                Assert.Equal(lo, bytes[i + 5]);
+                return;
+            }
+        }
+        Assert.Fail($"Command {(char)c0}{(char)c1} not found in stream.");
+    }
+
+    private static int LastIndexOfCommand(byte[] bytes, byte c0, byte c1, byte hi, byte lo)
+    {
+        for (var i = bytes.Length - 6; i >= 0; i--)
+        {
+            if (bytes[i] == 0xFF && bytes[i + 1] == 0xFD &&
+                bytes[i + 2] == c0 && bytes[i + 3] == c1 &&
+                bytes[i + 4] == hi && bytes[i + 5] == lo)
+            {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    private static short ReadInt16(byte[] bytes, int offset)
+    {
+        return unchecked((short)((bytes[offset] << 8) | bytes[offset + 1]));
+    }
+
+    internal static byte[] HexToBytes(string hex)
+    {
+        var clean = hex.Replace(" ", string.Empty).Replace("\n", string.Empty).Replace("\r", string.Empty);
+        var bytes = new byte[clean.Length / 2];
+        for (var i = 0; i < bytes.Length; i++)
+            bytes[i] = System.Convert.ToByte(clean.Substring(i * 2, 2), 16);
+        return bytes;
+    }
+}

OpenNest.Tests/GravographIS/NestPolylineExtractorTests.cs

@@ -0,0 +1,78 @@
+using OpenNest;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class NestPolylineExtractorTests
+{
+    [Fact]
+    public void ExtractPart_IncrementalProgram_ProducesAbsoluteCoordinates()
+    {
+        // 1x1 square in G91 (incremental) mode — the form OpenNest's UI writes
+        // to .nest files. Without absolute-mode handling the extractor plotted
+        // each EndPoint as if it were absolute, producing a 2x2 diamond.
+        var program = new Program(Mode.Incremental);
+        program.Codes.Add(new RapidMove(new Vector(0, 0)));
+        program.Codes.Add(new LinearMove(1, 0));
+        program.Codes.Add(new LinearMove(0, 1));
+        program.Codes.Add(new LinearMove(-1, 0));
+        program.Codes.Add(new LinearMove(0, -1));
+
+        var drawing = new Drawing("Square 1x1", program);
+        var part = new Part(drawing, new Vector(0.25, 46.75));
+
+        var polylines = new NestPolylineExtractor().ExtractPart(part);
+
+        Assert.Single(polylines);
+        var poly = polylines[0];
+        Assert.Equal(5, poly.Count);
+        Assert.Equal(new Vector(0.25, 46.75), poly[0]);
+        Assert.Equal(new Vector(1.25, 46.75), poly[1]);
+        Assert.Equal(new Vector(1.25, 47.75), poly[2]);
+        Assert.Equal(new Vector(0.25, 47.75), poly[3]);
+        Assert.Equal(new Vector(0.25, 46.75), poly[4]);
+    }
+
+    [Fact]
+    public void ExtractPartLayered_SplitsContinuousChainAtLayerChange()
+    {
+        // A single continuous chain (no rapid) that switches from Scribe to Cut
+        // must be split into two layer-uniform polylines sharing the seam vertex,
+        // so the post can emit a tool-change pause between engrave and cut.
+        var program = new Program(Mode.Absolute);
+        program.Codes.Add(new LinearMove(1, 0) { Layer = LayerType.Scribe });
+        program.Codes.Add(new LinearMove(2, 0) { Layer = LayerType.Scribe });
+        program.Codes.Add(new LinearMove(2, 1) { Layer = LayerType.Cut });
+        program.Codes.Add(new LinearMove(3, 1) { Layer = LayerType.Cut });
+
+        var drawing = new Drawing("Mixed", program);
+        var part = new Part(drawing, new Vector(0, 0));
+
+        var polylines = new NestPolylineExtractor().ExtractPartLayered(part);
+
+        Assert.Equal(2, polylines.Count);
+
+        Assert.Equal(LayerType.Scribe, polylines[0].Layer);
+        Assert.Equal(new[] { new Vector(0, 0), new Vector(1, 0), new Vector(2, 0) }, polylines[0].Points);
+
+        Assert.Equal(LayerType.Cut, polylines[1].Layer);
+        Assert.Equal(new[] { new Vector(2, 0), new Vector(2, 1), new Vector(3, 1) }, polylines[1].Points);
+    }
+
+    [Fact]
+    public void ExtractPartLayered_UniformChain_IsSinglePolyline()
+    {
+        var program = new Program(Mode.Absolute);
+        program.Codes.Add(new LinearMove(1, 0));
+        program.Codes.Add(new LinearMove(1, 1));
+
+        var part = new Part(new Drawing("Cut", program), new Vector(0, 0));
+
+        var polylines = new NestPolylineExtractor().ExtractPartLayered(part);
+
+        Assert.Single(polylines);
+        Assert.Equal(LayerType.Cut, polylines[0].Layer);
+    }
+}

OpenNest.Tests/GravographIS/PolylinePrePassTests.cs

@@ -0,0 +1,164 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.GravographIS;
+
+public class PolylinePrePassTests
+{
+    [Fact]
+    public void Stitch_TwoConnectedSegments_BecomeOnePolyline()
+    {
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(1, 0), new Vector(1, 1) },
+        };
+
+        var stitched = PolylinePrePass.Stitch(inputs);
+
+        Assert.Single(stitched);
+        Assert.Equal(3, stitched[0].Count);
+        Assert.Equal(new Vector(0, 0), stitched[0][0]);
+        Assert.Equal(new Vector(1, 0), stitched[0][1]);
+        Assert.Equal(new Vector(1, 1), stitched[0][2]);
+    }
+
+    [Fact]
+    public void Stitch_FourSegmentsFormingClosedSquare_BecomeOnePolyline()
+    {
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(1, 0), new Vector(1, 1) },
+            new[] { new Vector(1, 1), new Vector(0, 1) },
+            new[] { new Vector(0, 1), new Vector(0, 0) },
+        };
+
+        var stitched = PolylinePrePass.Stitch(inputs);
+
+        Assert.Single(stitched);
+        // Four edges + closing return-to-start = five vertices.
+        Assert.Equal(5, stitched[0].Count);
+    }
+
+    [Fact]
+    public void Stitch_ReversesOneSegmentToMakeAJoin()
+    {
+        // Second segment is given backward; stitcher should reverse it.
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(2, 0), new Vector(1, 0) },
+        };
+
+        var stitched = PolylinePrePass.Stitch(inputs);
+
+        Assert.Single(stitched);
+        Assert.Equal(3, stitched[0].Count);
+        Assert.Equal(new Vector(0, 0), stitched[0][0]);
+        Assert.Equal(new Vector(2, 0), stitched[0][stitched[0].Count - 1]);
+    }
+
+    [Fact]
+    public void Stitch_DisjointSegments_StayDistinct()
+    {
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(5, 5), new Vector(6, 5) },
+        };
+
+        var stitched = PolylinePrePass.Stitch(inputs);
+
+        Assert.Equal(2, stitched.Count);
+    }
+
+    [Fact]
+    public void Stitch_DropsZeroAndSinglePointPolylines()
+    {
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new Vector[] { },
+            new[] { new Vector(0, 0) },
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+        };
+
+        var stitched = PolylinePrePass.Stitch(inputs);
+
+        Assert.Single(stitched);
+        Assert.Equal(2, stitched[0].Count);
+    }
+
+    [Fact]
+    public void Reorder_ReducesTotalPenUpTravelVsWorstCase()
+    {
+        // Three short polylines at (0,0), (10,0), (5,0). The greedy NN starting
+        // from origin should pick (0,0)→(5,0)→(10,0) (travels of 4 + 4 ≈ 8) over
+        // the worst-case input order (0,0)→(10,0)→(5,0) (travels 9 + 4 ≈ 13).
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(0, 0), new Vector(1, 0) },
+            new[] { new Vector(10, 0), new Vector(11, 0) },
+            new[] { new Vector(5, 0), new Vector(6, 0) },
+        };
+
+        var reordered = PolylinePrePass.Reorder(inputs);
+
+        Assert.Equal(3, reordered.Count);
+        var travelBefore = TotalPenUpTravel(inputs);
+        var travelAfter = TotalPenUpTravel(reordered);
+        Assert.True(travelAfter < travelBefore,
+            $"Expected reorder to reduce pen-up travel; before={travelBefore}, after={travelAfter}");
+    }
+
+    [Fact]
+    public void Reorder_ReversesPolylineIfTailIsCloser()
+    {
+        // Origin (0,0); a single polyline whose tail is much closer to origin
+        // than its head. Reorder should flip it.
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(10, 0), new Vector(0.5, 0) },
+        };
+
+        var reordered = PolylinePrePass.Reorder(inputs, allowReverse: true);
+
+        Assert.Single(reordered);
+        Assert.Equal(new Vector(0.5, 0), reordered[0][0]);
+        Assert.Equal(new Vector(10, 0), reordered[0][1]);
+    }
+
+    [Fact]
+    public void Reorder_ReverseDisabled_KeepsDirection()
+    {
+        var inputs = new List<IReadOnlyList<Vector>>
+        {
+            new[] { new Vector(10, 0), new Vector(0.5, 0) },
+        };
+
+        var reordered = PolylinePrePass.Reorder(inputs, allowReverse: false);
+
+        Assert.Single(reordered);
+        Assert.Equal(new Vector(10, 0), reordered[0][0]);
+        Assert.Equal(new Vector(0.5, 0), reordered[0][1]);
+    }
+
+    private static double TotalPenUpTravel(IEnumerable<IReadOnlyList<Vector>> polylines)
+    {
+        var total = 0.0;
+        Vector? last = null;
+        foreach (var p in polylines)
+        {
+            if (p == null || p.Count < 2) continue;
+            if (last.HasValue)
+            {
+                var dx = p[0].X - last.Value.X;
+                var dy = p[0].Y - last.Value.Y;
+                total += System.Math.Sqrt(dx * dx + dy * dy);
+            }
+            last = p[p.Count - 1];
+        }
+        return total;
+    }
+}

OpenNest.Tests/IO/ChrFontTests.cs

@@ -0,0 +1,180 @@
+using OpenNest.Geometry;
+using OpenNest.IO;
+
+namespace OpenNest.Tests.IO;
+
+public class ChrFontTests
+{
+    private ChrFont LoadFont()
+    {
+        var path = TestConfig.GetExistingPath("ChrFontPath");
+        Skip.If(path == null, "ChrFontPath not configured in test-config.json or file not found");
+        return ChrFont.Read(path);
+    }
+
+    [SkippableFact]
+    public void Read_ParsesFontName()
+    {
+        var font = LoadFont();
+        Assert.Equal("US BLOCK 1L", font.Name);
+    }
+
+    [SkippableFact]
+    public void Read_ParsesVersion()
+    {
+        var font = LoadFont();
+        Assert.StartsWith("C1.", font.Version);
+    }
+
+    [SkippableFact]
+    public void Read_HasAsciiGlyphs()
+    {
+        var font = LoadFont();
+        Assert.True(font.HasGlyph('A'));
+        Assert.True(font.HasGlyph('Z'));
+        Assert.True(font.HasGlyph('0'));
+        Assert.True(font.HasGlyph(' '));
+    }
+
+    [SkippableFact]
+    public void Read_HasExtendedGlyphs()
+    {
+        var font = LoadFont();
+        Assert.True(font.HasGlyph(0xC7)); // C-cedilla
+    }
+
+    [SkippableFact]
+    public void Glyph_L_ProducesLines()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('L');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        Assert.True(entities.Count >= 2, $"Expected at least 2 entities for 'L', got {entities.Count}");
+        Assert.All(entities, e => Assert.Equal(EntityType.Line, e.Type));
+    }
+
+    [SkippableFact]
+    public void Glyph_O_ProducesEntities()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('O');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        Assert.True(entities.Count > 0);
+    }
+
+    [SkippableFact]
+    public void RenderText_ProducesEntities()
+    {
+        var font = LoadFont();
+        var entities = font.RenderText("HELLO", 1.0, new Vector(0, 0));
+        Assert.True(entities.Count > 0, "RenderText should produce entities");
+    }
+
+    [SkippableFact]
+    public void RenderText_ScalesCorrectly()
+    {
+        var font = LoadFont();
+
+        var small = font.RenderText("A", 0.5, Vector.Zero);
+        var large = font.RenderText("A", 2.0, Vector.Zero);
+
+        var smallBox = small.GetBoundingBox();
+        var largeBox = large.GetBoundingBox();
+
+        Assert.True(largeBox.Width > smallBox.Width);
+        Assert.True(largeBox.Length > smallBox.Length);
+    }
+
+    [SkippableFact]
+    public void RenderText_AdvancesCursor()
+    {
+        var font = LoadFont();
+        var abEntities = font.RenderText("AB", 1.0, Vector.Zero);
+        var aEntities = font.RenderText("A", 1.0, Vector.Zero);
+
+        var abBox = abEntities.GetBoundingBox();
+        var aBox = aEntities.GetBoundingBox();
+
+        Assert.True(abBox.Length > aBox.Length * 1.5,
+            $"AB width ({abBox.Length:F1}) should be significantly wider than A width ({aBox.Length:F1})");
+    }
+
+    [SkippableFact]
+    public void RenderText_MatchesGravographReference()
+    {
+        var font = LoadFont();
+
+        var height = 5.08;
+        var centerX = 50.8;
+        var centerY = 34.925;
+
+        var entities = font.RenderText("Text", height, Vector.Zero);
+        var rawBox = entities.GetBoundingBox();
+        var shiftX = centerX - (rawBox.Left + rawBox.Right) / 2;
+        var shiftY = centerY - (rawBox.Top + rawBox.Bottom) / 2;
+        foreach (var e in entities)
+            e.Offset(new Vector(shiftX, shiftY));
+        Assert.True(entities.Count > 0, "Should produce entities for 'Text'");
+
+        var box = entities.GetBoundingBox();
+
+        var refLeft = 43.53;
+        var refRight = 58.07;
+        var refBottom = 32.39;
+        var refTop = 37.47;
+
+        var tolerance = 0.5;
+
+        Assert.True(System.Math.Abs(box.Left - refLeft) < tolerance,
+            $"Left: ours={box.Left:F2}, ref={refLeft:F2}, diff={System.Math.Abs(box.Left - refLeft):F2}");
+        Assert.True(System.Math.Abs(box.Right - refRight) < tolerance,
+            $"Right: ours={box.Right:F2}, ref={refRight:F2}, diff={System.Math.Abs(box.Right - refRight):F2}");
+        Assert.True(System.Math.Abs(box.Bottom - refBottom) < tolerance,
+            $"Bottom: ours={box.Bottom:F2}, ref={refBottom:F2}, diff={System.Math.Abs(box.Bottom - refBottom):F2}");
+        Assert.True(System.Math.Abs(box.Top - refTop) < tolerance,
+            $"Top: ours={box.Top:F2}, ref={refTop:F2}, diff={System.Math.Abs(box.Top - refTop):F2}");
+
+        var actualCapHeight = box.Top - box.Bottom;
+        Assert.True(System.Math.Abs(actualCapHeight - height) < 0.5,
+            $"Cap height: ours={actualCapHeight:F2}, expected={height:F2}");
+    }
+
+    [SkippableFact]
+    public void MeasureTextWidth_IsConsistent()
+    {
+        var font = LoadFont();
+        var height = 5.08;
+        var measuredWidth = font.MeasureTextWidth("Text", height);
+        var entities = font.RenderText("Text", height, Vector.Zero);
+        var box = entities.GetBoundingBox();
+
+        Assert.True(measuredWidth >= box.Length,
+            $"Measured={measuredWidth:F2} should be >= rendered={box.Length:F2}");
+        Assert.True(measuredWidth - box.Length < 2.0,
+            $"Measured={measuredWidth:F2}, rendered={box.Length:F2}, diff={measuredWidth - box.Length:F2}");
+    }
+
+    [SkippableFact]
+    public void Glyph_t_HasCurveAtBottom()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('t');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        var lines = entities.Cast<Line>().ToList();
+
+        Assert.True(lines.Count >= 10, $"Expected at least 10 entities for 't', got {lines.Count}");
+
+        var curveLines = lines.Skip(1).Take(lines.Count - 3).ToList();
+        Assert.True(curveLines.Count >= 14, $"Expected at least 14 curve segments, got {curveLines.Count}");
+
+        var lastCurve = curveLines[^1];
+        Assert.True(lastCurve.EndPoint.X > curveLines[0].StartPoint.X,
+            $"Curve should end to the right of where it starts: start X={curveLines[0].StartPoint.X:F1}, end X={lastCurve.EndPoint.X:F1}");
+    }
+}

OpenNest.Tests/IO/RemoveDuplicateArcsTests.cs

@@ -0,0 +1,96 @@
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.IO;
+
+public class RemoveDuplicateArcsTests
+{
+    [Fact]
+    public void RemoveDuplicateArcs_RemovesArcMatchingCircle_SameLayer()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var line = new Line(0, 0, 10, 0) { Layer = layer };
+        var entities = new List<Entity> { circle, arc, line };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+        Assert.Contains(circle, entities);
+        Assert.Contains(line, entities);
+        Assert.DoesNotContain(arc, entities);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcOnDifferentLayer()
+    {
+        var layer1 = new Layer("cut");
+        var layer2 = new Layer("etch");
+        var circle = new Circle(10, 10, 5) { Layer = layer1 };
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer2 };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+        Assert.Contains(arc, entities);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcWithDifferentRadius()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(10, 10, 3, 0, Angle.ToRadians(90)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcWithDifferentCenter()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(20, 20, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_NoCircles_NoChange()
+    {
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90));
+        var line = new Line(0, 0, 10, 0);
+        var entities = new List<Entity> { arc, line };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_MultipleArcsMatchOneCircle_RemovesAll()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc1 = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var arc2 = new Arc(10, 10, 5, Angle.ToRadians(90), Angle.ToRadians(180)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc1, arc2 };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Single(entities);
+        Assert.Contains(circle, entities);
+    }
+}

OpenNest.Tests/Math/FractionTests.cs

@@ -0,0 +1,46 @@
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.Math;
+
+public class FractionTests
+{
+    [Theory]
+    [InlineData("3/8", 0.375)]
+    [InlineData("1 3/4", 1.75)]
+    [InlineData("1-3/4", 1.75)]
+    [InlineData("1/2", 0.5)]
+    public void Parse_ValidFraction_ReturnsDouble(string input, double expected)
+    {
+        var result = Fraction.Parse(input);
+
+        Assert.Equal(expected, result, 8);
+    }
+
+    [Theory]
+    [InlineData("3/8", true)]
+    [InlineData("abc", false)]
+    [InlineData("1 3/4", true)]
+    public void IsValid_ReturnsExpected(string input, bool expected)
+    {
+        Assert.Equal(expected, Fraction.IsValid(input));
+    }
+
+    [Fact]
+    public void TryParse_InvalidInput_ReturnsFalse()
+    {
+        var result = Fraction.TryParse("abc", out var value);
+
+        Assert.False(result);
+        Assert.Equal(0, value);
+    }
+
+    [Fact]
+    public void ReplaceFractionsWithDecimals_ReplacesFractionInString()
+    {
+        var result = Fraction.ReplaceFractionsWithDecimals("length is 1 3/4 inches");
+
+        Assert.Contains("1.75", result);
+        Assert.DoesNotContain("3/4", result);
+    }
+}

OpenNest.Tests/OpenNest.Tests.csproj

@@ -14,6 +14,7 @@
     <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" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
   </ItemGroup>
 
   <ItemGroup>
@@ -27,6 +28,7 @@
     <ProjectReference Include="..\OpenNest.Engine\OpenNest.Engine.csproj" />
     <ProjectReference Include="..\OpenNest.IO\OpenNest.IO.csproj" />
     <ProjectReference Include="..\OpenNest.Posts.Cincinnati\OpenNest.Posts.Cincinnati.csproj" />
+    <ProjectReference Include="..\OpenNest.Posts.GravographIS\OpenNest.Posts.GravographIS.csproj" />
     <ProjectReference Include="..\OpenNest\OpenNest.csproj" />
   </ItemGroup>
 
@@ -37,6 +39,9 @@
     <Content Include="Splitting\TestData\**\*">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <Content Include="test-config.json" Condition="Exists('test-config.json')">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
   </ItemGroup>
 
 </Project>

OpenNest.Tests/TestHelpers.cs

@@ -1,8 +1,37 @@
+using System.Text.Json;
 using OpenNest.CNC;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests;
 
+internal static class TestConfig
+{
+    private static readonly Lazy<Dictionary<string, string>> Config = new(() =>
+    {
+        var dir = AppContext.BaseDirectory;
+        for (var i = 0; i < 6; i++)
+        {
+            var path = Path.Combine(dir, "test-config.json");
+            if (File.Exists(path))
+            {
+                var json = File.ReadAllText(path);
+                return JsonSerializer.Deserialize<Dictionary<string, string>>(json) ?? new();
+            }
+            dir = Path.GetDirectoryName(dir)!;
+        }
+        return new();
+    });
+
+    public static string? Get(string key) =>
+        Config.Value.TryGetValue(key, out var val) ? val : null;
+
+    public static string? GetExistingPath(string key)
+    {
+        var path = Get(key);
+        return path != null && File.Exists(path) ? path : null;
+    }
+}
+
 internal static class TestHelpers
 {
     public static Part MakePartAt(double x, double y, double size = 1)

OpenNest.Training/Program.cs

@@ -89,8 +89,10 @@ int RunDataCollection(string dir, string dbPath, string saveDir, double s, strin
         new Size(48, 24), new Size(120, 10)
     };
 
-    var dxfFiles = Directory.GetFiles(dir, "*.dxf", SearchOption.AllDirectories);
-    Console.WriteLine($"Found {dxfFiles.Length} DXF files");
+    var dxfFiles = Directory.GetFiles(dir, "*.dxf", SearchOption.AllDirectories)
+        .Concat(Directory.GetFiles(dir, "*.dwg", SearchOption.AllDirectories))
+        .ToArray();
+    Console.WriteLine($"Found {dxfFiles.Length} CAD files");
     var resolvedDb = dbPath.EndsWith(".db", StringComparison.OrdinalIgnoreCase) ? dbPath : dbPath + ".db";
     Console.WriteLine($"Database: {Path.GetFullPath(resolvedDb)}");
     Console.WriteLine($"Sheet sizes: {sheetSuite.Length} configurations");

OpenNest.sln

@@ -30,6 +30,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "PostProcessors", "PostProce
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Posts.Cincinnati", "OpenNest.Posts.Cincinnati\OpenNest.Posts.Cincinnati.csproj", "{FB1B2EB2-9D80-4499-BA93-B4E2F295A532}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Posts.GravographIS", "OpenNest.Posts.GravographIS\OpenNest.Posts.GravographIS.csproj", "{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}"
+EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenNest.Data", "OpenNest.Data\OpenNest.Data.csproj", "{A0B4B48E-1DF0-4DD3-B42C-B9B7779EA8B0}"
 EndProject
 Global
@@ -186,12 +188,25 @@ Global
 		{A0B4B48E-1DF0-4DD3-B42C-B9B7779EA8B0}.Release|x64.Build.0 = Release|Any CPU
 		{A0B4B48E-1DF0-4DD3-B42C-B9B7779EA8B0}.Release|x86.ActiveCfg = Release|Any CPU
 		{A0B4B48E-1DF0-4DD3-B42C-B9B7779EA8B0}.Release|x86.Build.0 = Release|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|x64.Build.0 = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Debug|x86.Build.0 = Debug|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40}.Release|x64.ActiveCfg = Release|Any CPU
+		{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
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{FB1B2EB2-9D80-4499-BA93-B4E2F295A532} = {4052CFAC-1F12-48BE-872D-F503C3B65D7E}
+		{3A6B8E7E-9B5F-4D2C-8AE3-2C9F5E3D1A40} = {4052CFAC-1F12-48BE-872D-F503C3B65D7E}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {86FE17B3-F764-40AE-BCAA-F26B470CA05C}

OpenNest/Actions/ActionCutOff.cs

@@ -16,15 +16,11 @@ namespace OpenNest.Actions
         private CutOffSettings settings;
         private CutOffAxis lockedAxis = CutOffAxis.Vertical;
         private Dictionary<Part, Entity> perimeterCache;
-        private readonly Timer debounceTimer;
-        private bool regeneratePending;
 
         public ActionCutOff(PlateView plateView)
             : base(plateView)
         {
             settings = plateView.CutOffSettings;
-            debounceTimer = new Timer { Interval = 16 };
-            debounceTimer.Tick += OnDebounce;
             ConnectEvents();
         }
 
@@ -40,8 +36,6 @@ namespace OpenNest.Actions
 
         public override void DisconnectEvents()
         {
-            debounceTimer.Stop();
-            debounceTimer.Dispose();
             plateView.MouseMove -= OnMouseMove;
             plateView.MouseDown -= OnMouseDown;
             plateView.KeyDown -= OnKeyDown;
@@ -58,18 +52,6 @@ namespace OpenNest.Actions
 
         private void OnMouseMove(object sender, MouseEventArgs e)
         {
-            regeneratePending = true;
-            debounceTimer.Start();
-        }
-
-        private void OnDebounce(object sender, System.EventArgs e)
-        {
-            debounceTimer.Stop();
-
-            if (!regeneratePending)
-                return;
-
-            regeneratePending = false;
             var pt = plateView.CurrentPoint;
             previewCutOff = new CutOff(pt, lockedAxis);
             previewCutOff.Regenerate(plateView.Plate, settings, perimeterCache);

OpenNest/ArchUnits.cs

@@ -1,4 +1,4 @@
-using OpenNest.IO.Bom;
+using OpenNest.Math;
 using System;
 using System.Drawing;
 using System.Text;

OpenNest/Controls/CadText.cs

@@ -0,0 +1,16 @@
+using System.Drawing;
+using OpenNest.Geometry;
+
+namespace OpenNest.Controls
+{
+    public class CadText
+    {
+        public Vector Position { get; set; }
+        public string Value { get; set; }
+        public double Height { get; set; }
+        public double Rotation { get; set; }
+        public string LayerName { get; set; }
+        public StringAlignment HAlign { get; set; }
+        public StringAlignment VAlign { get; set; }
+    }
+}

OpenNest/Controls/EntityView.cs

@@ -29,15 +29,18 @@ namespace OpenNest.Controls
         public List<Entity> SimplifierToleranceRight { get; set; }
         public List<Entity> OriginalEntities { get; set; }
         public bool ShowEntityLabels { get; set; }
+        public List<CadText> Texts { get; set; } = new List<CadText>();
 
         private readonly Pen gridPen = new Pen(Color.FromArgb(70, 70, 70));
         private readonly Dictionary<int, Pen> penCache = new Dictionary<int, Pen>();
         private readonly Font labelFont = new Font("Segoe UI", 7f);
         private readonly SolidBrush labelBrush = new SolidBrush(Color.FromArgb(220, 255, 255, 200));
         private readonly SolidBrush labelBackBrush = new SolidBrush(Color.FromArgb(33, 40, 48));
+        private readonly SolidBrush textBrush = new SolidBrush(Color.FromArgb(180, 200, 200, 200));
 
         public event EventHandler<Line> LinePicked;
         public event EventHandler PickCancelled;
+        public event EventHandler<CadText> TextConvertRequested;
 
         private bool isPickingBendLine;
         public bool IsPickingBendLine
@@ -74,6 +77,13 @@ namespace OpenNest.Controls
                 if (line != null)
                     LinePicked?.Invoke(this, line);
             }
+
+            if (e.Button == MouseButtons.Right)
+            {
+                var text = HitTestText(e.Location);
+                if (text != null)
+                    ShowTextContextMenu(text, e.Location);
+            }
         }
 
         protected override void OnPaint(PaintEventArgs e)
@@ -116,6 +126,8 @@ namespace OpenNest.Controls
                 DrawEntity(e.Graphics, entity, pen);
             }
 
+            DrawTexts(e.Graphics);
+
             if (ShowEntityLabels)
                 DrawEntityLabels(e.Graphics);
 
@@ -324,6 +336,41 @@ namespace OpenNest.Controls
             return bestLine;
         }
 
+        private CadText HitTestText(Point controlPoint)
+        {
+            if (Texts == null || Texts.Count == 0)
+                return null;
+
+            var worldPoint = PointControlToWorld(controlPoint);
+            var tolerance = LengthGuiToWorld(8);
+
+            foreach (var text in Texts)
+            {
+                if (string.IsNullOrEmpty(text.Value))
+                    continue;
+
+                var estimatedWidth = text.Height * text.Value.Length * 0.6;
+                var minX = text.Position.X - tolerance;
+                var maxX = text.Position.X + estimatedWidth + tolerance;
+                var minY = text.Position.Y - tolerance;
+                var maxY = text.Position.Y + text.Height + tolerance;
+
+                if (worldPoint.X >= minX && worldPoint.X <= maxX &&
+                    worldPoint.Y >= minY && worldPoint.Y <= maxY)
+                    return text;
+            }
+
+            return null;
+        }
+
+        private void ShowTextContextMenu(CadText text, Point location)
+        {
+            var menu = new ContextMenuStrip();
+            var item = menu.Items.Add($"Convert \"{text.Value}\" to Geometry");
+            item.Click += (s, e) => TextConvertRequested?.Invoke(this, text);
+            menu.Show(this, location);
+        }
+
         private void DrawEntityLabels(Graphics g)
         {
             for (var i = 0; i < Entities.Count; i++)
@@ -408,6 +455,7 @@ namespace OpenNest.Controls
                 labelFont.Dispose();
                 labelBrush.Dispose();
                 labelBackBrush.Dispose();
+                textBrush.Dispose();
             }
             base.Dispose(disposing);
         }
@@ -474,6 +522,34 @@ namespace OpenNest.Controls
                 diameter);
         }
 
+        private void DrawTexts(Graphics g)
+        {
+            if (Texts == null || Texts.Count == 0)
+                return;
+
+            using var sf = new StringFormat();
+
+            foreach (var text in Texts)
+            {
+                var pos = PointWorldToGraph(text.Position);
+                var fontSize = LengthWorldToGui(text.Height);
+                if (fontSize < 2f) continue;
+
+                var state = g.Save();
+                g.TranslateTransform(pos.X, pos.Y);
+
+                if (text.Rotation != 0)
+                    g.RotateTransform((float)OpenNest.Math.Angle.ToDegrees(text.Rotation));
+
+                sf.Alignment = text.HAlign;
+                sf.LineAlignment = text.VAlign;
+
+                using var font = new Font("Segoe UI", fontSize, GraphicsUnit.Pixel);
+                g.DrawString(text.Value, font, textBrush, 0, 0, sf);
+                g.Restore(state);
+            }
+        }
+
         private void DrawPoint(Graphics g, Vector pt, Pen pen)
         {
             var pt1 = PointWorldToGraph(pt);

OpenNest/Controls/FileListControl.cs

@@ -22,6 +22,7 @@ namespace OpenNest.Controls
         public HashSet<Guid> SuppressedEntityIds { get; set; }
         public Box Bounds { get; set; }
         public int EntityCount { get; set; }
+        public List<CadText> Texts { get; set; } = new();
     }
 
     public class FileListControl : Control

OpenNest/Forms/BestFitViewerForm.cs

@@ -45,6 +45,7 @@ namespace OpenNest.Forms
 
         public BestFitResult SelectedResult { get; private set; }
         public Drawing SelectedDrawing => activeDrawing;
+        public List<Part> SelectedParts { get; private set; }
 
         public BestFitViewerForm(DrawingCollection drawings, Plate plate, Units units = Units.Inches)
         {
@@ -318,12 +319,12 @@ namespace OpenNest.Forms
             var cell = new BestFitCell(colorScheme);
             cell.PartColor = partColor;
             cell.Dock = DockStyle.Fill;
+
+            var parts = result.BuildCanonicalParts();
             cell.Plate.Size = new Geometry.Size(
                 result.BoundingHeight,
                 result.BoundingWidth);
 
-            var parts = result.BuildParts(drawing);
-
             foreach (var part in parts)
                 cell.Plate.Parts.Add(part);
 
@@ -332,6 +333,7 @@ namespace OpenNest.Forms
             cell.DoubleClick += (sender, e) =>
             {
                 SelectedResult = result;
+                SelectedParts = result.BuildSourceParts(drawing);
                 DialogResult = DialogResult.OK;
                 Close();
             };

OpenNest/Forms/BomImportForm.cs

@@ -165,7 +165,8 @@ namespace OpenNest.Forms
                 else
                 {
                     var lookupName = item.FileName;
-                    if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase))
+                    if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)
+                        || lookupName.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase))
                         lookupName = Path.GetFileNameWithoutExtension(lookupName);
 
                     if (matchedPaths.TryGetValue(lookupName, out var dxfPath))

OpenNest/Forms/CadConverterForm.cs

@@ -45,6 +45,7 @@ namespace OpenNest.Forms
             filterPanel.AddBendLineClicked += OnAddBendLineClicked;
             entityView1.LinePicked += OnLinePicked;
             entityView1.PickCancelled += OnPickCancelled;
+            entityView1.TextConvertRequested += OnTextConvertRequested;
             btnSplit.Click += OnSplitClicked;
             numQuantity.ValueChanged += OnQuantityChanged;
             txtCustomer.TextChanged += OnCustomerChanged;
@@ -92,7 +93,8 @@ namespace OpenNest.Forms
                     Customer = string.Empty,
                     Bends = result.Bends,
                     Bounds = result.Bounds,
-                    EntityCount = result.Entities.Count
+                    EntityCount = result.Entities.Count,
+                    Texts = ExtractTexts(result.Document),
                 };
 
                 if (InvokeRequired)
@@ -152,6 +154,7 @@ namespace OpenNest.Forms
             entityView1.Entities.Clear();
             entityView1.Entities.AddRange(item.Entities);
             entityView1.Bends = item.Bends ?? new List<Bend>();
+            entityView1.Texts = item.Texts ?? new List<CadText>();
 
             item.Entities.ForEach(e => e.IsVisible = true);
             if (item.Entities.Any(e => e.Layer != null))
@@ -461,6 +464,115 @@ namespace OpenNest.Forms
             filterPanel.SetPickMode(false);
         }
 
+        private void OnTextConvertRequested(object sender, Controls.CadText text)
+        {
+            var item = CurrentItem;
+            if (item == null) return;
+
+            var font = LoadChrFont();
+            if (font == null) return;
+
+            var layer = new Geometry.Layer("ENGRAVE")
+            {
+                Color = System.Drawing.Color.Cyan,
+                IsVisible = true,
+            };
+
+            var entities = font.RenderText(text.Value, text.Height, Geometry.Vector.Zero, layer);
+            if (entities.Count > 0)
+            {
+                var box = entities.GetBoundingBox();
+                var shiftX = text.HAlign switch
+                {
+                    System.Drawing.StringAlignment.Center => text.Position.X - (box.Left + box.Right) / 2,
+                    System.Drawing.StringAlignment.Far => text.Position.X - box.Right,
+                    _ => text.Position.X - box.Left,
+                };
+                var shiftY = text.VAlign switch
+                {
+                    System.Drawing.StringAlignment.Center => text.Position.Y - (box.Top + box.Bottom) / 2,
+                    System.Drawing.StringAlignment.Near => text.Position.Y - box.Top,
+                    _ => text.Position.Y - box.Bottom,
+                };
+                var shift = new Geometry.Vector(shiftX, shiftY);
+                foreach (var e in entities)
+                    e.Offset(shift);
+            }
+            if (entities.Count == 0)
+            {
+                MessageBox.Show($"No geometry produced for \"{text.Value}\".", "Convert Text",
+                    MessageBoxButtons.OK, MessageBoxIcon.Information);
+                return;
+            }
+
+            item.Entities.AddRange(entities);
+            item.Texts.Remove(text);
+            item.EntityCount = item.Entities.Count;
+            item.Bounds = item.Entities.GetBoundingBox();
+
+            entityView1.Entities.Clear();
+            entityView1.Entities.AddRange(item.Entities);
+            entityView1.Texts = item.Texts;
+            filterPanel.LoadItem(item.Entities, item.Bends);
+            entityView1.Invalidate();
+            staleProgram = true;
+            lblEntityCount.Text = $"{item.EntityCount} entities";
+        }
+
+        private ChrFont cachedChrFont;
+        private string cachedChrFontPath;
+
+        private ChrFont LoadChrFont()
+        {
+            if (cachedChrFont != null)
+                return cachedChrFont;
+
+            // Look for .CHR files next to the app, then prompt
+            var appDir = System.IO.Path.GetDirectoryName(Application.ExecutablePath);
+            var candidates = Directory.GetFiles(appDir, "*.CHR", SearchOption.TopDirectoryOnly);
+
+            string fontPath;
+            if (candidates.Length == 1)
+            {
+                fontPath = candidates[0];
+            }
+            else if (candidates.Length > 1)
+            {
+                fontPath = PromptForChrFile(appDir);
+            }
+            else
+            {
+                fontPath = PromptForChrFile(null);
+            }
+
+            if (fontPath == null)
+                return null;
+
+            try
+            {
+                cachedChrFont = ChrFont.Read(fontPath);
+                cachedChrFontPath = fontPath;
+                return cachedChrFont;
+            }
+            catch (Exception ex)
+            {
+                MessageBox.Show($"Error loading font: {ex.Message}", "Font Error",
+                    MessageBoxButtons.OK, MessageBoxIcon.Error);
+                return null;
+            }
+        }
+
+        private static string PromptForChrFile(string initialDir)
+        {
+            using var dlg = new OpenFileDialog
+            {
+                Title = "Select Engraving Font (.CHR)",
+                Filter = "Gravograph Font (*.CHR)|*.CHR",
+                InitialDirectory = initialDir ?? "",
+            };
+            return dlg.ShowDialog() == DialogResult.OK ? dlg.FileName : null;
+        }
+
         private void OnDragEnter(object sender, DragEventArgs e)
         {
             if (e.Data.GetDataPresent(DataFormats.FileDrop))
@@ -473,7 +585,8 @@ namespace OpenNest.Forms
             {
                 var files = (string[])e.Data.GetData(DataFormats.FileDrop);
                 var dxfFiles = files.Where(f =>
-                    f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)).ToArray();
+                    f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase) ||
+                    f.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase)).ToArray();
                 if (dxfFiles.Length > 0)
                     AddFiles(dxfFiles);
             }
@@ -803,6 +916,110 @@ namespace OpenNest.Forms
 
         #endregion
 
+        private static List<CadText> ExtractTexts(ACadSharp.CadDocument doc)
+        {
+            var texts = new List<CadText>();
+            if (doc == null) return texts;
+
+            foreach (var entity in doc.Entities)
+            {
+                switch (entity)
+                {
+                    case ACadSharp.Entities.MText mtext:
+                        var (mh, mv) = MapAttachmentPoint(mtext.AttachmentPoint);
+                        texts.Add(new CadText
+                        {
+                            Position = new Vector(mtext.InsertPoint.X, mtext.InsertPoint.Y),
+                            Value = ReplaceControlCodes(StripMTextFormatting(mtext.Value)),
+                            Height = mtext.Height,
+                            Rotation = mtext.Rotation,
+                            LayerName = mtext.Layer?.Name,
+                            HAlign = mh,
+                            VAlign = mv,
+                        });
+                        break;
+
+                    case ACadSharp.Entities.TextEntity text:
+                        var useAlignment = text.HorizontalAlignment != 0
+                            || text.VerticalAlignment != 0;
+                        var pt = useAlignment ? text.AlignmentPoint : text.InsertPoint;
+                        var ha = text.HorizontalAlignment switch
+                        {
+                            ACadSharp.Entities.TextHorizontalAlignment.Center => System.Drawing.StringAlignment.Center,
+                            ACadSharp.Entities.TextHorizontalAlignment.Right => System.Drawing.StringAlignment.Far,
+                            _ => System.Drawing.StringAlignment.Near,
+                        };
+                        var va = text.VerticalAlignment switch
+                        {
+                            ACadSharp.Entities.TextVerticalAlignmentType.Middle => System.Drawing.StringAlignment.Center,
+                            ACadSharp.Entities.TextVerticalAlignmentType.Top => System.Drawing.StringAlignment.Near,
+                            ACadSharp.Entities.TextVerticalAlignmentType.Bottom => System.Drawing.StringAlignment.Far,
+                            _ => System.Drawing.StringAlignment.Far,
+                        };
+                        texts.Add(new CadText
+                        {
+                            Position = new Vector(pt.X, pt.Y),
+                            Value = ReplaceControlCodes(text.Value),
+                            Height = text.Height,
+                            Rotation = text.Rotation,
+                            LayerName = text.Layer?.Name,
+                            HAlign = ha,
+                            VAlign = va,
+                        });
+                        break;
+                }
+            }
+
+            return texts;
+        }
+
+        private static (System.Drawing.StringAlignment h, System.Drawing.StringAlignment v) MapAttachmentPoint(
+            ACadSharp.Entities.AttachmentPointType apt)
+        {
+            var h = apt switch
+            {
+                ACadSharp.Entities.AttachmentPointType.TopCenter
+                    or ACadSharp.Entities.AttachmentPointType.MiddleCenter
+                    or ACadSharp.Entities.AttachmentPointType.BottomCenter => System.Drawing.StringAlignment.Center,
+                ACadSharp.Entities.AttachmentPointType.TopRight
+                    or ACadSharp.Entities.AttachmentPointType.MiddleRight
+                    or ACadSharp.Entities.AttachmentPointType.BottomRight => System.Drawing.StringAlignment.Far,
+                _ => System.Drawing.StringAlignment.Near,
+            };
+            var v = apt switch
+            {
+                ACadSharp.Entities.AttachmentPointType.MiddleLeft
+                    or ACadSharp.Entities.AttachmentPointType.MiddleCenter
+                    or ACadSharp.Entities.AttachmentPointType.MiddleRight => System.Drawing.StringAlignment.Center,
+                ACadSharp.Entities.AttachmentPointType.BottomLeft
+                    or ACadSharp.Entities.AttachmentPointType.BottomCenter
+                    or ACadSharp.Entities.AttachmentPointType.BottomRight => System.Drawing.StringAlignment.Far,
+                _ => System.Drawing.StringAlignment.Near,
+            };
+            return (h, v);
+        }
+
+        private static string StripMTextFormatting(string text)
+        {
+            if (string.IsNullOrEmpty(text)) return text;
+            var result = System.Text.RegularExpressions.Regex.Replace(text, @"\\[A-Za-z][^;]*;", "");
+            result = result.Replace("{", "").Replace("}", "");
+            return result.Trim();
+        }
+
+        private static string ReplaceControlCodes(string text)
+        {
+            if (string.IsNullOrEmpty(text)) return text;
+            return text
+                .Replace("%%p", "±")
+                .Replace("%%P", "±")
+                .Replace("%%d", "°")
+                .Replace("%%D", "°")
+                .Replace("%%c", "⌀")
+                .Replace("%%C", "⌀")
+                .Replace("%%%", "%");
+        }
+
         private void filterPanel_Paint(object sender, PaintEventArgs e)
         {
 

OpenNest/Forms/EditNestForm.cs

@@ -329,7 +329,7 @@ namespace OpenNest.Forms
         {
             var dlg = new OpenFileDialog();
             dlg.Multiselect = true;
-            dlg.Filter = "DXF Files (*.dxf) | *.dxf";
+            dlg.Filter = "CAD Files (*.dxf;*.dwg)|*.dxf;*.dwg|DXF Files (*.dxf)|*.dxf|DWG Files (*.dwg)|*.dwg";
 
             if (dlg.ShowDialog() != DialogResult.OK)
                 return;
@@ -346,7 +346,6 @@ namespace OpenNest.Forms
             drawings.ForEach(d => Nest.Drawings.Add(d));
 
             UpdateDrawingList();
-            tabControl1.SelectedIndex = 1;
         }
 
         public bool Export()

OpenNest/Forms/MainForm.cs

@@ -686,7 +686,8 @@ namespace OpenNest.Forms
             {
                 if (form.ShowDialog(this) == DialogResult.OK && form.SelectedResult != null)
                 {
-                    var parts = form.SelectedResult.BuildParts(form.SelectedDrawing);
+                    var parts = form.SelectedParts
+                        ?? form.SelectedResult.BuildSourceParts(form.SelectedDrawing);
                     activeForm.PlateView.SetAction(typeof(ActionClone), parts);
                 }
             }

OpenNest/GraphicsHelper.cs

@@ -138,9 +138,20 @@ namespace OpenNest
                         break;
 
                     case CodeType.RapidMove:
+                        {
+                            var rapid = (RapidMove)code;
+                            var endpt = rapid.EndPoint;
+                            if (mode == Mode.Incremental)
+                                endpt += curpos;
+                            var dx = endpt.X - curpos.X;
+                            var dy = endpt.Y - curpos.Y;
+                            if (dx * dx + dy * dy > 0.001 * 0.001)
+                            {
                                 cutPath.StartFigure();
                                 leadPath.StartFigure();
-                        AddLine(cutPath, (RapidMove)code, mode, ref curpos);
+                            }
+                            curpos = endpt;
+                        }
                         break;
 
                     case CodeType.SubProgramCall:
@@ -300,8 +311,17 @@ namespace OpenNest
                         break;
 
                     case CodeType.RapidMove:
+                        {
+                            var rapid = (RapidMove)code;
+                            var endpt = rapid.EndPoint;
+                            if (mode == Mode.Incremental)
+                                endpt += curpos;
+                            var dx = endpt.X - curpos.X;
+                            var dy = endpt.Y - curpos.Y;
+                            if (dx * dx + dy * dy > 0.001 * 0.001)
                                 Flush();
-                        AddLine(path, (RapidMove)code, mode, ref curpos);
+                            curpos = endpt;
+                        }
                         break;
 
                     case CodeType.SubProgramCall:

tools/StreamGravographJob/Program.cs

@@ -0,0 +1,266 @@
+using System;
+using System.ComponentModel;
+using System.Diagnostics;
+using System.IO;
+using System.IO.Ports;
+using System.Runtime.InteropServices;
+using System.Threading;
+using Microsoft.Win32.SafeHandles;
+
+if (args.Length < 2)
+{
+    Console.Error.WriteLine("Usage:");
+    Console.Error.WriteLine("  StreamGravographJob <file.prn>   <COMx> [chunk=256] [flow=rtscts|xonxoff|none]");
+    Console.Error.WriteLine("  StreamGravographJob --gen <name> <outfile.prn>      # name: testA | testB | miniB | miniSquare");
+    Console.Error.WriteLine("  StreamGravographJob --inspect-nest <file.nest>");
+    Console.Error.WriteLine("  StreamGravographJob --from-nest    <file.nest> <outfile.prn>");
+    return 2;
+}
+
+// Inspect a .nest file: extract polylines via the post-processor pipeline and
+// report dimensions / bounding box / pen-up travel — no bytes written.
+if (args[0] == "--inspect-nest")
+{
+    if (args.Length < 2) { Console.Error.WriteLine("--inspect-nest requires <file.nest>"); return 2; }
+    var nestPath = args[1];
+    if (!File.Exists(nestPath)) { Console.Error.WriteLine($"Not found: {nestPath}"); return 3; }
+
+    using var fs = new FileStream(nestPath, FileMode.Open, FileAccess.Read);
+    var reader = new OpenNest.IO.NestReader(fs);
+    var nest = reader.Read();
+
+    Console.WriteLine($"Nest: {nest.Name}");
+    Console.WriteLine($"Units: {nest.Units}");
+    Console.WriteLine($"Plates: {nest.Plates.Count}");
+    var plateIdx = 0;
+    foreach (var plate in nest.Plates)
+    {
+        plateIdx++;
+        Console.WriteLine($"  Plate {plateIdx}: size={plate.Size.Length} x {plate.Size.Width}, quadrant={plate.Quadrant}, parts={plate.Parts.Count}");
+    }
+
+    var polylines = new OpenNest.Posts.GravographIS.NestPolylineExtractor().Extract(nest);
+    if (polylines.Count == 0)
+    {
+        Console.WriteLine("No polylines extracted.");
+        return 0;
+    }
+
+    double minX = double.PositiveInfinity, minY = double.PositiveInfinity;
+    double maxX = double.NegativeInfinity, maxY = double.NegativeInfinity;
+    int totalPts = 0;
+    foreach (var p in polylines)
+    {
+        foreach (var v in p)
+        {
+            if (v.X < minX) minX = v.X;
+            if (v.X > maxX) maxX = v.X;
+            if (v.Y < minY) minY = v.Y;
+            if (v.Y > maxY) maxY = v.Y;
+        }
+        totalPts += p.Count;
+    }
+    Console.WriteLine($"Polylines: {polylines.Count}, total points: {totalPts}");
+    Console.WriteLine($"Bounding box (inches): X ∈ [{minX:F3}, {maxX:F3}]  Y ∈ [{minY:F3}, {maxY:F3}]");
+    Console.WriteLine($"Extents: {maxX - minX:F3}\" × {maxY - minY:F3}\"");
+
+    // After running the pre-pass (stitch + reorder from origin) — what the writer will actually consume.
+    var prepared = OpenNest.Posts.GravographIS.PolylinePrePass.Prepare(polylines);
+    Console.WriteLine($"After stitch+reorder: {prepared.Count} polylines");
+
+    Console.WriteLine();
+    Console.WriteLine("--- Vertex dump (prepared, upper-left origin, with segment deltas) ---");
+    var pi = 0;
+    foreach (var poly in prepared)
+    {
+        pi++;
+        Console.WriteLine($"Polyline {pi}: {poly.Count} points");
+        var cumX = 0.0; var cumY = 0.0;
+        for (var i = 0; i < poly.Count; i++)
+        {
+            var v = poly[i];
+            if (i == 0)
+            {
+                Console.WriteLine($"  [{i}] ({v.X,7:F3}, {v.Y,7:F3})   first DR travel from upper-left origin=({v.X,+7:F3}, {v.Y,+7:F3})");
+            }
+            else
+            {
+                var dx = v.X - poly[i - 1].X;
+                var dy = v.Y - poly[i - 1].Y;
+                cumX += dx;
+                cumY += dy;
+                Console.WriteLine($"  [{i}] ({v.X,7:F3}, {v.Y,7:F3})   Δ=({dx,+7:F3}, {dy,+7:F3})   cum from origin=({cumX,+7:F3}, {cumY,+7:F3})");
+            }
+        }
+    }
+    return 0;
+}
+
+// Convert a .nest file to a .prn job via the full post-processor pipeline.
+if (args[0] == "--from-nest")
+{
+    if (args.Length < 3) { Console.Error.WriteLine("--from-nest requires <file.nest> <outfile.prn>"); return 2; }
+    var nestPath = args[1];
+    var outFile = args[2];
+    if (!File.Exists(nestPath)) { Console.Error.WriteLine($"Not found: {nestPath}"); return 3; }
+
+    using var fs = new FileStream(nestPath, FileMode.Open, FileAccess.Read);
+    var nest = new OpenNest.IO.NestReader(fs).Read();
+    var post = new OpenNest.Posts.GravographIS.GravographISPostProcessor();
+    post.Post(nest, outFile);
+
+    var size = new FileInfo(outFile).Length;
+    Console.WriteLine($"Wrote {size} bytes → {outFile}");
+    return 0;
+}
+
+// Generator mode: run the live writer to produce a captured-test file on disk.
+if (args[0] == "--gen")
+{
+    if (args.Length < 3) { Console.Error.WriteLine("--gen requires <name> <outfile>"); return 2; }
+    var preset = args[1];
+    var outFile = args[2];
+    var polylines = preset.ToLowerInvariant() switch
+    {
+        "testa" => new System.Collections.Generic.List<System.Collections.Generic.IReadOnlyList<OpenNest.Geometry.Vector>>
+        {
+            new[] { new OpenNest.Geometry.Vector(1, 1), new OpenNest.Geometry.Vector(1, 3) },
+        },
+        "testb" => new System.Collections.Generic.List<System.Collections.Generic.IReadOnlyList<OpenNest.Geometry.Vector>>
+        {
+            new[] { new OpenNest.Geometry.Vector(1, 1), new OpenNest.Geometry.Vector(1, 3) },
+            new[] { new OpenNest.Geometry.Vector(4, 1), new OpenNest.Geometry.Vector(4, 3) },
+            new[] { new OpenNest.Geometry.Vector(4, 5), new OpenNest.Geometry.Vector(4, 7) },
+            new[] { new OpenNest.Geometry.Vector(1, 5), new OpenNest.Geometry.Vector(1, 7) },
+        },
+        // Same 4-polyline topology as testB (vertical lines + diagonal PU travels between them),
+        // shrunk to a 0.5" × 1.5" footprint so it stays right near the operator-set work origin.
+        "minib" => new System.Collections.Generic.List<System.Collections.Generic.IReadOnlyList<OpenNest.Geometry.Vector>>
+        {
+            new[] { new OpenNest.Geometry.Vector(0,   0),   new OpenNest.Geometry.Vector(0,   0.5) },
+            new[] { new OpenNest.Geometry.Vector(0.5, 0),   new OpenNest.Geometry.Vector(0.5, 0.5) },
+            new[] { new OpenNest.Geometry.Vector(0.5, 1),   new OpenNest.Geometry.Vector(0.5, 1.5) },
+            new[] { new OpenNest.Geometry.Vector(0,   1),   new OpenNest.Geometry.Vector(0,   1.5) },
+        },
+        // Closed 0.5" square as a SINGLE polyline of 5 points → 4-segment PD packet.
+        // Exercises multi-segment PD (one FF FD 50 44 00 00 followed by 4 records,
+        // no intermediate lifts) and bi-directional motion (X+, Y+, X−, Y−).
+        // Returns the head to its starting point so no manual jog needed after.
+        "minisquare" => new System.Collections.Generic.List<System.Collections.Generic.IReadOnlyList<OpenNest.Geometry.Vector>>
+        {
+            new[]
+            {
+                new OpenNest.Geometry.Vector(0,    0),
+                new OpenNest.Geometry.Vector(0.5,  0),
+                new OpenNest.Geometry.Vector(0.5,  0.5),
+                new OpenNest.Geometry.Vector(0,    0.5),
+                new OpenNest.Geometry.Vector(0,    0),
+            },
+        },
+        _ => throw new ArgumentException($"Unknown preset '{preset}' (try testA, testB, miniB, or miniSquare)."),
+    };
+
+    using var outFs = new FileStream(outFile, FileMode.Create, FileAccess.Write);
+    new OpenNest.Posts.GravographIS.GravographISWriter().Write(polylines, outFs);
+    Console.WriteLine($"Wrote {new FileInfo(outFile).Length} bytes via live writer → {outFile}");
+    return 0;
+}
+
+var file = args[0];
+var portName = args[1];
+var chunk = args.Length > 2 ? int.Parse(args[2]) : 256;
+var flowArg = args.Length > 3 ? args[3] : "rtscts";
+
+var handshake = flowArg.ToLowerInvariant() switch
+{
+    "rtscts" or "rts" or "cts" => Handshake.RequestToSend,
+    "xonxoff" or "xon" or "xoff" => Handshake.XOnXOff,
+    "none" => Handshake.None,
+    _ => throw new ArgumentException($"Unknown flow control '{flowArg}'."),
+};
+
+if (!File.Exists(file))
+{
+    Console.Error.WriteLine($"File not found: {file}");
+    return 3;
+}
+
+var bytes = File.ReadAllBytes(file);
+Console.WriteLine($"File: {file}");
+Console.WriteLine($"Size: {bytes.Length} bytes");
+Console.WriteLine($"Header: {BitConverter.ToString(bytes, 0, Math.Min(7, bytes.Length)).Replace('-', ' ')}");
+
+var ports = SerialPort.GetPortNames();
+Array.Sort(ports);
+Console.WriteLine($"Available COM ports: {string.Join(", ", ports)}");
+if (Array.IndexOf(ports, portName) < 0)
+{
+    Console.Error.WriteLine($"{portName} not in available ports.");
+    return 4;
+}
+
+using var port = new SerialPort(portName, 9600, Parity.None, 8, StopBits.One)
+{
+    Handshake = handshake,
+    WriteTimeout = 30000,
+    ReadTimeout = 30000,
+    WriteBufferSize = 4096,
+    DtrEnable = true,
+};
+
+// Probe with the same CreateFile flags SerialStream uses, in this same process,
+// so we can tell SerialStream-specific failures apart from process-level access denials.
+{
+    const uint GENERIC_RW = 0x80000000u | 0x40000000u;
+    const uint OPEN_EXISTING = 3;
+    const uint FILE_FLAG_OVERLAPPED = 0x40000000u;
+    var devName = @"\\.\" + portName;
+    var handle = NativeMethods.CreateFileW(devName, GENERIC_RW, 0, IntPtr.Zero, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, IntPtr.Zero);
+    var err = Marshal.GetLastWin32Error();
+    if (handle.IsInvalid)
+    {
+        Console.WriteLine($"CreateFile(\"{devName}\", overlapped, exclusive) FAILED: win32={err} ({new Win32Exception(err).Message})");
+    }
+    else
+    {
+        Console.WriteLine($"CreateFile(\"{devName}\", overlapped, exclusive) OK — closing.");
+        handle.Close();
+    }
+}
+
+Console.WriteLine($"Opening {portName} 9600 8N1 handshake={handshake}...");
+port.Open();
+Console.WriteLine("Opened.");
+
+var sw = Stopwatch.StartNew();
+try
+{
+    for (var i = 0; i < bytes.Length; i += chunk)
+    {
+        var n = Math.Min(chunk, bytes.Length - i);
+        port.Write(bytes, i, n);
+    }
+    try { port.BaseStream.Flush(); } catch { /* advisory */ }
+    Thread.Sleep(500);
+}
+finally
+{
+    sw.Stop();
+    port.Close();
+}
+
+Console.WriteLine($"Sent {bytes.Length} bytes in {sw.ElapsedMilliseconds} ms. Port closed.");
+return 0;
+
+internal static class NativeMethods
+{
+    [DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode, EntryPoint = "CreateFileW")]
+    internal static extern SafeFileHandle CreateFileW(
+        string lpFileName,
+        uint dwDesiredAccess,
+        uint dwShareMode,
+        IntPtr lpSecurityAttributes,
+        uint dwCreationDisposition,
+        uint dwFlagsAndAttributes,
+        IntPtr hTemplateFile);
+}

tools/StreamGravographJob/StreamGravographJob.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RootNamespace>OpenNest.Tools.StreamGravographJob</RootNamespace>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.IO.Ports" Version="8.0.0" />
+    <ProjectReference Include="..\..\OpenNest.Posts.GravographIS\OpenNest.Posts.GravographIS.csproj" />
+    <ProjectReference Include="..\..\OpenNest.IO\OpenNest.IO.csproj" />
+  </ItemGroup>
+</Project>