fix(core): keep cut-offs in their cut sequence through regenerate and save

A cut-off's place in Plate.Parts is its cut sequence number, but
RegenerateCutOffs removed every cut-off part and appended it again, so
any part drag, fill or cut-off move sent the cut-offs to the end. The
nest file didn't store the position either, so reopening did the same.

RegenerateCutOffs now puts each cut-off back at its previous index (new
cut-offs go at the end), and CutOffDto.Sequence saves the index. Older
files without it load the cut-offs at the end, as before.

AGENTS.md

@@ -154,7 +154,7 @@ Keep vendor programming manuals and full-text extracts outside source control un
 - `Compactor` performs post-fill gravity compaction — after filling, parts are pushed toward a plate edge using directional distance calculations to close gaps between irregular shapes.
 - `FillScore` uses lexicographic comparison (count > utilization > compactness) to rank fill results consistently across all fill strategies. After its null/empty guards, `DefaultFillComparer` decides unequal counts without scoring; equal counts still use scores, and exact ties retain the current layout. `FillHelpers.FillPattern` computes eager scores only when no custom comparer is supplied; custom comparers remain authoritative and may perform their own scoring.
 - **Extents column pitch**: for finite valid geometry, finite pair height, and finite nonnegative spacing, `FillExtents.BuildColumn` uses `pair.Bbox.Width + partSpacing` directly. The old vertical slide calculation clamps to the same pitch, so it need not prepare boundaries or temporary test clones. Negative/nonfinite spacing or nonfinite pair height retains the legacy calculation: public/interactive callers do not all validate spacing. Do not remove `BuildPair` boundary preparation or the adjusted-column overlap fallback, or turn this shortcut into a geometry/validation policy change.
-- **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).
+- **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 each at its previous index in `Plate.Parts` (its cut sequence number; new cut-offs go at the end). 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; `CutOffDto.Sequence` restores each one's place in the cut sequence). Posts must follow `Plate.Parts` order for cut-offs too, not move them to the end.
 - **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). MCP, API, and Training projects use `ImportDrawing` for headless conversion. The console uses `Import` followed by `BuildDrawing` so it can report bend-repair outcomes. 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` and the saved `SCRIBE` layer (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.Core/Plate.cs

@@ -94,18 +94,40 @@ namespace OpenNest
         /// <summary>
         /// Regenerates all cut-off drawings and materializes them as parts.
         /// Existing cut-off parts are removed first, then each cut-off is
-        /// regenerated and added back if it produces any geometry.
+        /// regenerated and put back at the same place in the cut sequence
+        /// (<see cref="Parts"/> order). New cut-offs are added at the end.
         /// </summary>
         public void RegenerateCutOffs(CutOffSettings settings)
         {
-            // Remove existing cut-off parts
+            // Remember each cut-off's place in the cut sequence, so a part drag
+            // or cut-off move doesn't send it to the end of the sequence.
+            var sequence = new Dictionary<CutOff, int>();
+
             for (var i = Parts.Count - 1; i >= 0; i--)
             {
-                if (Parts[i].BaseDrawing.IsCutOff)
+                if (!Parts[i].BaseDrawing.IsCutOff)
-                    Parts.RemoveAt(i);
+                    continue;
+
+                var cutoff = CutOffs.FirstOrDefault(c => ReferenceEquals(c.Drawing, Parts[i].BaseDrawing));
+                if (cutoff != null)
+                    sequence[cutoff] = i;
+
+                Parts.RemoveAt(i);
             }
 
+            RegenerateCutOffs(settings, sequence);
+        }
+
+        /// <summary>
+        /// Regenerates all cut-off drawings and materializes them as parts, placing
+        /// each cut-off at its index in <paramref name="sequence"/> (its place in
+        /// <see cref="Parts"/> order). Cut-offs missing from it are added at the end.
+        /// Callers must remove existing cut-off parts first.
+        /// </summary>
+        public void RegenerateCutOffs(CutOffSettings settings, IReadOnlyDictionary<CutOff, int> sequence)
+        {
             var cache = BuildPerimeterCache(this);
+            var placed = new List<(int Index, Part Part)>();
 
             // Regenerate and materialize each cut-off
             foreach (var cutoff in CutOffs)
@@ -116,8 +138,17 @@ namespace OpenNest
                     continue;
 
                 var part = new Part(cutoff.Drawing);
-                Parts.Add(part);
+
+                if (sequence != null && sequence.TryGetValue(cutoff, out var index))
+                    placed.Add((index, part));
+                else
+                    Parts.Add(part);
             }
+
+            // Lowest index first: each insert then lands on its saved index, because
+            // every part sequenced before it is already in place.
+            foreach (var (index, part) in placed.OrderBy(p => p.Index))
+                Parts.Insert(System.Math.Clamp(index, 0, Parts.Count), part);
         }
 
         /// <summary>

OpenNest.IO/NestFormat.cs

@@ -87,6 +87,12 @@ namespace OpenNest.IO
             public string Axis { get; init; } = "vertical";
             public double? StartLimit { get; init; }
             public double? EndLimit { get; init; }
+
+            /// <summary>
+            /// Zero-based place in the plate's cut sequence (<c>Plate.Parts</c> order,
+            /// cut-offs included). Null in older files, which load it at the end.
+            /// </summary>
+            public int? Sequence { get; init; }
         }
 
         public record SizeDto

OpenNest.IO/NestReader.cs

@@ -372,6 +372,8 @@ namespace OpenNest.IO
                 // Cut-offs
                 if (p.CutOffs != null)
                 {
+                    var sequence = new Dictionary<CutOff, int>();
+
                     foreach (var cutoffDto in p.CutOffs)
                     {
                         var axis =
@@ -384,9 +386,12 @@ namespace OpenNest.IO
                             EndLimit = cutoffDto.EndLimit,
                         };
                         plate.CutOffs.Add(cutoff);
+
+                        if (cutoffDto.Sequence is int index)
+                            sequence[cutoff] = index;
                     }
 
-                    plate.RegenerateCutOffs(new CutOffSettings());
+                    plate.RegenerateCutOffs(new CutOffSettings(), sequence);
                 }
 
                 nest.Plates.Add(plate);

OpenNest.IO/NestWriter.cs

@@ -223,6 +223,16 @@ namespace OpenNest.IO
                 var cutoffs = new List<CutOffDto>();
                 foreach (var cutoff in plate.CutOffs)
                 {
+                    var sequence = -1;
+                    for (var j = 0; j < plate.Parts.Count; j++)
+                    {
+                        if (ReferenceEquals(plate.Parts[j].BaseDrawing, cutoff.Drawing))
+                        {
+                            sequence = j;
+                            break;
+                        }
+                    }
+
                     cutoffs.Add(
                         new CutOffDto
                         {
@@ -231,6 +241,7 @@ namespace OpenNest.IO
                             Axis = cutoff.Axis == CutOffAxis.Vertical ? "vertical" : "horizontal",
                             StartLimit = cutoff.StartLimit,
                             EndLimit = cutoff.EndLimit,
+                            Sequence = sequence >= 0 ? sequence : null,
                         }
                     );
                 }

OpenNest.Tests/CutOffs/CutOffSequenceTests.cs

@@ -0,0 +1,122 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.IO;
+
+namespace OpenNest.Tests.CutOffs;
+
+/// <summary>
+/// A cut-off's place in <c>Plate.Parts</c> is its cut sequence number, which the
+/// user sets and the posts follow. Regenerating cut-offs (after a part drag, fill
+/// or cut-off move) and saving must keep it.
+/// </summary>
+public class CutOffSequenceTests
+{
+    private static Drawing MakeSquare()
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 10)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 10)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return new Drawing("square", pgm);
+    }
+
+    /// <summary>Three parts along X with vertical cut-offs between them, the
+    /// cut-offs sequenced as 2 and 4: part, cut, part, cut, part.</summary>
+    private static Plate MakeSequencedPlate(Drawing drawing)
+    {
+        var plate = new Plate(60, 120);
+        plate.Parts.Add(new Part(drawing, new Vector(1, 2)));
+        plate.Parts.Add(new Part(drawing, new Vector(30, 2)));
+        plate.Parts.Add(new Part(drawing, new Vector(60, 2)));
+
+        plate.CutOffs.Add(new CutOff(new Vector(20, 0), CutOffAxis.Vertical));
+        plate.CutOffs.Add(new CutOff(new Vector(50, 0), CutOffAxis.Vertical));
+        plate.RegenerateCutOffs(new CutOffSettings());
+
+        // As ActionSetSequence does: remove, then insert at the chosen number.
+        SetSequence(plate, plate.CutOffs[0], 1);
+        SetSequence(plate, plate.CutOffs[1], 3);
+        return plate;
+    }
+
+    private static void SetSequence(Plate plate, CutOff cutOff, int index)
+    {
+        var part = plate.Parts.First(p => ReferenceEquals(p.BaseDrawing, cutOff.Drawing));
+        plate.Parts.Remove(part);
+        plate.Parts.Insert(index, part);
+    }
+
+    /// <summary>The cut sequence as names: "part" or the cut-off's X position.</summary>
+    private static string[] Sequence(Plate plate) =>
+        plate
+            .Parts.Select(p =>
+                p.BaseDrawing.IsCutOff ? $"cut@{p.BoundingBox.X:F0}" : $"part@{p.Location.X:F0}"
+            )
+            .ToArray();
+
+    private static readonly string[] Expected =
+    {
+        "part@1",
+        "cut@20",
+        "part@30",
+        "cut@50",
+        "part@60",
+    };
+
+    [Fact]
+    public void RegenerateCutOffs_KeepsEachCutOffInItsSequencePlace()
+    {
+        var plate = MakeSequencedPlate(MakeSquare());
+        Assert.Equal(Expected, Sequence(plate));
+
+        plate.RegenerateCutOffs(new CutOffSettings());
+
+        Assert.Equal(Expected, Sequence(plate));
+    }
+
+    [Fact]
+    public void RegenerateCutOffs_AddsNewCutOffAtTheEnd()
+    {
+        var plate = MakeSequencedPlate(MakeSquare());
+
+        plate.CutOffs.Add(new CutOff(new Vector(0, 40), CutOffAxis.Horizontal));
+        plate.RegenerateCutOffs(new CutOffSettings());
+
+        Assert.Equal(Expected, Sequence(plate).Take(5));
+        Assert.Equal(6, plate.Parts.Count);
+        Assert.Same(plate.CutOffs[2].Drawing, plate.Parts[5].BaseDrawing);
+    }
+
+    [Fact]
+    public void SaveAndReopen_KeepsCutOffSequence()
+    {
+        var drawing = MakeSquare();
+        var nest = new Nest("seq") { DateCreated = DateTime.Now, DateLastModified = DateTime.Now };
+        nest.Drawings.Add(drawing);
+        nest.Plates.Add(MakeSequencedPlate(drawing));
+
+        using var stream = new MemoryStream();
+        new NestWriter(nest).Write(stream);
+        stream.Position = 0;
+        var loaded = new NestReader(stream).Read();
+
+        Assert.Equal(Expected, Sequence(loaded.Plates[0]));
+    }
+
+    [Fact]
+    public void RegenerateCutOffs_OutOfRangeSequence_AppendsInsteadOfThrowing()
+    {
+        // A damaged file can name a sequence past the end of the plate.
+        var plate = new Plate(60, 120);
+        plate.Parts.Add(new Part(MakeSquare(), new Vector(1, 2)));
+        var cutOff = new CutOff(new Vector(20, 0), CutOffAxis.Vertical);
+        plate.CutOffs.Add(cutOff);
+
+        plate.RegenerateCutOffs(new CutOffSettings(), new Dictionary<CutOff, int> { [cutOff] = 99 });
+
+        Assert.Equal(2, plate.Parts.Count);
+        Assert.Same(cutOff.Drawing, plate.Parts[1].BaseDrawing);
+    }
+}