feat(core): mismatch drop and part copy

Two remaining pin rules from the drawing library plan:

- D3: a library drawing added to a nest whose material, grade or
  thickness differ from the library record now really arrives without
  its cut pins. The insert already warned and reported KeepPins = false;
  it now clears the copy's pins, because they were authored for the
  library material and thickness. The library link still records the
  revision the copy came from.
- A copy of a placement (Clone, CloneAtOffset) keeps its drawing pins
  off, so copying or patterning an overridden part does not silently
  bring the drawing's pins back. Clearing lead-ins keeps it too: pins-off
  is a placement choice, not lead-in state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Core/Part.cs

@@ -432,11 +432,13 @@ namespace OpenNest
         /// Copies the lead-in state that goes with a copied program. Without it a copy of a
         /// lead-in part reads its rotation from the rebuilt program (zero), and lead-in
         /// assignment does not know to strip the copied lead-ins before adding new ones.
+        /// A copy of a placement with drawing pins off keeps them off.
         /// </summary>
         private void CopyLeadInStateFrom(Part source)
         {
             HasManualLeadIns = source.HasManualLeadIns;
             LeadInsLocked = source.LeadInsLocked;
+            DrawingPinsOff = source.DrawingPinsOff;
             CuttingParameters = source.CuttingParameters;
             preLeadInRotation = source.preLeadInRotation;
         }

OpenNest.Data/LibraryDrawingInsert.cs

@@ -74,9 +74,9 @@ public sealed class LibraryDrawingInsert
     public int Quantity { get; }
 
     /// <summary>
-    /// For a new copy, true when the library drawing's cut pins may be used in this nest:
-    /// the library material, grade and thickness match the nest's. An added quantity
-    /// leaves the existing copy as it is.
+    /// For a new copy, true when the library drawing's cut pins come with it: the library
+    /// material, grade and thickness match the nest's. Otherwise the copy has no pins. An
+    /// added quantity leaves the existing copy as it is.
     /// </summary>
     public bool KeepPins { get; }
 
@@ -142,6 +142,10 @@ public sealed class LibraryDrawingInsert
         drawing.Material = new Material(record.MaterialName, record.MaterialGrade, drawing.Material?.Density ?? 0);
         drawing.Quantity.Required = quantity;
         drawing.Library = link;
+        // Pins were authored for the library material and thickness; elsewhere the nest's
+        // cutting settings apply (D3). The link still records the revision the copy came from.
+        if (differences.Count > 0)
+            drawing.CutPins.Clear();
         return new LibraryDrawingInsert(nest, LibraryInsertKind.AddDrawing, drawing, quantity,
             keepPins: differences.Count == 0, warnings, "");
     }

OpenNest.Tests/CuttingStrategy/PartLeadInTransformTests.cs

@@ -182,4 +182,24 @@ public class PartLeadInTransformTests
         Assert.Equal(before.Width, after.Length, 6);
         Assert.Equal(before.Length, after.Width, 6);
     }
+
+    [Fact]
+    public void Copies_KeepDrawingPinsOff()
+    {
+        var drawing = MakeSquareWithHole();
+        var clean = MakeCleanPart(drawing, QuarterTurn, new Vector(2, 3));
+        clean.DrawingPinsOff = true;
+        var withLeadIns = MakeLeadInPart(drawing, QuarterTurn);
+        withLeadIns.DrawingPinsOff = true;
+
+        Assert.True(((Part)clean.Clone()).DrawingPinsOff);
+        Assert.True(clean.CloneAtOffset(new Vector(1, 1)).DrawingPinsOff);
+        Assert.True(((Part)withLeadIns.Clone()).DrawingPinsOff);
+        Assert.True(withLeadIns.CloneAtOffset(new Vector(1, 1)).DrawingPinsOff);
+        Assert.False(((Part)MakeCleanPart(drawing, 0, Vector.Zero).Clone()).DrawingPinsOff);
+
+        // Pins-off is a placement choice, not lead-in state: clearing lead-ins keeps it.
+        withLeadIns.RemoveLeadIns();
+        Assert.True(withLeadIns.DrawingPinsOff);
+    }
 }

OpenNest.Tests/Data/LibraryDrawingInsertTests.cs

@@ -1,5 +1,7 @@
 using System.Security.Cryptography;
+using OpenNest.CNC.CuttingStrategy;
 using OpenNest.Data;
+using OpenNest.Geometry;
 using OpenNest.Shapes;
 
 namespace OpenNest.Tests.Data;
@@ -37,6 +39,8 @@ public class LibraryDrawingInsertTests
         var drawing = new RectangleShape { Name = "old package name", Length = 4, Width = 2 }.GetDrawing();
         drawing.Material = new Material("Package material", "Package grade", 0.284);
         drawing.Customer = "Package customer";
+        drawing.CutPins.Add(new ContourCutPin(new Vector(4, 2), new LineLeadIn { Length = 0.25 }, new NoLeadOut(),
+            new NormalTab { Size = 0.03 }));
         return new LibraryPackage(PackageBytes, drawing, units, warnings);
     }
 
@@ -57,6 +61,7 @@ public class LibraryDrawingInsertTests
 
         var drawing = Assert.Single(nest.Drawings);
         Assert.Same(package.Drawing, drawing);
+        Assert.Equal(new Vector(4, 2), Assert.Single(drawing.CutPins).Point);
         Assert.Equal(("SYN-101", "Synthetic customer", 5), (drawing.Name, drawing.Customer, drawing.Quantity.Required));
         Assert.Equal(("Synthetic Steel", "Grade A", 0.284), (drawing.Material.Name, drawing.Material.Grade, drawing.Material.Density));
         var link = drawing.Library!;
@@ -98,8 +103,11 @@ public class LibraryDrawingInsertTests
         Assert.Contains(expected, warning);
         Assert.Contains("'SYN-101'", warning);
         Assert.Contains("cut pins are dropped", warning);
+        Assert.Empty(insert.Drawing!.CutPins);
         insert.Apply();
-        Assert.Single(nest.Drawings);
+        var drawing = Assert.Single(nest.Drawings);
+        Assert.Empty(drawing.CutPins);
+        Assert.NotNull(drawing.Library);
     }
 
     [Fact]