fix(qwen38flashnext): number plates in commit order and drop etch marks

BuildResult set PlateIndex to the stock index, so every sheet cut from
the same stock shared one index; OpenNest.Api maps plates by it.

Part geometry filtered only rapids, so scribe/etch moves counted as
material - the bug OpenNest fixed in 1b5e1b1. Use SpecialLayers.IsMaterial.

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

OpenNest.Engine.Qwen38FlashNext/Engine/JobSolver.cs

@@ -405,7 +405,7 @@ internal sealed class JobSolver
                 );
             }
             plates.Add(
-                new NestJobPlateResult(sheet.StockIndex, _job.Plates[sheet.StockIndex], placements)
+                new NestJobPlateResult(plates.Count, _job.Plates[sheet.StockIndex], placements)
             );
         }
 

OpenNest.Engine.Qwen38FlashNext/Engine/PartPreparation.cs

@@ -78,7 +78,7 @@ internal sealed class PartModel
                     DrawingJobMapper.ToProgram(part.Geometry)
                 )
             )
-                if (!ReferenceEquals(entity.Layer, SpecialLayers.Rapid))
+                if (SpecialLayers.IsMaterial(entity.Layer))
                     entities.Add(entity);
             if (entities.Count == 0)
                 return null;

OpenNest.Engine.Qwen38FlashNext/tests/Qwen38FlashNextNestingEngineTests.cs

@@ -107,6 +107,37 @@ public class Qwen38FlashNextNestingEngineTests
         Assert.Equal(1, huge.Unplaced);
     }
 
+    [Fact]
+    public void EtchMarksAreLeftOutOfNestingGeometry()
+    {
+        // A bend tick starts on material and ends 1.0 into a side notch, outside the part but
+        // inside its bounding box (the PEP case that crashed nesting before 1b5e1b1). As
+        // material it is open geometry leaving the part; as a mark it must be ignored.
+        var etched = Polyline((0, 0), (10, 0), (10, 4), (8, 4), (8, 6), (10, 6), (10, 10), (0, 10));
+        etched.Codes.Add(new RapidMove(7.5, 5));
+        etched.Codes.Add(new LinearMove(9, 5) { Layer = LayerType.Scribe });
+        var job = Job(new[] { Part("part", etched, 2, RotationPolicy.Fixed(0)) }, new[] { Stock("sheet", 10.4, 20.6, spacing: 0.2) });
+
+        var result = new Qwen38FlashNextNestingEngine().Solve(job);
+
+        AssertValid(job, result);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Equal(2, Assert.Single(result.Plates).Placements.Count);
+    }
+
+    [Fact]
+    public void PlateIndicesRunInCommitOrder()
+    {
+        // Every sheet comes from the same stock (index 0), so the stock index must not leak
+        // into PlateIndex: the host and OpenNest.Api treat it as the sheet's position.
+        var job = Job(new[] { Part("square", Rectangle(10, 10), 30) }, new[] { Stock("sheet", 25, 45, spacing: 0.25) });
+
+        var result = new Qwen38FlashNextNestingEngine().Solve(job);
+
+        Assert.True(result.Plates.Count > 1);
+        Assert.Equal(Enumerable.Range(0, result.Plates.Count), result.Plates.Select(p => p.PlateIndex));
+    }
+
     // ---- helpers -------------------------------------------------------------------------
 
     private static void AssertValid(NestJob job, NestJobResult result)