fix(avalonia): keep default view toggles out of settings and copy boxes for drawing

Write PlateViewDrawRapid/PlateViewDrawBounds only when changed from the default
or already saved, as the WinForms settings provider does, so a later default
change still applies. Give the render thread a copy of a broken common-line
part's box, and prune the label-point cache with the part paths.

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

OpenNest.Avalonia/Controls/PlateCanvas.cs

@@ -98,11 +98,15 @@ namespace OpenNest.Avalonia.Controls
             if (plate == null)
             {
                 paths.Clear();
+                labelPoints.Clear();
                 return;
             }
             var shown = new HashSet<Part>(plate.Parts);
             foreach (var stale in paths.Keys.Where(part => !shown.Contains(part)).ToList())
                 paths.Remove(stale);
+            var drawings = new HashSet<Drawing>(plate.Parts.Select(part => part.BaseDrawing));
+            foreach (var stale in labelPoints.Keys.Where(drawing => !drawings.Contains(drawing)).ToList())
+                labelPoints.Remove(stale);
         }
 
         public void ZoomToFit()
@@ -263,7 +267,11 @@ namespace OpenNest.Avalonia.Controls
                 foreach (var path in CommonLineGeometry.Paths(cached.Check.Spans, group.Kerf))
                     scene.CommonLines.Add(path.Points);
                 foreach (var problem in cached.Check.Problems)
-                    scene.CommonLineProblems.Add(problem.Part.BoundingBox);
+                {
+                    // A copy: moving the part changes its box in place while the render thread draws.
+                    var box = problem.Part.BoundingBox;
+                    scene.CommonLineProblems.Add(new Box(box.X, box.Y, box.Length, box.Width));
+                }
             }
         }
 

OpenNest.Desktop.Tests/Rendering/PlateSceneTests.cs

@@ -255,6 +255,25 @@ public class PlateViewOptionsTests
         Assert.False(read.DrawSupport);
     }
 
+    [Fact]
+    public void Untouched_defaults_stay_out_of_the_settings()
+    {
+        var settings = new Dictionary<string, string> { ["Other"] = "kept" };
+        new PlateViewOptions().WriteTo(settings);
+
+        Assert.Single(settings);
+    }
+
+    [Fact]
+    public void A_saved_toggle_set_back_to_its_default_is_written()
+    {
+        var settings = new Dictionary<string, string> { ["PlateViewDrawRapid"] = "True" };
+        new PlateViewOptions().WriteTo(settings);
+
+        Assert.Equal("False", settings["PlateViewDrawRapid"]);
+        Assert.False(settings.ContainsKey("PlateViewDrawBounds"));
+    }
+
     [Fact]
     public void Unreadable_values_are_defaults()
     {

OpenNest.Desktop/Rendering/PlateViewOptions.cs

@@ -45,11 +45,22 @@ public sealed class PlateViewOptions
         return options;
     }
 
-    /// <summary>Stores the rapids and bounds toggles in the WinForms format.</summary>
+    /// <summary>
+    /// Stores the rapids and bounds toggles in the WinForms format. As the WinForms settings
+    /// provider does, a toggle still at its default is left out unless the file already holds it,
+    /// so a later default change still applies.
+    /// </summary>
     public void WriteTo(IDictionary<string, string> settings)
     {
         ArgumentNullException.ThrowIfNull(settings);
-        settings[DrawRapidName] = UserSettingText.Format(DrawRapid);
-        settings[DrawBoundsName] = UserSettingText.Format(DrawBounds);
+        var defaults = new PlateViewOptions();
+        Write(settings, DrawRapidName, DrawRapid, defaults.DrawRapid);
+        Write(settings, DrawBoundsName, DrawBounds, defaults.DrawBounds);
+    }
+
+    private static void Write(IDictionary<string, string> settings, string name, bool value, bool fallback)
+    {
+        if (value != fallback || settings.ContainsKey(name))
+            settings[name] = UserSettingText.Format(value);
     }
 }