fix(plateview): keep nudged clones through dialogs

Windows reposts a mouse move when a dialog opens or closes, so Set
Offset Increment threw away arrow-key nudges by snapping the previews
back to the cursor. Only a real cursor move now moves them.

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

OpenNest.WinForms.Tests/Controls/ActionCloneTests.cs

@@ -74,4 +74,44 @@ public class ActionCloneTests
         view.SetAction(typeof(ActionSelect));
         Assert.False(view.ActionHandlesF1);
     }, TimeSpan.FromMinutes(1), "The STA test did not complete.");
+
+    [Fact]
+    public void ADialogsFakeMouseMoveLeavesNudgedPreviewsInPlace() => StaTestThread.Run(() =>
+    {
+        using var view = new PlateView { Plate = new Plate(48, 96), Size = new System.Drawing.Size(600, 600) };
+        view.ZoomToFit();
+        view.SetAction(typeof(ActionClone), Square("new"));
+        var preview = Assert.Single(view.SelectedParts);
+        MoveMouse(view, new System.Drawing.Point(300, 300));
+        var followed = preview.BasePart.BoundingBox.Location;
+
+        Nudge(view);
+        var nudged = preview.BasePart.BoundingBox.Location;
+        Assert.Equal(followed.X + view.OffsetIncrementDistance, nudged.X, 6);
+
+        // A repost of the last position, with no focus change.
+        MoveMouse(view, new System.Drawing.Point(300, 300));
+        Assert.Equal(nudged, preview.BasePart.BoundingBox.Location);
+
+        // Opening the dialog, then closing it: each post arrives where the cursor rests.
+        var rest = view.PointToClient(Cursor.Position);
+        Raise(view, "OnLostFocus", EventArgs.Empty);
+        MoveMouse(view, rest);
+        Assert.Equal(nudged, preview.BasePart.BoundingBox.Location);
+
+        Raise(view, "OnGotFocus", EventArgs.Empty);
+        MoveMouse(view, rest);
+        Assert.Equal(nudged, preview.BasePart.BoundingBox.Location);
+
+        // The next real move takes the previews back to the cursor.
+        MoveMouse(view, new System.Drawing.Point(rest.X + 20, rest.Y + 20));
+        Assert.NotEqual(nudged, preview.BasePart.BoundingBox.Location);
+    }, TimeSpan.FromMinutes(1), "The STA test did not complete.");
+
+    private static void MoveMouse(PlateView view, System.Drawing.Point point) =>
+        Raise(view, "OnMouseMove", new MouseEventArgs(MouseButtons.None, 0, point.X, point.Y, 0));
+
+    private static void Nudge(PlateView view) =>
+        typeof(PlateView).GetMethod("ProcessDialogKey", BindingFlags.Instance | BindingFlags.NonPublic)!
+            .Invoke(view, new object[] { Keys.Right });
 }

OpenNest/Actions/ActionClone.cs

@@ -16,6 +16,7 @@ namespace OpenNest.Actions
         private readonly List<Part> sourceParts;
 
         private double lastScale;
+        private System.Drawing.Point? restingCursor;
 
         public ActionClone(PlateView plateView, Drawing drawing)
             : this(plateView, new List<Part> { new Part(drawing) }) { }
@@ -27,6 +28,8 @@ namespace OpenNest.Actions
             plateView.MouseMove += plateView_MouseMove;
             plateView.MouseDown += plateView_MouseDown;
             plateView.Paint += plateView_Paint;
+            plateView.GotFocus += plateView_FocusChanged;
+            plateView.LostFocus += plateView_FocusChanged;
 
             sourceParts = partsToClone;
             parts = new List<LayoutPart>();
@@ -101,13 +104,24 @@ namespace OpenNest.Actions
             lastScale = plateView.ViewScale;
         }
 
+        // Windows posts a mouse move when a dialog opens or closes, though the mouse stayed
+        // put. Following it would throw away arrow-key nudges, so only a real move counts.
         private void plateView_MouseMove(object sender, MouseEventArgs e)
         {
+            if (e.Location == restingCursor)
+                return;
+
+            restingCursor = e.Location;
             var offset = plateView.CurrentPoint - parts.GetBoundingBox().Location;
             parts.ForEach(p => p.Offset(offset));
             plateView.Invalidate();
         }
 
+        // The cursor may have been moved to the dialog's OK button, so measure the rest
+        // position afresh whenever focus leaves or returns.
+        private void plateView_FocusChanged(object sender, System.EventArgs e) =>
+            restingCursor = plateView.PointToClient(Cursor.Position);
+
         public override bool SurvivesPlateChange => true;
 
         // F1 sets the part in place, as it always has; help stays on the Help menu.
@@ -121,6 +135,8 @@ namespace OpenNest.Actions
             plateView.MouseMove += plateView_MouseMove;
             plateView.MouseDown += plateView_MouseDown;
             plateView.Paint += plateView_Paint;
+            plateView.GotFocus += plateView_FocusChanged;
+            plateView.LostFocus += plateView_FocusChanged;
 
             SelectPreviews();
         }
@@ -131,6 +147,8 @@ namespace OpenNest.Actions
             plateView.MouseMove -= plateView_MouseMove;
             plateView.MouseDown -= plateView_MouseDown;
             plateView.Paint -= plateView_Paint;
+            plateView.GotFocus -= plateView_FocusChanged;
+            plateView.LostFocus -= plateView_FocusChanged;
 
             plateView.SelectedParts.Clear();
             plateView.Invalidate();