feat(ui): two-bucket preview parts in PlateView

Replace single temporaryParts list with stationaryParts (overall best,
full opacity) and activeParts (current strategy, reduced opacity).
Update SetPlate, Refresh, UpdateMatrix, DrawParts, and FillWithProgress
accordingly. Replace SetTemporaryParts/ClearTemporaryParts/AcceptTemporaryParts
with SetStationaryParts/SetActiveParts/ClearPreviewParts/AcceptPreviewParts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest/Controls/PlateView.cs

@@ -31,7 +31,8 @@ namespace OpenNest.Controls
         private Action currentAction;
         private Action previousAction;
         private List<LayoutPart> parts;
-        private List<LayoutPart> temporaryParts = new List<LayoutPart>();
+        private List<LayoutPart> stationaryParts = new List<LayoutPart>();
+        private List<LayoutPart> activeParts = new List<LayoutPart>();
         private Point middleMouseDownPoint;
         private Box activeWorkArea;
         private List<Box> debugRemnants;
@@ -149,7 +150,8 @@ namespace OpenNest.Controls
                 plate.PartAdded -= plate_PartAdded;
                 plate.PartRemoved -= plate_PartRemoved;
                 parts.Clear();
-                temporaryParts.Clear();
+                stationaryParts.Clear();
+                activeParts.Clear();
                 SelectedParts.Clear();
             }
 
@@ -408,7 +410,8 @@ namespace OpenNest.Controls
         public override void Refresh()
         {
             parts.ForEach(p => p.Update(this));
-            temporaryParts.ForEach(p => p.Update(this));
+            stationaryParts.ForEach(p => p.Update(this));
+            activeParts.ForEach(p => p.Update(this));
             Invalidate();
         }
 
@@ -503,24 +506,38 @@ namespace OpenNest.Controls
                 part.Draw(g, (i + 1).ToString());
             }
 
-            // Draw temporary (preview) parts
-            for (var i = 0; i < temporaryParts.Count; i++)
+            // Draw stationary preview parts (overall best — full opacity)
+            for (var i = 0; i < stationaryParts.Count; i++)
             {
-                var temp = temporaryParts[i];
+                var part = stationaryParts[i];
 
-                if (temp.IsDirty)
-                    temp.Update(this);
+                if (part.IsDirty)
+                    part.Update(this);
 
-                var path = temp.Path;
-                var pathBounds = path.GetBounds();
-
-                if (!pathBounds.IntersectsWith(viewBounds))
+                var path = part.Path;
+                if (!path.GetBounds().IntersectsWith(viewBounds))
                     continue;
 
                 g.FillPath(ColorScheme.PreviewPartBrush, path);
                 g.DrawPath(ColorScheme.PreviewPartPen, path);
             }
 
+            // Draw active preview parts (current strategy — reduced opacity)
+            for (var i = 0; i < activeParts.Count; i++)
+            {
+                var part = activeParts[i];
+
+                if (part.IsDirty)
+                    part.Update(this);
+
+                var path = part.Path;
+                if (!path.GetBounds().IntersectsWith(viewBounds))
+                    continue;
+
+                g.FillPath(ColorScheme.ActivePreviewPartBrush, path);
+                g.DrawPath(ColorScheme.ActivePreviewPartPen, path);
+            }
+
             if (DrawOffset && Plate.PartSpacing > 0)
                 DrawOffsetGeometry(g);
 
@@ -879,34 +896,49 @@ namespace OpenNest.Controls
             Plate.Parts.Add(part);
         }
 
-        public void SetTemporaryParts(List<Part> parts)
+        public void SetStationaryParts(List<Part> parts)
         {
-            temporaryParts.Clear();
+            stationaryParts.Clear();
 
             if (parts != null)
             {
                 foreach (var part in parts)
-                    temporaryParts.Add(LayoutPart.Create(part, this));
+                    stationaryParts.Add(LayoutPart.Create(part, this));
             }
 
             Invalidate();
         }
 
-        public void ClearTemporaryParts()
+        public void SetActiveParts(List<Part> parts)
         {
-            temporaryParts.Clear();
+            activeParts.Clear();
+
+            if (parts != null)
+            {
+                foreach (var part in parts)
+                    activeParts.Add(LayoutPart.Create(part, this));
+            }
+
             Invalidate();
         }
 
-        public int AcceptTemporaryParts()
+        public void ClearPreviewParts()
         {
-            var count = temporaryParts.Count;
+            stationaryParts.Clear();
+            activeParts.Clear();
+            Invalidate();
+        }
 
-            foreach (var layoutPart in temporaryParts)
-                Plate.Parts.Add(layoutPart.BasePart);
+        public void AcceptPreviewParts(List<Part> parts)
+        {
+            if (parts != null)
+            {
+                foreach (var part in parts)
+                    Plate.Parts.Add(part);
+            }
 
-            temporaryParts.Clear();
-            return count;
+            stationaryParts.Clear();
+            activeParts.Clear();
         }
 
         public async void FillWithProgress(List<Part> groupParts, Box workArea)
@@ -918,7 +950,12 @@ namespace OpenNest.Controls
             var progress = new Progress<NestProgress>(p =>
             {
                 progressForm.UpdateProgress(p);
-                SetTemporaryParts(p.BestParts);
+
+                if (p.IsOverallBest)
+                    SetStationaryParts(p.BestParts);
+                else
+                    SetActiveParts(p.BestParts);
+
                 ActiveWorkArea = p.ActiveWorkArea;
             });
 
@@ -932,20 +969,20 @@ namespace OpenNest.Controls
 
                 if (parts.Count > 0 && (!cts.IsCancellationRequested || progressForm.Accepted))
                 {
-                    AcceptTemporaryParts();
+                    AcceptPreviewParts(parts);
                     sw.Stop();
                     Status = $"Fill: {parts.Count} parts in {sw.ElapsedMilliseconds} ms";
                 }
                 else
                 {
-                    ClearTemporaryParts();
+                    ClearPreviewParts();
                 }
 
                 progressForm.ShowCompleted();
             }
             catch (Exception)
             {
-                ClearTemporaryParts();
+                ClearPreviewParts();
             }
             finally
             {
@@ -1082,7 +1119,8 @@ namespace OpenNest.Controls
         {
             base.UpdateMatrix();
             parts.ForEach(p => p.Update(this));
-            temporaryParts.ForEach(p => p.Update(this));
+            stationaryParts.ForEach(p => p.Update(this));
+            activeParts.ForEach(p => p.Update(this));
         }
     }
 }