fix(leadin): add close button to Place Lead-in side panel

The docked side panel could only be closed with Escape, which was
unreliable: MainForm consumes Escape before ActionLeadIn's KeyDown
handler, so with a part selected ActionManager called the action's
empty CancelAction and nothing happened; with nothing selected the
panel closed but was stored as the previous action, so the next
Escape reopened it.

- EditNestForm side panel gets a header with the panel title and an
  always-visible close button that ends the action.
- ActionLeadIn.CancelAction now steps back (unlock contour, then
  deselect part), replacing the dead KeyDown handler.
- Actions can opt out of Escape-resume (ResumeOnEscape); the lead-in
  action does, so a closed panel stays closed.

OpenNest.WinForms.Tests/Forms/LeadInSidePanelTests.cs

@@ -0,0 +1,64 @@
+using System.Runtime.ExceptionServices;
+using System.Windows.Forms;
+using OpenNest.Forms;
+
+namespace OpenNest.WinForms.Tests.Forms;
+
+public class LeadInSidePanelTests
+{
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void PanelClosesWithoutEscapeReopeningIt(bool useCloseButton) => RunSta(() =>
+    {
+        using var form = new EditNestForm(new Nest("lead-in panel"));
+        form.Show();
+
+        form.PlaceLeadIn_Click(null!, EventArgs.Empty);
+        Assert.True(form.IsSidePanelVisible);
+        Assert.Equal("Place Lead-in", form.PlateView.Status);
+
+        if (useCloseButton)
+        {
+            var close = Assert.IsType<Button>(
+                Assert.Single(form.Controls.Find("sidePanelCloseButton", true))
+            );
+            close.PerformClick();
+        }
+        else
+        {
+            form.PlateView.ProcessEscapeKey();
+        }
+
+        Assert.False(form.IsSidePanelVisible);
+        Assert.Equal("Select", form.PlateView.Status);
+
+        // Escape from Select normally resumes the previous action; it must not
+        // bring back a panel the user just closed.
+        form.PlateView.ProcessEscapeKey();
+        Assert.False(form.IsSidePanelVisible);
+        Assert.Equal("Select", form.PlateView.Status);
+    });
+
+    private static void RunSta(System.Action action)
+    {
+        Exception? failure = null;
+        var thread = new Thread(() =>
+        {
+            try
+            {
+                action();
+            }
+            catch (Exception ex)
+            {
+                failure = ex;
+            }
+        })
+        { IsBackground = true };
+        thread.SetApartmentState(ApartmentState.STA);
+        thread.Start();
+        Assert.True(thread.Join(TimeSpan.FromSeconds(60)), "The STA test did not complete.");
+        if (failure != null)
+            ExceptionDispatchInfo.Capture(failure).Throw();
+    }
+}

OpenNest/Actions/Action.cs

@@ -28,6 +28,11 @@ namespace OpenNest.Actions
 
         public virtual bool SurvivesPlateChange => false;
 
+        /// <summary>
+        /// Whether Escape from Select may bring this action back after it ends.
+        /// </summary>
+        public virtual bool ResumeOnEscape => true;
+
         public virtual void OnPlateChanged() { }
 
         public virtual void ConnectEvents() { }

OpenNest/Actions/ActionLeadIn.cs

@@ -55,7 +55,6 @@ namespace OpenNest.Actions
         {
             plateView.MouseMove += OnMouseMove;
             plateView.MouseDown += OnMouseDown;
-            plateView.KeyDown += OnKeyDown;
             plateView.Paint += OnPaint;
             ShowSidePanel();
         }
@@ -64,7 +63,6 @@ namespace OpenNest.Actions
         {
             plateView.MouseMove -= OnMouseMove;
             plateView.MouseDown -= OnMouseDown;
-            plateView.KeyDown -= OnKeyDown;
             plateView.Paint -= OnPaint;
 
             HideSidePanel();
@@ -72,23 +70,25 @@ namespace OpenNest.Actions
             contextMenu?.Dispose();
             contextMenu = null;
 
-            if (selectedLayoutPart != null)
+            DeselectPart();
-                selectedLayoutPart.IsSelected = false;
-
-            selectedLayoutPart = null;
-            selectedPart = null;
-            profile = null;
-            contours = null;
-            hasSnap = false;
-            activeSnapType = SnapType.None;
-            hoveredContour = null;
-            plateView.Invalidate();
         }
 
-        public override void CancelAction() { }
+        // Escape reaches here through ActionManager.ProcessEscapeKey while IsBusy:
+        // step back one level (unlock the contour, then release the part). Once
+        // nothing is selected, Escape ends the action and closes the side panel.
+        public override void CancelAction()
+        {
+            if (lockedContour != null)
+                UnlockContour();
+            else
+                DeselectPart();
+        }
 
         public override bool IsBusy() => selectedPart != null;
 
+        // Escape closes the side panel; a second Escape must not reopen it.
+        public override bool ResumeOnEscape => false;
+
         private void ShowSidePanel()
         {
             var form = plateView.FindForm() as EditNestForm;
@@ -119,7 +119,7 @@ namespace OpenNest.Actions
                 }
             }
 
-            form.ShowSidePanel(cuttingPanel);
+            form.ShowSidePanel(cuttingPanel, "Place Lead-in");
         }
 
         private void HideSidePanel()
@@ -249,19 +249,6 @@ namespace OpenNest.Actions
             }
         }
 
-        private void OnKeyDown(object sender, KeyEventArgs e)
-        {
-            if (e.KeyCode == Keys.Escape)
-            {
-                if (lockedContour != null)
-                    UnlockContour();
-                else if (selectedPart != null)
-                    DeselectPart();
-                else
-                    plateView.SetAction(typeof(ActionSelect));
-            }
-        }
-
         private void OnPaint(object sender, PaintEventArgs e)
         {
             var g = e.Graphics;

OpenNest/Controls/ActionManager.cs

@@ -28,6 +28,7 @@ namespace OpenNest.Controls
                 if (
                     type == typeof(Actions.ActionSelect)
                     && !(currentAction is Actions.ActionSelect)
+                    && currentAction.ResumeOnEscape
                 )
                     previousAction = currentAction;
                 else
@@ -75,6 +76,17 @@ namespace OpenNest.Controls
                 view.SetAction(typeof(Actions.ActionSelect));
         }
 
+        /// <summary>
+        /// Ends the current action at the user's explicit request (for example a
+        /// side panel's Close button). Unlike Escape, the ended action is not kept
+        /// for a later Escape to restore.
+        /// </summary>
+        public void EndAction()
+        {
+            SetAction(typeof(Actions.ActionSelect));
+            previousAction = null;
+        }
+
         public void RestorePreviousAction()
         {
             var action = previousAction;

OpenNest/Controls/PlateView.cs

@@ -487,6 +487,8 @@ namespace OpenNest.Controls
 
         public void ProcessEscapeKey() => actionManager.ProcessEscapeKey();
 
+        public void EndAction() => actionManager.EndAction();
+
         protected override bool ProcessDialogKey(Keys keyData)
         {
             // Only handle TAB, RETURN, ESC, and ARROW KEYS here.

OpenNest/Forms/EditNestForm.cs

@@ -53,6 +53,7 @@ namespace OpenNest.Forms
 
         private SplitContainer viewSplitContainer;
         private Panel sidePanel;
+        private Label sidePanelTitle;
 
         /// <summary>
         /// Used to distinguish between single/double click on drawing within drawinglistbox.
@@ -163,6 +164,40 @@ namespace OpenNest.Forms
                 BackColor = Color.White,
             };
 
+            // The header sits outside the scrolling content so Close stays visible.
+            sidePanelTitle = new Label
+            {
+                Dock = DockStyle.Fill,
+                AutoEllipsis = true,
+                TextAlign = ContentAlignment.MiddleLeft,
+                Font = new Font("Segoe UI", 9f, FontStyle.Bold),
+            };
+
+            var closeButton = new Button
+            {
+                Name = "sidePanelCloseButton",
+                Text = "\u00D7",
+                AccessibleName = "Close panel",
+                Dock = DockStyle.Right,
+                Width = 30,
+                Font = new Font("Segoe UI", 12f),
+                FlatStyle = FlatStyle.Flat,
+                FlatAppearance = { BorderSize = 0 },
+                Cursor = Cursors.Hand,
+            };
+            closeButton.Click += (s, e) => CloseSidePanel();
+            new ToolTip(components).SetToolTip(closeButton, "Close (Esc)");
+
+            var sidePanelHeader = new Panel
+            {
+                Dock = DockStyle.Top,
+                Height = 30,
+                BackColor = Color.FromArgb(240, 240, 240),
+                Padding = new Padding(8, 0, 0, 0),
+            };
+            sidePanelHeader.Controls.Add(sidePanelTitle);
+            sidePanelHeader.Controls.Add(closeButton);
+
             viewSplitContainer = new SplitContainer
             {
                 Dock = DockStyle.Fill,
@@ -173,14 +208,18 @@ namespace OpenNest.Forms
 
             viewSplitContainer.Panel1.Controls.Add(PlateView);
             viewSplitContainer.Panel2.Controls.Add(sidePanel);
+            viewSplitContainer.Panel2.Controls.Add(sidePanelHeader);
             viewSplitContainer.Panel2Collapsed = true;
         }
 
-        public void ShowSidePanel(Control content, int width = 390)
+        public bool IsSidePanelVisible => !viewSplitContainer.Panel2Collapsed;
+
+        public void ShowSidePanel(Control content, string title, int width = 390)
         {
             sidePanel.Controls.Clear();
             content.Dock = DockStyle.Fill;
             sidePanel.Controls.Add(content);
+            sidePanelTitle.Text = title;
             viewSplitContainer.SplitterDistance = viewSplitContainer.Width - width;
             viewSplitContainer.Panel2Collapsed = false;
         }
@@ -189,6 +228,17 @@ namespace OpenNest.Forms
         {
             viewSplitContainer.Panel2Collapsed = true;
             sidePanel.Controls.Clear();
+            sidePanelTitle.Text = string.Empty;
+        }
+
+        private void CloseSidePanel()
+        {
+            // Side panels belong to the plate action that opened them; ending the
+            // action hides its panel. Hide directly as well so Close always closes.
+            PlateView.EndAction();
+            if (IsSidePanelVisible)
+                HideSidePanel();
+            PlateView.Focus();
         }
 
         private static Button CreateNavButton(System.Drawing.Image image)