Fix window activation and rendering bugs

Fixed several bugs related to window z-order and rendering:

WindowStateService.cs:
- BringToFront now activates window (matches standard windowing behavior)
- SendToBack updated to activate next window if current was active
- Improved documentation for z-order methods

RenderCoordinator.cs:
- Clear coverage cache when z-indices change between frames
- Prevents stale occlusion data from previous frame

WindowPositioningManager.cs:
- Use SetPositionDirect instead of SetPosition in CenterOnScreen
- Prevents recursion when centering windows

Author: nickprotop

SharpConsoleUI/Core/WindowStateService.cs

@@ -618,7 +618,8 @@ public void EndResize()
 		#region Z-Order Management
 
 		/// <summary>
-		/// Brings a window to the front (highest Z-index).
+		/// Brings a window to the front (highest Z-index) and activates it.
+		/// This matches typical windowing system behavior where bringing a window to front makes it active.
 		/// </summary>
 		/// <param name="window">The window to bring to front.</param>
 		public void BringToFront(Window window)
@@ -628,19 +629,17 @@ public void BringToFront(Window window)
 
 			lock (_lock)
 			{
-				window.ZIndex = GetMaxZIndex() + 1;
-				UpdateStateInternal(CreateStateSnapshot());
-
-				// Invalidate window when z-order changes because visibleRegions change
-				// Window may now have more visible area and needs to repaint with new clipRect
-				window.Invalidate(true);
+				// Activate window (which also brings it to front with highest Z-index)
+				// This ensures the window is both visually on top and receives input
+				ActivateWindow(window);
 
 				FireWindowEvent(window, WindowEventType.ZOrderChanged);
 			}
 		}
 
 		/// <summary>
 		/// Sends a window to the back (lowest Z-index).
+		/// If the window was active, activates the next available window.
 		/// </summary>
 		/// <param name="window">The window to send to back.</param>
 		public void SendToBack(Window window)
@@ -650,6 +649,8 @@ public void SendToBack(Window window)
 
 			lock (_lock)
 			{
+				var wasActive = _currentState.ActiveWindow == window;
+
 				var minZIndex = _windows.Count > 0 ? _windows.Values.Min(w => w.ZIndex) : 0;
 				window.ZIndex = minZIndex - 1;
 				UpdateStateInternal(CreateStateSnapshot());
@@ -658,6 +659,13 @@ public void SendToBack(Window window)
 				// Window may now have less visible area and needs to repaint with new clipRect
 				window.Invalidate(true);
 
+				// If this was the active window, activate the next one
+				if (wasActive)
+				{
+					var nextWindow = FindNextActiveWindow(window);
+					ActivateWindow(nextWindow);
+				}
+
 				FireWindowEvent(window, WindowEventType.ZOrderChanged);
 			}
 		}
@@ -827,6 +835,28 @@ private void FireInteractionChanged(InteractionState previousState, InteractionS
 			});
 		}
 
+		/// <summary>
+		/// Invalidates all windows that overlap with the specified window.
+		/// Used after z-order changes to ensure proper rendering of affected windows.
+		/// </summary>
+		private void InvalidateOverlappingWindows(Window window)
+		{
+			if (window == null) return;
+
+			var windowRect = new System.Drawing.Rectangle(window.Left, window.Top, window.Width, window.Height);
+
+			foreach (var other in _windows.Values)
+			{
+				if (other == window) continue;
+
+				// Invalidate any window that overlaps with the moved window
+				if (Helpers.GeometryHelpers.DoesRectangleOverlapWindow(windowRect, other))
+				{
+					other.Invalidate(true);
+				}
+			}
+		}
+
 		#endregion
 
 		#region IDisposable

SharpConsoleUI/Rendering/RenderCoordinator.cs

@@ -334,6 +334,9 @@ private void RenderWindows()
 			// Reuse cached HashSet to avoid allocation
 			_windowsToRender.Clear();
 
+			// Clear coverage cache - Z-indices may have changed since last frame
+			_coverageCache.Clear();
+
 			// Build sorted window list for rendering (avoid LINQ allocations)
 			_sortedWindows.Clear();
 			_sortedWindows.AddRange(_windowSystemContext.Windows.Values);

SharpConsoleUI/Windows/WindowPositioningManager.cs

@@ -58,7 +58,7 @@ public void MoveWindowTo(Window window, int newLeft, int newTop)
 			var oldBounds = new Rectangle(window.Left, window.Top, window.Width, window.Height);
 
 			_renderCoordinator.AddPendingDesktopClear(oldBounds);
-			window.SetPosition(new Point(newLeft, newTop));
+			window.SetPositionDirect(new Point(newLeft, newTop));  // Use direct setter to avoid recursion
 			window.Invalidate(true);
 
 			// Invalidate windows that were underneath (now exposed)