fix: use background subview instead of draw(_:) for change-state coloring

draw(_:) with wantsLayer=true caused text to be invisible because the
fill painted on the cell's layer backing store while the text field
rendered on its own sublayer. Using a dedicated background NSView
positioned below the text field avoids layer compositing issues.

backgroundStyle didSet hides the background view when .emphasized
(row selected) so the native selection highlight shows through.

Author: datlechin

TablePro/Views/Results/DataGridCellView.swift

@@ -5,22 +5,40 @@
 
 import AppKit
 
-/// Custom cell view that draws change-state backgrounds via `draw(_:)` instead
-/// of `layer.backgroundColor`. AppKit's `NSTableRowView` sets `backgroundStyle`
-/// to `.emphasized` when the row is selected — we skip the custom background in
-/// that case so the native selection highlight shows through.
+/// Custom cell view that uses a background subview for change-state coloring.
+/// AppKit's `NSTableRowView` sets `backgroundStyle` to `.emphasized` when the
+/// row is selected — we hide the background view so the native selection highlight
+/// shows through.
 final class DataGridCellView: NSTableCellView {
-    var changeBackgroundColor: NSColor?
+    private lazy var backgroundView: NSView = {
+        let view = NSView()
+        view.wantsLayer = true
+        view.translatesAutoresizingMaskIntoConstraints = false
+        addSubview(view, positioned: .below, relativeTo: subviews.first)
+        NSLayoutConstraint.activate([
+            view.leadingAnchor.constraint(equalTo: leadingAnchor),
+            view.trailingAnchor.constraint(equalTo: trailingAnchor),
+            view.topAnchor.constraint(equalTo: topAnchor),
+            view.bottomAnchor.constraint(equalTo: bottomAnchor),
+        ])
+        return view
+    }()
 
-    override var backgroundStyle: NSView.BackgroundStyle {
-        didSet { needsDisplay = true }
+    var changeBackgroundColor: NSColor? {
+        didSet {
+            if let color = changeBackgroundColor {
+                backgroundView.layer?.backgroundColor = color.cgColor
+                backgroundView.isHidden = (backgroundStyle == .emphasized)
+            } else {
+                backgroundView.layer?.backgroundColor = nil
+                backgroundView.isHidden = true
+            }
+        }
     }
 
-    override func draw(_ dirtyRect: NSRect) {
-        if backgroundStyle != .emphasized, let color = changeBackgroundColor {
-            color.setFill()
-            dirtyRect.fill()
+    override var backgroundStyle: NSView.BackgroundStyle {
+        didSet {
+            backgroundView.isHidden = (backgroundStyle == .emphasized) || (changeBackgroundColor == nil)
         }
-        super.draw(dirtyRect)
     }
 }