Round notification close button (#5630)

Keep the hover close button fully inside the notification panel and derive its corner radius from the final bounds.

Author: ComputelessComputer

crates/notification-macos/swift-lib/src/NotificationButtons.swift

@@ -69,6 +69,11 @@ class CloseButton: NSButton, TrackableButton {
     NSSize(width: CloseButtonConfig.size, height: CloseButtonConfig.size)
   }
 
+  override func layout() {
+    super.layout()
+    layer?.cornerRadius = min(bounds.width, bounds.height) / 2
+  }
+
   override func updateTrackingAreas() {
     super.updateTrackingAreas()
     setupTrackingArea()

crates/notification-macos/swift-lib/src/NotificationManager+Creation.swift

@@ -270,12 +270,14 @@ extension NotificationManager {
     closeButton.translatesAutoresizingMaskIntoConstraints = false
     clickableView.addSubview(closeButton, positioned: .above, relativeTo: nil)
 
-    let buttonOffset =
+    let horizontalButtonOffset =
       isMacOS26() ? (CloseButtonConfig.size / 2) + 4 : (CloseButtonConfig.size / 2) - 2
+    let verticalButtonOffset = buttonOverhang() - (CloseButtonConfig.size / 2)
     NSLayoutConstraint.activate([
-      closeButton.centerYAnchor.constraint(equalTo: container.topAnchor, constant: buttonOffset),
+      closeButton.centerYAnchor.constraint(
+        equalTo: container.topAnchor, constant: verticalButtonOffset),
       closeButton.centerXAnchor.constraint(
-        equalTo: container.leadingAnchor, constant: buttonOffset),
+        equalTo: container.leadingAnchor, constant: horizontalButtonOffset),
       closeButton.widthAnchor.constraint(equalToConstant: CloseButtonConfig.size),
       closeButton.heightAnchor.constraint(equalToConstant: CloseButtonConfig.size),
     ])