macos: don't overwrite the .fullScreen styleMask option in reapplyHiddenStyle

macos/Sources/Features/Terminal/Window Styles/HiddenTitlebarTerminalWindow.swift

@@ -19,9 +19,7 @@ class HiddenTitlebarTerminalWindow: TerminalWindow {
         NotificationCenter.default.removeObserver(self)
     }
 
-    /// Apply the hidden titlebar style.
-    private func reapplyHiddenStyle() {
-        styleMask = [
+    private let hiddenStyleMask: NSWindow.StyleMask = [
         // We need `titled` in the mask to get the normal window frame
         .titled,
 
@@ -34,6 +32,15 @@ class HiddenTitlebarTerminalWindow: TerminalWindow {
         .miniaturizable,
     ]
 
+    /// Apply the hidden titlebar style.
+    private func reapplyHiddenStyle() {
+        // Apply our style mask while preserving the .fullScreen option
+        if styleMask.contains(.fullScreen) {
+            styleMask = hiddenStyleMask.union([.fullScreen])
+        } else {
+            styleMask = hiddenStyleMask
+        }
+
         // Hide the title
         titleVisibility = .hidden
         titlebarAppearsTransparent = true