Possible fix for fullscreen menu bar failing to appear

[m-thomson]

I've experienced similar issues to those described here: #479 (comment)

Namely, that the fullscreen behaviour sometimes breaks in various ways such as:

• the menu bar not appearing
• behaviour in MacOS Mission Control being broken:
  • not being able to drag the fullscreen VM out of the Spaces Bar to take it out of fullscreen
  • when hovering fullscreen apps in the MC Spaces Bar, an icon appears in the top left corner to take the window out of fullscreen mode; but it doesn't appear for the fullscreen VB window.
• Resizing the display where VB is fullscreened, causes the fullscreen VB window to enter a broken state where it continues to use the old resolution.
• I encountered these problems on Sequoia (I don't recall exact version) and Tahoe 26.7 (which I recently upgraded to).

Notably these problems have been intermittent; they don't always occur.

Secondly, the problem occurred only with an actual VM window and never with VB's main window showing the VM thumbnails.

With the help of an LLM (full disclosure) I believe I was able to trace the bug to a timing/race condition issue around line ~ 202 in WindowEnvironment.swift.

-            var effectiveNewValue = newValue
-            
-            // Can't remove .fullScreen when the window is in full screen (causes crash).
-            if cocoaWindow.styleMask.contains(.fullScreen) {
-                effectiveNewValue.insert(.fullScreen)
-            }
-            
             // TODO: HACK!
             /// Setting styleMask without this dispatch results in a crash when
             /// built with the macOS 15 SDK and running under macOS 15.
             /// The crash is a precondition failure: `setting value during update: 360192`.
             DispatchQueue.main.async {
+                var effectiveNewValue = newValue
+
+                // Can't remove .fullScreen when the window is in full screen (causes crash).
+                if cocoaWindow.styleMask.contains(.fullScreen) {
+                    effectiveNewValue.insert(.fullScreen)
+                }
+
                 cocoaWindow.styleMask = effectiveNewValue
             }

The proposed fix moves the .fullScreen check and assignment inside the queued code block so it reads and applies it at the same time; eliminating the possible race condition.

After applying this patch, all the problems I listed above are fixed on my system (Tahoe 26.7).

[insidegui]

Thanks for sharing. The proposed fix seems sound, so I've implemented it in #786 and it will ship as part of 2.2