On macOS 26 (Retina), a DocumentWindow with setUsingNativeTitleBar(true), whose content is laid out edge to edge, loses its outermost point at the left, right and bottom.
AppKit draws the window’s 1 pt frame over the content view.
At 2x, the two outermost pixels of the content are much lighter than the content itself: 69 where the background is 23, and 61–65 where our strip’s own pixels are 13–21 (grey levels, 0–255). So the frame is blended over the content rather than drawn outside it.
ResizableWindow::getBorderThickness() returns an empty border with a native title bar, so JUCE adds nothing there. On Windows the frame lies in the non-client area and the client area stays visible.
We now keep 1 pt clear ourselves: our DocumentWindow overrides getContentComponentBorder(), and the plugin editor insets its layout. Is this expected behaviour, or should JUCE keep the content area clear of the frame on macOS (for example through getContentComponentBorder() or the peer’s frame size), so that the content area is the visible area on every platform? Or is there a style mask we should set instead?
(This has not changed with JUCE 9)