Resizable Border oddness on Mac

We have avoided a full resizable border since (AFAIK) it needs to be visible, creating an actual border around our app. I can set the border width to 1, which looks fine, but is annoyingly difficult to ‘catch’ with the mouse pointer. So we’ve always used a resizable corner, and a custom titleBar.

If we use the native title bar, we get (I assume) the system supplied window which has resizing built in to every window edge without the need for the unsightly visible border. But the title bar itself is nasty.

I have just noticed since updating to JUCE6 that if I make my app fullscreen, then not-fullscreen, the Mac-style resize handles are suddenly available. best of both worlds, but it has to be done manually by the user.

So does anyone understand how/why this is happening? It would be great if we could harness this Mac-style resize border without the need for the visible 4px JUCE border.