Mucking around with this further - I quit Architect, relaunched it. In the opening dialogue (recent projects) there is a fullscreen toggle button. I tapped that, and then loaded my project. Lo and behold, the fullscreen button now appears in the menu and I can unfullscreen the app. I've tried to recreate the bug of the disappearing full screen button but haven't yet.
That's very odd. We've raised this issue with the Sencha Desktop Packager team and neither of our teams have been able to reproduce the issue. If you are able to find a way to reproduce it please let us know so that we can get it resolved.
I'm having the same problem. Architect is not actually in full screen mode, but it thinks it is. Because of this I cannot change the size of the window or move the window around the screen. Even the mac shortcut to toggle fullscreen will not work. I've tried restarting architect, and restarting my Mac but nothing is working.
I believed this issue was caused when I had architect open in fullscreen mode then I shutdown my Mac without closing architect. A message came up saying that architect prevented the computer from shutting down but then I clicked the dialog telling to computer to shut down anyways. So I'm guessing that when architect was force closed by the OS while in fullscreen mode it caused this issue.