I know you are determined to have us use one of the full screen modes, which I'm sure work great for games, but for apps (which lets not forget C3 is really good for) I have tried every possible way to have true responsiveness but I have come to the unfortunate conclusion that its really not possible?
A simple, standard app layout where the header and bottom menu bars simply adjust to the width only and the ability to then centre and resize the content too just doesn't seem possible.
To do the above, you have to have the fullscreen mode to off and resize the canvas, but resizing the canvas to something LESS that the initial layout size shifts everything off screen. There is no way at runtime to resize the layout (only scale)...
I am very surprised but this, it really does take away that native app feel as none of the standards fullscreen modes are suitable for app designs.
EDIT: I believe I have found a way but its not great, I have to have the layout size set to something very small (10x10) at edit time. - Not working correctly - also not viable.
EDIT: Am I wrong in thinking a Layer with its scale rate set to 0 shouldn't scale? It still scales down when I resize the window?