In Sketchup you have this snap but only for the rectangle during its drawing : maybe sufficient for the Golden number ?
Or can be also added during the "Helper line" in Moi ? (similar of the Middle Snap Line first level) ;)
A very artistic esoteric snap :)



Drawn in Moi ;)
This is this rectangle : Red square on the left - Side turned-down from the middle of the side's red square --> gives the new side on the right = Golden Rectangle
(Big side + Little side) / Big side = Golden Number = 1,618 033 988 7....