A crop handle straddles the picture's edge. With the photograph fitted
to the whole canvas, the bottom handles sat in the photo roll's band,
whose swipe handler takes every press inside it, and the bottom-left
one under the "Done Composing" row, which is declared after the overlay
and whose buttons press 44px tall. Both were drawn and could not be
grabbed: on a laptop-shaped window, one or the other for nearly any
photograph.
While composing, the canvas box is inset 16px from its clip and stops
above the band, the row's margin and the row's hit height. The band is
measured once, on the canvas, and the row reads it from there.