When a gesture stopped, the half-resolution draft was replaced by the
full-resolution frame in one step, a visible jump from soft to sharp.
FR-DSP-4 asks for a refinement that is smooth, not a jarring swap.
The canvas now keeps the last draft frame (`canvas-previous`) and draws
it over the sharp one, fading it out over 150 ms when the draft flag
clears. The fade costs no render: the draft is a refcount on the texture
it was drawn into, and the adjust pass ping-pongs between two output
targets, so the sharp frame is written into the other one. While a
gesture is drafting the layer is hidden and snapped opaque, so a new
drag shows its draft at once; past the fade it is hidden again, and a
settled canvas composites one image as before.
dtourolle
ade627a5d0