The clipboard spec selected text in the previous node's panel while it was
still sliding out after the paste, so the selection collapsed when it
unmounted and the canvas took the copy. The values spec read the panel's box
mid-slide-in, where the translate leaves the width a float off 400.
A bound chord used to be `preventDefault`ed before its handler ran, so the
canvas took every ⌘C and ⌘V whether or not the node clipboard would act —
which is what blocked copying selected text out of the chrome floating over
the canvas. A binding may now return `false` to decline the key; ⌘C does so
when there is a text selection or no node selected, ⌘V when nothing of ours
is stored.
stroblme