While a tool was busy (a drag in progress) the shortcut handler passed
only Up and Down to it, so the Rectangular and Polar Grid tools never
saw Left/Right, which add and remove columns (radial dividers). All four
arrows now go to the busy tool; the tools that use arrows for something
else (Gradient, Perspective Selection) ignore them while busy.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>