The live panel width while the resize handle is being dragged. The panel sits on the
RIGHT of the overlay, so moving the pointer LEFT grows it:
startWidth + (startX - clientX), clamped to the standard
[SURFACE_PANEL_MIN_WIDTH, 70% of the overlay] band.
The live panel width while the resize handle is being dragged. The panel sits on the RIGHT of the overlay, so moving the pointer LEFT grows it:
startWidth + (startX - clientX), clamped to the standard [SURFACE_PANEL_MIN_WIDTH, 70% of the overlay] band.