The shared right panel is collapsible with collapsedSize="0%", so dragging
the divider past minSize makes the library collapse it to zero without
going through the state that owns the panel. The panel disappears while
that state still reads open, leaving the divider draggable but inert and
the panel's trigger needing two clicks to bring it back.
Mirror a zero-width resize back into the owning state so a drag-collapse
closes the panel the same way its trigger does, and keep recording
non-zero widths there as the size to reopen at.