Function move_pin 

pub fn move_pin(
    indexed: &IndexedDocument<'_>,
    pin: PinId,
    to: PinSlot,
    builder: &mut CommitBuilder,
)

Inventory row “Move Pin”: drag a pin to another slot or the opposite edge. The slot the drop resolved to arrives decided (the gesture picks between the nearest slot and its neighbour against the live preview); a destination another pin already holds writes nothing.