A network engineer manages a pair of Nexus 9000 switches configured as a vPC domain acting as the aggregation layer for several downstream access switches connected via vPC port channels. Currently, only the vPC primary switch is configured as the STP root bridge, and the engineer notices that if the primary peer reloads, a spanning-tree reconvergence event occurs that briefly disrupts traffic. Which feature should the engineer enable to allow both vPC peers to present themselves as a single logical STP root and eliminate this reconvergence?