gscottar is correct. The first pick is protected. That is why the Cardinals only lost their second rounder this July for the signing of Contreras last December.
P.S. And to the issue of rebuilding the pitching pipeline being discussed on another thread, losing the 56th overall pick and about $1.5 million in signing bonus allocation hurts the rebuild of the pitching in the system. (I assumed it would have been a pitcher after they took the outfielder Davis in the first round. But that wasn’t assured since they didn’t take their first pitcher until the fourth round. That surprised me.)