The Cardinals acquire 2024 rotation help by using one or more of Tommy Edman, Ryan Helsley, Brendan Donovan, and/or Giovanny Gallegos in the package
The way John Mozeliak has been talking about this deadline, it's clear he believes their initial moves have not gotten them the 2024 rotation help they desire. That doesn't mean the packages they got back weren't good, it's just that those rental players were never going to get surefire rotation pieces for next year.
They technically do not have to get that done right now, but I know they would really like to have one of those new arms in St. Louis by the end of the deadline.
They still seem set on not trading Lars Nootbaar along with Jordan Walker, Paul Goldschmidt, and Nolan Arenado. Nolan Gorman remains unclear at the moment. But Bob Nightengale indicated that both Tommy Edman and Brendan Donovan are available in talks at the moment.
Ryan Helsley and Giovanny Gallegos have been rumored trade pieces as well since they are relievers with team control. Gallegos is having a down year but is still a really good option for a contender. Helsley has been injured but was one of the best closers in baseball last season.
I believe the Cardinals will use one or more of these players, and perhaps even packaged with some of the other names on this list, to get that cost-controlled starter.