With next week’s trade deadline approaching — and the Red Sox expected to upgrade their roster — it’s fair to assume some players on the current roster could find themselves in different roles by the time the calendar flips to August. On Monday, Walker Buehler took a step toward staking his case that he should remain in Boston’s rotation no matter who Craig Breslow brings in to fortify it. The Red Sox are confident in a top three of Garrett Crochet, Lucas Giolito and Brayan Bello but are looking for a rotation addition to fortify a group that will be without Hunter Dobbins and, most likely, Tanner Houck, for the stretch run.