spread the pasta out in a shallow bowl or on a sheet pan to cool completely.

This helps prevent residual heat from thinning the mayonnaise too much.
Prep the celery: While the pasta cools, wash the celery ribs thoroughly, paying attention to any grit near the base. Trim the ends and any fibrous outer strings, then finely dice the celery into small, even pieces.
Smaller dice means you get a pleasant crunch in every bite without overwhelming the soft pasta.
Make the simple