This PR fixes grade-visibility behavior in the Progress Tab API when staff users are masquerading as learners. Previously, subsection show_grades was computed using the real requester’s staff access, which could expose grades that the masqueraded learner should not see. Now, show_grades respects the masqueraded user’s permissions so the API response matches the learner view. Co-authored-by: Peter Pinch <pdpinch@mit.edu>