Senior capstone: a room-booking web app that four of us built and only I could explain

For our senior design capstone, four of us built a web app for booking study rooms in the campus library. React front end, a Node/Express API, Postgres behind it. On paper we split it evenly; in reality two people drifted and most of the backend plus the deployment landed on me and one other person. I owned the booking logic and the conflict check, meaning: don't let two people reserve the same room for overlapping times. My first version did a naive check and had a race, two requests could both pass the 'is it free' check and both insert. I fixed it with a database constraint using an exclusion constraint on the time range so the DB rejects overlaps, instead of trying to guard it in application code. We demoed it to the professor and a couple of librarians gave feedback, but it never actually ran in the library. The hardest interview moment was being asked to separate my contribution from the group's without throwing my teammates under the bus. I tried to be factual: here's what I committed, here's what I'd defer to them on. The interviewer seemed more interested in how I talked about the team than in the exclusion constraint itself.