Got asked to design something with actual constraints instead of the usual 'design Twitter' and froze anyway

Small company, five person eng team, and the system design round was just "how would you handle nightly reports that keep timing out." No whiteboard cliches, no read-heavy vs write-heavy framing to fall back on. Realized I'd only ever practiced the textbook problems and had nothing for a real messy one with actual numbers attached. Still got the offer, but I've stopped assuming interview prep from a course maps onto what companies actually ask.