How a practice app learned to say 'we cannot tell yet' instead of faking progress

CogniPrep, a score-tracking practice platform, discovered that displaying trend arrows based on linear regression slopes was misleading users with false improvement or decline signals. With only 8–12 data points typical in practice sessions, the app found that statistical significance testing alone was insufficient — a result could be significant yet still indicate decline, not improvement. A separate performance bug was also uncovered where the same database query was being executed twice sequentially on every dashboard load, doubling Postgres round trips unnecessarily. The fix involved passing pre-fetched session data as an optional parameter to the analytics engine, eliminating the redundant query while keeping call sites flexible. The broader lesson highlighted is that Next.js fetch deduplication applies only to the React rendering path, not to API route handlers.