• Engineered a containerized (Docker) Next.js/Node.js media showcasing application enforcing strict single-session-per-device authentication using JWTs and a Redis cache. • Resolved complex client-side race conditions during rapid user interactions by implementing a custom mutex lock for predictable state updates and seamless Optimistic UI rendering. • Engineered thread-safe, idempotent API routes to eliminate backend check-then-act race conditions, utilizing atomic Mongoose operators ($addToSet, $pull) to maintain strict database integrity under high-frequency traffic. • Streamlined backend data fetching and API response times by aggressively leveraging Mongoose's .lean() function to strip instantiation overhead from MongoDB documents. Plus, using atomic operations to prevent database inconsistency.