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This project started as a small commissioned task for a client’s capstone project. Initially, I was only hired to resolve a CORS policy issue blocking their system. After successfully delivering that fix, the client entrusted me with a full system revamp. I transformed their existing setup into a complete full-stack MERN application, redesigning both the frontend and backend architecture for scalability, maintainability, and performance.

While I already had experience building inventory management systems, this was my first time developing a POS system tightly integrated with inventory operations. The real challenge wasn’t just processing sales — it was preserving transactional integrity and inventory accuracy, especially around complex return and replacement workflows. With clearly defined business rules from the client and careful architectural decisions on my end, I was able to implement a robust solution that handled partial returns, item replacements, recalculated totals, and additional cash rendering without breaking the transaction flow.

On the backend, every sale, return, and replacement generates structured stock movement records linked to their respective transactions, ensuring traceability and audit readiness. Product quantities are bulk-updated efficiently, asynchronous sale number generation prevents race conditions, and coordinated operations maintain data consistency across collections.

On the frontend, I enforced state integrity by filtering API responses before committing them to state and applied a stale-while-revalidate caching strategy to reduce redundant requests. Complex return logic is encapsulated within controlled modal workflows to maintain predictable state transitions and prevent UI corruption.

Overall, this system was engineered to handle real-world edge cases while maintaining financial accuracy, reliable reporting, and clean inventory tracking — turning a simple bug fix request into a fully rebuilt, production-ready POS and inventory platform.