A production community marketplace platform — built and owned end-to-end as Technical Lead & Sole Engineer of the Fyjix lab.. Engineered a role-based backend with multi-tier user visibility, payment approval workflows, and referral-driven revenue distribution. Designed a tamper-evident audit system using cryptographic hashing and approval chain chaining — ensuring end-to-end data integrity without relying on blockchain infrastructure. Validated system performance under concurrent load using k6: • 14.8 approvals/second throughput • 36ms median latency • 52ms p95 latency Deployed across isolated dev, UAT, and production environments with stable release cycles and full environment parity. Built for real users. Runs in production.