KHAAD Setu: A Concurrency-Safe, Role-Separated Village-Center Marketplace Platform for Smallholder Farmers

Abstract—Smallholder farmers in India lose time and money to three recurring frictions: government schemes that are unclaimed because the tools publishing them are not usable by a digitally unfamiliar, non-English-reading farmer; a physical marketing chain that leaves one or two buyers in practical reach; and agronomic decisions made without structured data. We present an empirical engineering study of KHAAD Setu, a deployed village-center marketplace platform that addresses these frictions as one integrated system. The system comprises a 24-route, 49-service Express.js/PostgreSQL backend and a single Flutter codebase that compiles into three role-separated Android applications (farmer, village-center operator, platform administrator) sharing one design system and one API. Its core contributions are (i) a race-safe, SAVEPOINT-based multi-center stock-reservation design built on a single guarded UPDATE; (ii) a server-enforced role/flavor-separation pattern in which an app build can only narrow, never widen, an account's privileges; (iii) a self-built staged-rollout self-update mechanism with a provably monotonic rollout; (iv) a test-enforced Marathi/Hindi localisation layer; and (v) a deterministic scheme-eligibility engine over roughly fifty schemes. Verification comprises 440 backend and 604 frontend automated tests, all passing, and a direct inspection of the AWS EC2/RDS/Cloudflare-Worker deployment that found the repository documentation had drifted from reality. We report limitations with equal weight: roughly a dozen undeclared foreign keys, no CI/CD, partial localisation, an RDS connection that is encrypted but not certificate-verified, and no formal security audit or load test. This is a feasibility and engineering-verification study, not a field trial of farmer outcomes.