Our client is a leading technology provider in the retail industry, delivering modern point-of-sale and store operations solutions to retailers across multiple markets. As part of an ongoing platform modernization initiative, they are evolving their client architecture away from a legacy Java 8 Swing-based POS client toward a modular, offline-first, multi-platform model — supporting stationary POS terminals, self-checkout kiosks, and self-scanning devices across diverse retail environments. The shared business logic layer is built with Kotlin Multiplatform (KMP), targeting both JVM/Desktop and Android clients. This layer is the heart of the platform: it owns the domain rules, use cases, and data flows for critical retail operations — item registration, checkout, payment, customer management, and promotion handling — while remaining fully decoupled from platform-specific concerns and UI. Business continuity through offline operation, high testability, and performance under real retail conditions are non-negotiable priorities.