code-implementer

This skill should be used when the user asks to 'implement', 'write code', 'build a feature', 'create a function', 'add functionality', 'code this', 'make this work', or needs to write production code for Java/Spring Boot or TypeScript/Next.js following FP, DDD, and testability patterns. Ensures code follows functional core/imperative shell, proper invariants, Either-based error handling, and is designed for testing without mocks.