Concrete codegen implementation targeting Java (the host language). Provides JavaFunctionsCodeGen — emits a Java TransformationFunctions implementation (a JSON codec: transformTo / transformFrom) for a record ObjectDefinition. The Java target has no DefinitionCodeGen: the record IS the type declaration, so only the codec functions are generated. The emitted code is data (per the CodeGen-as-Functions doctrine) — produced at build time into ...