Framework-agnostic core: annotations (@WorkflowInterface, @ActivityInterface, ...), the deterministic replay engine, WorkflowClient, and Worker. Depends on nothing but protobuf/gRPC, Jackson (default DataConverter), and SLF4J (logging facade only — no bound implementation). No Spring, no Quarkus, no Micronaut, no application framework of any kind: every other module in this project depends on this one, never the other way around.