More specific: being too generic can be solved by downcasting in consumers without affecting the module boundary; being too specific cannot be solved without ch

More specific: being too generic can be solved by downcasting in consumers without affecting the module boundary; being too specific cannot be solved without changing inter-module interfaces. Having a generic callback interface exec(Map(object,object)) is ugly, but better than changing 76 upstream and downstream modules' interfaces with code ownership and release cycles across different vendors/organizations.