How do I replace a failing downcast without hiding an unexpected payload type?

A cast checks an existing object; it does not transform that object into another class. Follow the producer as well as the failing consumer. For a heterogeneous message boundary, use a type test such as if (payload instanceof String text) { consume(text); } else { rejectType(); } on a Java version supporting pattern matching for instanceof. Prefer a typed interface or sealed model when the producer is under your control. Do not catch ClassCastException around an entire request and pretend the payload was empty. Exercise each permitted type and one rejected type. If the class names look identical, inspect their class loaders; plugin isolation can make similarly named classes incompatible. This guard validates type, not the semantic contents of a message.