Instance
Sealed marker interface for all instance-bound exception invokers.
Implementations of this interface correspond to the different supported @ExceptionHandler method shapes on subscriber instances, such as:
(event: Event, throwable: Throwable)(event: Event)(throwable: Throwable)
Each concrete invoker encapsulates the compiled call target for a specific handler method, using either a LambdaMetafactory backed implementation or a reflective fallback. The event system treats these invokers uniformly at the type level while still allowing dispatch code to distinguish them via sealed hierarchy pattern matching when needed.