Callback before deleting an early response

[theodiefenthal]

When an engine.notify() is called with a response, COPPER can not know wheter a workflow will start waiting for that message later on or whether the message is "garbgabe" out of COPPERs view. Thus, it is stored as EarlyResponse inside COPPER and will be deleted after a configurable amount of time.

Before COPPER finally deletes such a response, a user might want to react to that deletion. He might at least want to add an entry to an audit log such that on debugging later on, one can see what happend to that message and that it existed afterall.

So we could/should offer a callback setter for the earlyResponseContainer (Transient engine) and inside deleteStaleResponse in the persistent engine. For a distributed engine, the callback shall be called exactly once but we cannot tell beforehand, which engine is going to call that callback, thus every engine must know how to handle that callback.