Old EDK API would only fire process errors on validation failure. The C API usefully triggers them on normal process disconnection as well. We can't currently forward the latter to the public C++ invitation API because a lot of code is written to not expect callback invocations in non-validation-failure cases e.g. normal remote process termination.

ProcessErrorCallback in the public invitation API should probably be replace with a new ProcessObserver interface that can observe events like OnError and OnDisconnect, both of which which can be deduced from error handler invocations within the existing C API.