Major Description
For handleInputInitializerEvent - this should be fairly straightfoward to handle. At the moment this is an inline call from within the AsyncDispatcher, and will end up causing a RuntimeException. The RuntimeException can be changed to a AMUserCodeException which will take care of this.
For onVertexStateUpdated, this eventually gets invoked from within RootInputInitializerManager. Catching exceptions there and sending a RootInputInitialzierFailedEvent should be enough to fix this ? May require some state machine changes to handle this event on a few more states.