Various technologies and techniques are disclosed that improve failure handling and debugging in message driven environments. A diagramming tool allows a user to graphically nest one or more functional components of the data flow diagram to create a fault handler. The fault handler is associated with a failure component to be called when a failure occurs within any one or more of the nested functional components. One or more application executables are synthesized from the data flow diagram. When the nested component is created at runtime, a causality is created for the nested component. The causality has an exception port for receiving fault messages that are unhandled within the nested data flow associated with the nested component. The causality also has a coordination port to allow any messages in the causality context and/or other applications to access the error history and the message coordination history.