Package success implements a very simple plugin that looks that the ResultSet.Success() value to determine if the process from the sandbox exited successfully.
Most engines implements ResultSet.Success() to mean the sub-process exited non-zero. In this plugin we use this in the Stopped() hook to ensure that tasks are declared "failed" if they had a non-zero exit code.
The attentive reader might think this is remarkably simple and stupid plugin. This is true, but it does display the concept of plugins and more importantly removes a special case that we would otherwise have to take into consideration in the runtime.