Currently the set of libraries included in the ESB runtime does not include jboss-rosetta.jar. However, that's one of the most important libraries since it includes the interfaces custom actions have to extend. Without this in the ESB runtime by default, users will have to add an "External Jar" to their build path to get custom actions to build.

jboss-as/server/default/deployers/esb.deployer/lib/jbossesb-rosetta.jar