Kie-maven-plugin documentation states that "the plugin also pre-generates many classes, making the runtime loading faster too." However these generated classes, together with the other metafiles necessary to use them, aren't added to the jar produced during the package phase.
Fixed by https://github.com/droolsjbpm/drools/commit/c572148c1
This fix has been also cherry-picked to 6.0.x branch with this commit https://github.com/droolsjbpm/drools/commit/94b9ccf810100c7ec3f8ed186111720ddb2729d3
Verified fixed in 6.0.1-ER1.