As others have done on this issue - I should just say "Never mind. I found the problem." And leave it there...
Instead, I'll set a good example and describe the solution. The culprits were two properties used when starting up jboss:
Code:
<sysproperty key="javax.xml.parsers.DocumentBuilderFactory" value="org.apache.crimson.jaxp.DocumentBuilderFactoryImpl" />
<sysproperty key="javax.xml.parsers.SAXParserFactory" value="org.apache.crimson.jaxp.SAXParserFactoryImpl" />
Removing these properties allowed, at least, the .har file to deploy. This may impact another aspect of my app, but that's a different issue.