It looks like I may have bitten off more than I can chew with this little project. I'm not completely certain, but it looks like the concept of an EGL Rich UI application using nothing but an HTTP server is not going to work. Unless I'm mistaken it looks like the Rich UI REST calls go through a proxy servlet. This is done for a practical reason; it allows the Rich UI to make calls to services other than the original host, a feat which is not allowed in normal AJAX calls. However, it does mean that even if the actual REST service is served by Apache (such as my RPG-CGI service), the proxy servlet still needs to be running in a web application server on the host.
Thus the vision of a Java-free Rich UI application has hit what may be a fatal roadblock. (Note: the reason it worked in debug is that evidently the workbench has that proxy server magically enabled. I still don't have all the details on that bit of sleight-of-hand, but I'll let you know if I get more specifics.)
It was still a useful learning experience, but all in all I'd have preferred a better outcome. In any case, I think it's time to put the Java-free RUI on the side and get back to traditional Rich UI development. And if nothing else, I've got a cool widget written.
Look for the "normal" version in the next day or two.