Ok. I got it. Finally. I had given up, but one night on my drive home I got a crazy idea...and it worked.

I created a Mason file that produces JavaScript, call it loader.mjs, that takes at least the "/somepath/foo.dynjs" as an argument in the query string. This satisfies the Mason handler's desire to have a physical file. The Mason code inside of the loader.mjs file calls the library that resolves the dynjs file, and I can $m->comp that result, and it all just simply works--session intact, etc.

In retrospect, of course this is the easiest way to do it. And, once of thought of it, it took me hardly 20 minutes to hook all of the pieces together in the correct way (after the hours over several days trying to make it work the other way above). Sigh.

jason.