Consider a program that inspects its own filename extension in order to discriminate whether it should be presented as an app or as an LP-style document. .html -> LP (with a go button?), .app.htm -> runnable.
This should probably be implemented as a reusable class. The program's own SystemB can delegate to it with something like:
let blotter = LPBlotter(document);
let did = blotter.blit(".html");
if (did) return; // ...
Additionally, we might seize the opportunity to do a lot of heavy lifting to allow said blotter to accept e.g. S4 messaging payloads.