Differentiate between request types

[lastmjs]

Not all requests for file extensions are equal. For example, requesting a JSON file as an ES module import is different from requesting a JSON file with the link rel manifest element...right now this will break, because a request for a manifest file will return a JavaScript module with the json exported. We will have the same problem for CSS and images. We need to somehow differentiate, and return files unmodified sometimes and modified other times. It would be nice if a request header for ES modules was set...but I'm not sure there is a standard one nor do I know how to set it for all ES modules with a Zwitterion build