There are a few situations where v2spa should prefetch test suite descriptors, reports, and timeseries data, but only if that would not interfere with loading data that the user has already explicitly requested. This feature probably belongs in the CacheRequestBase class, which already has a set of IN_PROGRESS instances to deduplicate requests. The RequestBase class could add a "Purpose: prefetch" header when the caller sets options.prefetch to indicate to the service worker that it may delay or cancel the request depending on load.