Cool.  Knowing that it is both possible and easy means we can focus on what is the right thing to do.  As this is an external cache (i.e., one that persists between calls, one that the caller is aware of etc) and one that may need time to time maintenance (yes, I did specify --force on the fetch, but things do go wrong), I claim that it is invaluable to have file names for which the purpose is readily recognizable.