Error in backend calling fetch more than once when archive is set

When we implemented the `Archive` object, we considered it will only store the items of a single `fetch` call. It can't be reused to store the raw responses of several fetch tasks.

If the archive is set, it will produce an error because the archive object is given when the object is initialized and not when `fetch` is called.

To fix this issue, #527 must be completed first.

Start by reading issue #527, then trace how the Archive object is initialized and supplied to fetch. Done means an archive can handle the raw responses from multiple fetch tasks without producing the reported error when it is set.

Written by the indexing model from the issue text.