A link import's tile lived in the Library view's own state, so a
remount or reload dropped it while the job kept running, and the asset
showed up later with no tile. Link imports now share the intake store
with file imports and are saved per account while they run; the
Library resumes them under the same key, which gets the job already
running. The engine answers a repeated key with the download in
flight, and a landed asset the listing already holds is not listed
twice.