The snapshot is written to the shared app group and read by tvOS with
the app not running, so clearing the cache in memory and on disk left
the previous login's feed sitting on the system home screen. Nothing
rewrote it: only a successful refresh and app launch ever did, so it
survived until whichever came first — and if nobody refreshed under the
new login, indefinitely.
Written from the cleared cache, which is what erases it.
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