The most common permanent receiver error arises for likes/boosts
when we don’t yet know the rlevant object and can't fetch it
due to the remote being overwhelmed or otherwise down.
Before this changes all retries were rather rapid
thus not giving the remote enough time to recover
and usually all failing. Now the remote has about 20
minutes to recover before we give up.
Transient errors from race conditions and (presumably)
weird database-cache interactions also occur regularly.
However, they resolve within the first one or two retries
and those intial retries still happen relatively quickly.
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