Ideally we’d like to split this up more and count most invalid documents
as an error, but silently drop e.g. Deletes for unknown objects.
However, this is hard to extract from the changeset and jobs canceled
with :discard don’t count as exceptions and I’m not aware of a idiomatic
way to cancel further retries while retaining the exception status.
Thus at least keep a log, but since superfluous "Delete"s
seem kinda frequent, don't log at error, only info level.
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