read() returned None for ENOENT, a refused read and malformed bytes alike, so
the carrier survey dropped an unreadable newer claim (its older alpha+beta copy
then executed again, replaying completed alpha) and write() replaced an
unreadable orphaned record (losing its restart obligation).
Only a missing file is absent now; a refused or malformed one raises
RecordUnknown (an OSError), so selection, claiming and the new pause's write
fail closed and leave every file for a later, readable retry.
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