PermissionError is a subclass of OSError, so it was caught by the
broad timeout/io handler and classified as transient. An unreadable
file would retry 5 times then DLQ — permissions don't fix themselves
without operator intervention.
Add an explicit PermissionError check before the OSError catch so
unreadable files go straight to the DLQ.
FileNotFoundError is a subclass of OSError, so it was caught by the
broad timeout/io handler and classified as transient. A file deleted
between discovery and fetch would retry 5 times on a file that's
permanently gone, then DLQ with a confusing error message.
Add an explicit FileNotFoundError check before the OSError catch so
deleted files go straight to the DLQ.
