A deletion that still fails after the backed-off retries is no longer
dropped. It moves to a dead letter queue retried after 24 hours, then to a
second one retried after 48 hours, and is dropped only if that fails too.
The id stays in the durable deletion ledger the whole time, so a restart
replays it instead of losing it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>