The default attempt budget was three, and with the 1s/2s/4s backoff a
destination that was unreachable for about ten seconds had its
notifications dead-lettered permanently. A webhook receiver rebooting
alongside the infrastructure it monitors is routine, not terminal.
Eight attempts under the same doubling schedule span roughly three
minutes before dead-lettering. Dead-letter semantics are unchanged.
Refs #1721
Contract-Neutral: Refs #1721: raises the default delivery attempt budget only; dead-letter semantics, retention, and outcome vocabulary unchanged, notifications.md pins no attempt count
rcourtman
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