- delivery_id is now generated once per firing and used for both the
X-Hermes-Delivery header and the signed body's delivery_id field —
previously they were two different uuid4s, breaking receiver-side
dedupe as documented.
- 3xx responses are no longer followed: urllib's default redirect
handler converts a redirected POST into a body-less GET, silently
dropping the signed payload. Redirects now log a misconfiguration
warning and count as delivery failure (no retry).
- Docs: receiver-side replay-protection guidance (dedupe on
delivery_id, timestamp freshness window) + redirect semantics.
- Tests: 5xx retry count, redirect-not-followed (sabotage-verified),
header/body delivery_id equality.
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