Function retry 

pub async fn retry(
    pool: &PgPool,
    actor: &Actor,
    delivery_id: Uuid,
) -> AppResult<Delivery>

Schedules a failed (or waiting) delivery again, now, with a fresh set of attempts. The delivery id stays the same, so receivers can deduplicate.

Invariants

• Permission: administrator (403); unknown delivery is “not found”; a delivery already sent (409) or of an inactive webhook (409) is refused.
• Locks: the delivery row (FOR UPDATE).
• Data: status back to pending, attempts reset to 0, due now.
• Audit: webhook.retry.
• Notifications / webhooks: none.
• Atomic: one transaction.