webhook_delivery_not_redrivable
This code is raised on a non-customer surface (the /internal voice-runtime audience or telephony provider callbacks). It is excluded from the customer OpenAPI document and is registered here so an operator reading a log line has one place to look.
webhook.delivery.redrive was asked for a delivery that is not exhausted. A pending or failed one is already on the retry ladder and needs nothing; a delivered one was received, and re-sending it would put the same event in front of the customer a second time on an operator's timescale rather than a retry's - which is the one duplicate the at-least-once contract does not prepare a consumer for (CANON fact 30). The same code answers the lost race, where the retry worker settled the row between the read and the write, so a redrive can never resurrect a delivery that succeeded (18-admin-console.md §6.5).
Problem shape
Every non-2xx response is an RFC 9457 application/problem+json body. The type URI below is stable and machine-matchable, so branch on the final path segment (the code) and treat the status as redundant confirmation. See the error-handling guide.
{
"type": "https://docs.vocapable.com/errors/webhook_delivery_not_redrivable",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}