Delivery-status webhook for broadcasts (alert on failed ack)

POST /message/broadcast returns a broadcast_id, but that only proves the request was accepted, not that anything delivered. During a recent outage, a completely dead queue and a healthy one looked identical

from the API — every call returned 200.

Two things would close this:

1. A message.ack.updated webhook (or confirm it exists) so we can alert on ack: -1 (failed) within minutes.

2. A broadcast-level delivery-status endpoint, like the per-message GET /messages/{unique_id}/status.

   
   Right now there's no supported way to detect that scheduled messages silently stopped sending.