Delivers runtime events to registered webhook endpoints.

Subscribes to the lattice:events PubSub topic. For every event, each matching active endpoint gets an HMAC-signed POST (see Syntropy.Webhooks.Signature) executed under the bounded Syntropy.WebhookTaskSupervisor with bounded retries and backoff. When the supervisor is saturated (max_children reached) the delivery is recorded as failed rather than crashing or queueing without bound. Destination URLs are re-checked against Syntropy.Webhooks.UrlPolicy right before each delivery, so a DNS record that starts resolving to a private address after registration is still blocked.

The HTTP transport can be overridden through the :syntropy, :webhook_http_post application env (a 3-arity function of url, body, headers), which the test suite uses to capture deliveries without opening sockets.