Send completed

A send run finished handing every recipient to the email provider, and the run was stamped with the completed_at this payload carries.

This is the dispatch milestone, not the delivery milestone. It says the provider accepted the messages; whether they landed in inboxes is what the delivery.* topics report, and those arrive later and one per recipient.

Named for the send rather than the article: one article can have several runs across retries, each with its own id at /sends/{send}. data.article_id is there for anyone routing by article.

Delivered as a single HTTPS POST to the consumer's registered endpoint, with the message as the JSON request body. Respond 2xx to acknowledge. Anything else, or a timeout, is retried with backoff, so acknowledge fast and do the work afterwards.