Subscriber created

Someone became a subscriber of the newsletter. Four paths land here: subscribing from inside the Commune app, finishing signup, accepting an invitation, and a CSV or ESP import.

Only the import path records where they came from. data.acquisition_source carries the provider there and is null on the other three, so null is the normal case for anybody who arrived through Commune itself rather than a sign that the origin was lost.

Reactivation counts. Unsubscribing does not delete a subscriber, so a returning reader comes back to subscribed rather than being recorded again. That still fires this topic, with data.resubscribed: true.

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.