Highlight created

A reader marked a passage of an article.

No user_id. A highlight is never attributed to a named reader anywhere in Commune, so this payload carries the same opaque owner_key GET /highlights/{highlight} does. It is the one topic whose payload cannot be resolved back to a person.

Fires on a new highlight only. Re-marking the same span of the same article is silent. So is attaching a chat message to a highlight that already exists, which is how a passage becomes a discussion; that fires message.created for the message instead.

A highlight created together with its discussion carries data.message_id from the start. One created on its own carries null and never gains a value on this topic.

A passage of a tag-scoped article can only be marked by someone in its audience.

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.