Subscriber tag added or removed

A tag was added to or taken off a subscriber. data.direction says which: assigned when the tag was put on, removed when it was taken off.

One topic carries both directions, so subscribing once is enough to mirror a segment's membership.

Applying a tag is idempotent, so re-applying one the subscriber already holds produces no second event. A tag is not a label: it scopes who an article is sent to and who may read it, so treat these as access changes.

Retiring the tag itself has no topic. It retires the tag for everyone at once rather than removing one assignment, so it does not fan out into one event per subscriber here.

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.