Segments on the API

We've added segments to the API: saved, reusable audiences — a named set of tag and metadata filters that you can apply as the audience of an email instead of rebuilding the same rules every send.

Five new endpoints:

• GET /v1/segments
• POST /v1/segments
• GET /v1/segments/{id}
• PATCH /v1/segments/{id}
• DELETE /v1/segments/{id}

Note that an email's audience is a snapshot: applying a segment copies its filters onto the email, so editing or deleting a segment never changes emails you've already sent or scheduled. Emails continue to accept filters directly; segments are purely additive, and no existing endpoints change behavior.