Oie Engine API

Native engine API for account metadata, XMPP connections, text conversations, reply composition, explicit room sessions, durable message acceptance, and replayable SSE. Credentials are write-only and stored only by the owning engine. All timestamps are UTC and entity/operation IDs are UUIDv7. HTML belongs to the BFF. Known problem responses link to their catalog entry in the Link header with rel="help". Send Prefer: oie-problem-documentation to include the URL in the Problem Details body.