<!-- - "MDR" is the human term for the Sent activities surface: GET /v3/messages/{id}/activities. There is no separate MDR endpoint. - Lifecycle: QUEUED - ROUTED - SENT - DELIVERED - READ (WhatsApp/RCS only), with FAILED at any stage and RECEIVED for inbound. - Sent exposes its own normalized error codes (AUTH , VALIDATION , RESOURCE , BUSINESS , CONFLICT 001, SERVICE 001, INTERNAL ) on the HTTP envelope, plus send-time per-message codes (ERR CONSENT BLOCKED, ERR ROUTE DENIED, ERR TEMPLATE PARAMS INVALID) on the message field. See references/mdr-status-codes.md. -- Messaging performance analy…