Source explanation
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MSG · Critical priority
Message + delivery services
Authoritative lifecycle producer for server acceptance and per-device delivery outcomes. It reports committed messaging state; clients cannot declare a message delivered.
WhatsApp example
A message is durably accepted in ap-south, routed to two registered devices, delivered to the phone in 132 ms, and remains pending on desktop.
Event grain
One lifecycle transition for one message and one recipient device. User-level delivery is derived later from device-level facts.
Delivery behavior
Publish only after the owned state transition commits. Retries reuse the logical event ID; delivery acknowledgements may arrive late or out of order.
Contract and join keys
Key by message or conversation where ordering matters; carry stable event_id, canonical message_id, event_time, device-grain outcome, retry count, region, and trace ID.
Downstream use
Delivery SLOs, retry analysis, queue health, multi-device metrics, support diagnostics, and certified delivery facts.
Privacy boundary
Payload remains ciphertext. Tokenize conversation and user identifiers; omit phone numbers, message text, and raw contact data.