Consumer Messaging Platform — WhatsApp-Class System · View 09 of 23

Offline Queuing and Retry Loop

The loop that makes delivery survive a device being off, offline or asleep — and the acknowledgement that closes it.

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The loop closes

Ciphertext is only deleted after a per-message acknowledgement from the device
No acknowledgement means the message is re-queued, not dropped
The thirty-day TTL is the only exit that is not an acknowledgement

Retry policy

Exponential backoff with jitter, capped so a fleet-wide reconnect does not stampede
Push is a wake signal only; the client pulls its own inbox after reconnecting
Drains are batched and ordered by server id to keep the client's write path sequential

Idempotency

The client discards duplicates by message id, so re-delivery is always safe
This is what lets the server choose at-least-once and stay simple
Receipts are idempotent for the same reason