Read receipts, delivered status and message synchronization

[mehalyna]

Task 7 — Read receipts, delivered status and message synchronization

Title: sync: implement message status (delivered/read) updates and sync across devices

Description

• When a message is broadcast, mark status='delivered' for recipients whose sockets acknowledged the message (consumer should send ack).
• When user marks messages read (via mark_read or automatically when viewing), update message docs and emit read_receipt via Channels to other participants.
• Ensure state changes persisted and visible via REST APIs (message status fields).

Acceptance

• Unit/integration test showing:

  • send_message → recipients receive event and ack,
  • ack triggers delivered status,
  • mark_read triggers read receipts to other participants.

Dependencies

• Task 3, Task 4, Task 5.

Notes

• Acknowledgement protocol should be lightweight (client emits ack with message id upon receipt).