Queue Acknowledgement
Problem
A broker sends a message to a worker.
Should the broker delete it immediately?
What if the worker crashes one millisecond later before processing it?
Solution — Acknowledgement
The consumer tells the broker when processing has reached the required success point.
Broker → message → Worker
↓
process
↓
ACK
Only then can the broker safely consider that delivery complete according to its semantics.
Core idea: acknowledgements let messaging systems distinguish delivery from successful consumption.