The architecture diagrams need to be augmented to explain the different considerations which become important at each level. For example: the difference between storing notifications versus processing them immediately and then discarding the notifications (or just storing the IDs), and the effect of these choices on HTTP timeouts.
Document issue for Option 1: if the consumer is tightly coupled with receiver, then HTTP timeouts run the risk of including the time taken to consume the notification which distorts the whole timeout aspect.
Document pros and cons of storing notifications versus not storing them
The architecture diagrams need to be augmented to explain the different considerations which become important at each level. For example: the difference between storing notifications versus processing them immediately and then discarding the notifications (or just storing the IDs), and the effect of these choices on HTTP timeouts.