gateway distributes multiple systems simultaneously

### Question

The upstream system is responsible for requesting the gateway, and the gateway simultaneously pushes (in parallel) to the downstream system. The failure of a single system's reception and processing does not affect other systems.
Our idea is: a downstream system corresponds to a selector, and since the gateway is a chain of responsibility mode, it concatenates and executes various selectors. So if the previous selector (receiving system) fails to execute, it will affect the reception of other systems。
May I ask how to implement this requirement

The issue names no files or tests, only the gateway's selector chain and downstream systems. Start by tracing how selectors are executed and how a downstream reception failure propagates through that chain. Done means one downstream failure no longer prevents other downstream systems from receiving and processing the request.

Written by the indexing model from the issue text.