The new $system.external interface (aka "InterSystems External Servers") is used to call/integrate with external language code/libraries, it replace the old gateways (for example Java gateway) that required the import of proxy objects.
For the old Java and .NET gateways Caché included two test/sample classes:
This classes are still included in IRIS as of 2023.1.1, but the documentation of the old gateways has been removed.
The idea is implementing THE SAME FUNCTIONALITY using the same .NET and Java external code/classes but using the new $system.external interface.
This would be an extremely useful source of information on how use/implement $system.external.
Unfortunately with the current available documentation it is not possible to implement that, so this would be possible only for someone within InterSystems using privileged access to information not available to us customers.
Thank you for submitting the idea.
This idea was implemented by InterSystems.