> For example, suppose a startup has an Express app that made downstream requests to Postgres, Redis, Kafka, other REST APIs, etc

And besides network calls network-bound requests, what about reading from sqlite, files, and interprocess communication.

What about ZeroMQ over UDP? A remote time service. Pulling from a git repo.

No really, I'm asking because I'm trying to figure out how to deal with all this in my tests right now, and I honestly have no idea. But I doubt Codeparrot is going to be able to intercept and intelligently mock everything.