> I mean, people usually call those 'feature' when they're built-in.
No, that's specious reasoning. A message queue is still a message queue if you use one provided by the OS. An exception is still an exception even if it's provided as a standard component. A state machine is still a state machine regardless of how you choose to implement your concrete implementation.
Design patterns are all about the patterns followed when designing something. That's it.
If I have to implement something similar myself in C++ however, I'll use a niche design pattern.