[beachy]

If the code detecting the error is a library/subordinate service then the same rule can be followed - should this be immediately brought to a human's attention?

The answer for a library will often be no, since the library doesn't "have the knowledge/context to decide whether it warrants alerting".

So in that case the library can log as info, and leave it to the caller to log as error if warranted (after learning about the error from return code/http status etc.).

When investigating the error, the human has access to the info details from the subordinate service.