> Does the business mandate we use a cache for this hot path? No, but the business set performance targets, and the cache was a sensible way to satisfy them. See the difference?

That's a non functional requirement (NFR).

If that exists, (fantastic!) then you should add that to the code. Some languages let you do hat directly on the rpc Apis/rest resources, i.e. java most commonly used frameworks let you define them via annotations.

And as the sister comment pointed out, yes, that cache becomes part of your spec to achieve that NFR