alt Hacker News> 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?
This seems confused. Specs are free to include as much or as little detail as they deem necessary. If a spec only wants to suggest vague performance goals and handwave the details, that's permitted. But if specs want to specify the exact means by which performance will be guaranteed, that's also permitted. And this isn't an anti-pattern, this is often very useful. For example, plenty of APIs in the real world specify algorithmic upper bounds for time and space consumption, which is useful in that they allow downstream consumers to have a greater understanding of what sort of performance their own systems will exhibit despite the API itself being a black box in other respects.
So the answer to the original question definitely isn't "no", it's "maybe, depending on the sort of guarantees we want to provide to our users".
I think we are actually saying the same thing! We could think of situations where the cache would be verboten (sensitive info), or where it would be mandatory, like in your example, or optional like in my example.
My aim was to voice disagreement with the "code is spec" crowd, whom I think are using a different (and in my opinion tautological / useless / counterproductive) definition of spec. Probably because they are mad that I use trigger words like Vibe and Maxxing, and they assume I can't even read the code I'm shipping. I digress.
In your "time complexity is a downstream requirement" example, which is a great one, I think you would prefer to have well-maintained written documentation of that criterion that lives outside of the procedural code itself, would you not? How much attention that doc gets is a matter of process and preference, but I'm advocating it should get more (spec-first).