I don't think that'll work. Asking for consent and retrieving the robots.txt is yet another request with a similar workload. So by that logic, we can't do anything on the internet. Since asking for consent is work and that requires consent, which requires consent... And if you're concerned with efficiency alone, cut the additional asking and complexity by just straightforward doing the single request.

Plus, it's not even that complex. Sending a few bytes of JSON with daily precalculated numbers is a fraction of what a single user interaction does. It's maybe zero point something of a request. Or with a lots of more zero's in-between if we look at what a server does each day. I mean every single refresh of the website or me opening the app loads several files, API endpoints, regularly loads hundreds of kilobytes of Javascript, images etc. There are lots of calculations and database requests involved to display several posts along with votes etc. I'd say one single pageview of me counts like the FediDB collecting sttats each day for like 1000 years.

I invented these numbers. They're wrong. But I think you get what I'm trying to say... For all practical purposes, these requests are for free and have zero cost. Plus if it's efficientcy, it's always a good idea not to ask to ask, but outright do it and deal with it while answering. So it rally can't be computational cost. It has to be consent.