> So I'll just reiterate my main point: a CI system must provide a workable caching mechanism if it want to be both snappy and reliable.

The problem is that none of the providers really do this out of the box. GHA kind of does it, but unless you run the runners yourself you’re still pulling it from somewhere remotely.

> I've worked for over a decade on one of the biggest Rails application in existence, and restoring the 800ish gems from cache was a matter of a handful of seconds.

I kind of suspected - the vast majority of orgs don’t have a team of people who can run this kind of a system. Most places with 10-20 devs (which was roughly the size of the team that ran the builds at our last org) have some sort of script, running on cheap as hell runners and they’re not running mirrors and baking base images on dependency changes.