This is why you have a Testing environment you can sandbox this kind of thing out on first ;-)

Or, as the old sawhorse goes, "every company has a Testing environment. Some companies are fortunate enough to have a separate production environment as well"

True in general, but I don't think this one's that simple. npm made a perfectly reasonable configuration change that incidentally happened to break yarn. Hard to predict since you can't sandbox every internet service that might be unexpectedly depending on you, and arguably not really npm's problem anyway. (Much to their credit, npm jumped on the issue and contacted their CloudFlare rep to help unbreak yarn, but I don't think they're responsible to proactively anticipate things like this.)

On the contrary this is exactly why you do it on a holiday weekend. Minimal impact to the world as hopefully your users are yarn installing a beer instead of a package.

This was our plan: prod load, but not super load, not a lot of work that we'd disrupt with bug shakeout. I don't have a good way to simulate production load on our staging environment right now (some day) and that wouldn't have shaken this one out anyway.

Someone is learning about “read only Fridays” the hard way.

Can it wait until the start of the next week? Almost always.