We definitely standardize runtime and compiler versions across runtime environments and build servers and have planned upgrade paths with rollback options.

Not so much a fork as a package cache - but usually for anything important, absolutely.

Yes. That is, you check in the binaries.

Do I do this for hobby projects? No, of course not. If my toy projects break, meh. But for production? Where breakage actually costs money? Damn right I do.

It's not only breakage, though. You want a hermetic build system, so you can build software reproducibly and consistently. There are few things more "fun" than building "the same" code on two machines, and one executable has a bug while the second doesn't. (OK. Compiler bugs are even more fun)

Should fork the OS its running on too! /s

Most def otherwise bad patches might ruin their production