[packetlost]

The traditional way is to reduce the surface area of the core package as much as possible, such that it sees less changes/releases overall.

The way I would do it with nix is: because everything gets hashed, just check that the built output with a new nix-pkg version matches the hash with the old version and fail out/fetch the older version as a second step. The rest is just finding ways to cache that build fail information so that you can share the result across users transparently.

[kaba0]

There is work on content-based hashing, but that is not only related to flakes. So that problem may get solved, and is likely the correct path forward.