Your Mac never compiles

Compiling a Rust workspace on a laptop turns it into a hand warmer, and CI on hosted macOS runners is slow and expensive. Most teams accept one or the other.

Here a package opts into macOS with one line: cross = true. The Linux CI fleet cross-compiles it for Apple silicon, pushes the closure to cache.ix.dev, and aliases the result into the native Darwin package set. A Mac running nix build substitutes the prebuilt binary instead of compiling anything. The package definition never learns any of this happened.

The design and its tradeoffs are written up in Plan 0009, which the fleet has since made load-bearing.