nix's bun loads through a glibc in the nix store, and bun build --compile
copied that loader into bin/quak, so nix-collect-garbage could break the
cron backup. The build moves into script/build-bin. On Linux it downloads
bun 1.3.13's release archive for the machine from GitHub: x86-64
(baseline) or arm64, glibc or musl. It checks the archive's SHA-256
before running it, and compiles with that bun, so the binary loads
through the system loader. macOS still runs bun through nix-shell.
Model: opus-5-5
