ci(mac): cache nix store between runs#22
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Repeated runs re-download the same Nix packages from cache.nixos.org every time, adding ~2m to the mac job. Cache the store keyed on init.sh's hash so subsequent runs find packages already present. A fallback prefix allows partial hits when only some deps changed. Store is capped at 1 GiB to stay within GHA cache limits. Co-Authored-By: Claude <noreply@anthropic.com>
Three issues made the cache ineffective: the key hashed init.sh but not flake.lock, so nix-darwin rebuilds from a nixpkgs update would reuse stale cache entries and miss when flake.lock changed. Flake input tarballs (~/.cache/nix) were not cached, so nixpkgs was re-downloaded every run regardless of store hits. The 1 GiB cap was too small for a full nix-darwin activation, causing evictions that forced re-downloads on the next run. Raised to 5 GiB to stay within the 10 GiB per-repo GitHub cache quota. Co-Authored-By: Claude <noreply@anthropic.com>
cache-nix-action's post-job step runs nix --version to calculate store size before saving. Because mac-nix-setup never wrote to GITHUB_PATH, nix was absent from PATH in the post-run environment, causing an exit 127 that silently skipped the cache save — meaning the cache was never populated and every run stayed slow. Writing /nix/var/nix/profiles/default/bin to GITHUB_PATH persists nix across all subsequent steps and post-run hooks. The explicit profile source in bash init.sh is no longer needed and is removed. Co-Authored-By: Claude <noreply@anthropic.com>
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Repeated runs re-download the same Nix packages from cache.nixos.org every time, adding ~2m to the mac job. Cache the store keyed on init.sh's hash so subsequent runs find packages already present. A fallback prefix allows partial hits when only some deps changed. Store is capped at 1 GiB to stay within GHA cache limits.