Fixing macOS Nix Evaluation and Git Stat-Cache False Positives

In this entry, I tackle three subtle setup bugs that only manifest on fresh Apple Silicon macOS installs. By analyzing Nix evaluation logs and Git index behavior, I platform-gate Linux-only packages like alsa-utils, collapse twenty-four lines of verbose setup chatter into a single status line, and eliminate a false 'local modifications' warning with git update-index --refresh.