- Load GitHub 403 retry helper only when available
- Fallback to plain `nix run` if retry function is not defined
- Prevent exit 127 when pkgmgr launcher is installed without retry script
- Fix E2E failure for `pkgmgr update pkgmgr --system`
https://chatgpt.com/share/693efd23-8b60-800f-adbb-9dfffc33f1f7
- Require retry_403.sh to exist and fail hard if missing
- Source retry helper unconditionally
- Run nix flake execution via run_with_github_403_retry
- Prevent transient GitHub API rate-limit failures during nix run
https://chatgpt.com/share/693ed83e-a2e8-800f-8c1b-d5d5afeaa6ad