package.el or straight.el for a reproducible Emacs config across machines?

Answer

For a single-user configuration that must work on machines with spotty network access, straight.el provides superior reproducibility because it allows for a local mirror of package repositories. If you have reliable network access and prefer a built-in solution, package.el is sufficient provided you commit the package-selected-packages list to version control.

Explanation (Likely)

Straight.el treats packages as git repositories, cloning them into ~/.emacs.d/straight/repos. Because the init.el file can specify exact revisions or branches, the resulting environment is deterministic across machines. When a local mirror is configured, straight.el pulls from that mirror rather than the internet, eliminating failures caused by network outages.

Package.el relies on a centralized archive (like MELPA). While it tracks which packages are installed via package-selected-packages, it does not natively lock the specific version of the package. A fresh install on a new machine will pull the latest version available in the archive at that moment, which can lead to "version drift" where different machines run different versions of the same package.

Confirmed Facts

• Both managers are subject to breaking changes during Emacs major version upgrades (e.g., 29 to 30) if the package code itself is incompatible.
• Straight.el can mitigate major-version conflicts by pointing straight-repository-dir to a version-specific path (e.g., ~/.emacs.d/29/straight/).
• Package.el requires manual maintenance of the package-selected-packages list to ensure a fresh install knows what to download.

Steps for straight.el (Offline-Friendly)

1. Clone a local mirror of the desired archives (e.g., MELPA) to a known path on your machines.
2. Configure the mirror in your init.el:

   (setq straight-mirror-dir (expand-file-name "straight/mirror" user-emacs-directory))

3. Declare packages using (straight-use-package 'package-name).
4. Verification: Start Emacs with -Q, load the config, and evaluate (straight-package-state) to verify the installed revisions match your expectations.

Steps for package.el (Network-Reliable)

1. Define your package-archives in init.el.
2. Maintain a list of required packages:

   (setq package-selected-packages '(magitProjectile ...))

3. Use a bootstrap routine to call package-install for any missing items in that list.
4. Verification: Start Emacs with -Q, load the config, and evaluate (package-installed-p 'package-name) for key dependencies.

Missing Diagnostic Detail

Do you have the disk space and administrative permission to maintain a local git mirror (several hundred MBs to GBs) on all three machines? If not, the mirror advantage of straight.el is negated.