chore: drop no-op allow-unfree settings and bump nixpkgs to 26.05

[0xgleb]

Motivation

The flake carried an allow-unfree = true nixConfig entry and a NIXPKGS_ALLOW_UNFREE=1 export in .envrc, and consuming repos were copying both on the assumption that packaging an unfree binary required them. Neither does anything here, so the pattern was spreading a cargo-culted trust prompt to every consumer.

Separately, the lock tracked the previous stable channel. Letting that drift means upgrades arrive as one large, awkward jump instead of small incremental ones.

Solution

• Drop allow-unfree from nixConfig. It is not a Nix setting: nix config show does not list it, and Nix emits warning: unknown setting 'allow-unfree' when a flake declares it.
• Drop NIXPKGS_ALLOW_UNFREE from .envrc. gitbutler-cli is permitted by the allowUnfreePredicate on this flake's own nixpkgs import, which is where the derivation is constructed; a consumer only references the finished derivation, so its own nixpkgs config never enters into it.
• Bump nixpkgs to nixos-26.05, and switch the devShell to pkgs.nixfmt -- nixfmt-rfc-style is an alias on this channel and evaluating it warns.

Verified with nix flake check (builds gitbutler-cli and runs the pr-stack-footer nushell suite) and by evaluating both the package and the devShell with NIXPKGS_ALLOW_UNFREE unset.

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 409cdd64-921e-4685-8cba-819b56c4e244

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}