fix: enable stickydisk again with new nix-installer-action

[jfroche]

Make sure the eval succeeds with both an empty /nix cache and a existing /nix cache.
Use the new nix installer.

Summary by CodeRabbit

• Chores

  • Switched to a new ephemeral Nix installer, standardized installer inputs, added max-jobs, and moved post-build hook into installer config.
  • Replaced long install steps with the ephemeral installer in CI, added cache mount and pre-install socket/ownership prep.
  • Updated installer version across images and scripts.

• Bug Fixes

  • Fixed installer invocation/heredoc handling to ensure configuration is applied.

• Documentation

  • Updated getting-started guide and version references to the new Nix release.

[samrose]

will the newer version cause any conflict with using slightly older version elsewhere?

[jfroche]

No there are no breaking change in 2.33 but I could also upgrade the other references because 2.33 comes with nice performance improvements. It should also fix the problem we had with IPC leak on macos with postgres (see NixOS/nix#14459), we might want to tell people to upgrade nix on their macos laptop to avoid this.

[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

.github/actions/nix-install-ephemeral/action.yml (1)

43-50: ⚠️ Potential issue | 🔴 Critical

Action and version references require correction.

The migration references NixOS/nix-installer-action, but the standard (documented) nix-installer action is DeterminateSystems/nix-installer-action. Additionally, installer-version: 2.33.1 appears incorrect—nix-installer uses 0.x versioning (e.g., 0.23.0), not 2.x. The value 2.33.1 matches Nix's version numbering, not the installer's, suggesting either a parameter mismatch or incorrect version reference.

Verify:

• The correct action owner and commit SHA
• Whether installer-version should reference a 0.x version or if this parameter should specify Nix version instead

[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

.github/actions/nix-install-ephemeral/action.yml (1)

43-50: ⚠️ Potential issue | 🔴 Critical

Revert installer-version: 2.33.2 — this version does not exist in nix-installer releases.

The installer-version parameter expects a version from the DeterminateSystems/nix-installer releases, which only provide v3.x versions (current latest: v3.15.2). The specified version 2.33.2 does not exist and will cause the workflow to fail at runtime.

If 2.33.2 is the desired Nix version, use a valid nix-installer version (e.g., v3.15.2 or latest) instead. The installer version is separate from the Nix package manager version being installed.

🧹 Nitpick comments (1)

.github/workflows/base-image-nightly.yml (1)

37-43: Version bump looks correct, but note the installer action inconsistency.

The Nix version bump to 2.33.2 is consistent with the PR objective. However, this workflow uses cachix/install-nix-action with install_url, while .github/actions/nix-install-ephemeral/action.yml was migrated to NixOS/nix-installer-action with installer-version.

If this inconsistency is intentional (e.g., different runner requirements), consider adding a comment explaining the choice. Otherwise, consider migrating this workflow to use the same installer action for consistency.