CI flake: macOS Nix store corruption (invalid store paths)

Problem

Intermittent CI failures on namespace-profile-macos-arm64 during Nix/devenv evaluation, before tests run.

Observed failure signature:

• Failed to convert config.cachix to JSON
• Evaluation error: Failed to get attribute 'package' (while evaluating cachix.package)
• Underlying Nix store error: path ...-make-symlinks-relative.sh is not valid (Darwin stdenv bootstrap)

This looks like runner / bundled Nix store cache corruption or missing store paths, not a test flake.

Example Failing Runs

• 2026-02-12: run 21937239839, job test (namespace-profile-macos-arm64) at commit 056bd8f2…
• 2026-02-09: run 21840384378, job test (namespace-profile-macos-arm64) shows the same signature

What To Collect Next Time

Please add to this issue:

• Link to the failing run + job
• Full nix-store --verify --repair output (now no longer truncated)
• Any mention of ... is not valid store paths
• Runner details (macOS version, runner image, Namespace cache settings if visible)

Hypothesis

The Namespace macOS runner 'bundled' Nix store/cache sometimes contains invalid DB entries or missing paths.

Options

• Fix/disable the problematic runner cache (preferred root-cause fix).
• Move macOS CI to GitHub-hosted runners to eliminate runner-state flakiness.
• (Optional) Capture artifacts / add structured diagnostics when the failure signature occurs.

Related PR: #200

Footnote: Created with assistance from an AI coding agent acting on behalf of the user.

Start with the failing test (namespace-profile-macos-arm64) jobs from runs 21937239839 and 21840384378. Collect the full nix-store --verify --repair output, invalid store paths, runner details, and Namespace cache settings. Done means identifying whether runner cache corruption is the cause and applying or documenting a selected mitigation.