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chore(ci): switch to cache-nix-action for Nix store caching #87

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ryoppippi merged 2 commits into from
Jan 3, 2026
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chore(ci): switch to cache-nix-action for Nix store caching #87

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chore(ci): switch to cache-nix-action for Nix store caching
ryoppippi Jan 3, 2026
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ryoppippi Jan 3, 2026
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11 changes: 5 additions & 6 deletions .github/actions/setup-nix/action.yaml
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Original file line number Diff line number Diff line change
@@ -1,18 +1,17 @@
name: "Setup Nix"
description: "Install Nix and configure Cachix"
description: "Install Nix and configure cache"
runs:
using: "composite"
steps:
- name: Install Nix
uses: cachix/install-nix-action@0b0e072294b088b73964f1d72dfdac0951439dbd # v31.8.4
uses: cachix/install-nix-action@4e002c8ec80594ecd40e759629461e26c8abed15 # v31.9.0
with:
github_access_token: ${{ github.token }}

- name: Setup Cachix (numtide)
uses: cachix/cachix-action@0fc020193b5a1fa3ac4575aa3a7d3aa6a35435ad # v16
- name: Cache Nix store
uses: nix-community/cache-nix-action@b426b118b6dc86d6952988d396aa7c6b09776d08 # v7
with:
name: numtide
authToken: ""
primary-key: nix-${{ runner.os }}
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Copilot AI Jan 3, 2026

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The cache key nix-${{ runner.os }} is too broad and doesn't include any dependency fingerprint. This means:

  1. The cache won't be invalidated when flake.lock changes, potentially causing builds to use stale dependencies
  2. Different jobs with different Nix store requirements will share the same cache, leading to cache thrashing

Consider including a hash of flake.lock in the key, such as nix-${{ runner.os }}-${{ hashFiles('flake.lock') }}, or use restore-keys to fall back to the OS-only key. The cache-nix-action documentation recommends including input hashes for proper cache invalidation.

Suggested change
primary-key: nix-${{ runner.os }}
primary-key: nix-${{ runner.os }}-${{ hashFiles('flake.lock') }}
fallback-key: nix-${{ runner.os }}

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@cubic-dev-ai cubic-dev-ai bot Jan 3, 2026 •
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P2: Cache key should include a hash of Nix dependency files to ensure cache invalidation when dependencies change. Without this, updates to flake.lock won't trigger cache refresh, potentially causing CI to use stale dependencies.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At .github/actions/setup-nix/action.yaml, line 14:

<comment>Cache key should include a hash of Nix dependency files to ensure cache invalidation when dependencies change. Without this, updates to `flake.lock` won&#39;t trigger cache refresh, potentially causing CI to use stale dependencies.</comment>

<file context>
@@ -1,18 +1,17 @@
       with:
-        name: numtide
-        authToken: &quot;&quot;
+        primary-key: nix-${{ runner.os }}
 
     - name: Load Nix development environment
</file context>
Suggested change
primary-key: nix-${{ runner.os }}
primary-key: nix-${{ runner.os }}-${{ hashFiles('flake.lock', 'flake.nix') }}
Fix with Cubic


- name: Load Nix development environment
shell: bash
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