fix(ci): bootstrap Yarn before dependency caching

Signed-off-by: Emiliano Suñé <2395873+esune@users.noreply.github.com>

Author: esune

.github/README.md

@@ -6,7 +6,7 @@ This folder defines automation for the BC Digital Trust Showcase monorepo (`fron
 
 **Path:** `.github/actions/setup-node/action.yml`
 
-**Purpose:** Install Node and enable Yarn dependency caching in one step.
+**Purpose:** Install Node, activate the repository's Yarn version through Corepack, and cache Yarn dependencies.
 
 **Inputs:**
 
@@ -16,7 +16,9 @@ This folder defines automation for the BC Digital Trust Showcase monorepo (`fron
 
 **Behaviour:**
 
-- Runs [`actions/setup-node@v4`](https://github.com/actions/setup-node) with `cache: yarn` and `cache-dependency-path: yarn.lock` (repository root). No separate `actions/cache` step and no `yarn` invocation before Node is installed.
+- Runs [`actions/setup-node@v4`](https://github.com/actions/setup-node) without Yarn caching so the runner's global Yarn version is not invoked during setup.
+- Enables Corepack, installs and verifies Yarn `4.18.0`, then caches the Yarn cache directory with a key containing the OS, Node version, Yarn version, and `yarn.lock` hash.
+- The cache key intentionally does not restore the previous `setup-node` Yarn cache; the old entry is left for GitHub's normal eviction policy.
 
 **Usage:**
 

.github/actions/setup-node/action.yml

@@ -1,5 +1,5 @@
 name: Setup NodeJS
-description: Setup NodeJS with caching
+description: Setup NodeJS with Corepack and Yarn caching
 author: 'timo@animo.id'
 
 inputs:
@@ -14,11 +14,23 @@ runs:
       uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
       with:
         node-version: ${{ inputs.node-version }}
-        cache: yarn
-        cache-dependency-path: yarn.lock
     - name: Enable Corepack
       shell: bash
-      run: corepack enable
+      run: |
+        corepack enable
+        corepack install --global yarn@4.18.0
+    - name: Verify Yarn version
+      shell: bash
+      run: test "$(yarn --version)" = "4.18.0"
+    - name: Get Yarn cache directory
+      id: yarn-cache-dir
+      shell: bash
+      run: echo "dir=$(yarn config get cacheFolder)" >> "$GITHUB_OUTPUT"
+    - name: Cache Yarn dependencies
+      uses: actions/cache@v4
+      with:
+        path: ${{ steps.yarn-cache-dir.outputs.dir }}
+        key: yarn-${{ runner.os }}-node-${{ inputs.node-version }}-yarn-4.18.0-${{ hashFiles('yarn.lock') }}
 
 branding:
   icon: scissors