SRE-915: Split the App private key out of the Renovate job (not viable)

.github/workflows/housekeeping-dependencies.yml

@@ -67,22 +67,26 @@ on:
         type: string
         default: disabled
 
-permissions:
-  actions: read
-  contents: read
-  id-token: write
+permissions: {}
 
 jobs:
-  renovate:
-    name: Renovate
+  # The only job that may hold `id-token: write` and see the App private key.
+  # Every step here must therefore stay a SHA-pinned third-party action or an
+  # inline `run`: a local `uses: ./...` resolves from the caller's checked-out
+  # tree, which any token with `contents: write` can rewrite, and that would
+  # undo the split.
+  #
+  # Renovate gets an installation token instead — an hour long, scoped to the
+  # calling repo, revocable, where the key is permanent and covers the whole
+  # installation.
+  token:
+    name: Mint installation token
     runs-on: ubuntu-24.04
-    concurrency:
-      cancel-in-progress: false
-      group: renovate
-    env:
-      is_pr: ${{ github.event_name == 'pull_request' }}
-      dry_run: ${{ github.event_name == 'pull_request' && 'extract' || inputs.dryRun || 'disabled' }}
-      repo_cache: ${{ inputs.repoCache || 'enabled' }}
+    permissions:
+      id-token: write
+    outputs:
+      workflow-ref: ${{ steps.workflow-ref.outputs.ref }}
+      installation-token: ${{ steps.app-token.outputs.token }}
 
     steps:
       - name: Resolve reusable workflow ref
@@ -96,15 +100,6 @@ jobs:
             const ref = job_workflow_ref.split('@')[1];
             core.setOutput('ref', ref);
 
-      - name: Checkout .github repo for the Renovate lockfile
-        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
-        with:
-          repository: hashintel/.github
-          ref: ${{ steps.workflow-ref.outputs.ref }}
-          sparse-checkout: |
-            package.json
-            package-lock.json
-
       - name: Authenticate Vault
         id: secrets
         uses: hashicorp/vault-action@892a26828f195e65540a40b4768ae4571f51ebfc # v4
@@ -129,6 +124,38 @@ jobs:
           owner: ${{ github.repository_owner }}
           repositories: ${{ steps.repo.outputs.name }}
 
+  renovate:
+    name: Renovate
+    needs: token
+    runs-on: ubuntu-24.04
+    permissions:
+      actions: read
+      contents: read
+    concurrency:
+      cancel-in-progress: false
+      group: renovate
+    env:
+      is_pr: ${{ github.event_name == 'pull_request' }}
+      dry_run: ${{ github.event_name == 'pull_request' && 'extract' || inputs.dryRun || 'disabled' }}
+      repo_cache: ${{ inputs.repoCache || 'enabled' }}
+
+    steps:
+      # Job outputs are not masked the way secrets are, so register the value
+      # before anything else in this job runs.
+      - name: Mask the installation token
+        env:
+          INSTALLATION_TOKEN: ${{ needs.token.outputs.installation-token }}
+        run: echo "::add-mask::$INSTALLATION_TOKEN"
+
+      - name: Checkout .github repo for the Renovate lockfile
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+        with:
+          repository: hashintel/.github
+          ref: ${{ needs.token.outputs.workflow-ref }}
+          sparse-checkout: |
+            package.json
+            package-lock.json
+
       - name: Setup Node.js
         uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
         with:
@@ -164,7 +191,7 @@ jobs:
       - name: Run Renovate
         env:
           LOG_LEVEL: ${{ inputs.logLevel || 'info' }}
-          RENOVATE_TOKEN: ${{ steps.app-token.outputs.token }}
+          RENOVATE_TOKEN: ${{ needs.token.outputs.installation-token }}
           RENOVATE_FORCE: ${{ inputs.overrideSchedule && '{"schedule":null}' || '' }}
           RENOVATE_DRY_RUN: ${{ env.dry_run == 'disabled' && 'null' || env.dry_run }}
           RENOVATE_PLATFORM_COMMIT: enabled