fix(release): restore the SignPath composite action when cutting from an older ref

Co-authored-by: Orca <help@stably.ai>

.github/workflows/release-cut.yml

@@ -1015,6 +1015,27 @@ jobs:
         with:
           ref: refs/tags/${{ needs.cut.outputs.tag }}
 
+      # Why: `uses: ./…` resolves from the checked-out tag, not from the workflow
+      # ref, so cutting from an older/off-main ref whose tree predates a composite
+      # action would fail the step with "Can't find 'action.yml'". Restore the
+      # actions directory from the commit this workflow file itself came from.
+      - name: Restore composite actions from the workflow ref
+        if: matrix.platform == 'win'
+        shell: bash
+        env:
+          WORKFLOW_SHA: ${{ github.workflow_sha }}
+        run: |
+          set -euo pipefail
+          action_path=".github/actions/install-signpath-module/action.yml"
+          if [ -f "$action_path" ]; then
+            echo "Composite actions already present at the cut ref."
+            exit 0
+          fi
+          echo "Cut ref predates $action_path; restoring it from $WORKFLOW_SHA."
+          git fetch --no-tags --depth=1 origin "$WORKFLOW_SHA"
+          git checkout "$WORKFLOW_SHA" -- .github/actions
+          test -f "$action_path"
+
       # pnpm must be on PATH before setup-node so setup-node can locate the store for caching.
       - name: Setup pnpm
         uses: pnpm/action-setup@v6

config/scripts/windows-signing-workflow-contract.test.mjs

@@ -104,6 +104,41 @@ describe('Windows signing workflow contract', () => {
     expect(installRun).toContain('throw "Unable to install the SignPath PowerShell module')
   })
 
+  it('still installs SignPath when the cut ref predates the composite action', () => {
+    const parsedWorkflow = readWorkflow('.github/workflows/release-cut.yml')
+    const steps = parsedWorkflow.jobs.build.steps
+    const stepNames = steps.map((step) => step.name)
+    const checkoutIndex = stepNames.indexOf('Checkout')
+    const restoreIndex = stepNames.indexOf('Restore composite actions from the workflow ref')
+    const installIndex = stepNames.indexOf('Install SignPath PowerShell module')
+
+    // Why: the build job checks out the cut tag, which for a hotfix cut from an
+    // older ref can predate `.github/actions/install-signpath-module`; without
+    // this restore the `uses: ./…` step dies on a missing action.yml.
+    expect(restoreIndex).toBeGreaterThan(checkoutIndex)
+    expect(restoreIndex).toBeLessThan(installIndex)
+
+    const restoreStep = steps[restoreIndex]
+    const restoreRun = restoreStep.run
+
+    expect(restoreStep.env.WORKFLOW_SHA).toBe('${{ github.workflow_sha }}')
+    expect(restoreRun).toContain('.github/actions/install-signpath-module/action.yml')
+    expect(restoreRun).toContain('git fetch --no-tags --depth=1 origin "$WORKFLOW_SHA"')
+    expect(restoreRun).toContain('git checkout "$WORKFLOW_SHA" -- .github/actions')
+
+    // Why: restoring the action must not turn signing into a soft dependency —
+    // a missing module still has to fail the Windows job, and the CDN fallback
+    // still has to reject an unexpected payload.
+    expect(steps[installIndex]['continue-on-error']).toBeUndefined()
+    expect(restoreStep['continue-on-error']).toBeUndefined()
+
+    const installRun = readWorkflow('.github/actions/install-signpath-module/action.yml').runs
+      .steps[0].run
+
+    expect(installRun).toContain('$actualHash -ne $expectedHash.ToUpperInvariant()')
+    expect(installRun).toContain('throw "SHA-256 mismatch for $source')
+  })
+
   it('shares one SignPath module install path between release and rehearsal', () => {
     const rehearsalWorkflow = readWorkflow('.github/workflows/windows-signing-rehearsal.yml')
     const stepNames = rehearsalWorkflow.jobs.rehearse.steps.map((step) => step.name)