[codex] run installer tests across platforms

.github/workflows/installer-tests.yml

@@ -0,0 +1,37 @@
+name: installer-tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  bash-installer-tests:
+    name: Bash installer tests (Ubuntu)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: Run Bash installer tests
+        shell: bash
+        run: bash ./scripts/test-installers.sh
+
+  powershell-installer-tests:
+    name: PowerShell installer tests (${{ matrix.os }})
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: Run PowerShell installer tests
+        shell: pwsh
+        run: ./scripts/test-installers.ps1

CHANGELOG.md

@@ -2,7 +2,9 @@
 
 ## Unreleased
 
-No changes yet.
+- Run the Bash installer suite on Ubuntu and the PowerShell installer suite on
+  both Ubuntu and Windows through a dedicated `installer-tests` GitHub Actions
+  workflow. The existing shared-rule drift workflow remains separate.
 
 ## 1.1.0 - 2026-07-05