ci: check Expo versions against the installed SDK

.github/workflows/expo-drift.yml

@@ -0,0 +1,33 @@
+name: Expo SDK drift
+
+on:
+  pull_request:
+    paths:
+      - package.json
+      - package-lock.json
+      - .github/workflows/expo-drift.yml
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: expo-drift-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  drift:
+    name: Expo SDK drift
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - name: Set up Node.js
+        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version-file: .node-version
+          cache: npm
+      - name: Install dependencies
+        run: npm ci
+      - name: Compare with Expo's current SDK patch versions
+        run: npx expo install --check

.github/workflows/mobile-ci.yml

@@ -29,6 +29,10 @@ jobs:
         run: npm ci
       - name: Check Expo project health
         run: npm run doctor
+        env:
+          # Check against the installed SDK, not Expo's live patch list, so a new Expo
+          # patch can't fail an unchanged commit. expo-drift.yml reports patch drift.
+          EXPO_OFFLINE: '1'
       - name: Lint
         run: npm run lint
       - name: Check formatting