ci: run the native engine's unit tests on pull requests into fullnative-dev

.github/workflows/ci.yml

@@ -17,3 +17,38 @@ jobs:
       - run: npm ci
       - run: npm run typecheck
       - run: npm test
+
+  native-engine:
+    # The native app (android-native/) on pull requests into fullnative-dev: engine unit tests, app compiles.
+    if: github.base_ref == 'fullnative-dev'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "17"
+      - uses: android-actions/setup-android@v3
+      # The NDK and CMake the engine module pins, read from its build file so they can't drift.
+      - name: Install NDK and CMake
+        run: |
+          ndk=$(sed -n 's/.*ndkVersion = "\(.*\)".*/\1/p' android-native/engine/build.gradle.kts)
+          cmake=$(sed -n 's/.*version = "\([0-9.]*\)".*/\1/p' android-native/engine/build.gradle.kts | head -1)
+          echo "NDK $ndk, CMake $cmake"
+          sdkmanager "ndk;$ndk" "cmake;$cmake"
+      - uses: gradle/actions/setup-gradle@v4
+      - name: Engine unit tests
+        working-directory: android-native
+        run: ./gradlew :engine:testDebugUnitTest
+      # The app has no unit tests; compiling its Kotlin catches app changes that no longer build.
+      - name: Compile the app
+        working-directory: android-native
+        run: ./gradlew :app:compileDebugKotlin
+      - name: Upload the test report
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: engine-test-report
+          path: android-native/engine/build/reports/tests/