ci: per-app build matrix with precise path triggers

.github/actions/build-android-app/action.yml

@@ -0,0 +1,123 @@
+name: Build Android app
+description: Build an Android demo app from this monorepo (with optional Expo prebuild)
+
+inputs:
+  app-path:
+    description: Path to the app workspace, relative to the repo root (e.g. apps/llm)
+    required: true
+  expo-prebuild:
+    description: Whether to run `expo prebuild --platform android` before the Gradle build
+    required: false
+    default: "true"
+  filter-name:
+    description: dorny/paths-filter filter name for this app+platform (e.g. llm-android). Used as the content-hash cache key so a previously-passing build can be skipped if nothing relevant has changed.
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - name: Setup Node.js
+      uses: actions/setup-node@v6
+      with:
+        node-version-file: .nvmrc
+        cache: "yarn"
+
+    - name: Install root dependencies
+      shell: bash
+      run: yarn install --immutable
+
+    - name: Compute build hash
+      id: hash
+      shell: bash
+      run: |
+        h=$(npx ts-node scripts/compute-app-hash.ts "${{ inputs.filter-name }}")
+        echo "key=build-${{ inputs.filter-name }}-$h" >> "$GITHUB_OUTPUT"
+
+    - name: Lookup pass marker
+      id: cache
+      uses: actions/cache/restore@v4
+      with:
+        path: ${{ runner.temp }}/ci-marker
+        key: ${{ steps.hash.outputs.key }}
+        lookup-only: true
+
+    - name: Skip notice
+      if: steps.cache.outputs.cache-hit == 'true'
+      shell: bash
+      run: echo "Skipping build — ${{ inputs.filter-name }} already passed at this content hash."
+
+    # ubuntu-latest ships with ~14 GB free, but a full Android build for any of
+    # the demo apps (Gradle cache + ExecuTorch native build + node_modules +
+    # third-party libs) regularly exceeds that and fails with "no space left on
+    # device". Reclaim ~10 GB by removing toolchains we don't use here.
+    - name: Free disk space
+      if: steps.cache.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        sudo rm -rf /usr/share/dotnet
+        sudo rm -rf /opt/ghc
+        sudo rm -rf /opt/hostedtoolcache/CodeQL
+        sudo docker system prune -af
+
+    - name: Setup Java 17
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: actions/setup-java@v5
+      with:
+        distribution: "zulu"
+        java-version: 17
+        cache: "gradle"
+
+    - name: Install Expo CLI
+      if: steps.cache.outputs.cache-hit != 'true' && inputs.expo-prebuild == 'true'
+      shell: bash
+      run: |
+        npm install -g @expo/cli
+        echo "$(npm prefix -g)/bin" >> $GITHUB_PATH
+
+    - name: Generate native Android project
+      if: steps.cache.outputs.cache-hit != 'true' && inputs.expo-prebuild == 'true'
+      working-directory: ${{ inputs.app-path }}
+      shell: bash
+      run: |
+        rm -rf android
+        npx expo prebuild --platform android --no-install
+
+    - name: Cache Gradle
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: actions/cache@v5
+      with:
+        path: |
+          ~/.gradle/caches
+          ~/.gradle/wrapper
+          ${{ inputs.app-path }}/android/.gradle
+        key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+        restore-keys: |
+          ${{ runner.os }}-gradle-
+
+    - name: Build app
+      if: steps.cache.outputs.cache-hit != 'true'
+      working-directory: ${{ inputs.app-path }}/android
+      shell: bash
+      run: |
+        ./gradlew assembleDebug \
+          --build-cache \
+          --parallel \
+          --daemon \
+          --configure-on-demand \
+          -PreactNativeArchitectures=arm64-v8a \
+          -Dorg.gradle.jvmargs="-Xmx4g -XX:+HeapDumpOnOutOfMemoryError" \
+          -Dorg.gradle.workers.max=4
+
+    - name: Save pass marker
+      if: steps.cache.outputs.cache-hit != 'true' && success()
+      shell: bash
+      run: |
+        mkdir -p "${{ runner.temp }}/ci-marker"
+        touch "${{ runner.temp }}/ci-marker/passed"
+
+    - name: Cache pass marker
+      if: steps.cache.outputs.cache-hit != 'true' && success()
+      uses: actions/cache/save@v4
+      with:
+        path: ${{ runner.temp }}/ci-marker
+        key: ${{ steps.hash.outputs.key }}

.github/actions/build-ios-app/action.yml

@@ -0,0 +1,118 @@
+name: Build iOS app
+description: Build an iOS demo app from this monorepo (with optional Expo prebuild)
+
+inputs:
+  app-path:
+    description: Path to the app workspace, relative to the repo root (e.g. apps/llm)
+    required: true
+  expo-prebuild:
+    description: Whether to run `expo prebuild --platform ios` before pod install
+    required: false
+    default: "true"
+  filter-name:
+    description: dorny/paths-filter filter name for this app+platform (e.g. llm-ios). Used as the content-hash cache key so a previously-passing build can be skipped if nothing relevant has changed.
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - name: Setup Node.js
+      uses: actions/setup-node@v6
+      with:
+        node-version-file: .nvmrc
+        cache: "yarn"
+
+    - name: Install root dependencies
+      shell: bash
+      run: yarn install --immutable
+
+    - name: Compute build hash
+      id: hash
+      shell: bash
+      run: |
+        h=$(npx ts-node scripts/compute-app-hash.ts "${{ inputs.filter-name }}")
+        echo "key=build-${{ inputs.filter-name }}-$h" >> "$GITHUB_OUTPUT"
+
+    - name: Lookup pass marker
+      id: cache
+      uses: actions/cache/restore@v4
+      with:
+        path: ${{ runner.temp }}/ci-marker
+        key: ${{ steps.hash.outputs.key }}
+        lookup-only: true
+
+    - name: Skip notice
+      if: steps.cache.outputs.cache-hit == 'true'
+      shell: bash
+      run: echo "Skipping build — ${{ inputs.filter-name }} already passed at this content hash."
+
+    - name: Setup Xcode
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: maxim-lobanov/setup-xcode@v1
+      with:
+        xcode-version: latest-stable
+
+    - name: Install Expo CLI
+      if: steps.cache.outputs.cache-hit != 'true' && inputs.expo-prebuild == 'true'
+      shell: bash
+      run: |
+        npm install -g @expo/cli
+        echo "$(npm prefix -g)/bin" >> $GITHUB_PATH
+
+    - name: Generate native iOS project
+      if: steps.cache.outputs.cache-hit != 'true' && inputs.expo-prebuild == 'true'
+      working-directory: ${{ inputs.app-path }}
+      shell: bash
+      run: |
+        rm -rf ios
+        npx expo prebuild --platform ios --no-install
+
+    - name: Cache CocoaPods
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: actions/cache@v5
+      with:
+        path: |
+          ~/Library/Caches/CocoaPods
+          ${{ inputs.app-path }}/ios/Pods
+        key: ${{ runner.os }}-pods-${{ inputs.filter-name }}-${{ hashFiles(format('{0}/ios/Podfile.lock', inputs.app-path)) }}
+        restore-keys: |
+          ${{ runner.os }}-pods-${{ inputs.filter-name }}-
+
+    - name: Install CocoaPods dependencies
+      if: steps.cache.outputs.cache-hit != 'true'
+      working-directory: ${{ inputs.app-path }}/ios
+      shell: bash
+      run: pod install
+
+    - name: Build app
+      if: steps.cache.outputs.cache-hit != 'true'
+      working-directory: ${{ inputs.app-path }}/ios
+      shell: bash
+      run: |
+        WORKSPACE=$(ls -d *.xcworkspace | head -n 1)
+        SCHEME="${WORKSPACE%.xcworkspace}"
+        set -o pipefail && xcodebuild \
+          -workspace "$WORKSPACE" \
+          -scheme "$SCHEME" \
+          -sdk iphonesimulator \
+          -configuration Debug \
+          -destination 'generic/platform=iOS Simulator' \
+          build \
+          CODE_SIGNING_ALLOWED=NO \
+          -jobs $(sysctl -n hw.ncpu) \
+          COMPILER_INDEX_STORE_ENABLE=NO \
+          ONLY_ACTIVE_ARCH=YES | xcbeautify
+
+    - name: Save pass marker
+      if: steps.cache.outputs.cache-hit != 'true' && success()
+      shell: bash
+      run: |
+        mkdir -p "${{ runner.temp }}/ci-marker"
+        touch "${{ runner.temp }}/ci-marker/passed"
+
+    - name: Cache pass marker
+      if: steps.cache.outputs.cache-hit != 'true' && success()
+      uses: actions/cache/save@v4
+      with:
+        path: ${{ runner.temp }}/ci-marker
+        key: ${{ steps.hash.outputs.key }}