feat(0.81, ci): add content-hash caching for SPM slice and compose jobs

- Cache slice builds keyed on source file hashes (Package.swift,
  ios-prebuild scripts, React/**, ReactCommon/**, Libraries/**)
- Cache composed xcframework with same hash key
- Skip toolchain setup, yarn install, and build steps on cache hit
- Only save caches on main/0.81-stable to avoid cache explosion

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Saadnajmi

.github/workflows/microsoft-build-spm.yml

@@ -226,35 +226,59 @@ jobs:
           filter: blob:none
           fetch-depth: 0
 
+      - name: Restore slice cache
+        id: cache-slice
+        uses: actions/cache/restore@v4
+        with:
+          key: v1-macos-core-${{ matrix.platform }}-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/spm/Debug/Build/Products
+            packages/react-native/.build/headers
+
       - name: Setup toolchain
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         uses: ./.github/actions/microsoft-setup-toolchain
         with:
           node-version: '22'
           platform: ${{ matrix.platform }}
 
       - name: Install npm dependencies
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         run: yarn install
 
       - name: Download Hermes artifacts
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         uses: actions/download-artifact@v4
         with:
           name: hermes-artifacts
           path: packages/react-native/.build/artifacts/hermes/destroot
 
       - name: Create Hermes version marker
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         working-directory: packages/react-native
         run: |
           VERSION=$(node -p "require('./package.json').version")
           echo "${VERSION}-Debug" > .build/artifacts/hermes/version.txt
 
       - name: Setup SPM workspace (using prebuilt Hermes)
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         working-directory: packages/react-native
         run: node scripts/ios-prebuild.js -s -f Debug
 
       - name: Build SPM (${{ matrix.platform }})
+        if: steps.cache-slice.outputs.cache-hit != 'true'
         working-directory: packages/react-native
         run: node scripts/ios-prebuild.js -b -f Debug -p ${{ matrix.platform }}
 
+      - name: Save slice cache
+        if: ${{ github.ref == 'refs/heads/main' || github.ref == 'refs/heads/0.81-stable' }}
+        uses: actions/cache/save@v4
+        with:
+          key: v1-macos-core-${{ matrix.platform }}-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/spm/Debug/Build/Products
+            packages/react-native/.build/headers
+
       - name: Upload headers
         uses: actions/upload-artifact@v4
         with:
@@ -278,50 +302,76 @@ jobs:
         with:
           filter: blob:none
 
+      - name: Restore compose cache
+        id: cache-xcframework
+        uses: actions/cache/restore@v4
+        with:
+          key: v1-macos-core-xcframework-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.xcframework.tar.gz
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.framework.dSYM.tar.gz
+
       - name: Setup toolchain
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         uses: ./.github/actions/microsoft-setup-toolchain
         with:
           node-version: '22'
           platform: ios
 
       - name: Install npm dependencies
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         run: yarn install
 
       - name: Download slice artifacts
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         uses: actions/download-artifact@v4
         with:
           pattern: prebuild-macos-core-slice-Debug-*
           path: packages/react-native/.build/output/spm/Debug/Build/Products
           merge-multiple: true
 
       - name: Download headers
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         uses: actions/download-artifact@v4
         with:
           pattern: prebuild-macos-core-headers-Debug-*
           path: packages/react-native/.build/headers
           merge-multiple: true
 
       - name: Verify downloaded artifacts
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         run: |
           echo "=== Products directory ==="
           ls -R packages/react-native/.build/output/spm/Debug/Build/Products/ | head -40
           echo "=== Headers directory ==="
           ls packages/react-native/.build/headers/ | head -20
 
       - name: Create XCFramework
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         working-directory: packages/react-native
         run: node scripts/ios-prebuild -c -f Debug
 
       - name: Compress XCFramework
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         run: |
           cd packages/react-native/.build/output/xcframeworks/Debug
           tar -cz -f ../ReactCoreDebug.xcframework.tar.gz React.xcframework
 
       - name: Compress dSYMs
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
         run: |
           cd packages/react-native/.build/output/xcframeworks/Debug/Symbols
           tar -cz -f ../../ReactCoreDebug.framework.dSYM.tar.gz .
 
+      - name: Save compose cache
+        if: ${{ github.ref == 'refs/heads/main' || github.ref == 'refs/heads/0.81-stable' }}
+        uses: actions/cache/save@v4
+        with:
+          key: v1-macos-core-xcframework-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.xcframework.tar.gz
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.framework.dSYM.tar.gz
+
       - name: Upload XCFramework
         uses: actions/upload-artifact@v4
         with: