test(mobile): exercise native signing in linked iOS Runner

Signed-off-by: Tom Brow <tomb@block.xyz>

.github/workflows/_ci-clients.yml

@@ -248,11 +248,18 @@ jobs:
           tail -n 5 "$build_log"
           "${xcode[@]}" -parallel-testing-enabled NO -only-testing:RunnerTests \
             test-without-building
+          /bin/bash scripts/test-mobile-linked-signing.sh "$device"
       - name: Build complete unsigned iOS release
         if: matrix.lane == 'release'
         run: |
           /bin/bash scripts/test-mobile-gateway-recipes.sh
           cd mobile && flutter build ios --release --no-codesign --no-pub
+          # Flutter does not support Release mode on the simulator. Check the
+          # actual device Release executable's exported symbols separately.
+          nm -gU build/ios/iphoneos/Buzz.app/Buzz > /tmp/buzz-release-symbols
+          for symbol in buzz_signer_create buzz_signer_sign buzz_signer_destroy; do
+            grep -Eq "[[:space:]]_${symbol}$" /tmp/buzz-release-symbols
+          done
 
   results:
     name: Results