fix(sandbox): harden image packaging integrity checks (#19552)

.github/actions/push-sandbox/action.yml

@@ -77,6 +77,14 @@ runs:
           --image google/gemini-cli-sandbox:${{ steps.image_tag.outputs.FINAL_TAG }} \
           --output-file final_image_uri.txt
         echo "uri=$(cat final_image_uri.txt)" >> $GITHUB_OUTPUT
+    - name: 'verify'
+      shell: 'bash'
+      run: |-
+        docker run --rm --entrypoint sh "${{ steps.docker_build.outputs.uri }}" -lc '
+          set -e
+          node -e "const fs=require(\"node:fs\"); JSON.parse(fs.readFileSync(\"/usr/local/share/npm-global/lib/node_modules/@google/gemini-cli/package.json\",\"utf8\")); JSON.parse(fs.readFileSync(\"/usr/local/share/npm-global/lib/node_modules/@google/gemini-cli-core/package.json\",\"utf8\"));"
+          /usr/local/share/npm-global/bin/gemini --version >/dev/null
+        '
     - name: 'publish'
       shell: 'bash'
       if: "${{ inputs.dry-run != 'true' }}"