Improve Vulkan SDK download resilience in CI workflow

- Added multiple fallback URLs for Vulkan SDK download from LunarG.
- Implemented error handling to ensure CI exits gracefully if all downloads fail.

Author: gpx1000

.github/workflows/simple_engine_ci.yml

@@ -84,9 +84,25 @@ jobs:
 
           echo "Downloading Vulkan SDK from LunarG..."
           # Use the official LunarG download endpoint (latest Linux tarball).
-          # We avoid distro packages so this matches what students are expected to do.
           SDK_TGZ="${RUNNER_TEMP}/vulkansdk-linux.tar.xz"
-          curl -L --fail -o "$SDK_TGZ" "https://sdk.lunarg.com/sdk/download/latest/linux/vulkansdk-linux-x86_64.tar.xz"
+
+          download_ok=0
+          for url in \
+            "https://sdk.lunarg.com/sdk/download/latest/linux/vulkan-sdk.tar.xz" \
+            "https://sdk.lunarg.com/sdk/download/latest/linux/vulkansdk-linux-x86_64.tar.xz" \
+            "https://sdk.lunarg.com/sdk/download/latest/linux/vulkan-sdk.tar.xz?Human=true" \
+            "https://sdk.lunarg.com/sdk/download/latest/linux/vulkansdk-linux-x86_64.tar.xz?Human=true"
+          do
+            echo "Attempting: $url"
+            if curl -L --fail -o "$SDK_TGZ" "$url"; then
+              download_ok=1
+              break
+            fi
+          done
+          if [ "$download_ok" -ne 1 ]; then
+            echo "Failed to download Vulkan SDK from LunarG (all endpoints returned non-200)." >&2
+            exit 1
+          fi
 
           SDK_DIR="${RUNNER_TEMP}/VulkanSDK"
           rm -rf "$SDK_DIR"