fix(toolchain): fix elpa-gpu installation in legacy way

Author: QuantumMisaka

toolchain/scripts/lib/config_manager.sh

@@ -481,6 +481,11 @@ config_validate() {
         CONFIG_CACHE["ARCH_NUM"]="no"
     fi
 
+    # Backward compatibility: also export ARCH_NUM to environment when set
+    if [[ -n "${CONFIG_CACHE[ARCH_NUM]}" ]]; then
+        export ARCH_NUM="${CONFIG_CACHE[ARCH_NUM]}"
+    fi
+    
     return 0
 }
 
@@ -606,6 +611,10 @@ config_export_to_env() {
     for key in "${!CONFIG_CACHE[@]}"; do
         export "$key"="${CONFIG_CACHE[$key]}"
     done
+
+    # Backward compatibility for stage scripts expecting uppercase GPU flags
+    # Installers (e.g., stage3/install_elpa.sh) read ENABLE_CUDA, not enable_cuda
+    export ENABLE_CUDA="${CONFIG_CACHE[enable_cuda]}"
 
     # Export package list variables
     export tool_list

toolchain/scripts/stage3/install_elpa.sh

@@ -114,9 +114,11 @@ case "$with_elpa" in
                 fi
             fi
             for TARGET in "cpu" "nvidia"; do
-                [ "$TARGET" = "nvidia" ] && [ "$ENABLE_CUDA" != "__TRUE__" ] && continue
+                # Accept both uppercase and lowercase GPU enable flags for compatibility
+                gpu_enabled="${ENABLE_CUDA:-${enable_cuda}}"
+                [ "$TARGET" = "nvidia" ] && [ "$gpu_enabled" != "__TRUE__" ] && continue
                 # disable cpu if cuda is enabled, only install one
-                [ "$TARGET" != "nvidia" ] && [ "$ENABLE_CUDA" = "__TRUE__" ] && continue
+                [ "$TARGET" != "nvidia" ] && [ "$gpu_enabled" = "__TRUE__" ] && continue
                 # extend the pkg_install_dir by TARGET
                 # this linking method is totally different from cp2k toolchain
                 # for cp2k, ref https://github.com/cp2k/cp2k/commit/6fe2fc105b8cded84256248f68c74139dd8fc2e9