fix document global for external Lua scripts in designer and Android

src/main/cpp/kernel.cpp

@@ -13,6 +13,7 @@
 #include <RmlUi/Core.h>
 #include <RmlUi/Lua.h>
 #include <RmlUi/Lua/Interpreter.h>
+#include <RmlUi/Lua/LuaType.h>
 #include "RmlUi_Renderer_GL3.h"
 #include <span>
 #include <ranges>
@@ -46,6 +47,19 @@ static std::string g_data_root;
 // Forward declarations
 static void SwitchAppSandbox(const std::string& app_id, const std::string& app_data_path);
 
+// Helper to set the 'document' global in Lua to the current document
+// This is needed for external script files (app.lua) that reference 'document'
+static void SetLuaDocumentGlobal(Rml::ElementDocument* doc) {
+    if (!doc) return;
+    lua_State* L = Rml::Lua::Interpreter::GetLuaState();
+    if (!L) return;
+
+    // Push the document using RmlUi's Lua type system
+    Rml::Lua::LuaType<Rml::ElementDocument>::push(L, doc, false);
+    lua_setglobal(L, "document");
+    Logger::Log(std::format("Set Lua 'document' global to: {}", doc->GetTitle().empty() ? "(untitled)" : doc->GetTitle().c_str()));
+}
+
 using namespace aidl::com::omixlab::mosis;
 using namespace aidl::android::hardware;
 
@@ -334,6 +348,7 @@ static int LuaLoadScreen(lua_State* L)
     if (g_document)
     {
         g_document->Show();
+        SetLuaDocumentGlobal(g_document);
         Logger::Log(std::format("Loaded screen: {}", path));
         lua_pushboolean(L, true);
     }
@@ -390,6 +405,7 @@ static int LuaGoHome(lua_State* L)
     if (g_document)
     {
         g_document->Show();
+        SetLuaDocumentGlobal(g_document);
         Logger::Log("Returned to home screen");
         lua_pushboolean(L, true);
     }
@@ -626,6 +642,7 @@ void Kernel::main_loop()
         return;
     }
     g_document->Show();
+    SetLuaDocumentGlobal(g_document);
 
     while (true)
     {