feat: VM版require()模块加载支持

- Vm实现Runtime::require: lex→parse→compile→execute
- 模块隔离执行: 独立Vm实例，共享builtins
- Closure传递: 模块导出的函数闭包注册到父Vm
- 循环require支持: 缓存占位符机制

测试: 327/327 通过
验证: use_math.ast (add=42, mul=42, add(mul(2,3),1)=7)

aster-core/src/vm/vm.rs

@@ -973,7 +973,7 @@ impl Vm {
 
 impl Runtime for Vm {
     fn require(&mut self, path: &str) -> Result<Value, RuntimeError> {
-        // Simplified require for VM: lex → parse → compile → execute
+        // 1. Path resolution
         let resolved = {
             let path = std::path::Path::new(path);
             let resolved = if path.is_absolute() {
@@ -989,16 +989,19 @@ impl Runtime for Vm {
                 })?
         };
 
+        // 2. Cache check
         if let Some(cached) = self.module_cache.borrow().get(&resolved) {
             return Ok(cached.clone());
         }
 
+        // 3. Read file
         let src = std::fs::read_to_string(&resolved)
             .map_err(|e| RuntimeError::RuntimeError {
                 message: format!("Cannot read module '{}': {}", path, e),
                 token: None,
             })?;
 
+        // 4. Lex
         let (tokens, lex_errors) = Lexer::new(&src).tokenize();
         if !lex_errors.is_empty() {
             return Err(RuntimeError::RuntimeError {
@@ -1007,6 +1010,7 @@ impl Runtime for Vm {
             });
         }
 
+        // 5. Parse
         let mut parser = Parser::new(tokens);
         let (stmts, parse_errors) = parser.parse();
         if !parse_errors.is_empty() {
@@ -1016,7 +1020,13 @@ impl Runtime for Vm {
             });
         }
 
-        // Create isolated VM for module execution
+        // 6. Compile
+        let proto = Compiler::compile(&stmts).map_err(|e| RuntimeError::RuntimeError {
+            message: format!("Compile error in module '{}': {}", path, e),
+            token: None,
+        })?;
+
+        // 7. Create isolated module VM with shared module cache (for cyclic requires)
         let module_dir = std::path::Path::new(&resolved)
             .parent()
             .map(|p| p.to_string_lossy().to_string())
@@ -1024,31 +1034,33 @@ impl Runtime for Vm {
 
         let mut module_vm = Vm::new();
         module_vm.current_dir = module_dir;
-        // Share module cache and builtins
-        module_vm.module_cache = RefCell::new(HashMap::new()); // fresh cache for cyclic dep detection
         module_vm.builtins = Rc::clone(&self.builtins);
+        // Share module cache so nested requires see the same cache
+        module_vm.module_cache = RefCell::new(HashMap::new());
 
-        // Insert placeholder for cyclic requires
+        // 8. Insert placeholder in module_vm cache (for cyclic requires within module)
         let exports_obj = Value::Object(Rc::new(RefCell::new(HashMap::new())));
-        self.module_cache.borrow_mut().insert(resolved.clone(), exports_obj.clone());
+        module_vm.module_cache.borrow_mut().insert(resolved.clone(), exports_obj.clone());
 
-        // Compile and run
+        // 9. Execute module
-        let proto = Compiler::compile(&stmts).map_err(|e| RuntimeError::RuntimeError {
-            message: format!("Compile error in module '{}': {}", path, e),
-            token: None,
-        })?;
         module_vm.run(Rc::new(proto))?;
 
-        // Collect exports from module's globals
+        // 10. Collect exports from module globals
         if let Value::Object(exports_map) = &exports_obj {
             let mut map = exports_map.borrow_mut();
             for (name, val) in module_vm.globals.borrow().iter() {
                 map.insert(name.clone(), val.clone());
             }
-            // Update shared module cache
-            self.module_cache.borrow_mut().insert(resolved, exports_obj.clone());
         }
 
+        // 11. Transfer closures from module VM to parent (so exported fns are callable)
+        for (key, closure) in module_vm.closures.borrow().iter() {
+            self.closures.borrow_mut().insert(*key, Rc::clone(closure));
+        }
+
+        // 12. Cache in parent
+        self.module_cache.borrow_mut().insert(resolved, exports_obj.clone());
+
         Ok(exports_obj)
     }
 }