fix: count pass 注册顶层 var 名，hoisted 函数声明可解析外层 var

crates/oxide_compiler/src/counter/stmt/declaration.rs

@@ -2,9 +2,22 @@ use super::*;
 
 impl Compiler {
     fn count_variable_declaration(&self, decl: &oxide_parser::VariableDeclaration<'_>, ctx: &mut CompileCtx) {
+        let is_var = matches!(decl.kind, VariableDeclarationKind::Var);
         for d in &decl.declarations {
             if let Some(init) = &d.init {
                 self.count_expression(init, ctx);
+                if is_var {
+                    if let oxide_parser::BindingPattern::BindingIdentifier(bi) = &d.id {
+                        // `var` hoisting: register the name during the count pass (mirrors
+                        // count_function_declaration) so function bodies emitted earlier in the
+                        // hoisting sub-pass can resolve it. count_binding_pattern would only
+                        // allocate a register without declaring the name.
+                        let reg = ctx.alloc_reg();
+                        let _ = ctx.declare_initialized(bi.name.as_str(), reg, VariableDeclarationKind::Var, false);
+                        ctx.projected_pc += 1; // STORE_VAR
+                        continue;
+                    }
+                }
                 self.count_binding_pattern(&d.id, ctx);
             } else {
                 ctx.alloc_reg();

crates/oxide_compiler/src/emitter/mod.rs

@@ -355,8 +355,19 @@ impl Compiler {
         &self, name: &str, src_reg: u8, kind: VariableDeclarationKind, is_const: bool, ctx: &mut CompileCtx,
     ) -> Result<(), String> {
         let var_reg = ctx.alloc_reg();
-        ctx.declare(name, var_reg, kind, is_const)?;
-        ctx.emit(opcode::encode(OpCode::STORE_VAR, var_reg, src_reg, if is_const { 1 } else { 0 }));
+        let target_reg = if matches!(kind, VariableDeclarationKind::Var) {
+            // `var` is hoisted, so the count pass already registered the name. A redeclare
+            // here reuses that existing register instead of erroring; the freshly allocated
+            // reg matches it (count/emit allocate in lock-step) so either resolves the same.
+            match ctx.declare(name, var_reg, kind, is_const) {
+                Ok(()) => var_reg,
+                Err(_) => ctx.lookup(name).unwrap_or(var_reg),
+            }
+        } else {
+            ctx.declare(name, var_reg, kind, is_const)?;
+            var_reg
+        };
+        ctx.emit(opcode::encode(OpCode::STORE_VAR, target_reg, src_reg, if is_const { 1 } else { 0 }));
         ctx.init_var(name);
         Ok(())
     }

crates/oxide_compiler/tests/symbol_table_tests.rs

@@ -30,22 +30,19 @@ fn symbol_table_nested_scopes() {
 }
 
 #[test]
-fn symbol_table_tdz_global_shadow() {
-    let result = std::panic::catch_unwind(|| {
-        compile_source("var x = 1; { var x = x; }");
-    });
-    assert!(result.is_err(), "TDZ: accessing x in its own initializer inside a block should error");
+fn symbol_table_var_self_init_in_block_is_legal() {
+    // `var` has no temporal dead zone and hoists to the function scope, so a block-level
+    // `var x = x` reads the same already-initialized binding — legal in JS, not an error.
+    let module = compile_source("var x = 1; { var x = x; }");
+    assert!(!module.bytecode.is_empty(), "var self-init in block should compile");
 }
 
 #[test]
-fn symbol_table_duplicate_var() {
-    let result = std::panic::catch_unwind(|| {
-        compile_source("var x = 1; var x = 2;");
-    });
-    assert!(
-        result.is_err(),
-        "duplicate var declaration in same scope should error (strict-mode semantics)"
-    );
+fn symbol_table_duplicate_var_is_legal() {
+    // Duplicate `var` in the same scope is legal in JavaScript (even in strict mode);
+    // only duplicate `let`/`const` declarations are a SyntaxError.
+    let module = compile_source("var x = 1; var x = 2;");
+    assert!(!module.bytecode.is_empty(), "duplicate var should compile");
 }
 
 #[test]