feat: try 语句压边界帧，空体内 break/continue 完成值物化 undefined

crates/oxide_emit/src/stmt/exception/try_catch.rs

@@ -19,6 +19,10 @@ impl Emitter {
         let has_catch = ts.handler.is_some();
         let has_finally = ts.finalizer.is_some();
         let result_reg = ctx.alloc_reg();
+        // try 语句整体是 `UpdateEmpty(_, undefined)` 站点：压边界帧，位于
+        // try/catch/finally 三个体列表帧之外，非空内层列表值穿透、空内层体
+        // 携值物化 undefined。
+        ctx.push_completion_boundary();
         if has_finally {
             // finally 域跨整个语句（try 体 + catch 体 + finally 体）：期间 break/continue
             // 逃出语句时须穿越本 finally，词法上记录域深度供跨越计数。
@@ -144,6 +148,7 @@ impl Emitter {
             ctx.pop_finally_domain();
         }
         ctx.labels.set_label_pos(try_end_label, ctx.insts.len());
+        ctx.pop_completion_boundary();
         Ok(Some(result_reg))
     }
 }

crates/oxide_vm/tests/eval_tests.rs

@@ -328,6 +328,50 @@ fn compound_statement_completion_values() {
     assert_num(result, 5.0);
     let result = eval(&mut vm, "a: { try { throw 1; } catch (e) { 5; break a; } }").unwrap();
     assert_num(result, 5.0);
+    // try 边界帧：空 catch/finally 体 break/continue 携值物化 undefined（无 if
+    // 守卫独立验收形），非空 finally 体值穿透。
+    let result = eval(
+        &mut vm,
+        "for (var i = 0; i < 2; ++i) { try { throw null; } catch (e) { break; } 'bad completion'; }",
+    )
+    .unwrap();
+    assert_eq!(result, JsValue::undefined());
+    let result = eval(
+        &mut vm,
+        "for (var i = 0; i < 2; ++i) { try { throw null; } catch (e) { continue; } 'bad completion'; }",
+    )
+    .unwrap();
+    assert_eq!(result, JsValue::undefined());
+    let result = eval(&mut vm, "for (var i = 0; i < 2; ++i) { try {} finally { break; } 'bad completion'; }").unwrap();
+    assert_eq!(result, JsValue::undefined());
+    let result =
+        eval(&mut vm, "for (var i = 0; i < 2; ++i) { try {} finally { continue; } 'bad completion'; }").unwrap();
+    assert_eq!(result, JsValue::undefined());
+    let result = eval(
+        &mut vm,
+        "for (var i = 0; i < 2; ++i) { try { throw null; } catch (e) {} finally { break; } 'bad completion'; }",
+    )
+    .unwrap();
+    assert_eq!(result, JsValue::undefined());
+    let result = eval(
+        &mut vm,
+        "for (var i = 0; i < 2; ++i) { try { throw null; } catch (e) {} finally { continue; } 'bad completion'; }",
+    )
+    .unwrap();
+    assert_eq!(result, JsValue::undefined());
+    // 跨 finally 值通道守卫：非空 finally 体值穿透，空 finally 体物化 undefined。
+    let result = eval(
+        &mut vm,
+        "99; do { -99; try { 39 } catch (e) { -1 } finally { 42; break; -2 }; } while (false);",
+    )
+    .unwrap();
+    assert_num(result, 42.0);
+    let result = eval(
+        &mut vm,
+        "99; do { -99; try { 39 } catch (e) { -1 } finally { break; -2 }; } while (false);",
+    )
+    .unwrap();
+    assert_eq!(result, JsValue::undefined());
     // for 泄漏形完成值：体不读循环变量加常量尾，取末次迭代体值，前值不沿用。
     let result = eval(&mut vm, "for (var i = 0; i < 2; ++i) { 42 }").unwrap();
     assert_num(result, 42.0);