fix(flow): 嵌套/协程函数体独立 break/continue 目标，越界即 fail-fast

- HandlesFor._HandleNestedFunctionLlvm：进入嵌套函数体前清空 loop_break_targets /
  loop_continue_targets，退出恢复——原实现会让嵌套函数体内的 break/continue 继承
  外层函数的跳转目标（生成跨函数 br，非法 IR）
- HandlesAsyncFunctions：协程体内循环之外的 break/continue 改为 FailFastError，
  不再静默不生成跳转

lib/core/Handles/HandlesAsyncFunctions.py

@@ -531,12 +531,19 @@ class AsyncFunctionHandle(BaseHandle):
                 self._HandleCoroFor(stmt, Gen)
                 continue
             if isinstance(stmt, ast.Break):
-                if Gen.loop_break_targets:
-                    Gen.builder.branch(Gen.loop_break_targets[-1])
+                if not Gen.loop_break_targets:
+                    # fail-fast：协程体内、循环之外的 break 无处可跳（不兜底）
+                    from lib.core.LLVMCG.FuncGen import FailFastError
+                    raise FailFastError(
+                        "break 只能用在循环或 match-case 体内（当前没有可跳出的目标）")
+                Gen.builder.branch(Gen.loop_break_targets[-1])
                 continue
             if isinstance(stmt, ast.Continue):
-                if Gen.loop_continue_targets:
-                    Gen.builder.branch(Gen.loop_continue_targets[-1])
+                if not Gen.loop_continue_targets:
+                    from lib.core.LLVMCG.FuncGen import FailFastError
+                    raise FailFastError(
+                        "continue 只能用在循环体内（当前没有可继续的循环）")
+                Gen.builder.branch(Gen.loop_continue_targets[-1])
                 continue
             if isinstance(stmt, ast.Pass):
                 continue

lib/core/Handles/HandlesFor.py

@@ -417,6 +417,8 @@ class ForHandle(BaseHandle):
         self.Trans.FunctionHandler._EmitFunctionLlvm(Node, Gen, extra_params=extra_params if extra_params else None)
         Gen.builder = saved_builder
         Gen.func = saved_func
+        Gen.loop_break_targets = saved_loop_break_targets
+        Gen.loop_continue_targets = saved_loop_continue_targets
         Gen.variables = saved_variables
         Gen._reg_values = saved_reg_values
         Gen.global_vars = saved_global_vars