fix(ffilib): translate_function_def 的 extern 分支也生成 runtime thunk

现场 temp/02/029af3a930989beb.text.ll 里 @add 是普通直接调用、没有 _ffilib 引用，说明 App 文件的 extern 走的是 translate_function_def 而不是 forward_declare_functions，thunk 校验挂错了地方。两处都挂：各自先查 find_func_in_module 去重；runtime=True 生成 thunk，runtime=False 保持原 declare 路径。

App/lib/core/Gen/Func/FuncGenDef.vp

@@ -767,6 +767,25 @@ novirtual class FuncGenDef(CallGenBase.CallGenBase):
         if (has_export != 0 or has_state != 0) and trans.ModuleSha1 is not None: self.Gen.CallGenBase.register_cexport_func(trans.ModuleSha1, fd.name)
 
         if is_extern_decl != 0:
+            # extern <lib> name(...)：runtime=True 在这里也生成 thunk（Phase A 的 extern 往往不走
+            # forward_declare_functions，两处都挂才覆盖全部路径；另一处靠 find_func_in_module 去重）。
+            if fd.ffi_lib is not None:
+                ffi_rt_d: int = ViperBuild.FfiHandleRuntime(fd.ffi_lib)
+                if ffi_rt_d < 0:
+                    self.Gen.TypeGenErr.fatal_error(fd, f"extern library handle '{fd.ffi_lib}' is not a ffilib.CDLL binding (declare it with ffilib.CDLL(...) first)", "NameError")
+                    return 0
+                if ffi_rt_d != 0:
+                    if self.Gen.CallGenBase.find_func_in_module(mod, mangled_name) is None:
+                        ffi_path_d: str = ViperBuild.FfiHandlePath(fd.ffi_lib)
+                        if ffi_path_d is None:
+                            self.Gen.TypeGenErr.fatal_error(fd, f"extern '{fd.name}' is bound to '{fd.ffi_lib}' but its library path was not recorded by Pass 0", "InternalCompilerError")
+                            return 0
+                        thunk_d: mlirlite.Function* = self._emit_runtime_ffi_thunk(pool, mod, trans, fd, ffi_path_d, ret_ty)
+                        if thunk_d is None: return 0
+                        thunk_max_d: int = 256
+                        if self.Gen.CallGenLeafKit.add_func_to_table(funcs_ptr, func_count, fd.name, thunk_d, thunk_max_d, None, 0, 0, pool) == 0: trans._func_count = func_count + 1
+                        self.Gen.CallGenLeafKit.update_global_func_spec(fd.name, thunk_d)
+                    return 0
             # Extern declaration function: emit a declare (declare only, no definition). First check whether
             # forward_declare_functions already created it to avoid a duplicate declare.
             existing_extern: mlirlite.Function* = self.Gen.CallGenBase.find_func_in_module(mod, mangled_name)