fix(openai): 增强 Codex 工具过滤和参数标准化

- codex_transform: 过滤无效工具，支持 Responses-style 和 ChatCompletions-style 格式
- tool_corrector: 添加 fetch 工具映射，修正 bash/edit 参数命名规范

backend/internal/service/openai_codex_transform_test.go

@@ -129,6 +129,37 @@ func TestFilterCodexInput_RemovesItemReferenceWhenNotPreserved(t *testing.T) {
 	require.False(t, hasID)
 }
 
+func TestApplyCodexOAuthTransform_NormalizeCodexTools_PreservesResponsesFunctionTools(t *testing.T) {
+	setupCodexCache(t)
+
+	reqBody := map[string]any{
+		"model": "gpt-5.1",
+		"tools": []any{
+			map[string]any{
+				"type":        "function",
+				"name":        "bash",
+				"description": "desc",
+				"parameters":  map[string]any{"type": "object"},
+			},
+			map[string]any{
+				"type":     "function",
+				"function": nil,
+			},
+		},
+	}
+
+	applyCodexOAuthTransform(reqBody)
+
+	tools, ok := reqBody["tools"].([]any)
+	require.True(t, ok)
+	require.Len(t, tools, 1)
+
+	first, ok := tools[0].(map[string]any)
+	require.True(t, ok)
+	require.Equal(t, "function", first["type"])
+	require.Equal(t, "bash", first["name"])
+}
+
 func TestApplyCodexOAuthTransform_EmptyInput(t *testing.T) {
 	// 空 input 应保持为空且不触发异常。
 	setupCodexCache(t)