docs: fix ssr fallback docs (#6527)

packages/document/main-doc/docs/en/guides/basic-features/render/ssr.mdx

@@ -113,7 +113,29 @@ If a Client Loader is defined for the route, it will be used to re-fetch the dat
 
 ### Component Rendering Error
 
-If a component throws an error during rendering, Modern.js automatically falls back to CSR mode and re-fetches the data. If re-rendering fails again, the `<ErrorBoundary>` component will be displayed.
+If the Data Loader executes correctly but the component rendering fails, SSR rendering will partially or completely fail, as shown in the following code:
+
+```tsx
+import { Await, useLoaderData } from '@modern-js/runtime/router';
+import { Suspense } from 'react';
+
+const Page = () => {
+  const data = useLoaderData();
+  const isNode = typeof window === 'undefined';
+  const undefinedVars = data.unDefined;
+  const definedVars = data.defined;
+
+  return (
+    <div>
+      {isNode ? undefinedVars.msg : definedVars.msg}
+    </div>
+  );
+};
+
+export default Page;
+```
+
+In this case, Modern.js will fallback the page to CSR and use the existing data from the Data Loader to render. If the rendering still fails, the `<ErrorBoundary>` component will be rendered.
 
 :::tip
 The behavior of component rendering errors is unaffected by `loaderFailureMode` and will not execute the Client Loader on the browser side.

packages/document/main-doc/docs/zh/guides/basic-features/render/ssr.mdx

@@ -118,7 +118,29 @@ Modern.js 也支持通过 [`server.ssr`](/configure/app/server/ssr) 配置项中
 
 ### 组件渲染报错
 
-当组件渲染报错时，Modern.js 会自动降级到 CSR 模式，并重新发起数据请求。如果重新渲染仍然出错，则展示 `<ErrorBoundary>` 组件。
+如果 Data Loader 执行正常，但组件渲染报错时，SSR 渲染将会部分或完全失败，例如以下代码：
+
+```tsx
+import { Await, useLoaderData } from '@modern-js/runtime/router';
+import { Suspense } from 'react';
+
+const Page = () => {
+  const data = useLoaderData();
+  const isNode = typeof window === 'undefined';
+  const undefinedVars = data.unDefined;
+  const definedVars = data.defined;
+
+  return (
+    <div>
+      {isNode ? undefinedVars.msg : definedVars.msg}
+    </div>
+  );
+};
+
+export default Page;
+```
+
+此时，Modern.js 会将页面降级为 CSR，并利用 Data Loader 中已有的数据渲染。如果重新渲染仍然出错，则展示 `<ErrorBoundary>` 组件。
 
 :::tip
 组件渲染报错的行为，不会受到 `loaderFailureMode` 的影响，也不会在浏览器端执行 Client Loader。