Handling different client and server content - not showing initial render

In the hydrateRoot page, it is mentioned that
"This way the initial render pass will render the same content as the server, avoiding mismatches, but an additional pass will happen synchronously right after hydration."

which means that the initial render on the playground should show "Is Server", but it shows directly "Is Client" which is very confusing for learners and doesn't show the real behavior.
I tired opening the sandbox in external window, and it indeed shows "Is Server" first and then changing to "Is Client" as expected.

In the Website:

In The sandbox (using the fork button):

从 hydrateRoot 页面中嵌入的 playground 开始，并将其行为与通过 fork 按钮打开的外部 sandbox 进行比较。复现该示例，并跟踪 playground 如何处理 hydration 及其初始渲染。完成标准是：嵌入的示例先短暂显示 "Is Server"，然后变为 "Is Client"，与文档所述的行为一致。