Janka UrygaandGitHub 0dba1c692b Allow SSR to finish microtasky work before flushing (#86311) ...

In a dynamic Fizz (SSR) render, rendering work is initially scheduled using microtasks, and a flush will be attempted when the stream gets pulled:
https://github.com/facebook/react/blob/8ac5f4eb3601f7381462f8b74ecf24d47259cc20/packages/react-dom/src/server/ReactDOMFizzServerNode.js#L386-L389
This can cause streaming metadata to flake between appearing in `<head>` and `<body>` depending on if whether it had enough microtasks to render before the flush occurred.
In general, if something is async, but available after a couple microtasks, then we shouldn't bother streaming it, it should just go into the initial HTML. We achieve this by waiting a task before allowing the stream to get pulled, which allows all the microtasky work to finish without delaying the response too much.

2025-11-20 13:35:38 +01:00

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