### Update
We removed the `<head>` element checking for root layout in #41621. Since we also need `<head>` for preload in the future, and also css-in-js will require that. We're adding back the `head` element checking to make sure user always provide valid root layout including it.
### Issue
An issue was reported [here](https://github.com/mui/material-ui/issues/34905#issuecomment-1331945868) that the Emotion/MUI site was suffering from FOUC.
After an inspection, I noticed that the SSRed HTML didn't contain the inserted styles at all - despite them being inserted through `useServerInsertedHTML`. I managed to debug it down and discovered that their layout was missing `<head></head>` and thus the stream transformer skipped the insertion altogether cause of this check:
fbc98abab3/packages/next/server/node-web-streams-helper.ts (L177-L183)
I've figured that at the very least we could surface this as a console error in development to nudge the user to fix the missing `<head/>`
cc @huozhi
Co-authored-by: Jiachi Liu <4800338+huozhi@users.noreply.github.com>
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