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## What and why

Closes #<!-- issue number (required: the issue must have a reply agreeing to the change) -->

<!-- One or two sentences: what this changes, from the viewer's side, and why. -->

## How

<!-- The approach, and anything a reviewer should look at closely. -->

## Tested on

- Headset and controllers:
- VR runtime / connection:
- Browser and version:
- Signed in to YouTube: yes / no
- What I tried in VR:

## Checklist

What the automatic summary and the Checks can't see:

- [ ] There's an agreed issue for this, and this PR does only that one thing.
- [ ] I understand every line of this change and can explain it in review.
- [ ] I tested it in a real VR session on the hardware listed above.
- [ ] YouTube access stays in `src/sites/youtube/page/youtube-*.js`; tunables are in the config files.
- [ ] Every new file and function has its comment, and comments I touched match the code.
- [ ] New files are in `manifest.json` in the right **order** (the summary only checks they're listed).
- [ ] No new permissions, or they were agreed in the issue.

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## Automatic summary

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