[whatwg/fetch] Bypass blob URL partitioning for top-level self fetches (PR #1879)

Implements the fetch spec side of bypassing partitioning when a top-level blob URL document attempts to fetch itself. For more info see: https://github.com/w3c/FileAPI/issues/210

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- [ ] At least two implementers are interested (and none opposed):
   * Implemented in Chromium: https://crbug.com/426787402
   * Possibly support from Safari: https://github.com/w3c/FileAPI/issues/210#issuecomment-3001278531
- [x] [Tests](https://github.com/web-platform-tests/wpt) are written and can be reviewed and commented upon at:
   * https://chromium-review.googlesource.com/c/chromium/src/+/7016969
- [ ] [Implementation bugs](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) are filed:
   * Chromium: https://crbug.com/426787402
   * Gecko: TODO
   * WebKit: TODO
   * Deno (not for CORS changes): TODO
- [ ] [MDN issue](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) is filed: TODO
- [X] The top of this comment includes a [clear commit message](https://github.com/whatwg/meta/blob/main/COMMITTING.md) to use. <!-- If you created this PR from a single commit, Github copied its message. Otherwise, you need to add a commit message yourself. -->

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<a href="https://whatpr.org/fetch/1879.html" title="Last updated on Nov 14, 2025, 4:07 PM UTC (ff58185)">Preview</a> | <a href="https://whatpr.org/fetch/1879/0e72db8...ff58185.html" title="Last updated on Nov 14, 2025, 4:07 PM UTC (ff58185)">Diff</a>
You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/fetch/pull/1879

-- Commit Summary --

  * Bypass blob URL partitioning for top-level self fetches

-- File Changes --

    M fetch.bs (38)

-- Patch Links --

https://github.com/whatwg/fetch/pull/1879.patch
https://github.com/whatwg/fetch/pull/1879.diff

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