Pasting from Google Docs nests images inside heading/paragraph blocks. #79541

Description

When copy/pasting content from Google Docs into the editor, images are sometimes placed inside a heading or paragraph block instead of becoming their own Image block.

The image is stored as raw <img> markup with a temporary blob: URL inside the text block, for example:

<!-- wp:paragraph -->
<p><img src="blob:http://localhost:8888/371c53b0-f8ab-4fe0-b838-248ddd01de9a" width="624" height="240">asdf</p>
<!-- /wp:paragraph -->

The image looks correct in the editor, and it even displays correctly on the published post in the same browser window — so the editor never signals that anything is wrong.

The problem: blob: URLs are temporary references that only exist in the memory of the browser that created them. Because the image lands inside a text block (heading/paragraph) rather than an Image block, it is never uploaded to the media library — only Image blocks run the blob-to-upload flow. The temporary blob: URL is therefore serialized verbatim into the saved post.

Result: the author sees the image fine, but when the post is opened in an incognito window or any other browser, the image is broken/invisible (the blob: URL resolves to nothing).

Technical detail

This looks like the same underlying issue as #21516.

The "Paragraph with image → Transform to Image" work in PR #68796 can help — but only when the editor/author is aware the image is misplaced and manually transforms it. In this case the author has no signal: the image renders correctly in the editor and on the published post (in their own browser), so they might never know to transform it.

Step-by-step reproduction instructions

This happens in two Google Docs scenarios:

1. When text (normal paragraph text or a heading) immediately follows an image with no blank line/space between them.

2. When using a heading or normal text, then pressing Shift+Enter, and then adding an image.
   In both cases the image gets merged into the heading/paragraph during copy/paste.

To reproduce:

1. Open the Sample Google Doc. It contains sample text with images arranged in the two scenarios above; you can copy/paste its content to replicate the bug.

2. Select all the content in the Google Doc and copy it.

3. In a new post in the editor, paste the content.

4. Notice the images are nested inside heading/paragraph blocks (switch to the Code editor view to confirm the <img> is inside <h2>/<p> with a blob: src).

5. Publish the post.

6. View the published post in the same browser → the image displays.

7. Open the same published post in an incognito window or a different browser → the image is broken/missing.

Screenshots, screen recording, code snippet

Environment info

WordPress version: 7.0
Gutenberg version: 23.4.0
Browser(s): Brave
OS: macOS
Source of pasted content: Google Docs

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure