[Mohammad Aatif Shaikh (aatif101)]

Description

Fixes #3343.

MarkdownInjectionScorer missed two image forms that renderers fetch automatically:

1. Shortcut-reference images (![logo] + [logo]: url) where the data is in the URL path. These were only flagged when the definition URL contained =.
2. Raw HTML <img> tags, which no pattern covered.

This PR adds two patterns:

• Markdown Image (shortcut reference): flags ![ref] only when a matching [ref]: url definition exists, since without one the text renders literally. It handles the definition appearing before or after the image, and labels match case-insensitively, as in CommonMark.
• HTML Image: flags <img ... src=...> and srcset=. It deliberately skips data-src, which browsers only fetch when page script copies it into src.

As in the issue: if you'd prefer this scorer to stay markdown-only, I'm happy to drop the HTML pattern. It's a single entry.

Known limitation, shared with the existing patterns: matches inside fenced code blocks are still flagged, and reference labels aren't whitespace-normalized.

Tests and Documentation

• Added 15 cases to tests/unit/score/regex/test_markdown_injection.py:
  • 4 shortcut-reference positives: path exfil, with a title, case-insensitive label, definition first.
  • 6 HTML <img> positives: quote styles, uppercase, extra attributes, srcset.
  • 5 lookalikes that must stay False: bare ![logo], mismatched label, prose mentioning "img src", <image>, data-src.
• Wrote the tests first and confirmed the positives failed before the fix.
• Full unit suite passes locally (uv run pytest tests/unit), and pre-commit passes on the changed files.
• Updated the class docstring. The scoring guide notebook describes this scorer generically ("images, links"), so I didn't change it and didn't run JupyText.

[Richard Lundeen (richlundeen)]

The shortcut-reference fix makes sense, but the new HTML Image pattern can match text inside another attribute. For example, <img alt="example src=https://example.com/p.png"> has no src or srcset attribute and fetches no image, but this pattern reports it as an image injection. The lookbehind only excludes data-src; it does not distinguish attribute values from attribute names.

Please keep this narrow: either drop the HTML entry and keep the Markdown fix, as offered in the description, or make the HTML match skip quoted attribute values and add this negative case. I would not add a new HTML parsing layer for this.

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