Three safety gaps in vision_analyze_tool:
1. Local files accepted without checking if they're actually images —
a renamed text file would get base64-encoded and sent to the model.
Now validates magic bytes (PNG, JPEG, GIF, BMP, WebP, SVG).
2. No website policy enforcement on image URLs — blocked domains could
be fetched via the vision tool. Now checks before download.
3. No redirect check — if an allowed URL redirected to a blocked domain,
the download would proceed. Now re-checks the final URL.
Fixed one test that needed _validate_image_url mocked to bypass DNS
resolution on the fake blocked.test domain (is_safe_url does DNS
checks that were added after the original PR).
Co-authored-by: GutSlabs <GutSlabs@users.noreply.github.com>
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