CF Workers AI has a ~4MB JSON body limit. Large cover images base64-encoded
can easily exceed this, causing Cloudflare to return a 502 Bad Gateway.
Added resizeRefImage() which scales the reference down so its longest side
≤ 768px (nearest-neighbour, re-encoded as JPEG) before passing it to the
GenerateImageFromReference call. Images already within the limit pass through
unchanged.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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