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AVIF is a modern image format that can provide smaller file sizes while maintaining high image quality, with support for features such as transparency and HDR. It is now practical for general web use because browser support is broad. As of April 10, 2026, "Can I Use" reports about 94.9% global support, including support in current Chrome, Firefox, Safari, and Edge releases:
https://caniuse.com/avif

This patch adds AVIF support to inline images, thumbnails, attachment previews, and automatic inline markup insertion, so AVIF attachments behave like other supported images.

This patch does not add AVIF support to PDF export, because the rbpdf gem does not currently support AVIF images.