Facts

An ImageAsset's facts are derived from its original once, where it enters, and stored beside it. describe is in the core; each inspector is the subpath of where it runs (/sharp, /browser, /cloudflare), and factsOf is foldkit-media/server's:

• describe(key, bytes) reads them through the Inspector: size, alpha, the SHA-256, and a ThumbHash where the inspector makes a thumbnail.
• inspectorSharp({ maxPixels? }) (Node) reads all of them; alpha is whether any pixel is transparent, so an opaque PNG still gets a placeholder.
• inspectorBrowser({ maxPixels? }) (foldkit-media/browser) reads them in the browser or a web worker, with its own decoder: an editor describes a file a reader dropped, ThumbHash and hash included, before anything is uploaded, and stores its facts beside the image (a rich-text Image's asset). What the browser cannot decode is refused.
• inspectorImages(binding) (Cloudflare) reads the size from info, which costs no transformation. It makes no thumbnail, since the binding's raw pixels are not offered offline, and takes every format but JPEG to be transparent; both cost a placeholder, never show a wrong one.
• factsOf(url, { allow, maxBytes?, cache?, fetch? }) describes an image a page names only by URL (a rich-text image), so it gets its box like any other. Only https on a host in allow (matched exactly), at its default port, is read, each redirect is checked again, and the body is limited as it streams. Given a KeyValueStore as cache, the facts are kept by URL and the original is asked for again with its ETag, so an unchanged one is not read twice.