A route registered as an upload route has its headers run through the middleware
first, so a request that isn't allowed is answered before any of its body is taken.
The body then goes to a file as it arrives, with a size limit, instead of into
memory. MultipartFile splits a multipart/form-data body that is in a file into its
parts without loading it.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
