Uploading a video or large file to the Library used to die at the serverless function body cap (~4.5MB) with a bare 413 Request Failed. Files over 4MB now stream directly from the browser to Vercel Blob via a presigned PUT URL, completely bypassing our function body limit. The upload-url route was also routed through the media-storage seam instead of importing the Blob SDK directly, closing a structural violation of the one-seam rule. Smaller uploads keep taking the cheap multipart path.