A request for several byte ranges gets a 206 multipart/byteranges whose
boundary the client needs to split the body. Rewriting it to
octet-stream lost the boundary. No browser runs that type as a script,
so it passes through.
(cherry picked from commit 9c37f41ff6)
Uploaded files come from this origin, so one served with a JavaScript
type could run as one of the app's own scripts. Browsers accept sixteen
spellings of that type, and Disk URLs sign the type they were minted
with, so refusing a list of types at upload can't cover links already
out there. Instead, a middleware rewrites the type of anything Active
Storage reads out that isn't plainly media, a PDF or plain text to
application/octet-stream, whatever the URL says.
(cherry picked from commit cad2d7211d)