Rework attachment storage and serving per the refined separation
scheme:
- Non-media uploads are stored as {hash}.file blobs (store_attachment)
— the original extension never lands on the filesystem, so the store
directory holds nothing double-click-executable. The original name
lives only in the URL: /_f/{hash}/{original-name}. The .file suffix
itself is rejected in URLs.
- Serving is strictly separated: /_f/{name} serves media only (hash
with or without extension, .orig. still blocked) and 404s .file
names; /_f/{name}/{filename} serves only {name}.file blobs, never
media, never by hash alone.
- Every /_f/ response now carries bare 'content-disposition:
attachment' (the URL's last segment already names the download) and
x-content-type-options: nosniff — media included. Subresource
fetches (<img>, <video>, favicons, the zoom viewer) ignore the
disposition, so inline media is unaffected, while a direct
navigation can never render or sniff a store file into something
executable in the site's origin. The mime-based script-carrier
forcing and the header filename are gone (subsumed).
- Message uploads treat SVG as media (rasterized derivatives; an
as-is-served .svg is script-inert inside <img>), and undecodable
fake images fall through to the .file attachment path.
LeoVasanko
6b34719397