Replaces the DB-blind `/media` ServeDir with a signed, DB-aware gateway at
`GET /media/{kind}/{id}`. Every media byte now flows through an HMAC-SHA256
signature check (minted into feed/upload DTOs for authenticated members; <img>
can't carry a Bearer header) plus a DB lookup:
- C1: export ZIP/HTML have no upload row, so they are unreachable by path —
download stays behind the authenticated /export endpoints.
- C2 (sink): responses carry X-Content-Type-Options: nosniff and a locked-down
CSP (default-src 'none'; sandbox), neutralizing any active content.
- C3 / H2: find_by_id filters deleted_at and the handler rejects ban-hidden
uploaders, so deleted and moderated artifacts 404 — and the unauthenticated
get_original alias (the H2 hole) is removed entirely.
- H10: delete paths (owner + host) now unlink original/preview/thumbnail after
commit; soft_delete returns the paths; an hourly reaper reclaims disk for
rows soft-deleted past a 1-day grace and hard-deletes them (FKs cascade).
Signed URLs are bucketed to a 1h window so they stay stable across feed polls
(browser cache hits) while expiring within 24h. media_token sign/verify has a
unit test (roundtrip + tamper + expiry).
Frontend: FeedUpload/pickMediaUrl now use the backend-provided signed
original_url; no client constructs a media path anymore.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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