Phase 6: media

Implements PLAN.md Phase 6: the media repository. Clients upload files,
reserve an mxc:// URI and upload to it later, download and ask for
thumbnails, all through the authenticated media endpoints of Matrix 1.11;
other servers download this server's media through the federation media
endpoints, and media uploaded elsewhere is fetched over federation on
first use and kept.

internal/mediaapi is the component. Content goes into a BlobStore named
by its SHA-256, so the same file uploaded twice is stored once and the
hash doubles as the ETag; the metadata that maps an mxc:// URI onto a
blob is in media_repository and media_thumbnails. The local-filesystem
store writes to a temporary file and renames it into place once hashed,
so nothing ever refers to half a file. A storage driver can bring its own
store through storage.BlobProvider, which is where PocketBase's
filesystem abstraction (local or S3) plugs in with Phase 10.

Reserved uploads belong to the user who made them, take one upload,
lapse after a day, and are capped per user; a download of one waits for
its content, woken in memory the moment it arrives, for as long as
timeout_ms allows.

Thumbnails come from a fixed set of configured sizes, so a thousand
requested sizes cannot mean a thousand resizes. They are made on first
request and kept, never enlarge, honour a JPEG's EXIF orientation, and
point at the original when it already fits. The pixel count is checked
from the header before anything is decoded, at most four resizes run at
once, and concurrent requests for the same thumbnail share one.

Remote media is fetched through the signed client: the multipart/mixed
answer of Matrix 1.11, with a fallback to the legacy download endpoint
for servers that answer M_UNRECOGNIZED, and Location redirects followed
by a dialer that refuses loopback, private and link-local addresses.
Concurrent requests share one fetch, detached from the request that
started it. With federation off nothing is fetched, and what was cached
before is still served.

Downloads carry a sandboxing CSP, nosniff, inline Content-Disposition
only for the types the spec lists as safe, and private immutable caching.
The unauthenticated legacy download endpoints are off by default behind
media.legacy_unauthenticated_downloads.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/internal/storage/postgres/migrations/0007_media.sql

@@ -0,0 +1,56 @@
+-- Media: the metadata of content uploaded here and of content fetched from
+-- other servers and kept, and of the thumbnails made from either.
+--
+-- The content itself is not in the database. It is in the blob store —
+-- files under media.base_path by default — named by its SHA-256, so the
+-- same bytes uploaded twice are stored once and a row here only says which
+-- blob an mxc:// URI refers to.
+--
+-- Timestamps are milliseconds since the Unix epoch, as everywhere else in
+-- Warp.
+
+CREATE TABLE IF NOT EXISTS media_repository (
+    -- The server name of the mxc:// URI: this server for an upload,
+    -- another for cached remote media.
+    media_origin  TEXT    NOT NULL,
+    media_id      TEXT    NOT NULL,
+    -- As uploaded, parameters included: "text/plain; charset=utf-8".
+    content_type  TEXT    NOT NULL DEFAULT '',
+    upload_name   TEXT    NOT NULL DEFAULT '',
+    file_size     BIGINT  NOT NULL DEFAULT 0,
+    -- Lower-case hex SHA-256 of the content; '' while pending.
+    sha256        TEXT    NOT NULL DEFAULT '',
+    -- The uploader; '' for remote media.
+    user_id       TEXT    NOT NULL DEFAULT '',
+    created_at_ms BIGINT  NOT NULL,
+    -- An ID handed out by POST /_matrix/media/v1/create whose content has
+    -- not been uploaded yet. It is deleted unused at expires_at_ms.
+    pending       BOOLEAN NOT NULL DEFAULT FALSE,
+    expires_at_ms BIGINT  NOT NULL DEFAULT 0,
+    PRIMARY KEY (media_origin, media_id)
+);
+
+-- Counting a user's pending uploads, and sweeping the expired ones.
+CREATE INDEX IF NOT EXISTS media_repository_pending_idx
+    ON media_repository (pending, user_id, expires_at_ms);
+
+-- Thumbnails, one per configured size that has been asked for.
+--
+-- There is no foreign key to media_repository: the thumbnail of remote
+-- media is fetched from its server on its own, and the original it was
+-- made from may never have been fetched here at all.
+CREATE TABLE IF NOT EXISTS media_thumbnails (
+    media_origin  TEXT    NOT NULL,
+    media_id      TEXT    NOT NULL,
+    -- The configured size the thumbnail answers, not the size of the
+    -- image: a "scale" thumbnail keeps the original's aspect ratio.
+    width         INTEGER NOT NULL,
+    height        INTEGER NOT NULL,
+    -- 'crop' or 'scale'.
+    method        TEXT    NOT NULL,
+    content_type  TEXT    NOT NULL,
+    file_size     BIGINT  NOT NULL,
+    sha256        TEXT    NOT NULL,
+    created_at_ms BIGINT  NOT NULL,
+    PRIMARY KEY (media_origin, media_id, width, height, method)
+);