Mark the byte downloader as the next checkpoint

docs/media-scraper.md

@@ -90,7 +90,12 @@ Indexes: `(kind, timestamp)` via `media_sources`, `channel` metadata in `scrape.
 
 ## Downloads and previews
 
-- `downloads` is a serial queue, one file at a time, 1-3 s apart, with a size cap
+**Planned (C10).** The schema has `file_bytes`, `preview_bytes`, `file_hash`, and `preview_hash`,
+and the command accepts `mode: "download"`, but nothing fetches bytes yet.
+
+The plan:
+
+- A serial download queue, one file at a time, 1-3 s apart, with a size cap
   (`media.maxFileBytes`, default 50 MiB) and 2 retries on network or 5xx errors.
 - `4xx` marks the URL expired. The item is re-fetched with its message later.
 - Previews use the Discord CDN resizer (`?width=320&height=320&format=webp`) and are stored by hash

docs/media.md

@@ -72,7 +72,9 @@ media-scrape/db/
 
 - `links` is the default. The archive stores the Discord CDN URL and the metadata. Nothing large is
   downloaded.
-- `download` fetches attachment bytes into `media/`. Deduplicated by hash.
+- `download` fetches attachment bytes into `media/`. Deduplicated by hash. **Not implemented yet**
+  (checkpoint C10): the command accepts the mode and the schema has the columns, but the download
+  queue is still owed.
 - Third-party embeds are **never downloaded**: YouTube, Instagram, X, TikTok, and every other
   embed stays a link with metadata.
 - Discord-hosted image and sticker previews are cached small (`thumbs/`, WebP, via the CDN