One of pending (pipeline in flight), success (parse + embed both completed),
failed (latest attempt failed), or skipped (format unsupported, never parsed).
Unsupported files are stored as-is; the indicator lets clients flag them in listings
rather than rejecting the upload.
signed_urlstring nullable
CloudFront signed URL on the new CDN for private content. Omitted when
signing is unavailable or the object is public.
uidstring required
updated_atstring date-time required
urlstring required
Deprecated: prefer signed_url when present. Kept for old clients.