Files

List files attached to a conversation, newest-first. Walks ``conversation_messages`` and extracts files from three sources: bot-emitted ``media``, user-uploaded URL parts of ``data``, and ``files`` content blocks on tool returns (a bot's ``send_files`` sends). Every URL is fresh at read time, by one of two mechanisms depending on the source. The first two persist a URL, which is re-signed here (S3 only — external URLs pass through unchanged). A block file deliberately persists **no** URL: its storage location is server-internal and its download is *minted* from the opaque ``file_id``, exactly as the content-block file endpoint does for the chat card. Both kinds therefore arrive at the client the same way — a short-lived URL that must not be persisted — by different routes.