chat.bsky.* — hosted Bluesky DMs. Password at+jwt sessions send atproto-proxy through the PDS (effective_proxy: explicit proxy, else session did_doc #bsky_chat, else ATP_CHAT_DID, else did:web:api.bsky.chat#bsky_chat). OAuth DPoP cannot be proxied: mint getServiceAuth (aud = service_aud, lxm = the XRPC) and call the chat host (default_host / ATP_CHAT_HOST) with that JWT (list_convos_service / get_convo_service / get_messages_service / send_message_service). This is a client for the hosted chat service, not an OSS chat backend. Official TestNetwork does not start chat.