oauth.sx now owns a client registry (loop/6) with register_client and the
client_credentials grant. A confidential client authenticates and gets a
token acting on its own behalf (subject = the client), no refresh token
(§4.4.3). A public client is unauthorized_client; any auth failure (unknown
client or wrong secret) is invalid_client — no client-existence oracle
(§5.2). identity-load-oauth! now pulls its deps. New tests/grants.sx.
158/158.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
