Returns a currently-valid access token, acquiring or renewing it internally as needed (e.g. an
OAuth2 client_credentials grant). Unlike TokenRefresher there is no pre-existing token to fall
back to on the very first call, so implementations may throw when no valid token can be
obtained at all — the executor lets that propagate as-is rather than forcing it through the
HTTP-response-shaped error handling used for a failed tool call.
Returns a currently-valid access token, acquiring or renewing it internally as needed (e.g. an OAuth2 client_credentials grant). Unlike TokenRefresher there is no pre-existing token to fall back to on the very first call, so implementations may throw when no valid token can be obtained at all — the executor lets that propagate as-is rather than forcing it through the HTTP-response-shaped error handling used for a failed tool call.