The token registry holds a logical clock (advance/now; the substrate has no
wall clock). Grants carry a Ttl; each access token carries an Expires
(Now-at-issue + Ttl, or infinity); introspect returns inactive once Now
reaches it. Refresh mints a fresh short-lived access token — short access
tokens, long refresh tokens. issue/4 and issue_grant/4 default to infinity so
all prior behaviour is unchanged. New tests/expiry.sx. token loop/6. 138/138.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>