VerificationUnavailable now carries an error class and never the fetch error,
whose text named the key-set URL. fetch_jwks returns the reqwest error so the
class is read from it, not from a string. run_refresh_loop loses its period
parameter: SESSION_REFRESH_PERIOD is decided in one place and a paused-clock
test observes it exactly and over twelve ticks.
Tests drive HeimdallClient::verify_access against a loopback issuer that
counts fetches (cache stored, read, ttl 299 s fresh and 301 s stale), a closed
port and a 503 (kept session and receipt, no URL in the error or the log line),
and nine wrong-algorithm tokens. The moved-session test also pins that the
newer claim is the one spent next.
Builds and passes under ygg-verify (28 of 28 in heimdall:: and refresh_loop_tests).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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