Follow-ups on the startup-burst memo:
- Populate the memo on the valid-token fast path as well. The startup
burst usually finds a VALID token, and each check_fn call still paid
two cross-process file locks + state reads to reach that return; the
original memo only engaged after a refresh. The token has at least
refresh_skew_seconds (>=120s) of life at that return, so a 5s memo can
never serve an expired token.
- Clear the module-level memo in test_nous_portal_staging_allowlist's
refresh-capture helper: with the fast-path populate, a token memoized
by an earlier test would otherwise short-circuit the refresh these
tests assert on (3 tests failed without this).
- Add dedicated memo behavior tests (TTL hit, TTL expiry, insecure
bypass) — the original PR shipped none. Mutation-checked: all 3 fail
against main's un-memoized function, pass on this branch.
kshitijk4poor