Copilot review on #2105: jwtExpiresAtMs is lenient — it parses the second of
any two-or-more dot-separated segments — so a structured opaque token such as
`opaque.<base64url({"exp":...})>` returned a parseable exp and could still
short-circuit re-authorization, recreating the replay loop.
isAccessTokenProvablyUnexpired now checks isJwtFormat first. Tests cover a
two-segment and a four-segment token whose payload decodes to a future exp.
Signed-off-by: cliffhall <cliff@futurescale.com>
deca2de604