Stripe doesn't guarantee event order. A late customer.subscription.
updated carrying an older period overwrote a newer current_period_end,
so graceExceeded flipped a paid member to 'late' and fired a false
'dues lapsed' email + access loss. applySubscription now reads the
stored period and keeps the later of stored vs incoming
(laterPeriodEnd, pure + tested); status still tracks latest sub.status
but grace is computed from the monotonic period.