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.
The webhook's money/status mapping (Basil field relocations, period
extraction, customer-id unwrap, status patch, invoice->payment row,
minor->major) lived inline in the route with zero test coverage - the
biggest untested critical path in the codebase. Extracted to a pure,
SDK-free lib/stripe/webhook-logic.ts (structural input types) and
refactored the route to only do signature verify + network + DB writes.
12 new tests cover the Basil edges and link/unlink + defaults. Behavior
unchanged; suite 514.
Moheeb Zara