fix(billing): stop an unpaid subscription from unlocking the paid limits

isPaidTier read a future stripeCurrentPeriodEnd as proof of payment, and
Stripe stamps a current period on an incomplete subscription all the
same. A checkout whose first charge failed therefore carried a period
end a month out with nothing paid behind it, and every ceiling the
cardless trial puts on an unpaid account (200 GB of storage, unlimited
projects, unlimited workspaces) came off with it.

Written as a deny list of the two statuses that mean no charge has ever
gone through, so a real customer whose renewal failed keeps the full
plan for the period they already paid for.

hasBillingAccess reads the same column the same way and is deliberately
left alone: being wrong there locks a paying customer out, and the SQL
in buildBillingAccessWhereInput has to move with it.

lib/billing.ts

@@ -25,6 +25,16 @@ const RECOVERABLE_SUBSCRIPTION_STATUSES = new Set<BillingSubscriptionStatus>([
   BillingSubscriptionStatus.INCOMPLETE,
 ]);
 
+// Statuses that mean no payment on this subscription has ever gone through.
+// Stripe stamps a current period on an `incomplete` subscription all the same,
+// so a checkout whose first charge failed leaves `stripeCurrentPeriodEnd` a
+// month into the future with nothing paid behind it. Every other status in the
+// enum follows at least one successful charge, or has no period end at all.
+const UNPAID_SUBSCRIPTION_STATUSES = new Set<BillingSubscriptionStatus>([
+  BillingSubscriptionStatus.INCOMPLETE,
+  BillingSubscriptionStatus.INCOMPLETE_EXPIRED,
+]);
+
 export const DEFAULT_TRIAL_PERIOD_DAYS = 7;
 const STORAGE_CLEANUP_GRACE_DAYS = 15;
 
@@ -96,6 +106,14 @@ export function isPaidTier(
     return true;
   }
 
+  // The period end alone is not proof of payment. Checked here and not in
+  // `hasBillingAccess`, which keeps granting access on a period end it did not
+  // question before: the cost of being wrong there is a customer locked out,
+  // while the cost of being wrong here is a free account holding 200 GB.
+  if (UNPAID_SUBSCRIPTION_STATUSES.has(subject.subscriptionStatus)) {
+    return false;
+  }
+
   return Boolean(
     subject.stripeCurrentPeriodEnd && subject.stripeCurrentPeriodEnd.getTime() > now.getTime()
   );