Function linkBillingCustomer

linkBillingCustomer(
    db: BillingDB,
    userId: string,
    customerId: string,
): Promise<void>
Persist the user's Stripe customer id WITHOUT touching subscriptionId — so a one-time top-up never clears a subscriber's subscriptionId (unlike upsertBillingAccount, which sets it). Idempotent on the userId PK.
Parameters
- db: BillingDB
- userId: string
- customerId: string
Returns Promise<void>
- Defined in packages/billing/src/account.ts:39