refactor(stripe): extract + unit-test webhook decision logic (R2)

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.

__tests__/stripe-webhook-logic.test.ts

@@ -0,0 +1,132 @@
+import { describe, it, expect } from 'vitest'
+import {
+  isoFromUnix,
+  customerIdOf,
+  subscriptionPeriodEnd,
+  invoiceMetadataMemberId,
+  invoiceLinePeriodEnd,
+  memberStatusPatch,
+  stripeInvoiceToPaymentRow,
+  minorToMajor,
+} from '@/lib/stripe/webhook-logic'
+
+describe('isoFromUnix', () => {
+  it('converts a positive unix seconds value to ISO', () => {
+    expect(isoFromUnix(1_700_000_000)).toBe(new Date(1_700_000_000_000).toISOString())
+  })
+  it('returns null for 0, negative, null, undefined, NaN', () => {
+    for (const v of [0, -1, null, undefined, NaN]) {
+      expect(isoFromUnix(v as number)).toBeNull()
+    }
+  })
+})
+
+describe('customerIdOf', () => {
+  it('handles string id, expanded object, empty, and nullish', () => {
+    expect(customerIdOf('cus_1')).toBe('cus_1')
+    expect(customerIdOf({ id: 'cus_2' })).toBe('cus_2')
+    expect(customerIdOf('')).toBeNull()
+    expect(customerIdOf(null)).toBeNull()
+    expect(customerIdOf(undefined)).toBeNull()
+    expect(customerIdOf({ id: null })).toBeNull()
+  })
+})
+
+describe('subscriptionPeriodEnd (Basil: period on item, not subscription)', () => {
+  it('reads item 0 current_period_end', () => {
+    expect(subscriptionPeriodEnd({ items: { data: [{ current_period_end: 1_700_000_000 }] } })).toBe(
+      new Date(1_700_000_000_000).toISOString(),
+    )
+  })
+  it('null when no items / no field', () => {
+    expect(subscriptionPeriodEnd({ items: { data: [] } })).toBeNull()
+    expect(subscriptionPeriodEnd({})).toBeNull()
+    expect(subscriptionPeriodEnd(null)).toBeNull()
+    expect(subscriptionPeriodEnd({ items: { data: [null] } })).toBeNull()
+  })
+})
+
+describe('invoiceMetadataMemberId (Basil: under parent.subscription_details)', () => {
+  it('reads the relocated metadata', () => {
+    expect(
+      invoiceMetadataMemberId({ parent: { subscription_details: { metadata: { member_id: 'm1' } } } }),
+    ).toBe('m1')
+  })
+  it('undefined when any level is missing or empty', () => {
+    expect(invoiceMetadataMemberId({})).toBeUndefined()
+    expect(invoiceMetadataMemberId({ parent: null })).toBeUndefined()
+    expect(invoiceMetadataMemberId({ parent: { subscription_details: { metadata: { member_id: '' } } } })).toBeUndefined()
+  })
+})
+
+describe('invoiceLinePeriodEnd', () => {
+  it('reads line 0 period end, null when absent', () => {
+    expect(invoiceLinePeriodEnd({ lines: { data: [{ period: { end: 1_700_000_000 } }] } })).toBe(
+      new Date(1_700_000_000_000).toISOString(),
+    )
+    expect(invoiceLinePeriodEnd({ lines: { data: [] } })).toBeNull()
+    expect(invoiceLinePeriodEnd({ lines: null })).toBeNull()
+    expect(invoiceLinePeriodEnd({})).toBeNull()
+  })
+})
+
+describe('memberStatusPatch (only current<->late)', () => {
+  it('current adds last_paid_at; late does not; null/undefined -> no patch', () => {
+    expect(memberStatusPatch('current', '2026-01-01T00:00:00.000Z')).toEqual({
+      status: 'current',
+      last_paid_at: '2026-01-01T00:00:00.000Z',
+    })
+    expect(memberStatusPatch('late', '2026-01-01T00:00:00.000Z')).toEqual({ status: 'late' })
+    expect(memberStatusPatch(null, 'x')).toBeNull()
+    expect(memberStatusPatch(undefined, 'x')).toBeNull()
+  })
+})
+
+describe('stripeInvoiceToPaymentRow', () => {
+  it('maps minor->major, upcases currency, links by member presence', () => {
+    const row = stripeInvoiceToPaymentRow({
+      inv: { id: 'in_1', amount_paid: 2500, currency: 'usd', customer_email: '[email protected]' },
+      spaceId: 's1',
+      memberId: 'm1',
+      eventId: 'evt_1',
+      nowIso: '2026-01-01T00:00:00.000Z',
+    })
+    expect(row).toMatchObject({
+      space_id: 's1',
+      member_id: 'm1',
+      platform: 'stripe',
+      amount: 25,
+      currency: 'USD',
+      status: 'linked',
+      link_status: 'linked',
+      external_id: 'in_1',
+      payer_email: '[email protected]',
+      from_identifier: '[email protected]',
+      transaction_date: '2026-01-01T00:00:00.000Z',
+      raw_data: { event_id: 'evt_1', invoice: 'in_1' },
+    })
+  })
+  it('unlinked + safe defaults when member/amount/currency/email missing', () => {
+    const row = stripeInvoiceToPaymentRow({
+      inv: { id: 'in_2' },
+      spaceId: 's1',
+      memberId: null,
+      eventId: 'evt_2',
+      nowIso: '2026-01-01T00:00:00.000Z',
+    })
+    expect(row.status).toBe('unlinked')
+    expect(row.link_status).toBe('unlinked')
+    expect(row.amount).toBe(0)
+    expect(row.currency).toBe('USD')
+    expect(row.description).toBe('Stripe membership dues')
+    expect(row.payer_email).toBeNull()
+  })
+})
+
+describe('minorToMajor', () => {
+  it('divides by 100, treats nullish as 0', () => {
+    expect(minorToMajor(2500)).toBe(25)
+    expect(minorToMajor(null)).toBe(0)
+    expect(minorToMajor(undefined)).toBe(0)
+  })
+})