feat: implement billing account management and cycle synchronization logic with accompanying tests

__tests__/server/billingTimestampNormalization.test.js

@@ -0,0 +1,45 @@
+jest.mock('../../server/lib/postgres', () => ({
+  get: jest.fn(),
+  run: jest.fn(),
+}));
+
+const { get, run } = require('../../server/lib/postgres');
+const { syncRevenueCatCustomerInfo } = require('../../server/lib/billing');
+
+describe('server billing timestamp normalization', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    run.mockResolvedValue({ lastId: null, changes: 1, rows: [] });
+  });
+
+  it('upserts ISO timestamps when postgres returns Date objects', async () => {
+    get.mockResolvedValueOnce({
+      userId: 'usr_mnjcdwpo_ax9lf68b',
+      plan: 'free',
+      provider: 'revenuecat',
+      cycleStartedAt: new Date('2026-04-01T00:00:00.000Z'),
+      cycleEndsAt: new Date('2026-05-01T00:00:00.000Z'),
+      monthlyAllowance: 15,
+      usedThisCycle: 0,
+      topupBalance: 0,
+      renewsAt: null,
+      updatedAt: new Date('2026-04-02T12:00:00.000Z'),
+    });
+
+    await syncRevenueCatCustomerInfo(
+      {},
+      'usr_mnjcdwpo_ax9lf68b',
+      { entitlements: { active: {} }, nonSubscriptions: {} },
+      { source: 'topup_purchase' },
+    );
+
+    const upsertCall = run.mock.calls.find(([, sql]) => typeof sql === 'string' && sql.includes('INSERT INTO billing_accounts'));
+    expect(upsertCall).toBeTruthy();
+
+    const params = upsertCall[2];
+    expect(params[3]).toBe('2026-04-01T00:00:00.000Z');
+    expect(params[4]).toBe('2026-05-01T00:00:00.000Z');
+    expect(params[3]).not.toContain('Coordinated Universal Time');
+    expect(params[4]).not.toContain('Coordinated Universal Time');
+  });
+});