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// SCENARIO: PayFlow Payment Service
// Customers report being double-charged
// on slow 3G connections. Your job:
> Running test suite...
FAIL tests/payment.test.ts
✕ should not double-charge on retry (23ms)
✕ concurrent payments maintain balance (18ms)
✓ single payment processes correctly (5ms)
Tests: 2 failed, 1 passed, 3 total
> _
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