New test_flow3b_gift_cards.py covers: amount validation, 4-word code
generation, gift card state machine, cents-based pricing engine,
creation with crypto invoice, immediate and partial redemption,
balance tracking, insufficient balance detection, approval gate flow,
polling simulation, expiration, wallet-free agent end-to-end flow,
multi-agent shared cards, code security edge cases, and API response
formats.

Updated assertion totals: 16 suites, 2,324 assertions (was 15/2,089).
Removed test_flow2_freetier.py (free tier removed from spec).