Live E2E testing against the real Sổ Bán Lẻ catalog (64 usable
products, avg price ~24k) showed the fixed maxQtyPerLine=3 capped the
achievable order total at ~4.86M regardless of retry count - a
structural ceiling, not bad luck. 7/10 test amounts above ~4.2M failed
with NO_PRODUCT_COMBO_MATCH every time.

Default per-line qty is now bounded only by the product's actual stock
(previously min(3, qty), now just qty), raising the real ceiling to
~2B on the current catalog. maxQtyPerLine is still available as an
explicit override for callers that want a cap.

Verified against the real catalog: all 7 previously-failing amounts
(4.2M-19.5M) now succeed, real order totals landing within the
50,000 tolerance band every time.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017KPzWwuTEeX2vXGXvyGn4q