PyLoan replaces an explicit 100 payment with a 919.10 final payment

Independent GERO audit of PyLoan 0.7.2. In a synthetic two-month loan with principal 1,000, annual interest 12% and an explicit payment of 100, the final scheduled payment becomes 919.10. Applying the documented explicit payment gives a final payment of 100 and residual principal of 819.10.

Official 0.7.2 and pinned current source: 408 payment-cap violations in 864 scenarios; targeted candidate: zero; restored original: 408. All 456 previously passing schedules and 60 additional controls are unchanged. The candidate matches official 0.7.0 on this grid. Twenty-four separate exact-Decimal differences up to 0.02 currency units remain, and the upstream unittest suite retains three baseline failure reports. The suite is not claimed green.

The known automatic-amortization fix in PR68 is credited. This report concerns its regression of the separately documented explicit-annuity mode. Vendor notified before publication: https://github.com/darius-lesch/pyloan/issues/70 . No upstream acceptance, bank deployment or borrower-loss measurement is claimed. Research and preparation were AI-assisted.

Report and executable evidence: https://github.com/kadyrbekovhamit-cyber/gero-numerical-observatory/tree/72df515db01e7f004d7cd84ae12250bb87a2f717/reports/pyloan-explicit-payment-final-balloon

Evidence ZIP SHA-256: 6be9658bd28e6bf72d9dac8add77319a703f4d6c7fedcacefee069604dfcc0a9. MIT license, original upstream notices retained. No video included.