FAILURE MAP
← Case archive

FA-58426 / Loan amortization schedules / Open access

Principal curtailment with recast or term shortening: payoff by curtailment · case 01

A loan paid off by an extra payment reports only the extra as the final payment.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The final payment omits the scheduled payment made in the same month.

THE FAILURE

The final payment omits the scheduled payment made in the same month.

Unsuccessful approach: Reporting only the scheduled payment omits the extra that cleared the loan.

Case contract

x = {'principal', 'rate_bp', 'months', 'prepay': {'k': extra cents after payment k}, 'mode': 'shorten'|'recast'}. The level payment is the exact annuity rounded half-up. Each month: interest = round_half_up(balance*bp/120000); if balance + interest <= payment or it is month n, pay balance + interest and stop. Otherwise reduce the balance by payment - interest, then apply the extra (capped at the balance). In recast mode a nonzero extra that leaves a balance re-levels the payment over the n - k remaining months. An extra that clears the balance ends the loan with final payment = payment + extra. Return {'months_paid', 'total_interest', 'final_payment', 'payments': payment history}.

Why this case matters

Amortization engines drive borrower statements, payoff quotes and investor remittances; a misplaced rounding step, boundary or ordering rule compounds across hundreds of periods.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    def level(P, n):
        if n <= 0 or P <= 0:
            return 0
        if bp == 0:
            exact = Fraction(P, n)
        else:
            r = Fraction(bp, 120000)
            exact = P * r / (1 - (1 + r) ** -n)
        return math.floor(exact + Fraction(1, 2))
    bp = x['rate_bp']
    n = x['months']
    bal = x['principal']
    pay = level(bal, n)
    history = [pay]
    total = 0
    k = 0
    final = 0
    while bal > 0 and k < n:
        k += 1
        interest = rnd(bal * bp, 120000)
        total += interest
        if bal + interest <= pay or k == n:
            final = bal + interest
            bal = 0
            break
        bal -= pay - interest
        extra = min(x['prepay'].get(str(k), 0), bal)
        if extra:
            bal -= extra
            if x['mode'] == 'recast' and bal > 0:
                pay = level(bal, n - k)
                history.append(pay)
            if bal == 0:
                final = extra
    return {'months_paid': k, 'total_interest': total, 'final_payment': final, 'payments': history}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: payoff by curtailment', {'principal': 60000, 'rate_bp': 0, 'months': 36, 'prepay': {'21': 5000, '12': 200000, '35': 2000000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 41663, 'payments': [1667]}], ['control 1', {'principal': 250000, 'rate_bp': 0, 'months': 12, 'prepay': {'10': 1000, '6': 5000, '7': 5000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 18501, 'payments': [20833, 20000, 19000, 18501]}], ['control 2', {'principal': 60000, 'rate_bp': 1200, 'months': 24, 'prepay': {'16': 5000, '9': 1000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 7480, 'final_payment': 2100, 'payments': [2824, 2753, 2099]}], ['control 3', {'principal': 100000, 'rate_bp': 1200, 'months': 6, 'prepay': {'5': 5000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 3478, 'final_payment': 12203, 'payments': [17255, 12203]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {'9': 5000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 3334, 'payments': [5000, 3333]}], ['control 5', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 32442, 'final_payment': 11778, 'payments': [11768]}], ['control 6', {'principal': 100000, 'rate_bp': 1200, 'months': 12, 'prepay': {'8': 20000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 6117, 'final_payment': 3760, 'payments': [8885, 3759]}]], [['regression: payoff by curtailment', {'principal': 100000, 'rate_bp': 0, 'months': 24, 'prepay': {'19': 200000, '18': 20000, '24': 5000}, 'mode': 'recast'}, {'months_paid': 19, 'total_interest': 0, 'final_payment': 4994, 'payments': [4167, 832]}], ['control 1', {'principal': 250000, 'rate_bp': 0, 'months': 24, 'prepay': {'24': 200000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 10409, 'payments': [10417]}], ['control 2', {'principal': 250000, 'rate_bp': 0, 'months': 6, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 41665, 'payments': [41667]}], ['control 3', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {'10': 5000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 12595, 'final_payment': 4326, 'payments': [4707, 4323]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 5000, 'payments': [5000]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 4159, 'payments': [4167]}], ['control 6', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 24, 'total_interest': 12979, 'final_payment': 4718, 'payments': [4707]}]], [['regression: payoff by curtailment', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {'12': 5000, '20': 20000, '4': 1000}, 'mode': 'shorten'}, {'months_paid': 20, 'total_interest': 11928, 'final_payment': 16495, 'payments': [4707]}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'months': 12, 'prepay': {'10': 1000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 3272, 'final_payment': 8101, 'payments': [8607, 8101]}], ['control 2', {'principal': 100000, 'rate_bp': 600, 'months': 6, 'prepay': {'5': 1000, '3': 20000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 1552, 'final_payment': 9220, 'payments': [16960, 10226, 9220]}], ['control 3', {'principal': 60000, 'rate_bp': 600, 'months': 24, 'prepay': {'15': 20000, '5': 1000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 3267, 'final_payment': 324, 'payments': [2659, 2604, 326]}], ['control 4', {'principal': 250000, 'rate_bp': 600, 'months': 36, 'prepay': {'10': 20000, '11': 1000}, 'mode': 'shorten'}, {'months_paid': 33, 'total_interest': 21026, 'final_payment': 6666, 'payments': [7605]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 12, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 8337, 'payments': [8333]}], ['control 6', {'principal': 60000, 'rate_bp': 600, 'months': 6, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 6, 'total_interest': 1055, 'final_payment': 10175, 'payments': [10176]}]], [['regression: payoff by curtailment', {'principal': 250000, 'rate_bp': 0, 'months': 12, 'prepay': {'7': 200000, '3': 5000}, 'mode': 'shorten'}, {'months_paid': 7, 'total_interest': 0, 'final_payment': 120002, 'payments': [20833]}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'months': 36, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 36, 'total_interest': 9520, 'final_payment': 3050, 'payments': [3042]}], ['control 2', {'principal': 60000, 'rate_bp': 0, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 2500, 'payments': [2500]}], ['control 3', {'principal': 250000, 'rate_bp': 1200, 'months': 12, 'prepay': {'1': 200000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 4349, 'final_payment': 2927, 'payments': [22212, 2921]}], ['control 4', {'principal': 60000, 'rate_bp': 600, 'months': 12, 'prepay': {'8': 5000}, 'mode': 'shorten'}, {'months_paid': 12, 'total_interest': 1867, 'final_payment': 63, 'payments': [5164]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 6, 'prepay': {'1': 5000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 15665, 'payments': [16667, 15667]}], ['control 6', {'principal': 60000, 'rate_bp': 0, 'months': 24, 'prepay': {'9': 5000, '24': 5000}, 'mode': 'shorten'}, {'months_paid': 22, 'total_interest': 0, 'final_payment': 2500, 'payments': [2500]}]], [['regression: payoff by curtailment', {'principal': 250000, 'rate_bp': 600, 'months': 12, 'prepay': {'8': 200000}, 'mode': 'shorten'}, {'months_paid': 8, 'total_interest': 7134, 'final_payment': 106515, 'payments': [21517]}], ['control 1', {'principal': 60000, 'rate_bp': 0, 'months': 6, 'prepay': {'4': 1000}, 'mode': 'shorten'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 9000, 'payments': [10000]}], ['control 2', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 24, 'total_interest': 32442, 'final_payment': 11778, 'payments': [11768]}], ['control 3', {'principal': 100000, 'rate_bp': 0, 'months': 6, 'prepay': {'3': 1000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 16333, 'payments': [16667, 16333]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {'10': 5000}, 'mode': 'shorten'}, {'months_paid': 11, 'total_interest': 0, 'final_payment': 5000, 'payments': [5000]}], ['control 5', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {'4': 1000, '9': 20000}, 'mode': 'shorten'}, {'months_paid': 22, 'total_interest': 29136, 'final_payment': 11008, 'payments': [11768]}], ['control 6', {'principal': 100000, 'rate_bp': 600, 'months': 36, 'prepay': {'22': 5000}, 'mode': 'shorten'}, {'months_paid': 35, 'total_interest': 9173, 'final_payment': 745, 'payments': [3042]}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: payoff by curtailment{'final_payment': 39996, 'months_paid': 12, 'payments': [1667], 'total_interest': 0}{'final_payment': 41663, 'months_paid': 12, 'payments': [1667], 'total_interest': 0}Failed
control 1{'final_payment': 18501, 'months_paid': 12, 'payments': [20833, 20000, 19000, 18501], 'total_interest': 0}{'final_payment': 18501, 'months_paid': 12, 'payments': [20833, 20000, 19000, 18501], 'total_interest': 0}Passed
control 2{'final_payment': 2100, 'months_paid': 24, 'payments': [2824, 2753, 2099], 'total_interest': 7480}{'final_payment': 2100, 'months_paid': 24, 'payments': [2824, 2753, 2099], 'total_interest': 7480}Passed
control 3{'final_payment': 12203, 'months_paid': 6, 'payments': [17255, 12203], 'total_interest': 3478}{'final_payment': 12203, 'months_paid': 6, 'payments': [17255, 12203], 'total_interest': 3478}Passed
control 4{'final_payment': 3334, 'months_paid': 12, 'payments': [5000, 3333], 'total_interest': 0}{'final_payment': 3334, 'months_paid': 12, 'payments': [5000, 3333], 'total_interest': 0}Passed
control 5{'final_payment': 11778, 'months_paid': 24, 'payments': [11768], 'total_interest': 32442}{'final_payment': 11778, 'months_paid': 24, 'payments': [11768], 'total_interest': 32442}Passed
control 6{'final_payment': 3760, 'months_paid': 12, 'payments': [8885, 3759], 'total_interest': 6117}{'final_payment': 3760, 'months_paid': 12, 'payments': [8885, 3759], 'total_interest': 6117}Passed

SHA-256 / 103a7197c4474a847db85c2b055e41d8fb019538f23d7f3fdcc822efeede4717

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    def level(P, n):
        if n <= 0 or P <= 0:
            return 0
        if bp == 0:
            exact = Fraction(P, n)
        else:
            r = Fraction(bp, 120000)
            exact = P * r / (1 - (1 + r) ** -n)
        return math.floor(exact + Fraction(1, 2))
    bp = x['rate_bp']
    n = x['months']
    bal = x['principal']
    pay = level(bal, n)
    history = [pay]
    total = 0
    k = 0
    final = 0
    while bal > 0 and k < n:
        k += 1
        interest = rnd(bal * bp, 120000)
        total += interest
        if bal + interest <= pay or k == n:
            final = bal + interest
            bal = 0
            break
        bal -= pay - interest
        extra = min(x['prepay'].get(str(k), 0), bal)
        if extra:
            bal -= extra
            if x['mode'] == 'recast' and bal > 0:
                pay = level(bal, n - k)
                history.append(pay)
            if bal == 0:
                final = pay
    return {'months_paid': k, 'total_interest': total, 'final_payment': final, 'payments': history}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: payoff by curtailment', {'principal': 60000, 'rate_bp': 0, 'months': 36, 'prepay': {'21': 5000, '12': 200000, '35': 2000000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 41663, 'payments': [1667]}], ['control 1', {'principal': 250000, 'rate_bp': 0, 'months': 12, 'prepay': {'10': 1000, '6': 5000, '7': 5000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 18501, 'payments': [20833, 20000, 19000, 18501]}], ['control 2', {'principal': 60000, 'rate_bp': 1200, 'months': 24, 'prepay': {'16': 5000, '9': 1000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 7480, 'final_payment': 2100, 'payments': [2824, 2753, 2099]}], ['control 3', {'principal': 100000, 'rate_bp': 1200, 'months': 6, 'prepay': {'5': 5000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 3478, 'final_payment': 12203, 'payments': [17255, 12203]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {'9': 5000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 3334, 'payments': [5000, 3333]}], ['control 5', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 32442, 'final_payment': 11778, 'payments': [11768]}], ['control 6', {'principal': 100000, 'rate_bp': 1200, 'months': 12, 'prepay': {'8': 20000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 6117, 'final_payment': 3760, 'payments': [8885, 3759]}]], [['regression: payoff by curtailment', {'principal': 100000, 'rate_bp': 0, 'months': 24, 'prepay': {'19': 200000, '18': 20000, '24': 5000}, 'mode': 'recast'}, {'months_paid': 19, 'total_interest': 0, 'final_payment': 4994, 'payments': [4167, 832]}], ['control 1', {'principal': 250000, 'rate_bp': 0, 'months': 24, 'prepay': {'24': 200000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 10409, 'payments': [10417]}], ['control 2', {'principal': 250000, 'rate_bp': 0, 'months': 6, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 41665, 'payments': [41667]}], ['control 3', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {'10': 5000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 12595, 'final_payment': 4326, 'payments': [4707, 4323]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 5000, 'payments': [5000]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 4159, 'payments': [4167]}], ['control 6', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 24, 'total_interest': 12979, 'final_payment': 4718, 'payments': [4707]}]], [['regression: payoff by curtailment', {'principal': 100000, 'rate_bp': 1200, 'months': 24, 'prepay': {'12': 5000, '20': 20000, '4': 1000}, 'mode': 'shorten'}, {'months_paid': 20, 'total_interest': 11928, 'final_payment': 16495, 'payments': [4707]}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'months': 12, 'prepay': {'10': 1000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 3272, 'final_payment': 8101, 'payments': [8607, 8101]}], ['control 2', {'principal': 100000, 'rate_bp': 600, 'months': 6, 'prepay': {'5': 1000, '3': 20000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 1552, 'final_payment': 9220, 'payments': [16960, 10226, 9220]}], ['control 3', {'principal': 60000, 'rate_bp': 600, 'months': 24, 'prepay': {'15': 20000, '5': 1000}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 3267, 'final_payment': 324, 'payments': [2659, 2604, 326]}], ['control 4', {'principal': 250000, 'rate_bp': 600, 'months': 36, 'prepay': {'10': 20000, '11': 1000}, 'mode': 'shorten'}, {'months_paid': 33, 'total_interest': 21026, 'final_payment': 6666, 'payments': [7605]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 12, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 0, 'final_payment': 8337, 'payments': [8333]}], ['control 6', {'principal': 60000, 'rate_bp': 600, 'months': 6, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 6, 'total_interest': 1055, 'final_payment': 10175, 'payments': [10176]}]], [['regression: payoff by curtailment', {'principal': 250000, 'rate_bp': 0, 'months': 12, 'prepay': {'7': 200000, '3': 5000}, 'mode': 'shorten'}, {'months_paid': 7, 'total_interest': 0, 'final_payment': 120002, 'payments': [20833]}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'months': 36, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 36, 'total_interest': 9520, 'final_payment': 3050, 'payments': [3042]}], ['control 2', {'principal': 60000, 'rate_bp': 0, 'months': 24, 'prepay': {}, 'mode': 'recast'}, {'months_paid': 24, 'total_interest': 0, 'final_payment': 2500, 'payments': [2500]}], ['control 3', {'principal': 250000, 'rate_bp': 1200, 'months': 12, 'prepay': {'1': 200000}, 'mode': 'recast'}, {'months_paid': 12, 'total_interest': 4349, 'final_payment': 2927, 'payments': [22212, 2921]}], ['control 4', {'principal': 60000, 'rate_bp': 600, 'months': 12, 'prepay': {'8': 5000}, 'mode': 'shorten'}, {'months_paid': 12, 'total_interest': 1867, 'final_payment': 63, 'payments': [5164]}], ['control 5', {'principal': 100000, 'rate_bp': 0, 'months': 6, 'prepay': {'1': 5000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 15665, 'payments': [16667, 15667]}], ['control 6', {'principal': 60000, 'rate_bp': 0, 'months': 24, 'prepay': {'9': 5000, '24': 5000}, 'mode': 'shorten'}, {'months_paid': 22, 'total_interest': 0, 'final_payment': 2500, 'payments': [2500]}]], [['regression: payoff by curtailment', {'principal': 250000, 'rate_bp': 600, 'months': 12, 'prepay': {'8': 200000}, 'mode': 'shorten'}, {'months_paid': 8, 'total_interest': 7134, 'final_payment': 106515, 'payments': [21517]}], ['control 1', {'principal': 60000, 'rate_bp': 0, 'months': 6, 'prepay': {'4': 1000}, 'mode': 'shorten'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 9000, 'payments': [10000]}], ['control 2', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {}, 'mode': 'shorten'}, {'months_paid': 24, 'total_interest': 32442, 'final_payment': 11778, 'payments': [11768]}], ['control 3', {'principal': 100000, 'rate_bp': 0, 'months': 6, 'prepay': {'3': 1000}, 'mode': 'recast'}, {'months_paid': 6, 'total_interest': 0, 'final_payment': 16333, 'payments': [16667, 16333]}], ['control 4', {'principal': 60000, 'rate_bp': 0, 'months': 12, 'prepay': {'10': 5000}, 'mode': 'shorten'}, {'months_paid': 11, 'total_interest': 0, 'final_payment': 5000, 'payments': [5000]}], ['control 5', {'principal': 250000, 'rate_bp': 1200, 'months': 24, 'prepay': {'4': 1000, '9': 20000}, 'mode': 'shorten'}, {'months_paid': 22, 'total_interest': 29136, 'final_payment': 11008, 'payments': [11768]}], ['control 6', {'principal': 100000, 'rate_bp': 600, 'months': 36, 'prepay': {'22': 5000}, 'mode': 'shorten'}, {'months_paid': 35, 'total_interest': 9173, 'final_payment': 745, 'payments': [3042]}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: payoff by curtailment{'final_payment': 1667, 'months_paid': 12, 'payments': [1667], 'total_interest': 0}{'final_payment': 41663, 'months_paid': 12, 'payments': [1667], 'total_interest': 0}Failed
control 1{'final_payment': 18501, 'months_paid': 12, 'payments': [20833, 20000, 19000, 18501], 'total_interest': 0}{'final_payment': 18501, 'months_paid': 12, 'payments': [20833, 20000, 19000, 18501], 'total_interest': 0}Passed
control 2{'final_payment': 2100, 'months_paid': 24, 'payments': [2824, 2753, 2099], 'total_interest': 7480}{'final_payment': 2100, 'months_paid': 24, 'payments': [2824, 2753, 2099], 'total_interest': 7480}Passed
control 3{'final_payment': 12203, 'months_paid': 6, 'payments': [17255, 12203], 'total_interest': 3478}{'final_payment': 12203, 'months_paid': 6, 'payments': [17255, 12203], 'total_interest': 3478}Passed
control 4{'final_payment': 3334, 'months_paid': 12, 'payments': [5000, 3333], 'total_interest': 0}{'final_payment': 3334, 'months_paid': 12, 'payments': [5000, 3333], 'total_interest': 0}Passed
control 5{'final_payment': 11778, 'months_paid': 24, 'payments': [11768], 'total_interest': 32442}{'final_payment': 11778, 'months_paid': 24, 'payments': [11768], 'total_interest': 32442}Passed
control 6{'final_payment': 3760, 'months_paid': 12, 'payments': [8885, 3759], 'total_interest': 6117}{'final_payment': 3760, 'months_paid': 12, 'payments': [8885, 3759], 'total_interest': 6117}Passed

SHA-256 / c4fd557ffff66c43b3f24ee627260989ef9f64377af1690d4c6f18f4b7fb11af

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Sign in to the archive ↗

Verification & scope

A deterministic bounded teaching model with stipulated toy lending rules stated in the contract; money is integer cents and rates are basis points; it makes no claim of conformance to any regulation, servicing standard or product. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:26.668341+00:00.

Case digest / d203bf80c7063323a24f1ea2fa19ac77c4339706cfd44ca6923504effdd8aeb1