FA-58591 / Loan amortization schedules / Open access

Negative amortization cap recast: cap threshold scale · case 01

Loans recast at the first cent of negative amortization.

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ROOT CAUSE

The cap percentage is ignored and any growth over principal triggers recast.

THE FAILURE

The cap percentage is ignored and any growth over principal triggers recast.

Unsuccessful approach: Comparing only the growth with the full cap percentage treats a 110% cap as 1100% growth.

Case contract

x = {'principal', 'rate_bp', 'min_payment', 'cap_pct_bp' (e.g. 11000 = 110% of principal), 'months'}. Each month interest = round_half_up(balance*bp/120000); the shortfall interest - payment (if positive) is deferred; balance += interest - payment. The first time balance*10000 exceeds principal*cap_pct_bp the loan recasts once: payment = level(balance, months - k) (exact annuity, half-up). Return {'balance', 'recast_month' or None, 'deferred', 'payment'}.

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']
    P = x['principal']
    n = x['months']
    bal = P
    pay = x['min_payment']
    deferred = 0
    recast = None
    limit = P * x['cap_pct_bp']
    for k in range(1, n + 1):
        interest = rnd(bal * bp, 120000)
        if pay < interest:
            deferred += interest - pay
        bal += interest - pay
        if recast is None and bal > P:
            recast = k
            pay = level(bal, n - k)
    return {'balance': bal, 'recast_month': recast, 'deferred': deferred, 'payment': pay}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: cap threshold scale', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 1063081, 'recast_month': None, 'deferred': 63081, 'payment': 10000}], ['regression: cap threshold scale, partial-repair probe', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 5000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 1, 'recast_month': 10, 'deferred': 52312, 'payment': 534061}], ['control 1', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 10000, 'cap_pct_bp': 10200, 'months': 12}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 10000}], ['control 2', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 3', {'principal': 1000000, 'rate_bp': 600, 'min_payment': 5000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 5000}], ['control 4', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 113849, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 5', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 0, 'recast_month': 2, 'deferred': 4040, 'payment': 22715}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'min_payment': 500, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 500}], ['control 2', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 3', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 10200, 'months': 36}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 5', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 6}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 6', {'principal': 100000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 96962, 'recast_month': None, 'deferred': 0, 'payment': 1000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 600, 'min_payment': 500, 'cap_pct_bp': 10200, 'months': 6}, {'balance': 203039, 'recast_month': None, 'deferred': 3039, 'payment': 500}], ['regression: cap threshold scale, partial-repair probe', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 4, 'recast_month': 2, 'deferred': 20200, 'payment': 113575}], ['control 1', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 2', {'principal': 1000000, 'rate_bp': 600, 'min_payment': 20000, 'cap_pct_bp': 10200, 'months': 24}, {'balance': 618521, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 3', {'principal': 100000, 'rate_bp': 600, 'min_payment': 2000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 90887, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 174636, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 5', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 500, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 222078, 'recast_month': 6, 'deferred': 22078, 'payment': 0}], ['control 1', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 6}, {'balance': 187696, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 2', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10200, 'months': 12}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 3', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 250, 'cap_pct_bp': 10100, 'months': 12}, {'balance': -3, 'recast_month': 1, 'deferred': 1750, 'payment': 10397}], ['control 5', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 10000, 'cap_pct_bp': 10200, 'months': 6}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 10000}], ['control 6', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 113849, 'recast_month': None, 'deferred': 0, 'payment': 4000}]], [['regression: cap threshold scale', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 1, 'recast_month': 10, 'deferred': 109498, 'payment': 571446}], ['control 1', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 2', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 24}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 3', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10200, 'months': 24}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 4', {'principal': 100000, 'rate_bp': 1200, 'min_payment': 1000, 'cap_pct_bp': 10500, 'months': 6}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 5', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 2500, 'cap_pct_bp': 10100, 'months': 24}, {'balance': -3, 'recast_month': 1, 'deferred': 17500, 'payment': 55625}], ['control 6', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 24}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}]]]
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 fixture	Actual	Expected	Outcome
regression: cap threshold scale	`{'balance': 0, 'deferred': 10000, 'payment': 214280, 'recast_month': 1}`	`{'balance': 1063081, 'deferred': 63081, 'payment': 10000, 'recast_month': None}`	Failed
regression: cap threshold scale, partial-repair probe	`{'balance': 4, 'deferred': 5000, 'payment': 96936, 'recast_month': 1}`	`{'balance': 1, 'deferred': 52312, 'payment': 534061, 'recast_month': 10}`	Failed
control 1	`{'balance': 1000000, 'deferred': 0, 'payment': 10000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 10000, 'recast_month': None}`	Passed
control 2	`{'balance': 200000, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	`{'balance': 200000, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	Passed
control 3	`{'balance': 1000000, 'deferred': 0, 'payment': 5000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 5000, 'recast_month': None}`	Passed
control 4	`{'balance': 113849, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	`{'balance': 113849, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	Passed
control 5	`{'balance': 1000000, 'deferred': 0, 'payment': 20000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 20000, 'recast_month': None}`	Passed

SHA-256 / 9b8b60bfc1577767e3a4cc4a86c5c5501f71b6edc2196ddeb380db6e2397acc6

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']
    P = x['principal']
    n = x['months']
    bal = P
    pay = x['min_payment']
    deferred = 0
    recast = None
    limit = P * x['cap_pct_bp']
    for k in range(1, n + 1):
        interest = rnd(bal * bp, 120000)
        if pay < interest:
            deferred += interest - pay
        bal += interest - pay
        if recast is None and (bal - P) * 10000 > limit:
            recast = k
            pay = level(bal, n - k)
    return {'balance': bal, 'recast_month': recast, 'deferred': deferred, 'payment': pay}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: cap threshold scale', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 1063081, 'recast_month': None, 'deferred': 63081, 'payment': 10000}], ['regression: cap threshold scale, partial-repair probe', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 5000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 1, 'recast_month': 10, 'deferred': 52312, 'payment': 534061}], ['control 1', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 10000, 'cap_pct_bp': 10200, 'months': 12}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 10000}], ['control 2', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 3', {'principal': 1000000, 'rate_bp': 600, 'min_payment': 5000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 5000}], ['control 4', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 113849, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 5', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 0, 'recast_month': 2, 'deferred': 4040, 'payment': 22715}], ['control 1', {'principal': 100000, 'rate_bp': 600, 'min_payment': 500, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 500}], ['control 2', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 3', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 10200, 'months': 36}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 5', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 6}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 6', {'principal': 100000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 96962, 'recast_month': None, 'deferred': 0, 'payment': 1000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 600, 'min_payment': 500, 'cap_pct_bp': 10200, 'months': 6}, {'balance': 203039, 'recast_month': None, 'deferred': 3039, 'payment': 500}], ['regression: cap threshold scale, partial-repair probe', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 4, 'recast_month': 2, 'deferred': 20200, 'payment': 113575}], ['control 1', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 2', {'principal': 1000000, 'rate_bp': 600, 'min_payment': 20000, 'cap_pct_bp': 10200, 'months': 24}, {'balance': 618521, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 3', {'principal': 100000, 'rate_bp': 600, 'min_payment': 2000, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 90887, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 174636, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 5', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10500, 'months': 12}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}]], [['regression: cap threshold scale', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 500, 'cap_pct_bp': 11000, 'months': 6}, {'balance': 222078, 'recast_month': 6, 'deferred': 22078, 'payment': 0}], ['control 1', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 6}, {'balance': 187696, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 2', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10200, 'months': 12}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 3', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 12}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 4', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 250, 'cap_pct_bp': 10100, 'months': 12}, {'balance': -3, 'recast_month': 1, 'deferred': 1750, 'payment': 10397}], ['control 5', {'principal': 1000000, 'rate_bp': 1200, 'min_payment': 10000, 'cap_pct_bp': 10200, 'months': 6}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 10000}], ['control 6', {'principal': 200000, 'rate_bp': 1200, 'min_payment': 4000, 'cap_pct_bp': 10100, 'months': 36}, {'balance': 113849, 'recast_month': None, 'deferred': 0, 'payment': 4000}]], [['regression: cap threshold scale', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 10000, 'cap_pct_bp': 11000, 'months': 12}, {'balance': 1, 'recast_month': 10, 'deferred': 109498, 'payment': 571446}], ['control 1', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 20000, 'cap_pct_bp': 11000, 'months': 36}, {'balance': 1000000, 'recast_month': None, 'deferred': 0, 'payment': 20000}], ['control 2', {'principal': 100000, 'rate_bp': 2400, 'min_payment': 2000, 'cap_pct_bp': 10100, 'months': 24}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 2000}], ['control 3', {'principal': 200000, 'rate_bp': 2400, 'min_payment': 4000, 'cap_pct_bp': 10200, 'months': 24}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 4000}], ['control 4', {'principal': 100000, 'rate_bp': 1200, 'min_payment': 1000, 'cap_pct_bp': 10500, 'months': 6}, {'balance': 100000, 'recast_month': None, 'deferred': 0, 'payment': 1000}], ['control 5', {'principal': 1000000, 'rate_bp': 2400, 'min_payment': 2500, 'cap_pct_bp': 10100, 'months': 24}, {'balance': -3, 'recast_month': 1, 'deferred': 17500, 'payment': 55625}], ['control 6', {'principal': 200000, 'rate_bp': 600, 'min_payment': 1000, 'cap_pct_bp': 11000, 'months': 24}, {'balance': 200000, 'recast_month': None, 'deferred': 0, 'payment': 1000}]]]
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 fixture	Actual	Expected	Outcome
regression: cap threshold scale	`{'balance': 1063081, 'deferred': 63081, 'payment': 10000, 'recast_month': None}`	`{'balance': 1063081, 'deferred': 63081, 'payment': 10000, 'recast_month': None}`	Passed
regression: cap threshold scale, partial-repair probe	`{'balance': 1063413, 'deferred': 63413, 'payment': 5000, 'recast_month': None}`	`{'balance': 1, 'deferred': 52312, 'payment': 534061, 'recast_month': 10}`	Failed
control 1	`{'balance': 1000000, 'deferred': 0, 'payment': 10000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 10000, 'recast_month': None}`	Passed
control 2	`{'balance': 200000, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	`{'balance': 200000, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	Passed
control 3	`{'balance': 1000000, 'deferred': 0, 'payment': 5000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 5000, 'recast_month': None}`	Passed
control 4	`{'balance': 113849, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	`{'balance': 113849, 'deferred': 0, 'payment': 4000, 'recast_month': None}`	Passed
control 5	`{'balance': 1000000, 'deferred': 0, 'payment': 20000, 'recast_month': None}`	`{'balance': 1000000, 'deferred': 0, 'payment': 20000, 'recast_month': None}`	Passed

SHA-256 / 5ac34ae2b6e6a1bf1c74c706a818bbd435bec4745ad229ff7279522333714c51

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.

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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 2026-09-29T14:46:28.158685+00:00.

Case digest / d610886ba141c5d452de2090971d8d1624f6554249310bcfd11137899330f242