FA-58786 / Loan amortization schedules / Open access

Installment due date calendar: holiday rollback · case 01

Modified-following roll-backs land on a holiday.

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

ROOT CAUSE

The backward roll only skips weekends.

THE FAILURE

The backward roll only skips weekends.

Unsuccessful approach: Skipping only holidays lands roll-backs on weekends.

Case contract

x = {'first_due': [y, m, d] (d may exceed the month length), 'count', 'roll': 'none'|'following'|'modified_following', 'holidays': ISO dates}. Installment i falls in month m+i on the anchor day d clamped to the month length (later months return to d). Unless roll is 'none', a Saturday, Sunday or holiday rolls forward to the next business day; under modified_following a roll that leaves the month instead rolls back to the previous business day. Return ISO date strings.

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 datetime
import calendar
N = 1
observations = []
def solve(x):
    y, m, d = x['first_due']
    hol = set(x['holidays'])
    def bad(t):
        return t.weekday() >= 5 or t.isoformat() in hol
    out = []
    for i in range(x['count']):
        mm = m - 1 + i
        yy = y + mm // 12
        mm = mm % 12 + 1
        dd = min(d, calendar.monthrange(yy, mm)[1])
        date = datetime.date(yy, mm, dd)
        adj = date
        if x['roll'] != 'none':
            while bad(adj):
                adj += datetime.timedelta(days=1)
            if x['roll'] == 'modified_following' and adj.month != date.month:
                adj = date
                while adj.weekday() >= 5:
                    adj -= datetime.timedelta(days=1)
        out.append(adj.isoformat())
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: holiday rollback', {'first_due': [2023, 9, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2023-12-25']}, ['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']], ['control 2', {'first_due': [2024, 7, 28], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2024-01-01']}, ['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']], ['control 3', {'first_due': [2024, 11, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']], ['control 4', {'first_due': [2024, 2, 5], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31', '2023-12-25']}, ['2024-02-05', '2024-03-05', '2024-04-05']], ['control 5', {'first_due': [2023, 8, 15], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-02-29', '2023-06-30']}, ['2023-08-15', '2023-09-15', '2023-10-16']], ['control 6', {'first_due': [2023, 3, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29']}, ['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']]], [['regression: holiday rollback', {'first_due': [2024, 1, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2023-12-25', '2024-03-29']}, ['2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28']], ['control 1', {'first_due': [2024, 9, 5], 'count': 13, 'roll': 'following', 'holidays': []}, ['2024-09-05', '2024-10-07', '2024-11-05', '2024-12-05', '2025-01-06', '2025-02-05', '2025-03-05', '2025-04-07', '2025-05-05', '2025-06-05', '2025-07-07', '2025-08-05', '2025-09-05']], ['control 2', {'first_due': [2023, 4, 5], 'count': 6, 'roll': 'following', 'holidays': ['2024-01-01', '2024-05-31', '2023-06-30']}, ['2023-04-05', '2023-05-05', '2023-06-05', '2023-07-05', '2023-08-07', '2023-09-05']], ['control 3', {'first_due': [2023, 6, 5], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05']], ['control 4', {'first_due': [2023, 11, 1], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-06-30', '2024-05-31']}, ['2023-11-01', '2023-12-01', '2024-01-01']], ['control 5', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'following', 'holidays': ['2024-01-01', '2024-12-31']}, ['2023-10-30', '2023-11-30', '2024-01-02', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 6', {'first_due': [2023, 7, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-12-31']}, ['2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29']]], [['regression: holiday rollback', {'first_due': [2023, 11, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-28', '2024-04-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-09-01', '2023-10-02', '2023-11-01']], ['control 2', {'first_due': [2024, 5, 1], 'count': 13, 'roll': 'none', 'holidays': []}, ['2024-05-01', '2024-06-01', '2024-07-01', '2024-08-01', '2024-09-01', '2024-10-01', '2024-11-01', '2024-12-01', '2025-01-01', '2025-02-01', '2025-03-01', '2025-04-01', '2025-05-01']], ['control 3', {'first_due': [2024, 10, 30], 'count': 3, 'roll': 'following', 'holidays': ['2024-05-31', '2023-06-30', '2024-03-29']}, ['2024-10-30', '2024-12-02', '2024-12-30']], ['control 4', {'first_due': [2023, 8, 30], 'count': 13, 'roll': 'following', 'holidays': []}, ['2023-08-30', '2023-10-02', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30']], ['control 5', {'first_due': [2023, 3, 15], 'count': 13, 'roll': 'none', 'holidays': []}, ['2023-03-15', '2023-04-15', '2023-05-15', '2023-06-15', '2023-07-15', '2023-08-15', '2023-09-15', '2023-10-15', '2023-11-15', '2023-12-15', '2024-01-15', '2024-02-15', '2024-03-15']], ['control 6', {'first_due': [2023, 2, 5], 'count': 3, 'roll': 'none', 'holidays': ['2024-03-29']}, ['2023-02-05', '2023-03-05', '2023-04-05']]], [['regression: holiday rollback', {'first_due': [2023, 10, 31], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-01-01', '2024-05-31']}, ['2023-10-31', '2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-31', '2024-08-30', '2024-09-30', '2024-10-31']], ['control 1', {'first_due': [2024, 8, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-08-15', '2024-09-16', '2024-10-15', '2024-11-15', '2024-12-16', '2025-01-15']], ['control 2', {'first_due': [2023, 10, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30']], ['control 3', {'first_due': [2023, 8, 1], 'count': 3, 'roll': 'following', 'holidays': []}, ['2023-08-01', '2023-09-01', '2023-10-02']], ['control 4', {'first_due': [2023, 2, 28], 'count': 3, 'roll': 'following', 'holidays': ['2023-12-25', '2024-05-31']}, ['2023-02-28', '2023-03-28', '2023-04-28']], ['control 5', {'first_due': [2024, 9, 28], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-01-01', '2024-05-31']}, ['2024-09-28', '2024-10-28', '2024-11-28', '2024-12-28', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-28', '2025-07-28', '2025-08-28', '2025-09-28']], ['control 6', {'first_due': [2024, 1, 5], 'count': 3, 'roll': 'none', 'holidays': ['2024-03-29', '2024-05-31']}, ['2024-01-05', '2024-02-05', '2024-03-05']]], [['regression: holiday rollback', {'first_due': [2024, 1, 29], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-02-29', '2023-12-25']}, ['2024-01-29', '2024-02-28', '2024-03-28']], ['regression: holiday rollback, partial-repair probe', {'first_due': [2023, 6, 30], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2023-06-30', '2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30']], ['control 1', {'first_due': [2024, 1, 29], 'count': 6, 'roll': 'none', 'holidays': []}, ['2024-01-29', '2024-02-29', '2024-03-29', '2024-04-29', '2024-05-29', '2024-06-29']], ['control 2', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'none', 'holidays': ['2024-01-01', '2024-03-29']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 3', {'first_due': [2024, 8, 5], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2024-08-05', '2024-09-05', '2024-10-07']], ['control 4', {'first_due': [2024, 9, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-02-29']}, ['2024-09-30', '2024-10-30', '2024-11-30', '2024-12-30', '2025-01-30', '2025-02-28']], ['control 5', {'first_due': [2023, 10, 28], 'count': 3, 'roll': 'following', 'holidays': ['2024-12-31']}, ['2023-10-30', '2023-11-28', '2023-12-28']]]]
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: holiday rollback	`['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']`	`['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']`	Failed
control 1	`['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']`	`['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']`	Passed
control 2	`['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']`	`['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']`	Passed
control 3	`['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']`	`['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']`	Passed
control 4	`['2024-02-05', '2024-03-05', '2024-04-05']`	`['2024-02-05', '2024-03-05', '2024-04-05']`	Passed
control 5	`['2023-08-15', '2023-09-15', '2023-10-16']`	`['2023-08-15', '2023-09-15', '2023-10-16']`	Passed
control 6	`['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']`	`['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']`	Passed

SHA-256 / affb9baf54b18f464d479eed6e63ac347eb511d844a226fd1437f3a0bc42771a

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
import calendar
N = 1
observations = []
def solve(x):
    y, m, d = x['first_due']
    hol = set(x['holidays'])
    def bad(t):
        return t.weekday() >= 5 or t.isoformat() in hol
    out = []
    for i in range(x['count']):
        mm = m - 1 + i
        yy = y + mm // 12
        mm = mm % 12 + 1
        dd = min(d, calendar.monthrange(yy, mm)[1])
        date = datetime.date(yy, mm, dd)
        adj = date
        if x['roll'] != 'none':
            while bad(adj):
                adj += datetime.timedelta(days=1)
            if x['roll'] == 'modified_following' and adj.month != date.month:
                adj = date
                while adj.isoformat() in hol:
                    adj -= datetime.timedelta(days=1)
        out.append(adj.isoformat())
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: holiday rollback', {'first_due': [2023, 9, 30], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2023-12-25']}, ['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']], ['control 2', {'first_due': [2024, 7, 28], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2024-01-01']}, ['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']], ['control 3', {'first_due': [2024, 11, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']], ['control 4', {'first_due': [2024, 2, 5], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31', '2023-12-25']}, ['2024-02-05', '2024-03-05', '2024-04-05']], ['control 5', {'first_due': [2023, 8, 15], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-02-29', '2023-06-30']}, ['2023-08-15', '2023-09-15', '2023-10-16']], ['control 6', {'first_due': [2023, 3, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29']}, ['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']]], [['regression: holiday rollback', {'first_due': [2024, 1, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2023-12-25', '2024-03-29']}, ['2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28']], ['control 1', {'first_due': [2024, 9, 5], 'count': 13, 'roll': 'following', 'holidays': []}, ['2024-09-05', '2024-10-07', '2024-11-05', '2024-12-05', '2025-01-06', '2025-02-05', '2025-03-05', '2025-04-07', '2025-05-05', '2025-06-05', '2025-07-07', '2025-08-05', '2025-09-05']], ['control 2', {'first_due': [2023, 4, 5], 'count': 6, 'roll': 'following', 'holidays': ['2024-01-01', '2024-05-31', '2023-06-30']}, ['2023-04-05', '2023-05-05', '2023-06-05', '2023-07-05', '2023-08-07', '2023-09-05']], ['control 3', {'first_due': [2023, 6, 5], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-06-05', '2023-07-05', '2023-08-05', '2023-09-05', '2023-10-05', '2023-11-05']], ['control 4', {'first_due': [2023, 11, 1], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-12-31', '2023-06-30', '2024-05-31']}, ['2023-11-01', '2023-12-01', '2024-01-01']], ['control 5', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'following', 'holidays': ['2024-01-01', '2024-12-31']}, ['2023-10-30', '2023-11-30', '2024-01-02', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 6', {'first_due': [2023, 7, 30], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-12-31']}, ['2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29']]], [['regression: holiday rollback', {'first_due': [2023, 11, 31], 'count': 6, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-05-31']}, ['2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-28', '2024-04-30']], ['control 1', {'first_due': [2023, 9, 1], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2023-09-01', '2023-10-02', '2023-11-01']], ['control 2', {'first_due': [2024, 5, 1], 'count': 13, 'roll': 'none', 'holidays': []}, ['2024-05-01', '2024-06-01', '2024-07-01', '2024-08-01', '2024-09-01', '2024-10-01', '2024-11-01', '2024-12-01', '2025-01-01', '2025-02-01', '2025-03-01', '2025-04-01', '2025-05-01']], ['control 3', {'first_due': [2024, 10, 30], 'count': 3, 'roll': 'following', 'holidays': ['2024-05-31', '2023-06-30', '2024-03-29']}, ['2024-10-30', '2024-12-02', '2024-12-30']], ['control 4', {'first_due': [2023, 8, 30], 'count': 13, 'roll': 'following', 'holidays': []}, ['2023-08-30', '2023-10-02', '2023-10-30', '2023-11-30', '2024-01-01', '2024-01-30', '2024-02-29', '2024-04-01', '2024-04-30', '2024-05-30', '2024-07-01', '2024-07-30', '2024-08-30']], ['control 5', {'first_due': [2023, 3, 15], 'count': 13, 'roll': 'none', 'holidays': []}, ['2023-03-15', '2023-04-15', '2023-05-15', '2023-06-15', '2023-07-15', '2023-08-15', '2023-09-15', '2023-10-15', '2023-11-15', '2023-12-15', '2024-01-15', '2024-02-15', '2024-03-15']], ['control 6', {'first_due': [2023, 2, 5], 'count': 3, 'roll': 'none', 'holidays': ['2024-03-29']}, ['2023-02-05', '2023-03-05', '2023-04-05']]], [['regression: holiday rollback', {'first_due': [2023, 10, 31], 'count': 13, 'roll': 'modified_following', 'holidays': ['2024-01-01', '2024-05-31']}, ['2023-10-31', '2023-11-30', '2023-12-29', '2024-01-31', '2024-02-29', '2024-03-29', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-31', '2024-08-30', '2024-09-30', '2024-10-31']], ['control 1', {'first_due': [2024, 8, 15], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2024-08-15', '2024-09-16', '2024-10-15', '2024-11-15', '2024-12-16', '2025-01-15']], ['control 2', {'first_due': [2023, 10, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-01-01']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30']], ['control 3', {'first_due': [2023, 8, 1], 'count': 3, 'roll': 'following', 'holidays': []}, ['2023-08-01', '2023-09-01', '2023-10-02']], ['control 4', {'first_due': [2023, 2, 28], 'count': 3, 'roll': 'following', 'holidays': ['2023-12-25', '2024-05-31']}, ['2023-02-28', '2023-03-28', '2023-04-28']], ['control 5', {'first_due': [2024, 9, 28], 'count': 13, 'roll': 'none', 'holidays': ['2023-06-30', '2024-01-01', '2024-05-31']}, ['2024-09-28', '2024-10-28', '2024-11-28', '2024-12-28', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-28', '2025-07-28', '2025-08-28', '2025-09-28']], ['control 6', {'first_due': [2024, 1, 5], 'count': 3, 'roll': 'none', 'holidays': ['2024-03-29', '2024-05-31']}, ['2024-01-05', '2024-02-05', '2024-03-05']]], [['regression: holiday rollback', {'first_due': [2024, 1, 29], 'count': 3, 'roll': 'modified_following', 'holidays': ['2024-03-29', '2024-02-29', '2023-12-25']}, ['2024-01-29', '2024-02-28', '2024-03-28']], ['regression: holiday rollback, partial-repair probe', {'first_due': [2023, 6, 30], 'count': 6, 'roll': 'modified_following', 'holidays': []}, ['2023-06-30', '2023-07-31', '2023-08-30', '2023-09-29', '2023-10-30', '2023-11-30']], ['control 1', {'first_due': [2024, 1, 29], 'count': 6, 'roll': 'none', 'holidays': []}, ['2024-01-29', '2024-02-29', '2024-03-29', '2024-04-29', '2024-05-29', '2024-06-29']], ['control 2', {'first_due': [2023, 10, 30], 'count': 13, 'roll': 'none', 'holidays': ['2024-01-01', '2024-03-29']}, ['2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30', '2024-10-30']], ['control 3', {'first_due': [2024, 8, 5], 'count': 3, 'roll': 'modified_following', 'holidays': []}, ['2024-08-05', '2024-09-05', '2024-10-07']], ['control 4', {'first_due': [2024, 9, 30], 'count': 6, 'roll': 'none', 'holidays': ['2024-02-29']}, ['2024-09-30', '2024-10-30', '2024-11-30', '2024-12-30', '2025-01-30', '2025-02-28']], ['control 5', {'first_due': [2023, 10, 28], 'count': 3, 'roll': 'following', 'holidays': ['2024-12-31']}, ['2023-10-30', '2023-11-28', '2023-12-28']]]]
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: holiday rollback	`['2023-09-30', '2023-10-30', '2023-11-30', '2023-12-30', '2024-01-30', '2024-02-29', '2024-03-30', '2024-04-30', '2024-05-30', '2024-06-30', '2024-07-30', '2024-08-30', '2024-09-30']`	`['2023-09-29', '2023-10-30', '2023-11-30', '2023-12-29', '2024-01-30', '2024-02-29', '2024-03-28', '2024-04-30', '2024-05-30', '2024-06-28', '2024-07-30', '2024-08-30', '2024-09-30']`	Failed
control 1	`['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']`	`['2023-09-01', '2023-10-02', '2023-11-01', '2023-12-01', '2024-01-01', '2024-02-01', '2024-03-01', '2024-04-01', '2024-05-01', '2024-06-03', '2024-07-01', '2024-08-01', '2024-09-02']`	Passed
control 2	`['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']`	`['2024-07-29', '2024-08-28', '2024-09-30', '2024-10-28', '2024-11-28', '2024-12-30', '2025-01-28', '2025-02-28', '2025-03-28', '2025-04-28', '2025-05-28', '2025-06-30', '2025-07-28']`	Passed
control 3	`['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']`	`['2024-11-15', '2024-12-16', '2025-01-15', '2025-02-17', '2025-03-17', '2025-04-15']`	Passed
control 4	`['2024-02-05', '2024-03-05', '2024-04-05']`	`['2024-02-05', '2024-03-05', '2024-04-05']`	Passed
control 5	`['2023-08-15', '2023-09-15', '2023-10-16']`	`['2023-08-15', '2023-09-15', '2023-10-16']`	Passed
control 6	`['2023-03-31', '2023-04-30', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']`	`['2023-03-31', '2023-04-28', '2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31']`	Failed

SHA-256 / c4881f39dd4e8a95361a5f9484cdc6b453f5a2e47063cc92bd6ff4b8930bac82

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.

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 2026-09-29T14:46:30.065824+00:00.

Case digest / 9db5f8311541a377ea22c593538856054ea8781fe32c2ebddb1635b832073d3c