FAILURE MAP
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FA-60781 / Loyalty points ledgers / Open access

Points plus cash split: negative room guard · case 01

When the price is below the minimum cash the member is credited points and charged more than the price.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The maximum point count is not floored at zero when the room is negative.

VERIFIED REPAIR

Clamp maximum points at zero.

Unsuccessful approach: Using the absolute room lets the member spend points on a purchase that allows none.

Case contract

Input {price, balance, cpp10 (point value in tenths of a cent), min_cash}. Points may cover at most price - min_cash (never negative): max points = floor((price - min_cash)*10/cpp10), limited by balance. Credit = floor(points*cpp10/10); cash = price - credit. Return {points, cash}.

Why this case matters

Member point balances, statements and the program liability depend on this ledger rule.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    room = x['price'] - x['min_cash']
    maxp = room * 10 // x['cpp10']
    pts = min(x['balance'], maxp)
    credit = pts * x['cpp10'] // 10
    return {'points': pts, 'cash': x['price'] - credit}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 501}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3001, 'cpp10': 10, 'min_cash': 100}, {'points': 3001, 'cash': 6999}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 2}, {'points': 7138, 'cash': 3}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 401}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 990}, {'points': 4, 'cash': 990}], ['odd credit', {'price': 2503, 'balance': 1238, 'cpp10': 13, 'min_cash': 3}, {'points': 1238, 'cash': 894}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 502}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3002, 'cpp10': 10, 'min_cash': 100}, {'points': 3002, 'cash': 6998}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 3}, {'points': 7137, 'cash': 4}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 402}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 980}, {'points': 8, 'cash': 980}], ['odd credit', {'price': 2503, 'balance': 1239, 'cpp10': 13, 'min_cash': 3}, {'points': 1239, 'cash': 893}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 503}, {'points': 7914, 'cash': 504}], ['balance limits', {'price': 10000, 'balance': 3003, 'cpp10': 10, 'min_cash': 100}, {'points': 3003, 'cash': 6997}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 4}, {'points': 7135, 'cash': 5}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 403}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 970}, {'points': 12, 'cash': 970}], ['odd credit', {'price': 2503, 'balance': 1240, 'cpp10': 13, 'min_cash': 3}, {'points': 1240, 'cash': 891}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 504}, {'points': 7913, 'cash': 505}], ['balance limits', {'price': 10000, 'balance': 3004, 'cpp10': 10, 'min_cash': 100}, {'points': 3004, 'cash': 6996}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 5}, {'points': 7134, 'cash': 6}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 404}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 960}, {'points': 16, 'cash': 960}], ['odd credit', {'price': 2503, 'balance': 1241, 'cpp10': 13, 'min_cash': 3}, {'points': 1241, 'cash': 890}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 505}, {'points': 7912, 'cash': 506}], ['balance limits', {'price': 10000, 'balance': 3005, 'cpp10': 10, 'min_cash': 100}, {'points': 3005, 'cash': 6995}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 6}, {'points': 7132, 'cash': 7}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 405}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 950}, {'points': 20, 'cash': 950}], ['odd credit', {'price': 2503, 'balance': 1242, 'cpp10': 13, 'min_cash': 3}, {'points': 1242, 'cash': 889}]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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
points cover most{'cash': 502, 'points': 7915}{'cash': 502, 'points': 7915}Passed
balance limits{'cash': 6999, 'points': 3001}{'cash': 6999, 'points': 3001}Passed
fractional value{'cash': 3, 'points': 7138}{'cash': 3, 'points': 7138}Passed
price below minimum cash{'cash': 401, 'points': -101}{'cash': 300, 'points': 0}Failed
exact minimum{'cash': 990, 'points': 4}{'cash': 990, 'points': 4}Passed
odd credit{'cash': 894, 'points': 1238}{'cash': 894, 'points': 1238}Passed

SHA-256 / 1973cf9721874e7ef7398cedba8878e9580c205893cf869dd27c0b17210039ac

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    room = x['price'] - x['min_cash']
    maxp = abs(room) * 10 // x['cpp10']
    pts = min(x['balance'], maxp)
    credit = pts * x['cpp10'] // 10
    return {'points': pts, 'cash': x['price'] - credit}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 501}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3001, 'cpp10': 10, 'min_cash': 100}, {'points': 3001, 'cash': 6999}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 2}, {'points': 7138, 'cash': 3}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 401}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 990}, {'points': 4, 'cash': 990}], ['odd credit', {'price': 2503, 'balance': 1238, 'cpp10': 13, 'min_cash': 3}, {'points': 1238, 'cash': 894}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 502}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3002, 'cpp10': 10, 'min_cash': 100}, {'points': 3002, 'cash': 6998}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 3}, {'points': 7137, 'cash': 4}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 402}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 980}, {'points': 8, 'cash': 980}], ['odd credit', {'price': 2503, 'balance': 1239, 'cpp10': 13, 'min_cash': 3}, {'points': 1239, 'cash': 893}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 503}, {'points': 7914, 'cash': 504}], ['balance limits', {'price': 10000, 'balance': 3003, 'cpp10': 10, 'min_cash': 100}, {'points': 3003, 'cash': 6997}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 4}, {'points': 7135, 'cash': 5}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 403}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 970}, {'points': 12, 'cash': 970}], ['odd credit', {'price': 2503, 'balance': 1240, 'cpp10': 13, 'min_cash': 3}, {'points': 1240, 'cash': 891}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 504}, {'points': 7913, 'cash': 505}], ['balance limits', {'price': 10000, 'balance': 3004, 'cpp10': 10, 'min_cash': 100}, {'points': 3004, 'cash': 6996}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 5}, {'points': 7134, 'cash': 6}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 404}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 960}, {'points': 16, 'cash': 960}], ['odd credit', {'price': 2503, 'balance': 1241, 'cpp10': 13, 'min_cash': 3}, {'points': 1241, 'cash': 890}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 505}, {'points': 7912, 'cash': 506}], ['balance limits', {'price': 10000, 'balance': 3005, 'cpp10': 10, 'min_cash': 100}, {'points': 3005, 'cash': 6995}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 6}, {'points': 7132, 'cash': 7}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 405}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 950}, {'points': 20, 'cash': 950}], ['odd credit', {'price': 2503, 'balance': 1242, 'cpp10': 13, 'min_cash': 3}, {'points': 1242, 'cash': 889}]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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
points cover most{'cash': 502, 'points': 7915}{'cash': 502, 'points': 7915}Passed
balance limits{'cash': 6999, 'points': 3001}{'cash': 6999, 'points': 3001}Passed
fractional value{'cash': 3, 'points': 7138}{'cash': 3, 'points': 7138}Passed
price below minimum cash{'cash': 199, 'points': 101}{'cash': 300, 'points': 0}Failed
exact minimum{'cash': 990, 'points': 4}{'cash': 990, 'points': 4}Passed
odd credit{'cash': 894, 'points': 1238}{'cash': 894, 'points': 1238}Passed

SHA-256 / ec9fcb9355ba6cc832fd5e6f143c0540d5efb35962779e7715a78c430bdc9fd2

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    room = x['price'] - x['min_cash']
    maxp = max(0, room * 10 // x['cpp10'])
    pts = min(x['balance'], maxp)
    credit = pts * x['cpp10'] // 10
    return {'points': pts, 'cash': x['price'] - credit}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 501}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3001, 'cpp10': 10, 'min_cash': 100}, {'points': 3001, 'cash': 6999}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 2}, {'points': 7138, 'cash': 3}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 401}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 990}, {'points': 4, 'cash': 990}], ['odd credit', {'price': 2503, 'balance': 1238, 'cpp10': 13, 'min_cash': 3}, {'points': 1238, 'cash': 894}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 502}, {'points': 7915, 'cash': 502}], ['balance limits', {'price': 10000, 'balance': 3002, 'cpp10': 10, 'min_cash': 100}, {'points': 3002, 'cash': 6998}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 3}, {'points': 7137, 'cash': 4}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 402}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 980}, {'points': 8, 'cash': 980}], ['odd credit', {'price': 2503, 'balance': 1239, 'cpp10': 13, 'min_cash': 3}, {'points': 1239, 'cash': 893}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 503}, {'points': 7914, 'cash': 504}], ['balance limits', {'price': 10000, 'balance': 3003, 'cpp10': 10, 'min_cash': 100}, {'points': 3003, 'cash': 6997}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 4}, {'points': 7135, 'cash': 5}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 403}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 970}, {'points': 12, 'cash': 970}], ['odd credit', {'price': 2503, 'balance': 1240, 'cpp10': 13, 'min_cash': 3}, {'points': 1240, 'cash': 891}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 504}, {'points': 7913, 'cash': 505}], ['balance limits', {'price': 10000, 'balance': 3004, 'cpp10': 10, 'min_cash': 100}, {'points': 3004, 'cash': 6996}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 5}, {'points': 7134, 'cash': 6}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 404}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 960}, {'points': 16, 'cash': 960}], ['odd credit', {'price': 2503, 'balance': 1241, 'cpp10': 13, 'min_cash': 3}, {'points': 1241, 'cash': 890}]], [['points cover most', {'price': 10000, 'balance': 50000, 'cpp10': 12, 'min_cash': 505}, {'points': 7912, 'cash': 506}], ['balance limits', {'price': 10000, 'balance': 3005, 'cpp10': 10, 'min_cash': 100}, {'points': 3005, 'cash': 6995}], ['fractional value', {'price': 4999, 'balance': 99999, 'cpp10': 7, 'min_cash': 6}, {'points': 7132, 'cash': 7}], ['price below minimum cash', {'price': 300, 'balance': 1000, 'cpp10': 10, 'min_cash': 405}, {'points': 0, 'cash': 300}], ['exact minimum', {'price': 1000, 'balance': 100000, 'cpp10': 25, 'min_cash': 950}, {'points': 20, 'cash': 950}], ['odd credit', {'price': 2503, 'balance': 1242, 'cpp10': 13, 'min_cash': 3}, {'points': 1242, 'cash': 889}]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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
points cover most{'cash': 502, 'points': 7915}{'cash': 502, 'points': 7915}Passed
balance limits{'cash': 6999, 'points': 3001}{'cash': 6999, 'points': 3001}Passed
fractional value{'cash': 3, 'points': 7138}{'cash': 3, 'points': 7138}Passed
price below minimum cash{'cash': 300, 'points': 0}{'cash': 300, 'points': 0}Passed
exact minimum{'cash': 990, 'points': 4}{'cash': 990, 'points': 4}Passed
odd credit{'cash': 894, 'points': 1238}{'cash': 894, 'points': 1238}Passed

SHA-256 / 6a3a096f75629960c941299f5b1f3aa96e6ad7e702b531f61a3cf1fcd888a4e7

Verification & scope

Stipulated bounded loyalty-program model with explicit toy rules; not any real program terms. 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 2026-09-29T14:46:48.820379+00:00.

Case digest / dc8430ee0f0af0c3c868b3a4cb68ac11cec3b0707c67422c299d4162349106a1