FAILURE MAP
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FA-59641 / Subscription proration billing / Open access

Minimum threshold for invoicing prorations: carried amount inclusion · case 01

Small deferred prorations from earlier cycles are never billed.

Verified by executionVariant 1 · 10 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The carried amount is dropped when computing pending prorations.

THE FAILURE

The carried amount is dropped when computing pending prorations.

Unsuccessful approach: The attempt includes carry but ignores new credit lines.

Case contract

Input {lines, threshold, carried}. Pending = carried + sum(lines). Pending >= threshold is invoiced now; pending <= -threshold is credited to the balance now; anything in between is carried to the next cycle. Return [invoiced, credited, carry].

Why this case matters

Tiny proration amounts are deferred to avoid micro-charges, but must not be lost.

1 / The failure

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

N = 1
observations = []
def solve(x):
    pending = sum(x['lines'])
    if pending >= x['threshold']:
        return [pending, 0, 0]
    if pending <= -x['threshold']:
        return [0, -pending, 0]
    return [0, 0, pending]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('regression (boundary)', {'lines': [30], 'threshold': 50, 'carried': 20}, [50, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-50, 150], 'threshold': 100, 'carried': 0}, [100, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-100], 'threshold': 100, 'carried': 0}, [0, 100, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [481], 'threshold': 100, 'carried': 0}, [481, 0, 0]), ('normal control', {'lines': [207], 'threshold': 500, 'carried': 0}, [0, 0, 207]), ('normal control', {'lines': [429], 'threshold': 100, 'carried': 0}, [429, 0, 0]), ('normal control', {'lines': [97], 'threshold': 50, 'carried': 0}, [97, 0, 0])], [('regression', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('regression (boundary)', {'lines': [], 'threshold': 100, 'carried': 100}, [100, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('partial-repair probe', {'lines': [61, 426, -138, 400], 'threshold': 50, 'carried': 0}, [749, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [344], 'threshold': 100, 'carried': 0}, [344, 0, 0]), ('normal control', {'lines': [], 'threshold': 50, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [326, 112, 108, 591], 'threshold': 50, 'carried': 0}, [1137, 0, 0]), ('normal control', {'lines': [127], 'threshold': 100, 'carried': 0}, [127, 0, 0])], [('regression', {'lines': [340, -379, -241], 'threshold': 50, 'carried': -6}, [0, 286, 0]), ('regression (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('partial-repair probe', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('partial-repair probe', {'lines': [-381, 116], 'threshold': 500, 'carried': 0}, [0, 0, -265]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [341], 'threshold': 500, 'carried': 0}, [0, 0, 341]), ('normal control', {'lines': [], 'threshold': 500, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [], 'threshold': 100, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [225], 'threshold': 500, 'carried': 0}, [0, 0, 225])], [('regression', {'lines': [-497, -497, -32, -352], 'threshold': 50, 'carried': -49}, [0, 1427, 0]), ('regression', {'lines': [], 'threshold': 500, 'carried': 499}, [0, 0, 499]), ('partial-repair probe', {'lines': [340, -379, -241], 'threshold': 50, 'carried': -6}, [0, 286, 0]), ('partial-repair probe', {'lines': [-95, 305], 'threshold': 100, 'carried': 0}, [210, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [120, 341, 183, 393], 'threshold': 500, 'carried': 0}, [1037, 0, 0]), ('normal control', {'lines': [376], 'threshold': 500, 'carried': 0}, [0, 0, 376]), ('normal control', {'lines': [458], 'threshold': 100, 'carried': 0}, [458, 0, 0]), ('normal control', {'lines': [239], 'threshold': 100, 'carried': 0}, [239, 0, 0])], [('regression', {'lines': [382, -579, 100], 'threshold': 500, 'carried': 299}, [0, 0, 202]), ('regression', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('partial-repair probe', {'lines': [-95, 305], 'threshold': 100, 'carried': 0}, [210, 0, 0]), ('partial-repair probe', {'lines': [145, -201, 592, 509], 'threshold': 500, 'carried': 0}, [1045, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [336], 'threshold': 100, 'carried': 0}, [336, 0, 0]), ('normal control', {'lines': [41], 'threshold': 500, 'carried': 0}, [0, 0, 41]), ('normal control', {'lines': [360], 'threshold': 500, 'carried': 0}, [0, 0, 360]), ('normal control', {'lines': [263, 589], 'threshold': 100, 'carried': 0}, [852, 0, 0])]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), 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
regression (boundary) 0[0, 60, 0][0, 50, 0]Failed
regression (boundary) 1[0, 0, 30][50, 0, 0]Failed
partial-repair probe (boundary) 2[100, 0, 0][100, 0, 0]Passed
partial-repair probe (boundary) 3[0, 100, 0][0, 100, 0]Passed
boundary control 4[500, 0, 0][500, 0, 0]Passed
boundary control 5[50, 0, 0][50, 0, 0]Passed
normal control 6[481, 0, 0][481, 0, 0]Passed
normal control 7[0, 0, 207][0, 0, 207]Passed
normal control 8[429, 0, 0][429, 0, 0]Passed
normal control 9[97, 0, 0][97, 0, 0]Passed

SHA-256 / 37656c965a5608125d46d584e34564292d68eb07df70f640c79e902df177825e

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    pending = x['carried'] + sum(l for l in x['lines'] if l > 0)
    if pending >= x['threshold']:
        return [pending, 0, 0]
    if pending <= -x['threshold']:
        return [0, -pending, 0]
    return [0, 0, pending]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('regression (boundary)', {'lines': [30], 'threshold': 50, 'carried': 20}, [50, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-50, 150], 'threshold': 100, 'carried': 0}, [100, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-100], 'threshold': 100, 'carried': 0}, [0, 100, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [481], 'threshold': 100, 'carried': 0}, [481, 0, 0]), ('normal control', {'lines': [207], 'threshold': 500, 'carried': 0}, [0, 0, 207]), ('normal control', {'lines': [429], 'threshold': 100, 'carried': 0}, [429, 0, 0]), ('normal control', {'lines': [97], 'threshold': 50, 'carried': 0}, [97, 0, 0])], [('regression', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('regression (boundary)', {'lines': [], 'threshold': 100, 'carried': 100}, [100, 0, 0]), ('partial-repair probe (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('partial-repair probe', {'lines': [61, 426, -138, 400], 'threshold': 50, 'carried': 0}, [749, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [344], 'threshold': 100, 'carried': 0}, [344, 0, 0]), ('normal control', {'lines': [], 'threshold': 50, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [326, 112, 108, 591], 'threshold': 50, 'carried': 0}, [1137, 0, 0]), ('normal control', {'lines': [127], 'threshold': 100, 'carried': 0}, [127, 0, 0])], [('regression', {'lines': [340, -379, -241], 'threshold': 50, 'carried': -6}, [0, 286, 0]), ('regression (boundary)', {'lines': [-60], 'threshold': 50, 'carried': 10}, [0, 50, 0]), ('partial-repair probe', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('partial-repair probe', {'lines': [-381, 116], 'threshold': 500, 'carried': 0}, [0, 0, -265]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [341], 'threshold': 500, 'carried': 0}, [0, 0, 341]), ('normal control', {'lines': [], 'threshold': 500, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [], 'threshold': 100, 'carried': 0}, [0, 0, 0]), ('normal control', {'lines': [225], 'threshold': 500, 'carried': 0}, [0, 0, 225])], [('regression', {'lines': [-497, -497, -32, -352], 'threshold': 50, 'carried': -49}, [0, 1427, 0]), ('regression', {'lines': [], 'threshold': 500, 'carried': 499}, [0, 0, 499]), ('partial-repair probe', {'lines': [340, -379, -241], 'threshold': 50, 'carried': -6}, [0, 286, 0]), ('partial-repair probe', {'lines': [-95, 305], 'threshold': 100, 'carried': 0}, [210, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [120, 341, 183, 393], 'threshold': 500, 'carried': 0}, [1037, 0, 0]), ('normal control', {'lines': [376], 'threshold': 500, 'carried': 0}, [0, 0, 376]), ('normal control', {'lines': [458], 'threshold': 100, 'carried': 0}, [458, 0, 0]), ('normal control', {'lines': [239], 'threshold': 100, 'carried': 0}, [239, 0, 0])], [('regression', {'lines': [382, -579, 100], 'threshold': 500, 'carried': 299}, [0, 0, 202]), ('regression', {'lines': [518, -386], 'threshold': 500, 'carried': 499}, [631, 0, 0]), ('partial-repair probe', {'lines': [-95, 305], 'threshold': 100, 'carried': 0}, [210, 0, 0]), ('partial-repair probe', {'lines': [145, -201, 592, 509], 'threshold': 500, 'carried': 0}, [1045, 0, 0]), ('boundary control', {'lines': [250, 250], 'threshold': 500, 'carried': 0}, [500, 0, 0]), ('boundary control', {'lines': [40, 10], 'threshold': 50, 'carried': 0}, [50, 0, 0]), ('normal control', {'lines': [336], 'threshold': 100, 'carried': 0}, [336, 0, 0]), ('normal control', {'lines': [41], 'threshold': 500, 'carried': 0}, [0, 0, 41]), ('normal control', {'lines': [360], 'threshold': 500, 'carried': 0}, [0, 0, 360]), ('normal control', {'lines': [263, 589], 'threshold': 100, 'carried': 0}, [852, 0, 0])]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), 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
regression (boundary) 0[0, 0, 10][0, 50, 0]Failed
regression (boundary) 1[50, 0, 0][50, 0, 0]Passed
partial-repair probe (boundary) 2[150, 0, 0][100, 0, 0]Failed
partial-repair probe (boundary) 3[0, 0, 0][0, 100, 0]Failed
boundary control 4[500, 0, 0][500, 0, 0]Passed
boundary control 5[50, 0, 0][50, 0, 0]Passed
normal control 6[481, 0, 0][481, 0, 0]Passed
normal control 7[0, 0, 207][0, 0, 207]Passed
normal control 8[429, 0, 0][429, 0, 0]Passed
normal control 9[97, 0, 0][97, 0, 0]Passed

SHA-256 / b6cf441e27fe9c3cc1734eb359991209eaeebbe01875bdfe8f2a32d809c409a0

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 10 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.

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Verification & scope

A deterministic teaching model of a stipulated billing rule. It makes no claim to reproduce any billing provider's exact behaviour and is not billing software. 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 2026-09-29T14:46:38.174494+00:00.

Case digest / b9f26d520b3a0a0b96d399f7390704c550df57ba5ed2e976809681e9b36943af