FAILURE MAP
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FA-60076 / Inventory cost layering / Open access

First-expired-first-out lot picking: same-expiry tie-break · case 01

Among lots with the same expiry the pick order is unstable against the stated lot-id rule.

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

ROOT CAUSE

Ties on expiry are broken by descending unit cost instead of lot id.

THE FAILURE

Ties on expiry are broken by descending unit cost instead of lot id.

Unsuccessful approach: Breaking ties by descending lot id reverses the stipulated order.

Case contract

Input {lots:[[lot,qty,expiry_day,unit_cost]], today, order_qty, min_shelf}. A lot is eligible when expiry_day - today >= min_shelf. Eligible lots are picked by earliest expiry, ties by lot id ascending. If eligible stock < order_qty return {"error":"insufficient","available":eligible qty}. Return {picks:[[lot,qty]], cost}.

Why this case matters

Inventory valuation and cost-of-goods decisions depend on this rule.

1 / The failure

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

N = 1
observations = []
def solve(x):
    today = x['today']
    elig = [l for l in x['lots'] if l[2] - today >= x['min_shelf']]
    avail = sum(l[1] for l in elig)
    if avail < x['order_qty']:
        return {'error': 'insufficient', 'available': avail}
    elig.sort(key=lambda l: (l[2], -l[3]))
    need = x['order_qty']
    picks = []
    cost = 0
    for lot, qty, exp, unit in elig:
        if need == 0:
            break
        take = min(need, qty)
        picks.append([lot, take])
        cost += take * unit
        need -= take
    return {'picks': picks, 'cost': cost}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 7, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 2]], 'cost': 80}], ['shelf boundary', {'lots': [['A', 4, 106, 10], ['B', 4, 200, 11]], 'today': 101, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 6, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 6, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 381, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 8, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 3]], 'cost': 90}], ['shelf boundary', {'lots': [['A', 4, 107, 10], ['B', 4, 200, 11]], 'today': 102, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 7, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 7, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 382, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 6, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 1]], 'cost': 70}], ['shelf boundary', {'lots': [['A', 4, 108, 10], ['B', 4, 200, 11]], 'today': 103, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 8, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 8, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 383, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 7, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 2]], 'cost': 80}], ['shelf boundary', {'lots': [['A', 4, 109, 10], ['B', 4, 200, 11]], 'today': 104, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 9, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 9, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 384, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 8, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 3]], 'cost': 90}], ['shelf boundary', {'lots': [['A', 4, 110, 10], ['B', 4, 200, 11]], 'today': 105, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 10, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 10, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 385, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]]]
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
earliest expiry{'cost': 80, 'picks': [['L1', 5], ['L3', 2]]}{'cost': 80, 'picks': [['L1', 5], ['L3', 2]]}Passed
shelf boundary{'cost': 30, 'picks': [['A', 3]]}{'cost': 30, 'picks': [['A', 3]]}Passed
insufficient{'available': 4, 'error': 'insufficient'}{'available': 4, 'error': 'insufficient'}Passed
tie by lot{'cost': 23, 'picks': [['Z9', 2], ['A1', 1]]}{'cost': 22, 'picks': [['A1', 2], ['Z9', 1]]}Failed
expired skipped{'cost': 8, 'picks': [['NEW', 4]]}{'cost': 8, 'picks': [['NEW', 4]]}Passed
zero order{'cost': 0, 'picks': []}{'cost': 0, 'picks': []}Passed
big lots small order{'cost': 9, 'picks': [['C2', 1], ['A4', 1]]}{'cost': 9, 'picks': [['C2', 1], ['A4', 1]]}Passed

SHA-256 / ed747aa1c90d96517d0582dce9594bc0d5023c87fc515d54a88c085505df1eb1

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    today = x['today']
    elig = [l for l in x['lots'] if l[2] - today >= x['min_shelf']]
    avail = sum(l[1] for l in elig)
    if avail < x['order_qty']:
        return {'error': 'insufficient', 'available': avail}
    elig.sort(key=lambda l: (l[2], l[0]), reverse=True)
    elig.sort(key=lambda l: l[2])
    need = x['order_qty']
    picks = []
    cost = 0
    for lot, qty, exp, unit in elig:
        if need == 0:
            break
        take = min(need, qty)
        picks.append([lot, take])
        cost += take * unit
        need -= take
    return {'picks': picks, 'cost': cost}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 7, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 2]], 'cost': 80}], ['shelf boundary', {'lots': [['A', 4, 106, 10], ['B', 4, 200, 11]], 'today': 101, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 6, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 6, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 381, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 8, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 3]], 'cost': 90}], ['shelf boundary', {'lots': [['A', 4, 107, 10], ['B', 4, 200, 11]], 'today': 102, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 7, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 7, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 382, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 6, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 1]], 'cost': 70}], ['shelf boundary', {'lots': [['A', 4, 108, 10], ['B', 4, 200, 11]], 'today': 103, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 8, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 8, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 383, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 7, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 2]], 'cost': 80}], ['shelf boundary', {'lots': [['A', 4, 109, 10], ['B', 4, 200, 11]], 'today': 104, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 9, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 9, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 384, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]], [['earliest expiry', {'lots': [['L3', 5, 120, 10], ['L1', 5, 110, 12], ['L2', 5, 130, 9]], 'today': 100, 'order_qty': 8, 'min_shelf': 5}, {'picks': [['L1', 5], ['L3', 3]], 'cost': 90}], ['shelf boundary', {'lots': [['A', 4, 110, 10], ['B', 4, 200, 11]], 'today': 105, 'order_qty': 3, 'min_shelf': 5}, {'picks': [['A', 3]], 'cost': 30}], ['insufficient', {'lots': [['A', 4, 150, 10], ['B', 9, 101, 11]], 'today': 100, 'order_qty': 10, 'min_shelf': 10}, {'error': 'insufficient', 'available': 4}], ['tie by lot', {'lots': [['Z9', 2, 140, 8], ['A1', 2, 140, 7], ['M5', 9, 150, 6]], 'today': 100, 'order_qty': 3, 'min_shelf': 1}, {'picks': [['A1', 2], ['Z9', 1]], 'cost': 22}], ['expired skipped', {'lots': [['OLD', 50, 90, 1], ['NEW', 10, 300, 2]], 'today': 100, 'order_qty': 4, 'min_shelf': 0}, {'picks': [['NEW', 4]], 'cost': 8}], ['zero order', {'lots': [['A', 3, 150, 10]], 'today': 100, 'order_qty': 0, 'min_shelf': 0}, {'picks': [], 'cost': 0}], ['big lots small order', {'lots': [['B7', 100, 400, 3], ['C2', 1, 385, 5], ['A4', 2, 390, 4]], 'today': 100, 'order_qty': 2, 'min_shelf': 30}, {'picks': [['C2', 1], ['A4', 1]], 'cost': 9}]]]
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
earliest expiry{'cost': 80, 'picks': [['L1', 5], ['L3', 2]]}{'cost': 80, 'picks': [['L1', 5], ['L3', 2]]}Passed
shelf boundary{'cost': 30, 'picks': [['A', 3]]}{'cost': 30, 'picks': [['A', 3]]}Passed
insufficient{'available': 4, 'error': 'insufficient'}{'available': 4, 'error': 'insufficient'}Passed
tie by lot{'cost': 23, 'picks': [['Z9', 2], ['A1', 1]]}{'cost': 22, 'picks': [['A1', 2], ['Z9', 1]]}Failed
expired skipped{'cost': 8, 'picks': [['NEW', 4]]}{'cost': 8, 'picks': [['NEW', 4]]}Passed
zero order{'cost': 0, 'picks': []}{'cost': 0, 'picks': []}Passed
big lots small order{'cost': 9, 'picks': [['C2', 1], ['A4', 1]]}{'cost': 9, 'picks': [['C2', 1], ['A4', 1]]}Passed

SHA-256 / 8154029cfc63c452774e98d92ea1cd61ac93deecbe4c482f6c003a30bb49fffc

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.

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Verification & scope

Stipulated bounded teaching model with explicit toy rules; not an accounting-standard implementation. 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 2026-09-29T14:46:42.379360+00:00.

Case digest / 967696f43d4a3138f9e0428c36c341633fd673a899edb5a6e3a19e1cb9047c61