FAILURE MAP
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FA-59851 / Inventory cost layering / Open access

FIFO perpetual issue: same-cost receipt merge · case 01

A receipt at a different price is folded into the previous layer, so later issues use the stale price.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The merge test only checks that some layer exists, not that its unit cost matches the receipt.

THE FAILURE

The merge test only checks that some layer exists, not that its unit cost matches the receipt.

Unsuccessful approach: Merging within a one-cent tolerance still blends distinct prices into one layer.

Case contract

Input {layers:[[qty,unit_cost]] oldest first, events:[["recv",qty,unit_cost]|["issue",qty]]}. Issues consume the oldest layer first; an issue larger than on-hand is rejected whole and reported as "short"; a receipt at exactly the newest layer cost merges into it; receipts of zero or negative quantity are ignored. Return {cogs:[per-issue cost or "short"], layers}.

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):
    layers = [list(l) for l in x['layers']]
    out = []
    for ev in x['events']:
        if ev[0] == 'recv':
            q, c = ev[1], ev[2]
            if q <= 0:
                continue
            if layers:
                layers[-1][0] += q
            else:
                layers.append([q, c])
            continue
        need = ev[1]
        onhand = sum(l[0] for l in layers)
        if need > onhand:
            out.append('short')
            continue
        cost = 0
        while need > 0:
            idx = 0
            take = min(need, layers[idx][0])
            cost += take * layers[idx][1]
            layers[idx][0] -= take
            need -= take
            if layers[idx][0] == 0:
                layers.pop(idx)
        out.append(cost)
    return {'cogs': out, 'layers': layers}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 8]]}, {'cogs': [860], 'layers': [[7, 120]]}], ['exact depletion', {'layers': [[4, 50], [1, 70]], 'events': [['issue', 5]]}, {'cogs': [270], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 4], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 13], ['issue', 4], ['recv', 1, 13]]}, {'cogs': [46], 'layers': [[4, 13]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 1, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[2, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 31], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [2, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': []}], ['price decline', {'layers': [[2, 61], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [122], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 9]]}, {'cogs': [980], 'layers': [[6, 120]]}], ['exact depletion', {'layers': [[4, 50], [2, 70]], 'events': [['issue', 6]]}, {'cogs': [340], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 5], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 14], ['issue', 4], ['recv', 1, 14]]}, {'cogs': [48], 'layers': [[4, 14]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 2, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[3, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 32], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [3, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[1, 9]]}], ['price decline', {'layers': [[2, 62], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [124], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 7]]}, {'cogs': [740], 'layers': [[8, 120]]}], ['exact depletion', {'layers': [[4, 50], [3, 70]], 'events': [['issue', 7]]}, {'cogs': [410], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 6], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 15], ['issue', 4], ['recv', 1, 15]]}, {'cogs': [50], 'layers': [[4, 15]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 3, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[4, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 33], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [4, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[2, 9]]}], ['price decline', {'layers': [[2, 63], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [126], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 8]]}, {'cogs': [860], 'layers': [[7, 120]]}], ['exact depletion', {'layers': [[4, 50], [4, 70]], 'events': [['issue', 8]]}, {'cogs': [480], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 7], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 16], ['issue', 4], ['recv', 1, 16]]}, {'cogs': [52], 'layers': [[4, 16]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 4, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[5, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 34], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [5, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[3, 9]]}], ['price decline', {'layers': [[2, 64], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [128], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 9]]}, {'cogs': [980], 'layers': [[6, 120]]}], ['exact depletion', {'layers': [[4, 50], [5, 70]], 'events': [['issue', 9]]}, {'cogs': [550], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 8], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 17], ['issue', 4], ['recv', 1, 17]]}, {'cogs': [54], 'layers': [[4, 17]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 5, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[6, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 35], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [6, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[4, 9]]}], ['price decline', {'layers': [[2, 65], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [130], 'layers': [[3, 45]]}]]]
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
span two layers{'cogs': [860], 'layers': [[7, 120]]}{'cogs': [860], 'layers': [[7, 120]]}Passed
exact depletion{'cogs': [270], 'layers': []}{'cogs': [270], 'layers': []}Passed
short rejected{'cogs': ['short', 180], 'layers': [[1, 90]]}{'cogs': ['short', 180], 'layers': [[1, 90]]}Passed
receipt then issue{'cogs': [40], 'layers': [[4, 10]]}{'cogs': [46], 'layers': [[4, 13]]}Failed
same cost merge{'cogs': [40], 'layers': [[5, 40]]}{'cogs': [40], 'layers': [[2, 40], [3, 41]]}Failed
zero receipt{'cogs': [50], 'layers': [[4, 25]]}{'cogs': [50], 'layers': [[4, 25]]}Passed
multi issue{'cogs': [5, 16, 9], 'layers': []}{'cogs': [5, 16, 9], 'layers': []}Passed
price decline{'cogs': [122], 'layers': [[3, 45]]}{'cogs': [122], 'layers': [[3, 45]]}Passed

SHA-256 / 4a54d1dacf7c0d11de73a2f8101994e5fdb8c69e4200c2c47e166f44ba170e1a

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    layers = [list(l) for l in x['layers']]
    out = []
    for ev in x['events']:
        if ev[0] == 'recv':
            q, c = ev[1], ev[2]
            if q <= 0:
                continue
            if layers and abs(layers[-1][1] - c) <= 1:
                layers[-1][0] += q
            else:
                layers.append([q, c])
            continue
        need = ev[1]
        onhand = sum(l[0] for l in layers)
        if need > onhand:
            out.append('short')
            continue
        cost = 0
        while need > 0:
            idx = 0
            take = min(need, layers[idx][0])
            cost += take * layers[idx][1]
            layers[idx][0] -= take
            need -= take
            if layers[idx][0] == 0:
                layers.pop(idx)
        out.append(cost)
    return {'cogs': out, 'layers': layers}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 8]]}, {'cogs': [860], 'layers': [[7, 120]]}], ['exact depletion', {'layers': [[4, 50], [1, 70]], 'events': [['issue', 5]]}, {'cogs': [270], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 4], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 13], ['issue', 4], ['recv', 1, 13]]}, {'cogs': [46], 'layers': [[4, 13]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 1, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[2, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 31], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [2, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': []}], ['price decline', {'layers': [[2, 61], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [122], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 9]]}, {'cogs': [980], 'layers': [[6, 120]]}], ['exact depletion', {'layers': [[4, 50], [2, 70]], 'events': [['issue', 6]]}, {'cogs': [340], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 5], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 14], ['issue', 4], ['recv', 1, 14]]}, {'cogs': [48], 'layers': [[4, 14]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 2, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[3, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 32], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [3, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[1, 9]]}], ['price decline', {'layers': [[2, 62], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [124], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 7]]}, {'cogs': [740], 'layers': [[8, 120]]}], ['exact depletion', {'layers': [[4, 50], [3, 70]], 'events': [['issue', 7]]}, {'cogs': [410], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 6], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 15], ['issue', 4], ['recv', 1, 15]]}, {'cogs': [50], 'layers': [[4, 15]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 3, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[4, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 33], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [4, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[2, 9]]}], ['price decline', {'layers': [[2, 63], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [126], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 8]]}, {'cogs': [860], 'layers': [[7, 120]]}], ['exact depletion', {'layers': [[4, 50], [4, 70]], 'events': [['issue', 8]]}, {'cogs': [480], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 7], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 16], ['issue', 4], ['recv', 1, 16]]}, {'cogs': [52], 'layers': [[4, 16]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 4, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[5, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 34], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [5, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[3, 9]]}], ['price decline', {'layers': [[2, 64], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [128], 'layers': [[3, 45]]}]], [['span two layers', {'layers': [[5, 100], [10, 120]], 'events': [['issue', 9]]}, {'cogs': [980], 'layers': [[6, 120]]}], ['exact depletion', {'layers': [[4, 50], [5, 70]], 'events': [['issue', 9]]}, {'cogs': [550], 'layers': []}], ['short rejected', {'layers': [[3, 90]], 'events': [['issue', 8], ['issue', 2]]}, {'cogs': ['short', 180], 'layers': [[1, 90]]}], ['receipt then issue', {'layers': [[2, 10]], 'events': [['recv', 5, 17], ['issue', 4], ['recv', 1, 17]]}, {'cogs': [54], 'layers': [[4, 17]]}], ['same cost merge', {'layers': [[2, 40]], 'events': [['recv', 5, 40], ['recv', 3, 41], ['issue', 1]]}, {'cogs': [40], 'layers': [[6, 40], [3, 41]]}], ['zero receipt', {'layers': [[6, 25]], 'events': [['recv', 0, 35], ['issue', 2]]}, {'cogs': [50], 'layers': [[4, 25]]}], ['multi issue', {'layers': [[1, 5], [1, 7], [6, 9]], 'events': [['issue', 1], ['issue', 2], ['issue', 1]]}, {'cogs': [5, 16, 9], 'layers': [[4, 9]]}], ['price decline', {'layers': [[2, 65], [3, 45]], 'events': [['issue', 2]]}, {'cogs': [130], 'layers': [[3, 45]]}]]]
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
span two layers{'cogs': [860], 'layers': [[7, 120]]}{'cogs': [860], 'layers': [[7, 120]]}Passed
exact depletion{'cogs': [270], 'layers': []}{'cogs': [270], 'layers': []}Passed
short rejected{'cogs': ['short', 180], 'layers': [[1, 90]]}{'cogs': ['short', 180], 'layers': [[1, 90]]}Passed
receipt then issue{'cogs': [46], 'layers': [[4, 13]]}{'cogs': [46], 'layers': [[4, 13]]}Passed
same cost merge{'cogs': [40], 'layers': [[5, 40]]}{'cogs': [40], 'layers': [[2, 40], [3, 41]]}Failed
zero receipt{'cogs': [50], 'layers': [[4, 25]]}{'cogs': [50], 'layers': [[4, 25]]}Passed
multi issue{'cogs': [5, 16, 9], 'layers': []}{'cogs': [5, 16, 9], 'layers': []}Passed
price decline{'cogs': [122], 'layers': [[3, 45]]}{'cogs': [122], 'layers': [[3, 45]]}Passed

SHA-256 / 1d98c37521453238a192ddba7e28eff3ee58b12284050afac1c9a9913d4ecf50

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

This mechanism has 8 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 2026-09-29T14:46:40.179149+00:00.

Case digest / a4ab3f098adac9e00dc782a1c5490058626018e8983df2923eefd9eebf3d23d7