FAILURE MAP
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FA-72216 / Error-correcting codes / Open access

LT peeling releases only original degree-one symbols · case 01

Higher-degree symbols are never peeled, leaving many sources unresolved.

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

ROOT CAUSE

The release test checks the original neighbour count instead of the number of unresolved neighbours.

THE FAILURE

The release test checks the original neighbour count instead of the number of unresolved neighbours.

Unsuccessful approach: Also requiring original degree at most two still ignores degree-three symbols.

Case contract

Peeling (belief-propagation) decoder for an LT fountain code over bytes. symbols is a list of [neighbour indices, XOR of those source symbols]. Repeatedly find an encoded symbol with exactly one unresolved neighbour, resolve it as the value XOR all resolved neighbours, and continue until a full pass makes no progress. Return the k source values with None for unresolved ones.

Why this case matters

Broadcast and storage systems use fountain codes; peeling must continue as long as new degree-one symbols appear.

1 / The failure

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

N = 1
observations = []
def solve(symbols, k):
    src = [None] * k
    changed = True
    while changed:
        changed = False
        for nbrs, val in symbols:
            unknown = [i for i in nbrs if src[i] is None]
            if len(nbrs) != 1 or len(unknown) != 1:
                continue
            x = val
            for i in nbrs:
                if src[i] is not None:
                    x ^= src[i]
            src[unknown[0]] = x
            changed = True
    return src
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]], ['control [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...', [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]], 4], [100, 106, 96, 151]]], [['regression [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]], ['regression [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...', [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]], 4], [100, 106, 96, 151]], ['partial-repair [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]]], [['regression [[[[2, 5], 36], [[1, 3, 4], 222], [[0, 1], 103], [[1, 3, 5], 190], ...', [[[[2, 5], 36], [[1, 3, 4], 222], [[0, 1], 103], [[1, 3, 5], 190], [[2, 4], 68], [[5], 61], [[2], 25], [[2], 25], [[2], 25]], 6], [None, None, 25, None, 93, 61]], ['regression [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]]], [['regression [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]], ['regression [[[[0, 1], 5], [[1], 3]], 2]', [[[[0, 1], 5], [[1], 3]], 2], [6, 3]], ['partial-repair [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]]], [['regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]]]]
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
regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3][None, None, 186][87, 225, 186]Failed
regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4][93, 110, None, 40][93, 110, 53, 40]Failed
partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...[None, None, 28, None, None][249, 52, 28, 13, 241]Failed
control [[[[0, 1], 1]], 2][None, None][None, None]Passed
control [[], 2][None, None][None, None]Passed
control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3][9, None, None][9, None, None]Passed
control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...[59, None, None, None, None, 71][59, 190, 199, 1, 191, 71]Failed
control [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...[None, 106, None, 151][100, 106, 96, 151]Failed

SHA-256 / fb3cfa807a19802b3f6cedd086a91732811ffa29d8ba782727d1c80e0cc4da9d

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(symbols, k):
    src = [None] * k
    changed = True
    while changed:
        changed = False
        for nbrs, val in symbols:
            unknown = [i for i in nbrs if src[i] is None]
            if len(unknown) != 1 or len(nbrs) > 2:
                continue
            x = val
            for i in nbrs:
                if src[i] is not None:
                    x ^= src[i]
            src[unknown[0]] = x
            changed = True
    return src
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]], ['control [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...', [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]], 4], [100, 106, 96, 151]]], [['regression [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]], ['regression [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...', [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]], 4], [100, 106, 96, 151]], ['partial-repair [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]]], [['regression [[[[2, 5], 36], [[1, 3, 4], 222], [[0, 1], 103], [[1, 3, 5], 190], ...', [[[[2, 5], 36], [[1, 3, 4], 222], [[0, 1], 103], [[1, 3, 5], 190], [[2, 4], 68], [[5], 61], [[2], 25], [[2], 25], [[2], 25]], 6], [None, None, 25, None, 93, 61]], ['regression [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]]], [['regression [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]], ['regression [[[[0, 1], 5], [[1], 3]], 2]', [[[[0, 1], 5], [[1], 3]], 2], [6, 3]], ['partial-repair [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3]', [[[[0, 1], 249], [[0, 1], 249], [[0, 1, 2], 202], [[0], 87]], 3], [87, 174, 51]], ['partial-repair [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...', [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0, 2, 4], 67], [[1, 2, 4], 198], [[0], 59], [[5], 71]], 6], [59, 190, 199, 1, 191, 71]]], [['regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]', [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3], [87, 225, 186]], ['regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4]', [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4], [93, 110, 53, 40]], ['partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...', [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2, 4], 217]], 5], [249, 52, 28, 13, 241]], ['control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3]', [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3], [9, None, None]], ['control [[[[0, 1], 1]], 2]', [[[[0, 1], 1]], 2], [None, None]], ['control [[], 2]', [[], 2], [None, None]], ['control [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], ...', [[[[0, 1, 5], 222], [[4], 144], [[2, 5, 6], 16], [[1, 2, 4], 104], [[3], 251], [[0, 2, 4], 177], [[6], 49], [[0, 6], 54]], 7], [7, 222, 38, 251, 144, 7, 49]], ['control [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...', [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], 114]], 5], [114, 137, None, None, 166]]]]
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
regression [[[[0, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3][87, None, 186][87, 225, 186]Failed
regression [[[[1], 110], [[3], 40], [[0, 2, 3], 64], [[2, 3], 29], [[0], 93]], 4][93, 110, 53, 40][93, 110, 53, 40]Passed
partial-repair [[[[2, 4], 237], [[0, 1, 3], 192], [[1, 3], 57], [[2], 28], [[1, 2,...[None, None, 28, None, 241][249, 52, 28, 13, 241]Failed
control [[[[0, 1], 1]], 2][None, None][None, None]Passed
control [[], 2][None, None][None, None]Passed
control [[[[0], 9], [[0, 1, 2], 1], [[1, 2], 3]], 3][9, None, None][9, None, None]Passed
control [[[[0, 1, 5], 194], [[0, 4], 132], [[0, 1], 133], [[3, 5], 70], [[0...[59, 190, None, 1, 191, 71][59, 190, 199, 1, 191, 71]Failed
control [[[[3], 151], [[1, 3], 253], [[0, 2], 4], [[1], 106], [[0, 1], 14]]...[100, 106, 96, 151][100, 106, 96, 151]Passed

SHA-256 / c144dd58f1452c08f1d525bc54723269623f2b7c8a38be6f8edf1f9c9d208327

HELD IN THE MEMBER ARCHIVE

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.

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, bounded teaching model of the named code under the stated contract; not a production codec. 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 2026-09-29T14:48:36.567487+00:00.

Case digest / 148535997a86e4e9fff8618fdd16e2934b8d894017885ac0b76a0e622f02687e