FAILURE MAP
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FA-71906 / Error-correcting codes / Open access

Repetition decoder accepts a truncated final block · case 01

A stream cut mid-block decodes a partial block as if complete.

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

ROOT CAUSE

The length check is missing, so the last short block votes with fewer copies.

THE FAILURE

The length check is missing, so the last short block votes with fewer copies.

Unsuccessful approach: Rejecting only streams shorter than one block still accepts truncated tails.

Case contract

Decode an n-fold repetition code sent in contiguous blocks of n symbols; each received symbol is 0, 1 or None (erasure). Erasures do not vote. The bit is the majority of non-erased symbols; a tie (including an all-erased block) yields None. fixed_count counts non-erased symbols outvoted in decided blocks. A length that is not a multiple of n, or n < 1, returns None. Return [bits, fixed_count].

Why this case matters

Robust control channels repeat critical flags and must treat erased symbols differently from zeros.

1 / The failure

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

N = 1
observations = []
def solve(r, n):
    if n < 1:
        return None
    out, fixed_count = [], 0
    for g in range(0, len(r), n):
        grp = [x for x in r[g:g + n] if x is not None]
        ones = sum(grp)
        zeros = len(grp) - ones
        if ones == zeros:
            out.append(None)
            continue
        b = 1 if ones > zeros else 0
        out.append(b)
        fixed_count += min(ones, zeros)
    return [out, fixed_count]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[1, 1, 0], 3]', [[1, 1, 0], 3], [[1], 1]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]], ['control [[1, 1, null], 3]', [[1, 1, None], 3], [[1], 0]], ['control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5]', [[1, 1, 0, None, 0, None, 0, 0, 0, 1], 5], [[None, 0], 1]], ['control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5]', [[0, 1, 0, 1, 0, None, 1, 0, 1, 1], 5], [[0, 1], 3]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]], ['control [[1], 1]', [[1], 1], [[1], 0]], ['control [[1, 1, null, 0, 1, null, 0, null], 2]', [[1, 1, None, 0, 1, None, 0, None], 2], [[1, 0, 1, 0], 0]], ['control [[1, 0, null, null, 1, 1], 3]', [[1, 0, None, None, 1, 1], 3], [[None, 1], 0]], ['control [[0, 1, null, 0, 0, 1, 0, 0, 0, 0], 5]', [[0, 1, None, 0, 0, 1, 0, 0, 0, 0], 5], [[0, 0], 2]], ['control [[1, null, 0], 3]', [[1, None, 0], 3], [[None], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[1, null, 0], 3]', [[1, None, 0], 3], [[None], 0]], ['control [[null, null, null], 3]', [[None, None, None], 3], [[None], 0]], ['control [[1, 0, 0, 1, 1, 0], 3]', [[1, 0, 0, 1, 1, 0], 3], [[0, 1], 2]], ['control [[0, 1, 1, 1, 0, 0, null, 1], 4]', [[0, 1, 1, 1, 0, 0, None, 1], 4], [[1, 0], 2]], ['control [[1, null, null], 3]', [[1, None, None], 3], [[1], 0]], ['control [[0, null, 1, 1, 1], 5]', [[0, None, 1, 1, 1], 5], [[1], 1]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, null, 1, 1, 1], 5]', [[0, None, 1, 1, 1], 5], [[1], 1]], ['control [[1, 0], 2]', [[1, 0], 2], [[None], 0]], ['control [[1, 1, 0, 0, 0, 1, 1, 1, 0], 3]', [[1, 1, 0, 0, 0, 1, 1, 1, 0], 3], [[1, 0, 1], 3]], ['control [[null, 0, 1, 0, null, 1], 3]', [[None, 0, 1, 0, None, 1], 3], [[None, None], 0]], ['control [[1, 1, 0], 3]', [[1, 1, 0], 3], [[1], 1]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]], ['control [[1, 1, null], 3]', [[1, 1, None], 3], [[1], 0]], ['control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5]', [[1, 1, 0, None, 0, None, 0, 0, 0, 1], 5], [[None, 0], 1]], ['control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5]', [[0, 1, 0, 1, 0, None, 1, 0, 1, 1], 5], [[0, 1], 3]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]], ['control [[1], 1]', [[1], 1], [[1], 0]]]]
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 [[1, 1], 3][[1], 0]NoneFailed
partial-repair [[], 3][[], 0][[], 0]Passed
control [[1, 1, 0], 3][[1], 1][[1], 1]Passed
control [[0, null, 1], 3][[None], 0][[None], 0]Passed
control [[1, 1, null], 3][[1], 0][[1], 0]Passed
control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5][[None, 0], 1][[None, 0], 1]Passed
control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5][[0, 1], 3][[0, 1], 3]Passed
control [[0, 0, null, null], 4][[0], 0][[0], 0]Passed

SHA-256 / a82f2b522ee866e2411c2398a996c24efcd6f091a492e51b0cdd1b802e97c19c

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(r, n):
    if n < 1 or len(r) < n:
        return None
    out, fixed_count = [], 0
    for g in range(0, len(r), n):
        grp = [x for x in r[g:g + n] if x is not None]
        ones = sum(grp)
        zeros = len(grp) - ones
        if ones == zeros:
            out.append(None)
            continue
        b = 1 if ones > zeros else 0
        out.append(b)
        fixed_count += min(ones, zeros)
    return [out, fixed_count]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[1, 1, 0], 3]', [[1, 1, 0], 3], [[1], 1]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]], ['control [[1, 1, null], 3]', [[1, 1, None], 3], [[1], 0]], ['control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5]', [[1, 1, 0, None, 0, None, 0, 0, 0, 1], 5], [[None, 0], 1]], ['control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5]', [[0, 1, 0, 1, 0, None, 1, 0, 1, 1], 5], [[0, 1], 3]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]], ['control [[1], 1]', [[1], 1], [[1], 0]], ['control [[1, 1, null, 0, 1, null, 0, null], 2]', [[1, 1, None, 0, 1, None, 0, None], 2], [[1, 0, 1, 0], 0]], ['control [[1, 0, null, null, 1, 1], 3]', [[1, 0, None, None, 1, 1], 3], [[None, 1], 0]], ['control [[0, 1, null, 0, 0, 1, 0, 0, 0, 0], 5]', [[0, 1, None, 0, 0, 1, 0, 0, 0, 0], 5], [[0, 0], 2]], ['control [[1, null, 0], 3]', [[1, None, 0], 3], [[None], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[1, null, 0], 3]', [[1, None, 0], 3], [[None], 0]], ['control [[null, null, null], 3]', [[None, None, None], 3], [[None], 0]], ['control [[1, 0, 0, 1, 1, 0], 3]', [[1, 0, 0, 1, 1, 0], 3], [[0, 1], 2]], ['control [[0, 1, 1, 1, 0, 0, null, 1], 4]', [[0, 1, 1, 1, 0, 0, None, 1], 4], [[1, 0], 2]], ['control [[1, null, null], 3]', [[1, None, None], 3], [[1], 0]], ['control [[0, null, 1, 1, 1], 5]', [[0, None, 1, 1, 1], 5], [[1], 1]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, null, 1, 1, 1], 5]', [[0, None, 1, 1, 1], 5], [[1], 1]], ['control [[1, 0], 2]', [[1, 0], 2], [[None], 0]], ['control [[1, 1, 0, 0, 0, 1, 1, 1, 0], 3]', [[1, 1, 0, 0, 0, 1, 1, 1, 0], 3], [[1, 0, 1], 3]], ['control [[null, 0, 1, 0, null, 1], 3]', [[None, 0, 1, 0, None, 1], 3], [[None, None], 0]], ['control [[1, 1, 0], 3]', [[1, 1, 0], 3], [[1], 1]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]]], [['regression [[1, 1], 3]', [[1, 1], 3], None], ['partial-repair [[], 3]', [[], 3], [[], 0]], ['control [[0, null, 1], 3]', [[0, None, 1], 3], [[None], 0]], ['control [[1, 1, null], 3]', [[1, 1, None], 3], [[1], 0]], ['control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5]', [[1, 1, 0, None, 0, None, 0, 0, 0, 1], 5], [[None, 0], 1]], ['control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5]', [[0, 1, 0, 1, 0, None, 1, 0, 1, 1], 5], [[0, 1], 3]], ['control [[0, 0, null, null], 4]', [[0, 0, None, None], 4], [[0], 0]], ['control [[1], 1]', [[1], 1], [[1], 0]]]]
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 [[1, 1], 3]NoneNonePassed
partial-repair [[], 3]None[[], 0]Failed
control [[1, 1, 0], 3][[1], 1][[1], 1]Passed
control [[0, null, 1], 3][[None], 0][[None], 0]Passed
control [[1, 1, null], 3][[1], 0][[1], 0]Passed
control [[1, 1, 0, null, 0, null, 0, 0, 0, 1], 5][[None, 0], 1][[None, 0], 1]Passed
control [[0, 1, 0, 1, 0, null, 1, 0, 1, 1], 5][[0, 1], 3][[0, 1], 3]Passed
control [[0, 0, null, null], 4][[0], 0][[0], 0]Passed

SHA-256 / fcbbfd809ad540bf79a33609e919896ec5da30a172670c79f7f0c96a49d39771

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.

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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 2026-09-29T14:48:33.728757+00:00.

Case digest / a9837cc04e6e5e3a0e02ae7295f66c95c99716fb79cdafbd7f603da9a909e956