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FA-45096 / Data systems / Open access

Scatter uses update position instead of target address · case 01

Scatter uses update position instead of target address.

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

ROOT CAUSE

masked-scatter-update: Scatter uses update position instead of target address.

THE FAILURE

masked-scatter-update: Scatter uses update position instead of target address.

Unsuccessful approach: Always targeting lane zero also ignores the scatter address.

Case contract

Apply an ordered scatter update to a column using [target-index,value,is-valid,is-selected] records. Unselected writes do nothing; selected null writes clear validity. Repeated targets use the final selected write, and untouched lanes retain both payload visibility and validity.

Why this case matters

A bounded deterministic data engine model makes representation and changelog faults reproducible.

1 / The failure

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

N = 1
observations = []
def solve(d):
    try:
        values,valid,updates=d
        values=list(values); valid=list(valid)
        for target,value,known,selected in updates:
            if not selected: continue
            values[updates.index([target,value,known,selected])]=value
            valid[target]=known
        return [v if valid[i] else None for i,v in enumerate(values)]
    except (IndexError, KeyError, ValueError, StopIteration) as exc:
        return {"representation_error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('nonzero target', solve([[1, 2, 3], [True, True, True], [[2, 4, True, True]]]), [1, 2, 4])
    check('masked value', solve([[1, 2], [True, True], [[1, 3, True, False]]]), [1, 2])
    check('masked null', solve([[1, 2], [True, True], [[1, 3, False, False]]]), [1, 2])
    check('selected null', solve([[1, 2], [True, True], [[1, 3, False, True]]]), [1, None])
    check('resurrect null', solve([[1, 2], [True, False], [[1, 3, True, True]]]), [1, 3])
    check('repeated target', solve([[1, 2], [True, True], [[1, 3, True, True], [1, 4, True, True]]]), [1, 4])
    check('middle validity', solve([[1, 2, 3], [True, True, True], [[1, 4, False, True]]]), [1, None, 3])
    check('no writes', solve([[1, 2], [False, True], []]), [None, 2])
elif N == 2:
    check('nonzero target', solve([[2, 3, 4], [True, True, True], [[2, 5, True, True]]]), [2, 3, 5])
    check('masked value', solve([[2, 3], [True, True], [[1, 4, True, False]]]), [2, 3])
    check('masked null', solve([[2, 3], [True, True], [[1, 4, False, False]]]), [2, 3])
    check('selected null', solve([[2, 3], [True, True], [[1, 4, False, True]]]), [2, None])
    check('resurrect null', solve([[2, 3], [True, False], [[1, 4, True, True]]]), [2, 4])
    check('repeated target', solve([[2, 3], [True, True], [[1, 4, True, True], [1, 5, True, True]]]), [2, 5])
    check('middle validity', solve([[2, 3, 4], [True, True, True], [[1, 5, False, True]]]), [2, None, 4])
    check('no writes', solve([[2, 3], [False, True], []]), [None, 3])
elif N == 3:
    check('nonzero target', solve([[3, 4, 5], [True, True, True], [[2, 6, True, True]]]), [3, 4, 6])
    check('masked value', solve([[3, 4], [True, True], [[1, 5, True, False]]]), [3, 4])
    check('masked null', solve([[3, 4], [True, True], [[1, 5, False, False]]]), [3, 4])
    check('selected null', solve([[3, 4], [True, True], [[1, 5, False, True]]]), [3, None])
    check('resurrect null', solve([[3, 4], [True, False], [[1, 5, True, True]]]), [3, 5])
    check('repeated target', solve([[3, 4], [True, True], [[1, 5, True, True], [1, 6, True, True]]]), [3, 6])
    check('middle validity', solve([[3, 4, 5], [True, True, True], [[1, 6, False, True]]]), [3, None, 5])
    check('no writes', solve([[3, 4], [False, True], []]), [None, 4])
elif N == 4:
    check('nonzero target', solve([[4, 5, 6], [True, True, True], [[2, 7, True, True]]]), [4, 5, 7])
    check('masked value', solve([[4, 5], [True, True], [[1, 6, True, False]]]), [4, 5])
    check('masked null', solve([[4, 5], [True, True], [[1, 6, False, False]]]), [4, 5])
    check('selected null', solve([[4, 5], [True, True], [[1, 6, False, True]]]), [4, None])
    check('resurrect null', solve([[4, 5], [True, False], [[1, 6, True, True]]]), [4, 6])
    check('repeated target', solve([[4, 5], [True, True], [[1, 6, True, True], [1, 7, True, True]]]), [4, 7])
    check('middle validity', solve([[4, 5, 6], [True, True, True], [[1, 7, False, True]]]), [4, None, 6])
    check('no writes', solve([[4, 5], [False, True], []]), [None, 5])
elif N == 5:
    check('nonzero target', solve([[5, 6, 7], [True, True, True], [[2, 8, True, True]]]), [5, 6, 8])
    check('masked value', solve([[5, 6], [True, True], [[1, 7, True, False]]]), [5, 6])
    check('masked null', solve([[5, 6], [True, True], [[1, 7, False, False]]]), [5, 6])
    check('selected null', solve([[5, 6], [True, True], [[1, 7, False, True]]]), [5, None])
    check('resurrect null', solve([[5, 6], [True, False], [[1, 7, True, True]]]), [5, 7])
    check('repeated target', solve([[5, 6], [True, True], [[1, 7, True, True], [1, 8, True, True]]]), [5, 8])
    check('middle validity', solve([[5, 6, 7], [True, True, True], [[1, 8, False, True]]]), [5, None, 7])
    check('no writes', solve([[5, 6], [False, True], []]), [None, 6])
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
nonzero target[4, 2, 3][1, 2, 4]Failed
masked value[1, 2][1, 2]Passed
masked null[1, 2][1, 2]Passed
selected null[3, None][1, None]Failed
resurrect null[3, 2][1, 3]Failed
repeated target[3, 4][1, 4]Failed
middle validity[4, None, 3][1, None, 3]Failed
no writes[None, 2][None, 2]Passed

SHA-256 / 21cfb581913fe40bb09fad06fda1c6ac1d263ab0fc7b8eda5b8f3592222d9659

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(d):
    try:
        values,valid,updates=d
        values=list(values); valid=list(valid)
        for target,value,known,selected in updates:
            if not selected: continue
            values[0]=value
            valid[target]=known
        return [v if valid[i] else None for i,v in enumerate(values)]
    except (IndexError, KeyError, ValueError, StopIteration) as exc:
        return {"representation_error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('nonzero target', solve([[1, 2, 3], [True, True, True], [[2, 4, True, True]]]), [1, 2, 4])
    check('masked value', solve([[1, 2], [True, True], [[1, 3, True, False]]]), [1, 2])
    check('masked null', solve([[1, 2], [True, True], [[1, 3, False, False]]]), [1, 2])
    check('selected null', solve([[1, 2], [True, True], [[1, 3, False, True]]]), [1, None])
    check('resurrect null', solve([[1, 2], [True, False], [[1, 3, True, True]]]), [1, 3])
    check('repeated target', solve([[1, 2], [True, True], [[1, 3, True, True], [1, 4, True, True]]]), [1, 4])
    check('middle validity', solve([[1, 2, 3], [True, True, True], [[1, 4, False, True]]]), [1, None, 3])
    check('no writes', solve([[1, 2], [False, True], []]), [None, 2])
elif N == 2:
    check('nonzero target', solve([[2, 3, 4], [True, True, True], [[2, 5, True, True]]]), [2, 3, 5])
    check('masked value', solve([[2, 3], [True, True], [[1, 4, True, False]]]), [2, 3])
    check('masked null', solve([[2, 3], [True, True], [[1, 4, False, False]]]), [2, 3])
    check('selected null', solve([[2, 3], [True, True], [[1, 4, False, True]]]), [2, None])
    check('resurrect null', solve([[2, 3], [True, False], [[1, 4, True, True]]]), [2, 4])
    check('repeated target', solve([[2, 3], [True, True], [[1, 4, True, True], [1, 5, True, True]]]), [2, 5])
    check('middle validity', solve([[2, 3, 4], [True, True, True], [[1, 5, False, True]]]), [2, None, 4])
    check('no writes', solve([[2, 3], [False, True], []]), [None, 3])
elif N == 3:
    check('nonzero target', solve([[3, 4, 5], [True, True, True], [[2, 6, True, True]]]), [3, 4, 6])
    check('masked value', solve([[3, 4], [True, True], [[1, 5, True, False]]]), [3, 4])
    check('masked null', solve([[3, 4], [True, True], [[1, 5, False, False]]]), [3, 4])
    check('selected null', solve([[3, 4], [True, True], [[1, 5, False, True]]]), [3, None])
    check('resurrect null', solve([[3, 4], [True, False], [[1, 5, True, True]]]), [3, 5])
    check('repeated target', solve([[3, 4], [True, True], [[1, 5, True, True], [1, 6, True, True]]]), [3, 6])
    check('middle validity', solve([[3, 4, 5], [True, True, True], [[1, 6, False, True]]]), [3, None, 5])
    check('no writes', solve([[3, 4], [False, True], []]), [None, 4])
elif N == 4:
    check('nonzero target', solve([[4, 5, 6], [True, True, True], [[2, 7, True, True]]]), [4, 5, 7])
    check('masked value', solve([[4, 5], [True, True], [[1, 6, True, False]]]), [4, 5])
    check('masked null', solve([[4, 5], [True, True], [[1, 6, False, False]]]), [4, 5])
    check('selected null', solve([[4, 5], [True, True], [[1, 6, False, True]]]), [4, None])
    check('resurrect null', solve([[4, 5], [True, False], [[1, 6, True, True]]]), [4, 6])
    check('repeated target', solve([[4, 5], [True, True], [[1, 6, True, True], [1, 7, True, True]]]), [4, 7])
    check('middle validity', solve([[4, 5, 6], [True, True, True], [[1, 7, False, True]]]), [4, None, 6])
    check('no writes', solve([[4, 5], [False, True], []]), [None, 5])
elif N == 5:
    check('nonzero target', solve([[5, 6, 7], [True, True, True], [[2, 8, True, True]]]), [5, 6, 8])
    check('masked value', solve([[5, 6], [True, True], [[1, 7, True, False]]]), [5, 6])
    check('masked null', solve([[5, 6], [True, True], [[1, 7, False, False]]]), [5, 6])
    check('selected null', solve([[5, 6], [True, True], [[1, 7, False, True]]]), [5, None])
    check('resurrect null', solve([[5, 6], [True, False], [[1, 7, True, True]]]), [5, 7])
    check('repeated target', solve([[5, 6], [True, True], [[1, 7, True, True], [1, 8, True, True]]]), [5, 8])
    check('middle validity', solve([[5, 6, 7], [True, True, True], [[1, 8, False, True]]]), [5, None, 7])
    check('no writes', solve([[5, 6], [False, True], []]), [None, 6])
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
nonzero target[4, 2, 3][1, 2, 4]Failed
masked value[1, 2][1, 2]Passed
masked null[1, 2][1, 2]Passed
selected null[3, None][1, None]Failed
resurrect null[3, 2][1, 3]Failed
repeated target[4, 2][1, 4]Failed
middle validity[4, None, 3][1, None, 3]Failed
no writes[None, 2][None, 2]Passed

SHA-256 / 5b20f05806e7a337d7f656593e917d4e4cfee9271386762c57331de189600ce1

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

Offline stipulated semantics over valid small inputs; no performance, concurrency, or production-engine conformance claim. 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 2026-09-29T14:44:18.937174+00:00.

Case digest / 2051db0a407efd23cd26ef693ef1b4c09323b6d8adeaa05e63a431d9fd4c67c6