FA-44511 / Data systems / Open access
Dense union decoding exposes a null child payload · case 01
Dense union decoding exposes a null child payload.
ROOT CAUSE
dense-union-gather: Dense union decoding exposes a null child payload.
THE FAILURE
dense-union-gather: Dense union decoding exposes a null child payload.
Unsuccessful approach: Whole-buffer validity hides unrelated present child lanes.
Case contract
Decode a dense tagged union. Tags select named child buffers through a tag map; offsets address those buffers independently of output position. Parent and selected child validity both apply. Emit [child-name,value] for valid parents, None for null parents.
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:
tags,offsets,names,children,valid,parent,selection=d
out=[]
for row in selection:
tag=tags[row]
name=names[str(tag)]
offset=offsets[row]
value=children[name][offset]
out.append([name,value] if parent[row] else None)
return out
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('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [1, 2, 3], 'b': [4, 5, 6]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 1], ['a', 2], ['b', 4]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [1, 2]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 2]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [True], [0, 0]]), [['a', 1], ['a', 1]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [1, 2], 'b': [3, 4]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 4]])
elif N == 2:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [2, 3, 4], 'b': [5, 6, 7]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 2], ['a', 3], ['b', 5]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [2, 3]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 3]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [True], [0, 0]]), [['a', 2], ['a', 2]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [2, 3], 'b': [4, 5]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 5]])
elif N == 3:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [3, 4, 5], 'b': [6, 7, 8]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 3], ['a', 4], ['b', 6]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [3, 4]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 4]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [True], [0, 0]]), [['a', 3], ['a', 3]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [3, 4], 'b': [5, 6]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 6]])
elif N == 4:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [4, 5, 6], 'b': [7, 8, 9]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 4], ['a', 5], ['b', 7]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [4, 5]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 5]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [True], [0, 0]]), [['a', 4], ['a', 4]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [4, 5], 'b': [6, 7]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 7]])
elif N == 5:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [5, 6, 7], 'b': [8, 9, 10]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 5], ['a', 6], ['b', 8]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [5, 6]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 6]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [True], [0, 0]]), [['a', 5], ['a', 5]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [5, 6], 'b': [7, 8]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 8]])
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| mixed tags | [['a', 1], ['a', 2], ['b', 4]] | [['a', 1], ['a', 2], ['b', 4]] | Passed |
| child null | [['a', 1], ['a', 2]] | [['a', None], ['a', 2]] | Failed |
| parent null | [None] | [None] | Passed |
| repeat row | [['a', 1], ['a', 1]] | [['a', 1], ['a', 1]] | Passed |
| empty selection | [] | [] | Passed |
| second tag | [['b', 4]] | [['b', 4]] | Passed |
SHA-256 / db36eb8d9352188e6c6bc853d759417f3def828b65433a81ccd1c594444ea7ed
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(d):
try:
tags,offsets,names,children,valid,parent,selection=d
out=[]
for row in selection:
tag=tags[row]
name=names[str(tag)]
offset=offsets[row]
value=children[name][offset] if all(valid[name]) else None
out.append([name,value] if parent[row] else None)
return out
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('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [1, 2, 3], 'b': [4, 5, 6]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 1], ['a', 2], ['b', 4]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [1, 2]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 2]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [True], [0, 0]]), [['a', 1], ['a', 1]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [1]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [1, 2], 'b': [3, 4]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 4]])
elif N == 2:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [2, 3, 4], 'b': [5, 6, 7]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 2], ['a', 3], ['b', 5]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [2, 3]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 3]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [True], [0, 0]]), [['a', 2], ['a', 2]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [2]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [2, 3], 'b': [4, 5]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 5]])
elif N == 3:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [3, 4, 5], 'b': [6, 7, 8]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 3], ['a', 4], ['b', 6]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [3, 4]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 4]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [True], [0, 0]]), [['a', 3], ['a', 3]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [3]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [3, 4], 'b': [5, 6]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 6]])
elif N == 4:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [4, 5, 6], 'b': [7, 8, 9]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 4], ['a', 5], ['b', 7]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [4, 5]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 5]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [True], [0, 0]]), [['a', 4], ['a', 4]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [4]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [4, 5], 'b': [6, 7]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 7]])
elif N == 5:
check('mixed tags', solve([[7, 9, 7], [1, 0, 0], {'7': 'a', '9': 'b'}, {'a': [5, 6, 7], 'b': [8, 9, 10]}, {'a': [True, True, True], 'b': [True, True, True]}, [True, True, True], [2, 0, 1]]), [['a', 5], ['a', 6], ['b', 8]])
check('child null', solve([[7, 7], [0, 1], {'7': 'a'}, {'a': [5, 6]}, {'a': [False, True]}, [True, True], [0, 1]]), [['a', None], ['a', 6]])
check('parent null', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [False], [0]]), [None])
check('repeat row', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [True], [0, 0]]), [['a', 5], ['a', 5]])
check('empty selection', solve([[7], [0], {'7': 'a'}, {'a': [5]}, {'a': [True]}, [True], []]), [])
check('second tag', solve([[9], [1], {'7': 'a', '9': 'b'}, {'a': [5, 6], 'b': [7, 8]}, {'a': [True, True], 'b': [True, True]}, [True], [0]]), [['b', 8]])
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| mixed tags | [['a', 1], ['a', 2], ['b', 4]] | [['a', 1], ['a', 2], ['b', 4]] | Passed |
| child null | [['a', None], ['a', None]] | [['a', None], ['a', 2]] | Failed |
| parent null | [None] | [None] | Passed |
| repeat row | [['a', 1], ['a', 1]] | [['a', 1], ['a', 1]] | Passed |
| empty selection | [] | [] | Passed |
| second tag | [['b', 4]] | [['b', 4]] | Passed |
SHA-256 / 15b8cff71d4d54fb1b9c1218f10d2886024afbe3d0cf92d0886d415eefd92a4f
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 6 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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Sign in to the archive ↗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 2026-09-29T14:44:13.047233+00:00.
Case digest / 831cee2905e7a5576a06ade54e8926194b39b4f37e6385855c7556efc8f544f7