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FA-47126 / Bounded deques / Open access

Deque compaction retains old arena length as logical length · case 01

Deque compaction retains old arena length as logical length.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Deque compaction retains old arena length as logical length.

THE FAILURE

Deque compaction retains old arena length as logical length.

Unsuccessful approach: The partial repair still applies the incorrect transition to an admitted boundary or multi-element case.

Case contract

Compact a deque node arena using its logical live-ID chain. Preserve chain order, remap nullable stable cursors, return old-to-new relocation map, advance epoch, and identify reclaimed old storage IDs.

Why this case matters

Controlled bounded deque implementation model with explicit storage and lifecycle observations.

1 / The failure

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

N = 1
observations = []
def solve(x):
    records,order,cursors,epoch=x
    mapping={old:new for new,old in enumerate(order)}
    storage=[records[old] for old in order]
    chain=list(range(len(order)))
    updated=[mapping.get(c) if c is not None else None for c in cursors]
    version=epoch+1
    freed=sorted(set(range(len(records)))-set(order))
    count=len(records)
    return [storage,chain,updated,mapping,version,freed,count]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,None,N+1,N+2],[3,0,2],[0,3,None],2]), {1: [[3, 1, 2], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 2: [[4, 2, 3], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 3: [[5, 3, 4], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 4: [[6, 4, 5], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 5: [[7, 5, 6], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3]}[N])
check('1', solve([[None,N,None],[1],[1,None],0]), {1: [[1], [0], [0, None], {1: 0}, 1, [0, 2], 1], 2: [[2], [0], [0, None], {1: 0}, 1, [0, 2], 1], 3: [[3], [0], [0, None], {1: 0}, 1, [0, 2], 1], 4: [[4], [0], [0, None], {1: 0}, 1, [0, 2], 1], 5: [[5], [0], [0, None], {1: 0}, 1, [0, 2], 1]}[N])
check('2', solve([[N,N+1,N+2],[2,1,0],[0,1,2],4]), {1: [[3, 2, 1], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 2: [[4, 3, 2], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 3: [[5, 4, 3], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 4: [[6, 5, 4], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 5: [[7, 6, 5], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3]}[N])
check('3', solve([[],[],[None],1]), {1: [[], [], [None], {}, 2, [], 0], 2: [[], [], [None], {}, 2, [], 0], 3: [[], [], [None], {}, 2, [], 0], 4: [[], [], [None], {}, 2, [], 0], 5: [[], [], [None], {}, 2, [], 0]}[N])
check('4', solve([[N,N+1],[0,1],[],3]), {1: [[1, 2], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 2: [[2, 3], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 3: [[3, 4], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 4: [[4, 5], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 5: [[5, 6], [0, 1], [], {0: 0, 1: 1}, 4, [], 2]}[N])
check('5', solve([[None,N,None,N+1,None],[3,1],[3,1,None],5]), {1: [[2, 1], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 2: [[3, 2], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 3: [[4, 3], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 4: [[5, 4], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 5: [[6, 5], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2]}[N])
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
0[[3, 1, 2], [0, 1, 2], [1, 0, None], {'0': 1, '2': 2, '3': 0}, 3, [1], 4][[3, 1, 2], [0, 1, 2], [1, 0, None], {'0': 1, '2': 2, '3': 0}, 3, [1], 3]Failed
1[[1], [0], [0, None], {'1': 0}, 1, [0, 2], 3][[1], [0], [0, None], {'1': 0}, 1, [0, 2], 1]Failed
2[[3, 2, 1], [0, 1, 2], [2, 1, 0], {'0': 2, '1': 1, '2': 0}, 5, [], 3][[3, 2, 1], [0, 1, 2], [2, 1, 0], {'0': 2, '1': 1, '2': 0}, 5, [], 3]Passed
3[[], [], [None], {}, 2, [], 0][[], [], [None], {}, 2, [], 0]Passed
4[[1, 2], [0, 1], [], {'0': 0, '1': 1}, 4, [], 2][[1, 2], [0, 1], [], {'0': 0, '1': 1}, 4, [], 2]Passed
5[[2, 1], [0, 1], [0, 1, None], {'1': 1, '3': 0}, 6, [0, 2, 4], 5][[2, 1], [0, 1], [0, 1, None], {'1': 1, '3': 0}, 6, [0, 2, 4], 2]Failed

SHA-256 / 4be71f95166eef64c334182700ab64b27b156d02bcde5e60dadfd9e2fc533a1e

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    records,order,cursors,epoch=x
    mapping={old:new for new,old in enumerate(order)}
    storage=[records[old] for old in order]
    chain=list(range(len(order)))
    updated=[mapping.get(c) if c is not None else None for c in cursors]
    version=epoch+1
    freed=sorted(set(range(len(records)))-set(order))
    count=len(order) if not order else len(records)
    return [storage,chain,updated,mapping,version,freed,count]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,None,N+1,N+2],[3,0,2],[0,3,None],2]), {1: [[3, 1, 2], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 2: [[4, 2, 3], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 3: [[5, 3, 4], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 4: [[6, 4, 5], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3], 5: [[7, 5, 6], [0, 1, 2], [1, 0, None], {3: 0, 0: 1, 2: 2}, 3, [1], 3]}[N])
check('1', solve([[None,N,None],[1],[1,None],0]), {1: [[1], [0], [0, None], {1: 0}, 1, [0, 2], 1], 2: [[2], [0], [0, None], {1: 0}, 1, [0, 2], 1], 3: [[3], [0], [0, None], {1: 0}, 1, [0, 2], 1], 4: [[4], [0], [0, None], {1: 0}, 1, [0, 2], 1], 5: [[5], [0], [0, None], {1: 0}, 1, [0, 2], 1]}[N])
check('2', solve([[N,N+1,N+2],[2,1,0],[0,1,2],4]), {1: [[3, 2, 1], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 2: [[4, 3, 2], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 3: [[5, 4, 3], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 4: [[6, 5, 4], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3], 5: [[7, 6, 5], [0, 1, 2], [2, 1, 0], {2: 0, 1: 1, 0: 2}, 5, [], 3]}[N])
check('3', solve([[],[],[None],1]), {1: [[], [], [None], {}, 2, [], 0], 2: [[], [], [None], {}, 2, [], 0], 3: [[], [], [None], {}, 2, [], 0], 4: [[], [], [None], {}, 2, [], 0], 5: [[], [], [None], {}, 2, [], 0]}[N])
check('4', solve([[N,N+1],[0,1],[],3]), {1: [[1, 2], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 2: [[2, 3], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 3: [[3, 4], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 4: [[4, 5], [0, 1], [], {0: 0, 1: 1}, 4, [], 2], 5: [[5, 6], [0, 1], [], {0: 0, 1: 1}, 4, [], 2]}[N])
check('5', solve([[None,N,None,N+1,None],[3,1],[3,1,None],5]), {1: [[2, 1], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 2: [[3, 2], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 3: [[4, 3], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 4: [[5, 4], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2], 5: [[6, 5], [0, 1], [0, 1, None], {3: 0, 1: 1}, 6, [0, 2, 4], 2]}[N])
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
0[[3, 1, 2], [0, 1, 2], [1, 0, None], {'0': 1, '2': 2, '3': 0}, 3, [1], 4][[3, 1, 2], [0, 1, 2], [1, 0, None], {'0': 1, '2': 2, '3': 0}, 3, [1], 3]Failed
1[[1], [0], [0, None], {'1': 0}, 1, [0, 2], 3][[1], [0], [0, None], {'1': 0}, 1, [0, 2], 1]Failed
2[[3, 2, 1], [0, 1, 2], [2, 1, 0], {'0': 2, '1': 1, '2': 0}, 5, [], 3][[3, 2, 1], [0, 1, 2], [2, 1, 0], {'0': 2, '1': 1, '2': 0}, 5, [], 3]Passed
3[[], [], [None], {}, 2, [], 0][[], [], [None], {}, 2, [], 0]Passed
4[[1, 2], [0, 1], [], {'0': 0, '1': 1}, 4, [], 2][[1, 2], [0, 1], [], {'0': 0, '1': 1}, 4, [], 2]Passed
5[[2, 1], [0, 1], [0, 1, None], {'1': 1, '3': 0}, 6, [0, 2, 4], 5][[2, 1], [0, 1], [0, 1, None], {'1': 1, '3': 0}, 6, [0, 2, 4], 2]Failed

SHA-256 / 4b6c4f0a78b36c3d29d1156931963a11bb2b8b1475fc54bd847384adb5c89d55

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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Verification & scope

Offline finite deterministic model; no claim of production implementation or concurrent memory-model conformance. 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 2026-09-29T14:44:38.467666+00:00.

Case digest / ccf3be9c806167a3d5de9406bf114e596594c3028ee7d66045a3f718e920abbd