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FA-45931 / Bounded deques / Open access

Shrink decrements available capacity by pre-shrink occupancy · case 01

Shrink decrements available capacity by pre-shrink occupancy.

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

ROOT CAUSE

Free capacity is based on released entries as if they remained live.

THE FAILURE

Free capacity is based on released entries as if they remained live.

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

Case contract

Shrink an occupied logical deque to a smaller bound, retaining the newest suffix. Return retained values, evicted prefix, a linear backing allocation, and free capacity.

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):
    items, bound = x
    lost = max(0, len(items) - bound)
    evicted = items[:lost]
    kept = items[lost:]
    slots = kept + [None] * (bound - len(kept))
    free = bound - len(items)
    return [kept, evicted, slots, free]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('drop oldest pair', solve([[N,N+1,N+2,N+3],2]), [[N+2,N+3],[N,N+1],[N+2,N+3],0])
check('zero bound', solve([[N,N+1],0]), [[],[N,N+1],[],0])
check('spare capacity', solve([[N],3]), [[N],[],[N,None,None],2])
check('same bound', solve([[N,N+1],2]), [[N,N+1],[],[N,N+1],0])
check('empty', solve([[],2]), [[],[],[None,None],2])
check('drop one of three', solve([[N,N+1,N+2],2]), [[N+1,N+2],[N],[N+1,N+2],0])
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
drop oldest pair[[3, 4], [1, 2], [3, 4], -2][[3, 4], [1, 2], [3, 4], 0]Failed
zero bound[[], [1, 2], [], -2][[], [1, 2], [], 0]Failed
spare capacity[[1], [], [1, None, None], 2][[1], [], [1, None, None], 2]Passed
same bound[[1, 2], [], [1, 2], 0][[1, 2], [], [1, 2], 0]Passed
empty[[], [], [None, None], 2][[], [], [None, None], 2]Passed
drop one of three[[2, 3], [1], [2, 3], -1][[2, 3], [1], [2, 3], 0]Failed

SHA-256 / c29d27245695afbd9056b02fe6bd96da931dc84a6f3296d17cebb97aef2da2a9

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    items, bound = x
    lost = max(0, len(items) - bound)
    evicted = items[:lost]
    kept = items[lost:]
    slots = kept + [None] * (bound - len(kept))
    free = max(0, bound - len(items)) + lost
    return [kept, evicted, slots, free]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('drop oldest pair', solve([[N,N+1,N+2,N+3],2]), [[N+2,N+3],[N,N+1],[N+2,N+3],0])
check('zero bound', solve([[N,N+1],0]), [[],[N,N+1],[],0])
check('spare capacity', solve([[N],3]), [[N],[],[N,None,None],2])
check('same bound', solve([[N,N+1],2]), [[N,N+1],[],[N,N+1],0])
check('empty', solve([[],2]), [[],[],[None,None],2])
check('drop one of three', solve([[N,N+1,N+2],2]), [[N+1,N+2],[N],[N+1,N+2],0])
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
drop oldest pair[[3, 4], [1, 2], [3, 4], 2][[3, 4], [1, 2], [3, 4], 0]Failed
zero bound[[], [1, 2], [], 2][[], [1, 2], [], 0]Failed
spare capacity[[1], [], [1, None, None], 2][[1], [], [1, None, None], 2]Passed
same bound[[1, 2], [], [1, 2], 0][[1, 2], [], [1, 2], 0]Passed
empty[[], [], [None, None], 2][[], [], [None, None], 2]Passed
drop one of three[[2, 3], [1], [2, 3], 1][[2, 3], [1], [2, 3], 0]Failed

SHA-256 / b8f5b78c788caa475c898830117ae7e34a74abe7a4446a6fdb4b1ee1cd3eff51

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 2026-09-29T14:44:27.153197+00:00.

Case digest / 9bb6bef36c19512d7aebf2ddc979b6ef17f27e83172bf705645ee2f91ac2e706