FA-45886 / Bounded deques / Open access

Consume flags a boundary-touch as a split memory region · case 01

Consume flags a boundary-touch as a split memory region.

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

ROOT CAUSE

An end-exclusive interval touching the boundary is mistaken for crossing it.

THE FAILURE

An end-exclusive interval touching the boundary is mistaken for crossing it.

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

Case contract

Consume min(requested,size) slots from a ring. Report new head, count, cleared physical slots, and whether its occupied arc crossed the physical boundary.

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):
    cap, head, size, requested = x
    count = min(requested, size)
    cleared = [(head + i) % cap for i in range(count)]
    new_head = (head + count) % cap
    remaining = size - count
    crossed = head + count >= cap
    return [new_head, remaining, cleared, crossed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('wrap consume', solve([N+5,N+4,4,3]), [2,1,[N+4,0,1],True])
check('oversized consume', solve([N+5,1,2,4]), [3,0,[1,2],False])
check('empty', solve([N+5,2,0,4]), [2,0,[],False])
check('zero consume', solve([N+5,2,3,0]), [2,3,[],False])
check('exact boundary', solve([N+5,N+3,2,2]), [0,0,[N+3,N+4],False])
check('single retained', solve([N+5,1,3,2]), [3,1,[1,2],False])
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
wrap consume	`[2, 1, [5, 0, 1], True]`	`[2, 1, [5, 0, 1], True]`	Passed
oversized consume	`[3, 0, [1, 2], False]`	`[3, 0, [1, 2], False]`	Passed
empty	`[2, 0, [], False]`	`[2, 0, [], False]`	Passed
zero consume	`[2, 3, [], False]`	`[2, 3, [], False]`	Passed
exact boundary	`[0, 0, [4, 5], True]`	`[0, 0, [4, 5], False]`	Failed
single retained	`[3, 1, [1, 2], False]`	`[3, 1, [1, 2], False]`	Passed

SHA-256 / 03dae7593aed420b86f8627e512497250a011be38cd17f0e36a238510c1cf9d5

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    cap, head, size, requested = x
    count = min(requested, size)
    cleared = [(head + i) % cap for i in range(count)]
    new_head = (head + count) % cap
    remaining = size - count
    crossed = count > 0 and head + count >= cap
    return [new_head, remaining, cleared, crossed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('wrap consume', solve([N+5,N+4,4,3]), [2,1,[N+4,0,1],True])
check('oversized consume', solve([N+5,1,2,4]), [3,0,[1,2],False])
check('empty', solve([N+5,2,0,4]), [2,0,[],False])
check('zero consume', solve([N+5,2,3,0]), [2,3,[],False])
check('exact boundary', solve([N+5,N+3,2,2]), [0,0,[N+3,N+4],False])
check('single retained', solve([N+5,1,3,2]), [3,1,[1,2],False])
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
wrap consume	`[2, 1, [5, 0, 1], True]`	`[2, 1, [5, 0, 1], True]`	Passed
oversized consume	`[3, 0, [1, 2], False]`	`[3, 0, [1, 2], False]`	Passed
empty	`[2, 0, [], False]`	`[2, 0, [], False]`	Passed
zero consume	`[2, 3, [], False]`	`[2, 3, [], False]`	Passed
exact boundary	`[0, 0, [4, 5], True]`	`[0, 0, [4, 5], False]`	Failed
single retained	`[3, 1, [1, 2], False]`	`[3, 1, [1, 2], False]`	Passed

SHA-256 / 6d945225b4d39b042b3cfc997fecf6bbdd04d82ca9f0bc55c0cebfbecca07ecb

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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:44:26.745919+00:00.

Case digest / 5f57658e984645814a928fab5011c5e9ea68a81b836c3ea73ca1efcc2ce62101