FA-006 / Caching / Open access

An expired cache entry survives its deadline · case 01

An entry remains visible at precisely its expiration instant.

Verified by executionVariant 1 · 3 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The expiration comparison treats the deadline as an inclusive valid instant.

VERIFIED REPAIR

Treat the valid interval as insertion time inclusive and expiration time exclusive.

Unsuccessful approach: Subtracting one tick expires values before their actual deadline.

Case contract

Treat the valid interval as insertion time inclusive and expiration time exclusive.

Why this case matters

A compact reasoning and repair task with executable evidence.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(value, now, expires):
    return value if now <= expires else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('exact expiration', solve('record', N, N), None)
check('last valid half tick', solve('record', N-0.5, N), 'record')
check('past deadline', solve('record', N+1, N), None)
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
exact expiration	`record`	`None`	Failed
last valid half tick	`record`	`record`	Passed
past deadline	`None`	`None`	Passed

SHA-256 / f913cbdf9831d939d8dc0c0506d685ddb6628c67bb964c788fa18ac6bd2f70dd

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(value, now, expires):
    return value if now < expires - 1 else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('exact expiration', solve('record', N, N), None)
check('last valid half tick', solve('record', N-0.5, N), 'record')
check('past deadline', solve('record', N+1, N), None)
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
exact expiration	`None`	`None`	Passed
last valid half tick	`None`	`record`	Failed
past deadline	`None`	`None`	Passed

SHA-256 / 041030b16cdb07eb54d70503580e94633ea6ab5c956a68b63252a8f17c20377c

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(value, now, expires):
    return value if now < expires else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('exact expiration', solve('record', N, N), None)
check('last valid half tick', solve('record', N-0.5, N), 'record')
check('past deadline', solve('record', N+1, N), None)
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
exact expiration	`None`	`None`	Passed
last valid half tick	`record`	`record`	Passed
past deadline	`None`	`None`	Passed

SHA-256 / 32628d76a52605e8ff3d5b61888981c4953bc5e4383a5f21cfe1911e8337de30

Verification & scope

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 2026-09-29T14:36:49.844634+00:00.

Case digest / 2945a1c4c96085530fcadb1a4d493c4c79a2df79c99c40d429dc8b71c13bd947