FA-10406 / Caching / Open access

An uncacheable oversized value flushes unrelated cache entries · case 01

An uncacheable oversized value flushes unrelated cache entries.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

An oversized candidate enters the eviction loop before its cacheability is checked.

THE FAILURE

An oversized candidate enters the eviction loop before its cacheability is checked.

Unsuccessful approach: Rejecting values equal to budget excludes a valid single-entry cache.

Case contract

Input weights and budget are nonnegative; existing total fits budget. If candidate weight exceeds budget, bypass without modifying entries; otherwise replace/promote then evict oldest until it fits.

Why this case matters

A deterministic cache state transformation. Inputs are copied or treated as immutable; no remote storage, real clock, or concurrent interleaving is simulated.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(entries, incoming, budget):
    out=[x for x in entries if x[0] != incoming[0]]+[incoming]
    while out and sum(x[1] for x in out)>budget:
        out.pop(0)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([['a', 2], ['b', 2]], ['c', 8], 5)), [['a', 2], ['b', 2]])
check('fixture 2', solve(*([['a', 2]], ['b', 5], 5)), [['b', 5]])
check('fixture 3', solve(*([], ['a', 0], 0)), [['a', 0]])
check('fixture 4', solve(*([['a', 2]], ['b', 1], 5)), [['a', 2], ['b', 1]])
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
fixture 1	`[]`	`[['a', 2], ['b', 2]]`	Failed
fixture 2	`[['b', 5]]`	`[['b', 5]]`	Passed
fixture 3	`[['a', 0]]`	`[['a', 0]]`	Passed
fixture 4	`[['a', 2], ['b', 1]]`	`[['a', 2], ['b', 1]]`	Passed

SHA-256 / e441c238d4b19cb790df27929ee9ae822c5e2d425de10a2af9f966cd1ec66750

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(entries, incoming, budget):
    if incoming[1]>=budget:
        return list(entries)
    out=[x for x in entries if x[0] != incoming[0]]+[incoming]
    while sum(x[1] for x in out)>budget:
        out.pop(0)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([['a', 2], ['b', 2]], ['c', 8], 5)), [['a', 2], ['b', 2]])
check('fixture 2', solve(*([['a', 2]], ['b', 5], 5)), [['b', 5]])
check('fixture 3', solve(*([], ['a', 0], 0)), [['a', 0]])
check('fixture 4', solve(*([['a', 2]], ['b', 1], 5)), [['a', 2], ['b', 1]])
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
fixture 1	`[['a', 2], ['b', 2]]`	`[['a', 2], ['b', 2]]`	Passed
fixture 2	`[['a', 2]]`	`[['b', 5]]`	Failed
fixture 3	`[]`	`[['a', 0]]`	Failed
fixture 4	`[['a', 2], ['b', 1]]`	`[['a', 2], ['b', 1]]`	Passed

SHA-256 / 4beaef92745a71bf4bc92d51aed9bdad4ebcbb10c07d7938c1e3fe47112324f2

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 4 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

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 2026-09-29T14:38:38.673024+00:00.

Case digest / cf6a93a67f72694585b4096a7806cda953ba97fd0f6a9b3f47fe3d2fc5088cc1