FA-10416 / Caching / Open access

Creating a record leaves its cached absence visible · case 01

Creating a record leaves its cached absence visible.

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

ROOT CAUSE

The write-through creation path does not replace prior negative cache state.

VERIFIED REPAIR

Preserve the cache-state invariant: Write-through creation stores the supplied value under key whether the cache held an old value, negative None, or no entry; unrelated entries are preserved.

Unsuccessful approach: Updating only a non-None hit skips both negative entries and newly created keys.

Case contract

Write-through creation stores the supplied value under key whether the cache held an old value, negative None, or no entry; unrelated entries are preserved.

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(cache, key, value):
    return dict(cache)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*({'a': None}, 'a', 'new')), {'a': 'new'})
check('fixture 2', solve(*({}, 'a', 0)), {'a': 0})
check('fixture 3', solve(*({'a': 'old', 'b': None}, 'a', 'new')), {'a': 'new', 'b': None})
check('fixture 4', solve(*({'a': False}, 'a', True)), {'a': True})
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': None}`	`{'a': 'new'}`	Failed
fixture 2	`{}`	`{'a': 0}`	Failed
fixture 3	`{'a': 'old', 'b': None}`	`{'a': 'new', 'b': None}`	Failed
fixture 4	`{'a': False}`	`{'a': True}`	Failed

SHA-256 / 6cfa06eac5adcba92bc580c06b2e2f6b254aa1e439196815a90af2b82a1857a0

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(cache, key, value):
    out=dict(cache)
    if out.get(key) is not None:
        out[key]=value
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*({'a': None}, 'a', 'new')), {'a': 'new'})
check('fixture 2', solve(*({}, 'a', 0)), {'a': 0})
check('fixture 3', solve(*({'a': 'old', 'b': None}, 'a', 'new')), {'a': 'new', 'b': None})
check('fixture 4', solve(*({'a': False}, 'a', True)), {'a': True})
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': None}`	`{'a': 'new'}`	Failed
fixture 2	`{}`	`{'a': 0}`	Failed
fixture 3	`{'a': 'new', 'b': None}`	`{'a': 'new', 'b': None}`	Passed
fixture 4	`{'a': True}`	`{'a': True}`	Passed

SHA-256 / 07b94a24d63766e809c335fc71a5761a28ea7b81109962cf35aecad99dd554fb

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(cache, key, value):
    out=dict(cache)
    out[key]=value
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*({'a': None}, 'a', 'new')), {'a': 'new'})
check('fixture 2', solve(*({}, 'a', 0)), {'a': 0})
check('fixture 3', solve(*({'a': 'old', 'b': None}, 'a', 'new')), {'a': 'new', 'b': None})
check('fixture 4', solve(*({'a': False}, 'a', True)), {'a': True})
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': 'new'}`	`{'a': 'new'}`	Passed
fixture 2	`{'a': 0}`	`{'a': 0}`	Passed
fixture 3	`{'a': 'new', 'b': None}`	`{'a': 'new', 'b': None}`	Passed
fixture 4	`{'a': True}`	`{'a': True}`	Passed

SHA-256 / a2dbde1738d5a6e03c771c057b5fd184e1966e6614667f3afb94fcde2969f215

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 2026-09-29T14:38:38.758048+00:00.

Case digest / a1d9136dd99033200b73d2d73a8e045e3f3d7d7a98e9e3d96d071037eb4530d6