FA-10491 / Caching / Open access

A not-modified revalidation response replaces the cached body with an empty payload · case 01

A not-modified revalidation response replaces the cached body with an empty payload.

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

ROOT CAUSE

Refresh uses a validation-only response payload as the new representation body.

THE FAILURE

Refresh uses a validation-only response payload as the new representation body.

Unsuccessful approach: Always retaining the old body discards a genuinely modified representation.

Case contract

Entry is [body,validated-at]. Response is [modified-or-not-modified,body-or-None,validated-at]. Preserve old body only for not-modified; always update validation time.

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(entry, response):
    return [response[1],response[2]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(['body', 1], ['not-modified', None, 2])), ['body', 2])
check('fixture 2', solve(*(['old', 1], ['modified', 'new', 2])), ['new', 2])
check('fixture 3', solve(*(['', 1], ['not-modified', None, 3])), ['', 3])
check('fixture 4', solve(*(['old', 1], ['modified', '', 4])), ['', 4])
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	`[None, 2]`	`['body', 2]`	Failed
fixture 2	`['new', 2]`	`['new', 2]`	Passed
fixture 3	`[None, 3]`	`['', 3]`	Failed
fixture 4	`['', 4]`	`['', 4]`	Passed

SHA-256 / 8d1ef70822856056323bcb3174cc6aef6389878c60a983c68afd85e10c20fab5

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(entry, response):
    return [entry[0],response[2]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(['body', 1], ['not-modified', None, 2])), ['body', 2])
check('fixture 2', solve(*(['old', 1], ['modified', 'new', 2])), ['new', 2])
check('fixture 3', solve(*(['', 1], ['not-modified', None, 3])), ['', 3])
check('fixture 4', solve(*(['old', 1], ['modified', '', 4])), ['', 4])
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	`['body', 2]`	`['body', 2]`	Passed
fixture 2	`['old', 2]`	`['new', 2]`	Failed
fixture 3	`['', 3]`	`['', 3]`	Passed
fixture 4	`['old', 4]`	`['', 4]`	Failed

SHA-256 / 2f04bd760bad751e22440981db601c22f446583657e10e3ade3fe96d0e0769a2

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 2026-09-29T14:38:39.419388+00:00.

Case digest / 3fec02ceac789ba7dd0ee79983de82873d925a580bec695efb7dae51a7dce772