FA-26491 / HTTP ranges / Open access

Cached fragments with different validators cannot be joined · case 01

Cached fragments with different validators cannot be joined.

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

ROOT CAUSE

The cache-revision-splice decision uses return "".join(p for tag,p in fragments).

VERIFIED REPAIR

Apply the bounded decision exactly: return "".join(p for tag,p in fragments) if len({tag for tag,p in fragments})<=1 else None

Unsuccessful approach: The partial repair uses return "".join(p for tag,p in fragments) if len({tag for tag,p in fragments if p})<=1 else None, which still violates the stated contract.

Case contract

Fragments are [strong-validator,payload] in byte order. Return their joined body when all validators agree, None otherwise; no fragments returns empty.

Why this case matters

Range responses combine representation identity, conditional requests, framing, and partial-object state.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(fragments):
    return "".join(p for tag,p in fragments)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-revision-splice fixture 0', solve([["a","x"*N],["b","y"]]), None)
check('cache-revision-splice fixture 1', solve([["a","x"],["b",""]]), None)
check('cache-revision-splice fixture 2', solve([["a","x"*N],["a","y"]]), "x"*N+"y")
check('cache-revision-splice fixture 3', solve([]), "")
check('cache-revision-splice fixture 4', solve([["a",""]]), "")
check('cache-revision-splice fixture 5', solve([["a","x"]]), "x")
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
cache-revision-splice fixture 0	`xy`	`None`	Failed
cache-revision-splice fixture 1	`x`	`None`	Failed
cache-revision-splice fixture 2	`xy`	`xy`	Passed
cache-revision-splice fixture 3			Passed
cache-revision-splice fixture 4			Passed
cache-revision-splice fixture 5	`x`	`x`	Passed

SHA-256 / 1660ce9a8ad1b9017e21969dcbf03bc04c56f214f8f7c0d57526272f1eaacf64

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(fragments):
    return "".join(p for tag,p in fragments) if len({tag for tag,p in fragments if p})<=1 else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-revision-splice fixture 0', solve([["a","x"*N],["b","y"]]), None)
check('cache-revision-splice fixture 1', solve([["a","x"],["b",""]]), None)
check('cache-revision-splice fixture 2', solve([["a","x"*N],["a","y"]]), "x"*N+"y")
check('cache-revision-splice fixture 3', solve([]), "")
check('cache-revision-splice fixture 4', solve([["a",""]]), "")
check('cache-revision-splice fixture 5', solve([["a","x"]]), "x")
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
cache-revision-splice fixture 0	`None`	`None`	Passed
cache-revision-splice fixture 1	`x`	`None`	Failed
cache-revision-splice fixture 2	`xy`	`xy`	Passed
cache-revision-splice fixture 3			Passed
cache-revision-splice fixture 4			Passed
cache-revision-splice fixture 5	`x`	`x`	Passed

SHA-256 / faf2099a520dbc222a38984cd3f4e55d768e5c5b2dc0b26483c21739d7576cfb

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(fragments):
    return "".join(p for tag,p in fragments) if len({tag for tag,p in fragments})<=1 else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-revision-splice fixture 0', solve([["a","x"*N],["b","y"]]), None)
check('cache-revision-splice fixture 1', solve([["a","x"],["b",""]]), None)
check('cache-revision-splice fixture 2', solve([["a","x"*N],["a","y"]]), "x"*N+"y")
check('cache-revision-splice fixture 3', solve([]), "")
check('cache-revision-splice fixture 4', solve([["a",""]]), "")
check('cache-revision-splice fixture 5', solve([["a","x"]]), "x")
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
cache-revision-splice fixture 0	`None`	`None`	Passed
cache-revision-splice fixture 1	`None`	`None`	Passed
cache-revision-splice fixture 2	`xy`	`xy`	Passed
cache-revision-splice fixture 3			Passed
cache-revision-splice fixture 4			Passed
cache-revision-splice fixture 5	`x`	`x`	Passed

SHA-256 / e7008226af38e70ab7f105d4bcc7cd99e9566f87c9c864823bdbcaa007a907da

Verification & scope

Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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 2026-09-29T14:41:16.448858+00:00.

Case digest / b592bedb901261268ede1ec1e463ec1e4f3a0771c34cf618418879da8d90b981