FA-7201 / Network routing / Open access

Blackhole route terminates lookup instead of falling back · case 01

Blackhole route terminates lookup instead of falling back.

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

ROOT CAUSE

The faulty implementation uses `match if match is not None else fallback` for the blackhole-route-terminates-lookup-instead-of-falling-back decision.

VERIFIED REPAIR

Apply the explicit blackhole-route-terminates-lookup-instead-of-falling-back contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `None if match is None else match` and still violates a separate fixture.

Case contract

Bounded offline decision model: blackhole route terminates lookup instead of falling back. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic network routing model isolates the blackhole-route-terminates-lookup-instead-of-falling-back policy at a network component boundary.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(match, blackhole, fallback):
    return match if match is not None else fallback
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(None, True, 'default'), None)", "check('fixture 2', solve('a', False, 'default'), 'a')", "check('fixture 3', solve(None, False, 'default'), 'default')", "check('fixture 4', solve(None, False, None), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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 2	`a`	`a`	Passed
fixture 3	`default`	`default`	Passed
fixture 4	`None`	`None`	Passed
fixture 1	`default`	`None`	Failed

SHA-256 / f83981aa4ee9307cbfa497df6e10a26f0ef91e8e75a949ddd8bec0178272e538

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(match, blackhole, fallback):
    return None if match is None else match
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(None, True, 'default'), None)", "check('fixture 2', solve('a', False, 'default'), 'a')", "check('fixture 3', solve(None, False, 'default'), 'default')", "check('fixture 4', solve(None, False, None), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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 2	`a`	`a`	Passed
fixture 3	`None`	`default`	Failed
fixture 4	`None`	`None`	Passed
fixture 1	`None`	`None`	Passed

SHA-256 / 0968b86c87d5927429d1babceb7fb5a8661f8d12c53499f132fa6dd44f09f63c

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(match, blackhole, fallback):
    return None if blackhole else (match if match is not None else fallback)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(None, True, 'default'), None)", "check('fixture 2', solve('a', False, 'default'), 'a')", "check('fixture 3', solve(None, False, 'default'), 'default')", "check('fixture 4', solve(None, False, None), None)"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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 2	`a`	`a`	Passed
fixture 3	`default`	`default`	Passed
fixture 4	`None`	`None`	Passed
fixture 1	`None`	`None`	Passed

SHA-256 / 71eb15d23e5c24858c65e1c87e33f4a39b16c5db624654da59251b329be0a15e

Verification & scope

Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. 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 2026-09-29T14:38:09.240847+00:00.

Case digest / 298b963975a16136a506461f9eb9db8721be1e68573fa015d6a7cdc9a5b53672