FA-6976 / Proxy forwarding / Open access

Via loop detection matches hop identities not substrings · case 01

Via loop detection matches hop identities not substrings.

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

ROOT CAUSE

The faulty implementation uses `any(self_ in h for h in hops)` for the via-loop-detection-matches-hop-identities-not-substrings decision.

VERIFIED REPAIR

Apply the explicit via-loop-detection-matches-hop-identities-not-substrings contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `hops[-1] == self_ if hops else False` and still violates a separate fixture.

Case contract

Bounded offline decision model: via loop detection matches hop identities not substrings. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic proxy forwarding model isolates the via-loop-detection-matches-hop-identities-not-substrings 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(self_, hops):
    return any(self_ in h for h in hops)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('a', ['aa']), False)", "check('fixture 2', solve('a', ['a', 'b']), True)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('a', ['b', 'a']), True)"]
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	`True`	`True`	Passed
fixture 3	`False`	`False`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`True`	`False`	Failed

SHA-256 / af3a782eeb4650853805f90cd3bf4e6e313dc348fd67ea24c2c6458bf5b95069

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(self_, hops):
    return hops[-1] == self_ if hops else False
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('a', ['aa']), False)", "check('fixture 2', solve('a', ['a', 'b']), True)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('a', ['b', 'a']), True)"]
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	`False`	`True`	Failed
fixture 3	`False`	`False`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / af290f13738c0df67d7581817d73f53ed144015bb79e210bb1a5ee4c25626fe0

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(self_, hops):
    return self_ in hops
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('a', ['aa']), False)", "check('fixture 2', solve('a', ['a', 'b']), True)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('a', ['b', 'a']), True)"]
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	`True`	`True`	Passed
fixture 3	`False`	`False`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`False`	Passed

SHA-256 / a47ebbfff05f4994da19f4459db26c673eafa1d2bbb5240fb0ff31d87b916b13

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 2026-09-29T14:38:07.167391+00:00.

Case digest / 4eaf6196f7158347b7f6306b854feabecd9e016436eb943690543d9a2cd09b07