FA-7191 / Network routing / Open access

Policy route fallback occurs only after no policy match · case 01

Policy route fallback occurs only after no policy match.

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

ROOT CAUSE

The faulty implementation uses `decisions[0] if decisions else default` for the policy-route-fallback-occurs-only-after-no-policy-match decision.

VERIFIED REPAIR

Apply the explicit policy-route-fallback-occurs-only-after-no-policy-match contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `next((d for d in decisions if d not in ("continue","drop")),default)` and still violates a separate fixture.

Case contract

Given decisions, default, policy route fallback occurs only after no policy match. Return the protocol decision or transformed value; fields are validated and fixtures state boundary outcomes.

Why this case matters

This deterministic network routing model isolates the policy-route-fallback-occurs-only-after-no-policy-match 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(decisions, default):
    return decisions[0] if decisions else default
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['continue', 'route-a'], 'default'), 'route-a')", "check('fixture 2', solve(['drop', 'route-a'], 'default'), 'drop')", "check('fixture 3', solve(['continue'], 'default'), 'default')", "check('fixture 4', solve([], 'default'), 'default')"]
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	`drop`	`drop`	Passed
fixture 3	`continue`	`default`	Failed
fixture 4	`default`	`default`	Passed
fixture 1	`continue`	`route-a`	Failed

SHA-256 / 8ed8f860eb8642fb3852e366caab089e54ee5ea614c0596dd7bbe76da074d2a3

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(decisions, default):
    return next((d for d in decisions if d not in ("continue","drop")),default)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['continue', 'route-a'], 'default'), 'route-a')", "check('fixture 2', solve(['drop', 'route-a'], 'default'), 'drop')", "check('fixture 3', solve(['continue'], 'default'), 'default')", "check('fixture 4', solve([], 'default'), 'default')"]
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	`route-a`	`drop`	Failed
fixture 3	`default`	`default`	Passed
fixture 4	`default`	`default`	Passed
fixture 1	`route-a`	`route-a`	Passed

SHA-256 / 47681d5910a2d06e20d2989315e32ee1bc516dcf7f1d006cf4d48e2e690ff9e5

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(decisions, default):
    return next((d for d in decisions if d != "continue"),default)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['continue', 'route-a'], 'default'), 'route-a')", "check('fixture 2', solve(['drop', 'route-a'], 'default'), 'drop')", "check('fixture 3', solve(['continue'], 'default'), 'default')", "check('fixture 4', solve([], 'default'), 'default')"]
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	`drop`	`drop`	Passed
fixture 3	`default`	`default`	Passed
fixture 4	`default`	`default`	Passed
fixture 1	`route-a`	`route-a`	Passed

SHA-256 / 5c5d9c6ae40413fb8a756c25d5cdac724adf53b497849b35151354d2f235ce63

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 2026-09-29T14:38:09.201002+00:00.

Case digest / e899642dc6a40b86f845a851ac0ced673d8301ef193f6f2f90907346a54fbe2f