FA-12201 / Navigation route constraints / Open access

A destination-only road becomes a through-road shortcut · case 01

A destination-only road becomes a through-road shortcut in the controlled route-policy fixture.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Destination access is interpreted as universal permission.

VERIFIED REPAIR

Permit a destination-only segment when either trip endpoint belongs to its zone.

Unsuccessful approach: Requiring every trip to end locally incorrectly rejects trips that start inside the restricted zone.

Case contract

For this zone model public roads always permit travel, closed roads never do, and destination roads require origin or destination in the supplied zone.

Why this case matters

Navigation policies depend on road context that a shortest-path cost alone does not encode.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(access, zone, origin, destination):
    return access != 'closed'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
z = [N,N+1]
check('through traffic denied', solve('destination',z,N+9,N+10), False)
check('local arrival', solve('destination',z,N+9,N), True)
check('local departure', solve('destination',z,N,N+9), True)
check('internal trip', solve('destination',z,N,N+1), True)
check('public road', solve('public',z,N+9,N+10), True)
check('closed overrides local', solve('closed',z,N,N), False)
check('empty zone', solve('destination',[],N,N), False)
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
through traffic denied	`True`	`False`	Failed
local arrival	`True`	`True`	Passed
local departure	`True`	`True`	Passed
internal trip	`True`	`True`	Passed
public road	`True`	`True`	Passed
closed overrides local	`False`	`False`	Passed
empty zone	`True`	`False`	Failed

SHA-256 / 451009bc09db9b7f4cc7f34e0e43732b612c19cabfeeace5619f3b26d7942c2a

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(access, zone, origin, destination):
    return access == 'public' or (access == 'destination' and destination in zone)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
z = [N,N+1]
check('through traffic denied', solve('destination',z,N+9,N+10), False)
check('local arrival', solve('destination',z,N+9,N), True)
check('local departure', solve('destination',z,N,N+9), True)
check('internal trip', solve('destination',z,N,N+1), True)
check('public road', solve('public',z,N+9,N+10), True)
check('closed overrides local', solve('closed',z,N,N), False)
check('empty zone', solve('destination',[],N,N), False)
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
through traffic denied	`False`	`False`	Passed
local arrival	`True`	`True`	Passed
local departure	`False`	`True`	Failed
internal trip	`True`	`True`	Passed
public road	`True`	`True`	Passed
closed overrides local	`False`	`False`	Passed
empty zone	`False`	`False`	Passed

SHA-256 / 8afa1d4ed1c08a3415e3d6301fc2ef233b8fd8770e78eedda0130279c15ae7bd

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(access, zone, origin, destination):
    return access == 'public' or (access == 'destination' and (origin in zone or destination in zone))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
z = [N,N+1]
check('through traffic denied', solve('destination',z,N+9,N+10), False)
check('local arrival', solve('destination',z,N+9,N), True)
check('local departure', solve('destination',z,N,N+9), True)
check('internal trip', solve('destination',z,N,N+1), True)
check('public road', solve('public',z,N+9,N+10), True)
check('closed overrides local', solve('closed',z,N,N), False)
check('empty zone', solve('destination',[],N,N), False)
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
through traffic denied	`False`	`False`	Passed
local arrival	`True`	`True`	Passed
local departure	`True`	`True`	Passed
internal trip	`True`	`True`	Passed
public road	`True`	`True`	Passed
closed overrides local	`False`	`False`	Passed
empty zone	`False`	`False`	Passed

SHA-256 / 0e8c5b7644d05b7cbf4e10ae6cef736d1102f988300350197e37583cc6d2a35e

Verification & scope

Simplified deterministic offline policy model; not a production router or authoritative road guidance. 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 2026-09-29T14:38:54.795605+00:00.

Case digest / 05e4a8b4ee782ea687e682bbca13a36f1077391a6e21f2f46ed13e59cd8d1c5b