FA-4736 / Scoped mappings / Open access

Chainmap parents drops exactly one scope · case 01

The operation returns a result or retained state that violates this contract: The parents view removes only the current first scope and retains remaining scope boundaries; an empty parent chain exposes one empty map.

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

ROOT CAUSE

The current scope remains in the parents view.

VERIFIED REPAIR

The parents view removes only the current first scope and retains remaining scope boundaries; an empty parent chain exposes one empty map.

Unsuccessful approach: Flattening all bindings loses both parent-only membership and scope boundaries.

Case contract

The parents view removes only the current first scope and retains remaining scope boundaries; an empty parent chain exposes one empty map. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return x
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('two scopes', solve([{'a': 1}, {'a': 2}]), [{'a': 2}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('one empty scope', solve([{}]), [{}])
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
two scopes	`[{'a': 1}, {'a': 2}]`	`[{'a': 2}]`	Failed
three scopes	`[{'a': 1}, {'b': 2}, {'c': 3}]`	`[{'b': 2}, {'c': 3}]`	Failed
one scope	`[{'a': 1}]`	`[{}]`	Failed
one empty scope	`[{}]`	`[{}]`	Passed

SHA-256 / f56dff541d748a9d94088dff63d2889b23d2aac7f1a5ffd8125f572bf3411320

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return [dict(ChainMap(*x))]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('two scopes', solve([{'a': 1}, {'a': 2}]), [{'a': 2}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('one empty scope', solve([{}]), [{}])
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
two scopes	`[{'a': 1}]`	`[{'a': 2}]`	Failed
three scopes	`[{'a': 1, 'b': 2, 'c': 3}]`	`[{'b': 2}, {'c': 3}]`	Failed
one scope	`[{'a': 1}]`	`[{}]`	Failed
one empty scope	`[{}]`	`[{}]`	Passed

SHA-256 / 6789e006983d01774e7c4c3d5982a3dba2df02d86fd3d2b5c52bafde6007cbcc

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return ChainMap(*x).parents.maps
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('two scopes', solve([{'a': 1}, {'a': 2}]), [{'a': 2}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('one empty scope', solve([{}]), [{}])
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
two scopes	`[{'a': 2}]`	`[{'a': 2}]`	Passed
three scopes	`[{'b': 2}, {'c': 3}]`	`[{'b': 2}, {'c': 3}]`	Passed
one scope	`[{}]`	`[{}]`	Passed
one empty scope	`[{}]`	`[{}]`	Passed

SHA-256 / cd3bdfc2f8f89cbb60e91255195afcd49cab3f6d9adb153d51c6170498b25bdb

Verification & scope

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 2026-09-29T14:37:42.187593+00:00.

Case digest / 22ebd34fd5f4f5753357aa7550678bd292397bd917e3fe57bd9adb5f0d3c337f