FA-4756 / Scoped mappings / Open access

Chainmap clear only current scope · case 01

The operation returns a result or retained state that violates this contract: Clear erases only the first scope, preserving all outer bindings.

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

ROOT CAUSE

Clearing every scope destroys inherited state.

VERIFIED REPAIR

Clear erases only the first scope, preserving all outer bindings.

Unsuccessful approach: Replacing the entire chain with one empty scope discards parent scope structure.

Case contract

Clear erases only the first scope, preserving all outer bindings. 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 [{} for m in x]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer preserved', solve([{'a': 2}, {'a': 1}]), [{}, {'a': 1}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{}, {'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('empty top', solve([{}, {'a': 1}]), [{}, {'a': 1}])
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
outer preserved	`[{}, {}]`	`[{}, {'a': 1}]`	Failed
three scopes	`[{}, {}, {}]`	`[{}, {'b': 2}, {'c': 3}]`	Failed
one scope	`[{}]`	`[{}]`	Passed
empty top	`[{}, {}]`	`[{}, {'a': 1}]`	Failed

SHA-256 / 95a2606d118e7baa4b90daacda1662abbe89b9ca48fd26326786846f25ad9044

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 [{}]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer preserved', solve([{'a': 2}, {'a': 1}]), [{}, {'a': 1}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{}, {'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('empty top', solve([{}, {'a': 1}]), [{}, {'a': 1}])
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
outer preserved	`[{}]`	`[{}, {'a': 1}]`	Failed
three scopes	`[{}]`	`[{}, {'b': 2}, {'c': 3}]`	Failed
one scope	`[{}]`	`[{}]`	Passed
empty top	`[{}]`	`[{}, {'a': 1}]`	Failed

SHA-256 / d5a4ee71809428d65f9d261fed9d2c69a4605b614ea51f6e6b901badf3ee8b04

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):
    c=ChainMap(*[dict(m) for m in x]); c.clear(); return c.maps
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer preserved', solve([{'a': 2}, {'a': 1}]), [{}, {'a': 1}])
check('three scopes', solve([{'a': 1}, {'b': 2}, {'c': 3}]), [{}, {'b': 2}, {'c': 3}])
check('one scope', solve([{'a': 1}]), [{}])
check('empty top', solve([{}, {'a': 1}]), [{}, {'a': 1}])
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
outer preserved	`[{}, {'a': 1}]`	`[{}, {'a': 1}]`	Passed
three scopes	`[{}, {'b': 2}, {'c': 3}]`	`[{}, {'b': 2}, {'c': 3}]`	Passed
one scope	`[{}]`	`[{}]`	Passed
empty top	`[{}, {'a': 1}]`	`[{}, {'a': 1}]`	Passed

SHA-256 / 65263f9184d4820b06882d8942c31692645c213a80f75d6f5344d4b490544ef1

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 2026-09-29T14:37:42.492143+00:00.

Case digest / 7ced3986c93d19a8084bf67ced18526079556013aa9e4616431f8738438d16d5