{"abstract":"List overlays accumulate obsolete values.","category":"Configuration","checks":8,"contract":"Merge mappings left to right. None deletes a key, false and zero are retained, lists replace instead of concatenate, and mapping values replace atomically.","evaluation_group":"xt-config-overlay","failed_approach":"The attempted repair substitutes else: result[key] = list(dict.fromkeys(result.get(key, []) + value)) if isinstance(value, list) else value. Fixture 6 still yields {'a': [1, 2]} instead of {'a': [2]}.","family":"xt-config-overlay-list-replace","id":"FA-9596","implementations":{"attempt":{"sha256":"6278858febf6389bd5a9cacbf572c757d9079d691bd2c3f79f0ad7dc7fa23cf8","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(layers):\n    result = {}\n    for layer in layers:\n        for key, value in layer.items():\n            if value is None: result.pop(key, None)\n            else: result[key] = list(dict.fromkeys(result.get(key, []) + value)) if isinstance(value, list) else value\n    return result\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve([]), {})\ncheck('fixture 2', solve([{'a': 1}, {'a': 2}]), {'a': 2})\ncheck('fixture 3', solve([{'a': 1}, {'a': None}]), {})\ncheck('fixture 4', solve([{'a': True}, {'a': False}]), {'a': False})\ncheck('fixture 5', solve([{'a': 2}, {'a': 0}]), {'a': 0})\ncheck('fixture 6', solve([{'a': [1]}, {'a': [2]}]), {'a': [2]})\ncheck('fixture 7', solve([{'a': {'x': 1}}, {'a': {'y': 2}}]), {'a': {'y': 2}})\ncheck('fixture 8', solve([{'a': 1}, {'b': 2}]), {'a': 1, 'b': 2})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"d8ac9112690fe34f99b790e8dd0bb0b91beb66d1394277963aecc2dc93864cd6","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(layers):\n    result = {}\n    for layer in layers:\n        for key, value in layer.items():\n            if value is None: result.pop(key, None)\n            else: result[key] = result.get(key, []) + value if isinstance(value, list) else value\n    return result\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve([]), {})\ncheck('fixture 2', solve([{'a': 1}, {'a': 2}]), {'a': 2})\ncheck('fixture 3', solve([{'a': 1}, {'a': None}]), {})\ncheck('fixture 4', solve([{'a': True}, {'a': False}]), {'a': False})\ncheck('fixture 5', solve([{'a': 2}, {'a': 0}]), {'a': 0})\ncheck('fixture 6', solve([{'a': [1]}, {'a': [2]}]), {'a': [2]})\ncheck('fixture 7', solve([{'a': {'x': 1}}, {'a': {'y': 2}}]), {'a': {'y': 2}})\ncheck('fixture 8', solve([{'a': 1}, {'b': 2}]), {'a': 1, 'b': 2})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"8845a91a710aed09a7bf06ad103edfcb31567144e9bbc2f1bf66b53475a06d40","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(layers):\n    result = {}\n    for layer in layers:\n        for key, value in layer.items():\n            if value is None: result.pop(key, None)\n            else: result[key] = value\n    return result\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve([]), {})\ncheck('fixture 2', solve([{'a': 1}, {'a': 2}]), {'a': 2})\ncheck('fixture 3', solve([{'a': 1}, {'a': None}]), {})\ncheck('fixture 4', solve([{'a': True}, {'a': False}]), {'a': False})\ncheck('fixture 5', solve([{'a': 2}, {'a': 0}]), {'a': 0})\ncheck('fixture 6', solve([{'a': [1]}, {'a': [2]}]), {'a': [2]})\ncheck('fixture 7', solve([{'a': {'x': 1}}, {'a': {'y': 2}}]), {'a': {'y': 2}})\ncheck('fixture 8', solve([{'a': 1}, {'b': 2}]), {'a': 1, 'b': 2})\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xt-config-overlay-list-replace","generated_at":"2026-09-29T14:38:31.410972+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"An offline model of explicit configuration overlay, suitable for testing build and release tooling without external services.","repair":"Replace lists atomically.","root_cause":"The implementation substitutes else: result[key] = result.get(key, []) + value if isinstance(value, list) else value for else: result[key] = value, so list overlays accumulate obsolete values.","sha256":"afed320b814612beff0ebbb4c93f2a3cc527f3a2c9071a6399296aaa704cb7a7","title":"Explicit configuration overlay: List overlays accumulate obsolete values · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":40.769,"exit_code":1,"observations":[{"actual":{},"check":"fixture 1","expected":{},"passed":true},{"actual":{"a":2},"check":"fixture 2","expected":{"a":2},"passed":true},{"actual":{},"check":"fixture 3","expected":{},"passed":true},{"actual":{"a":false},"check":"fixture 4","expected":{"a":false},"passed":true},{"actual":{"a":0},"check":"fixture 5","expected":{"a":0},"passed":true},{"actual":{"a":[1,2]},"check":"fixture 6","expected":{"a":[2]},"passed":false},{"actual":{"a":{"y":2}},"check":"fixture 7","expected":{"a":{"y":2}},"passed":true},{"actual":{"a":1,"b":2},"check":"fixture 8","expected":{"a":1,"b":2},"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 2\", \"actual\": {\"a\": 2}, \"expected\": {\"a\": 2}, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": {\"a\": false}, \"expected\": {\"a\": false}, \"passed\": true}, {\"check\": \"fixture 5\", \"actual\": {\"a\": 0}, \"expected\": {\"a\": 0}, \"passed\": true}, {\"check\": \"fixture 6\", \"actual\": {\"a\": [1, 2]}, \"expected\": {\"a\": [2]}, \"passed\": false}, {\"check\": \"fixture 7\", \"actual\": {\"a\": {\"y\": 2}}, \"expected\": {\"a\": {\"y\": 2}}, \"passed\": true}, {\"check\": \"fixture 8\", \"actual\": {\"a\": 1, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.642,"exit_code":1,"observations":[{"actual":{},"check":"fixture 1","expected":{},"passed":true},{"actual":{"a":2},"check":"fixture 2","expected":{"a":2},"passed":true},{"actual":{},"check":"fixture 3","expected":{},"passed":true},{"actual":{"a":false},"check":"fixture 4","expected":{"a":false},"passed":true},{"actual":{"a":0},"check":"fixture 5","expected":{"a":0},"passed":true},{"actual":{"a":[1,2]},"check":"fixture 6","expected":{"a":[2]},"passed":false},{"actual":{"a":{"y":2}},"check":"fixture 7","expected":{"a":{"y":2}},"passed":true},{"actual":{"a":1,"b":2},"check":"fixture 8","expected":{"a":1,"b":2},"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 2\", \"actual\": {\"a\": 2}, \"expected\": {\"a\": 2}, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": {\"a\": false}, \"expected\": {\"a\": false}, \"passed\": true}, {\"check\": \"fixture 5\", \"actual\": {\"a\": 0}, \"expected\": {\"a\": 0}, \"passed\": true}, {\"check\": \"fixture 6\", \"actual\": {\"a\": [1, 2]}, \"expected\": {\"a\": [2]}, \"passed\": false}, {\"check\": \"fixture 7\", \"actual\": {\"a\": {\"y\": 2}}, \"expected\": {\"a\": {\"y\": 2}}, \"passed\": true}, {\"check\": \"fixture 8\", \"actual\": {\"a\": 1, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":38.3,"exit_code":0,"observations":[{"actual":{},"check":"fixture 1","expected":{},"passed":true},{"actual":{"a":2},"check":"fixture 2","expected":{"a":2},"passed":true},{"actual":{},"check":"fixture 3","expected":{},"passed":true},{"actual":{"a":false},"check":"fixture 4","expected":{"a":false},"passed":true},{"actual":{"a":0},"check":"fixture 5","expected":{"a":0},"passed":true},{"actual":{"a":[2]},"check":"fixture 6","expected":{"a":[2]},"passed":true},{"actual":{"a":{"y":2}},"check":"fixture 7","expected":{"a":{"y":2}},"passed":true},{"actual":{"a":1,"b":2},"check":"fixture 8","expected":{"a":1,"b":2},"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 2\", \"actual\": {\"a\": 2}, \"expected\": {\"a\": 2}, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": {}, \"expected\": {}, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": {\"a\": false}, \"expected\": {\"a\": false}, \"passed\": true}, {\"check\": \"fixture 5\", \"actual\": {\"a\": 0}, \"expected\": {\"a\": 0}, \"passed\": true}, {\"check\": \"fixture 6\", \"actual\": {\"a\": [2]}, \"expected\": {\"a\": [2]}, \"passed\": true}, {\"check\": \"fixture 7\", \"actual\": {\"a\": {\"y\": 2}}, \"expected\": {\"a\": {\"y\": 2}}, \"passed\": true}, {\"check\": \"fixture 8\", \"actual\": {\"a\": 1, \"b\": 2}, \"expected\": {\"a\": 1, \"b\": 2}, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}