{"abstract":"A later retrieval channel overwrites earlier candidates.","category":"Vector retrieval ranking","checks":6,"contract":"Return unique IDs from both channel lists, ordered by descending score then ID; repeated IDs keep their greatest score.","contract_signature":"left, right","evaluation_group":"vector-retrieval-candidate-union","failed_approach":"Concatenating and sorting leaves duplicate identities in the result.","family":"w3-vector-retrieval-ranking-candidate-union","id":"FA-99466","implementations":{"attempt":{"sha256":"b3f6cf4591dcaceff3a841f313e361bef463acb7fbd5ad5c4e84f7d9542ffa1a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(left, right):\n    return [x[0] for x in sorted(left+right,key=lambda x:(-x[1],x[0]))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both channels',solve([['a',N]], [['b',N+1]]),['b','a'])\ncheck('duplicate collapse',solve([['x',1]], [['x',N+2]]),['x'])\ncheck('best duplicate score',solve([['x',N]], [['x',N+2],['y',N+1]]),['x','y'])\ncheck('left empty',solve([], [['b',N],['a',N+1]]),['a','b'])\ncheck('right empty',solve([['b',N],['a',N+1]], []),['a','b'])\ncheck('both empty',solve([], []),[])\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":"76ac37b43f36f072adb7a1362c655df6aba19a6e98306873baf2b42edb11b8c4","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(left, right):\n    return [x[0] for x in sorted(right,key=lambda x:(-x[1],x[0]))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both channels',solve([['a',N]], [['b',N+1]]),['b','a'])\ncheck('duplicate collapse',solve([['x',1]], [['x',N+2]]),['x'])\ncheck('best duplicate score',solve([['x',N]], [['x',N+2],['y',N+1]]),['x','y'])\ncheck('left empty',solve([], [['b',N],['a',N+1]]),['a','b'])\ncheck('right empty',solve([['b',N],['a',N+1]], []),['a','b'])\ncheck('both empty',solve([], []),[])\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":"Inputs are small exact toy vectors and scores. No production index, ANN recall, embedding quality, or latency claim is implied. 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":"w3-vector-retrieval-ranking-candidate-union","generated_at":"2026-09-30T16:48:24.474259+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"An offline vector retrieval toy model isolates one ranking contract from embedding generation, storage, and serving.","root_cause":"The right candidate source replaces the left source, or concatenation preserves duplicate hits.","sha256":"eb96ef34703fe7b60d4100e4049ca87964bc5a9bef135253559b525a29749836","title":"Vector retrieval: A later retrieval channel overwrites earlier candidates · case 01","variant":1,"variant_policy":"The fixture code references N, supplied as 1 through 5. Fixed boundary checks may repeat. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":28.037,"exit_code":1,"observations":[{"actual":["b","a"],"check":"both channels","expected":["b","a"],"passed":true},{"actual":["x","x"],"check":"duplicate collapse","expected":["x"],"passed":false},{"actual":["x","y","x"],"check":"best duplicate score","expected":["x","y"],"passed":false},{"actual":["a","b"],"check":"left empty","expected":["a","b"],"passed":true},{"actual":["a","b"],"check":"right empty","expected":["a","b"],"passed":true},{"actual":[],"check":"both empty","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both channels\", \"actual\": [\"b\", \"a\"], \"expected\": [\"b\", \"a\"], \"passed\": true}, {\"check\": \"duplicate collapse\", \"actual\": [\"x\", \"x\"], \"expected\": [\"x\"], \"passed\": false}, {\"check\": \"best duplicate score\", \"actual\": [\"x\", \"y\", \"x\"], \"expected\": [\"x\", \"y\"], \"passed\": false}, {\"check\": \"left empty\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}, {\"check\": \"right empty\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}, {\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":26.36,"exit_code":1,"observations":[{"actual":["b"],"check":"both channels","expected":["b","a"],"passed":false},{"actual":["x"],"check":"duplicate collapse","expected":["x"],"passed":true},{"actual":["x","y"],"check":"best duplicate score","expected":["x","y"],"passed":true},{"actual":["a","b"],"check":"left empty","expected":["a","b"],"passed":true},{"actual":[],"check":"right empty","expected":["a","b"],"passed":false},{"actual":[],"check":"both empty","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both channels\", \"actual\": [\"b\"], \"expected\": [\"b\", \"a\"], \"passed\": false}, {\"check\": \"duplicate collapse\", \"actual\": [\"x\"], \"expected\": [\"x\"], \"passed\": true}, {\"check\": \"best duplicate score\", \"actual\": [\"x\", \"y\"], \"expected\": [\"x\", \"y\"], \"passed\": true}, {\"check\": \"left empty\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}, {\"check\": \"right empty\", \"actual\": [], \"expected\": [\"a\", \"b\"], \"passed\": false}, {\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}