{"abstract":"A stop sequence split across chunks is missed.","category":"Model output stopping rules","checks":6,"contract":"Given chunks and a nonempty stop string, concatenate logically and return emitted text before first occurrence and stop flag. Chunk boundaries have no semantic effect.","contract_signature":"text_chunks, stop","evaluation_group":"w3-output-chunk-stop","failed_approach":"Checking individual chunks can trim a local match but cannot recognize a marker crossing a boundary.","family":"w3-model-output-stopping-rules-chunk-boundary-stop","id":"FA-100796","implementations":{"attempt":{"sha256":"499a55d0f58db236eb8f13a9d00463b085a722e76330e703dda52e1d83c8aa7c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(text_chunks, stop):\n    joined=''.join(text_chunks)\n    for chunk in text_chunks:\n        if stop in chunk:return joined[:joined.find(stop)],True\n    return joined,False\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('split two chunks',solve(['ab','cd','z'],'bc'),('a',True))\ncheck('single chunk',solve(['xSTOPy'],'STOP'),('x',True))\ncheck('no marker',solve(['abc','def'],'ZZ'),('abcdef',False))\ncheck('empty chunks',solve([], 'x'),('',False))\ncheck('marker across empty chunk',solve(['a','','xy'],'xy'),('a',True))\ncheck('marker at boundary',solve(['a','b'],'ab'),('',True))\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":"b4513d6cda969a1235599a48300826f18e68f8d6dc964202f2f51ab40deafb1b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(text_chunks, stop):\n    joined=''.join(text_chunks)\n    found=any(stop in chunk for chunk in text_chunks)\n    return joined,found\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('split two chunks',solve(['ab','cd','z'],'bc'),('a',True))\ncheck('single chunk',solve(['xSTOPy'],'STOP'),('x',True))\ncheck('no marker',solve(['abc','def'],'ZZ'),('abcdef',False))\ncheck('empty chunks',solve([], 'x'),('',False))\ncheck('marker across empty chunk',solve(['a','','xy'],'xy'),('a',True))\ncheck('marker at boundary',solve(['a','b'],'ab'),('',True))\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 toy contract covers the supplied token records only; it does not claim compatibility with a particular model runtime or tokenizer. 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-model-output-stopping-rules-chunk-boundary-stop","generated_at":"2026-09-30T16:48:39.593504+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic output-control model isolates one finish or streaming boundary from any particular runtime.","root_cause":"The matcher checks chunks independently, so markers split between chunks are missed.","sha256":"5d9e42c8e75ba3a9b9fb8b19754d2b19a69ec012e2cd402bb3681429bcdf8ec7","title":"Output stopping: A stop sequence split across chunks is missed · case 01","variant":1,"variant_policy":"The same explicitly authored fixtures repeat across all five numbered records; runtime N is unused. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":29.553,"exit_code":1,"observations":[{"actual":["abcdz",false],"check":"split two chunks","expected":["a",true],"passed":false},{"actual":["x",true],"check":"single chunk","expected":["x",true],"passed":true},{"actual":["abcdef",false],"check":"no marker","expected":["abcdef",false],"passed":true},{"actual":["",false],"check":"empty chunks","expected":["",false],"passed":true},{"actual":["a",true],"check":"marker across empty chunk","expected":["a",true],"passed":true},{"actual":["ab",false],"check":"marker at boundary","expected":["",true],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"split two chunks\", \"actual\": [\"abcdz\", false], \"expected\": [\"a\", true], \"passed\": false}, {\"check\": \"single chunk\", \"actual\": [\"x\", true], \"expected\": [\"x\", true], \"passed\": true}, {\"check\": \"no marker\", \"actual\": [\"abcdef\", false], \"expected\": [\"abcdef\", false], \"passed\": true}, {\"check\": \"empty chunks\", \"actual\": [\"\", false], \"expected\": [\"\", false], \"passed\": true}, {\"check\": \"marker across empty chunk\", \"actual\": [\"a\", true], \"expected\": [\"a\", true], \"passed\": true}, {\"check\": \"marker at boundary\", \"actual\": [\"ab\", false], \"expected\": [\"\", true], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":32.939,"exit_code":1,"observations":[{"actual":["abcdz",false],"check":"split two chunks","expected":["a",true],"passed":false},{"actual":["xSTOPy",true],"check":"single chunk","expected":["x",true],"passed":false},{"actual":["abcdef",false],"check":"no marker","expected":["abcdef",false],"passed":true},{"actual":["",false],"check":"empty chunks","expected":["",false],"passed":true},{"actual":["axy",true],"check":"marker across empty chunk","expected":["a",true],"passed":false},{"actual":["ab",false],"check":"marker at boundary","expected":["",true],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"split two chunks\", \"actual\": [\"abcdz\", false], \"expected\": [\"a\", true], \"passed\": false}, {\"check\": \"single chunk\", \"actual\": [\"xSTOPy\", true], \"expected\": [\"x\", true], \"passed\": false}, {\"check\": \"no marker\", \"actual\": [\"abcdef\", false], \"expected\": [\"abcdef\", false], \"passed\": true}, {\"check\": \"empty chunks\", \"actual\": [\"\", false], \"expected\": [\"\", false], \"passed\": true}, {\"check\": \"marker across empty chunk\", \"actual\": [\"axy\", true], \"expected\": [\"a\", true], \"passed\": false}, {\"check\": \"marker at boundary\", \"actual\": [\"ab\", false], \"expected\": [\"\", true], \"passed\": false}], \"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."}}