{"abstract":"Bit reservoir loses codes that cross byte boundaries.","category":"Compression format semantics","checks":6,"contract":"Pack nonnegative values less than 2**width consecutively least-significant-bit first, yielding integer bytes with zero high padding. Width is 1..8.","contract_signature":"values, width","evaluation_group":"model-d07fffb3a51ab16f","failed_approach":"Packing globally in most-significant-bit order reverses the specified wire convention.","family":"z-compression-lsb-reservoir","id":"FA-11611","implementations":{"attempt":{"sha256":"a47a71e6ae9ac9d2303ea774ef9850e1bb92a4c5f8f127946be9959f1e66b632","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(values, width):\n    bits=''.join(format(v,'0'+str(width)+'b') for v in values)\n    bits += '0' * ((-len(bits))%8)\n    return [int(bits[i:i+8],2) for i in range(0,len(bits),8)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('cross byte',solve([N,N,N],3),[(N+8*N+64*N)&255,(N+8*N+64*N)>>8])\ncheck('one bit',solve([1],1),[1])\ncheck('empty',solve([],3),[])\ncheck('byte codes',solve([1,255],8),[1,255])\ncheck('full byte',solve([1,2],4),[33])\ncheck('zero tail',solve([0,1,0],4),[16,0])\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":"3d6dcd3b290b2faa9e4185b93a8527cdc797be1918c1c1b4f663295daf3a21dc","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(values, width):\n    return list(values)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('cross byte',solve([N,N,N],3),[(N+8*N+64*N)&255,(N+8*N+64*N)>>8])\ncheck('one bit',solve([1],1),[1])\ncheck('empty',solve([],3),[])\ncheck('byte codes',solve([1,255],8),[1,255])\ncheck('full byte',solve([1,2],4),[33])\ncheck('zero tail',solve([0,1,0],4),[16,0])\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":"Controlled educational model, not a complete implementation of a production compression format. 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":"z-compression-lsb-reservoir","generated_at":"2026-09-29T14:38:49.375310+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small offline codec model isolates a compression-specific failure without external files or libraries.","root_cause":"Each code is placed into a separate byte instead of a shared bit reservoir.","sha256":"9d6b609df81fadca5e709277fc79a76adbbffbb202191a4c0b03481434025c61","title":"Bit reservoir loses codes that cross byte boundaries · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":42.751,"exit_code":1,"observations":[{"actual":[36,128],"check":"cross byte","expected":[73,0],"passed":false},{"actual":[128],"check":"one bit","expected":[1],"passed":false},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[1,255],"check":"byte codes","expected":[1,255],"passed":true},{"actual":[18],"check":"full byte","expected":[33],"passed":false},{"actual":[1,0],"check":"zero tail","expected":[16,0],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"cross byte\", \"actual\": [36, 128], \"expected\": [73, 0], \"passed\": false}, {\"check\": \"one bit\", \"actual\": [128], \"expected\": [1], \"passed\": false}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"byte codes\", \"actual\": [1, 255], \"expected\": [1, 255], \"passed\": true}, {\"check\": \"full byte\", \"actual\": [18], \"expected\": [33], \"passed\": false}, {\"check\": \"zero tail\", \"actual\": [1, 0], \"expected\": [16, 0], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.213,"exit_code":1,"observations":[{"actual":[1,1,1],"check":"cross byte","expected":[73,0],"passed":false},{"actual":[1],"check":"one bit","expected":[1],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[1,255],"check":"byte codes","expected":[1,255],"passed":true},{"actual":[1,2],"check":"full byte","expected":[33],"passed":false},{"actual":[0,1,0],"check":"zero tail","expected":[16,0],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"cross byte\", \"actual\": [1, 1, 1], \"expected\": [73, 0], \"passed\": false}, {\"check\": \"one bit\", \"actual\": [1], \"expected\": [1], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"byte codes\", \"actual\": [1, 255], \"expected\": [1, 255], \"passed\": true}, {\"check\": \"full byte\", \"actual\": [1, 2], \"expected\": [33], \"passed\": false}, {\"check\": \"zero tail\", \"actual\": [0, 1, 0], \"expected\": [16, 0], \"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."}}