{"abstract":"Every multi-byte delta decodes too large, e.g. [129, 0] reads as 16512 instead of 128.","category":"MIDI event timing","checks":8,"contract":"Input a list of byte values. Decode consecutive variable-length quantities (7 data bits per byte, bit 7 = continuation, most significant first, at most 4 bytes each). Return the list of values; return None for a byte outside 0..255, a quantity whose fourth byte still has the continuation bit, or a truncated final quantity.","contract_signature":"x","evaluation_group":"w2-midi-event-timing-vlq-decode","failed_approach":"Stripping the flag but shifting by eight bits packs groups as bytes, so [129, 0] reads as 256.","family":"w2-midi-event-timing-vlq-decode-group-assembly","id":"FA-81361","implementations":{"attempt":{"sha256":"b3b82f386bfe28ae7a10955ee9295ccd333ded9fb3d94e38a7d4e9e32504510a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    if not isinstance(x, list):\n        return None\n    values = []\n    cur = 0\n    count = 0\n    for b in x:\n        if not isinstance(b, int) or b < 0 or b > 255:\n            return None\n        cur = (cur << 8) | (b & 0x7F)\n        count += 1\n        if b & 0x80:\n            if count == 4:\n                return None\n            continue\n        values.append(cur)\n        cur = 0\n        count = 0\n    if count:\n        return None\n    return values\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[([0], [0]), ([127], [127]), ([129, 0], [128]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None), ([], [])], [([192, 0], [8192]), ([255, 255, 255, 127], [268435455]), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([], []), ([256], None), ([-1], None), ([1, 2, 3], [1, 2, 3])], [([129, 0], [128]), ([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([-1], None), ([1, 2, 3], [1, 2, 3])], [([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0])], [([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0]), ([129, 0, 129, 0, 129, 0], [128, 128, 128]), ([143, 255, 255, 127], [33554431])]]\nfor i, (args, expected) in enumerate(fixtures[N-1]):\n    check(\"oracle %d\" % i, solve(args), expected)\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":"1294c82d3084bc5c57b80fdc98fcd8ca5a96b69e261a8cf017d41b837f33a595","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    if not isinstance(x, list):\n        return None\n    values = []\n    cur = 0\n    count = 0\n    for b in x:\n        if not isinstance(b, int) or b < 0 or b > 255:\n            return None\n        cur = (cur << 7) | b\n        count += 1\n        if b & 0x80:\n            if count == 4:\n                return None\n            continue\n        values.append(cur)\n        cur = 0\n        count = 0\n    if count:\n        return None\n    return values\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[([0], [0]), ([127], [127]), ([129, 0], [128]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None), ([], [])], [([192, 0], [8192]), ([255, 255, 255, 127], [268435455]), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([], []), ([256], None), ([-1], None), ([1, 2, 3], [1, 2, 3])], [([129, 0], [128]), ([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([-1], None), ([1, 2, 3], [1, 2, 3])], [([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0])], [([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0]), ([129, 0, 129, 0, 129, 0], [128, 128, 128]), ([143, 255, 255, 127], [33554431])]]\nfor i, (args, expected) in enumerate(fixtures[N-1]):\n    check(\"oracle %d\" % i, solve(args), expected)\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":"A deterministic bounded teaching model with a stipulated toy contract; it is not a complete Standard MIDI File or MIDI 1.0/2.0 implementation. 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":"w2-midi-event-timing-vlq-decode-group-assembly","generated_at":"2026-09-29T14:50:02.413351+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.","root_cause":"Bytes are appended to the accumulator without stripping the continuation bit.","sha256":"bd38e4c99913af7d2b45c0d35f02133ad1bea579364e0a0d505bcc0f0fd14891","title":"Variable-length quantity stream decoder: continuation flag kept in the value · 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":42.121,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[127],"check":"oracle 1","expected":[127],"passed":true},{"actual":[256],"check":"oracle 2","expected":[128],"passed":false},{"actual":[65536],"check":"oracle 3","expected":[16384],"passed":false},{"actual":[2139062143],"check":"oracle 4","expected":[268435455],"passed":false},{"actual":null,"check":"oracle 5","expected":null,"passed":true},{"actual":null,"check":"oracle 6","expected":null,"passed":true},{"actual":[],"check":"oracle 7","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"oracle 0\", \"actual\": [0], \"expected\": [0], \"passed\": true}, {\"check\": \"oracle 1\", \"actual\": [127], \"expected\": [127], \"passed\": true}, {\"check\": \"oracle 2\", \"actual\": [256], \"expected\": [128], \"passed\": false}, {\"check\": \"oracle 3\", \"actual\": [65536], \"expected\": [16384], \"passed\": false}, {\"check\": \"oracle 4\", \"actual\": [2139062143], \"expected\": [268435455], \"passed\": false}, {\"check\": \"oracle 5\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 6\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 7\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.631,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[127],"check":"oracle 1","expected":[127],"passed":true},{"actual":[16512],"check":"oracle 2","expected":[128],"passed":false},{"actual":[2113536],"check":"oracle 3","expected":[16384],"passed":false},{"actual":[536870911],"check":"oracle 4","expected":[268435455],"passed":false},{"actual":null,"check":"oracle 5","expected":null,"passed":true},{"actual":null,"check":"oracle 6","expected":null,"passed":true},{"actual":[],"check":"oracle 7","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"oracle 0\", \"actual\": [0], \"expected\": [0], \"passed\": true}, {\"check\": \"oracle 1\", \"actual\": [127], \"expected\": [127], \"passed\": true}, {\"check\": \"oracle 2\", \"actual\": [16512], \"expected\": [128], \"passed\": false}, {\"check\": \"oracle 3\", \"actual\": [2113536], \"expected\": [16384], \"passed\": false}, {\"check\": \"oracle 4\", \"actual\": [536870911], \"expected\": [268435455], \"passed\": false}, {\"check\": \"oracle 5\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 6\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 7\", \"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."}}