{"abstract":"A stream ending in a byte with the continuation bit set, like [129], returns [] instead of None.","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":"Emitting the partial value invents a delta from a truncated stream.","family":"w2-midi-event-timing-vlq-decode-truncated-tail","id":"FA-81376","implementations":{"attempt":{"sha256":"71bb5c96d38b59e18e78f2e9ecc051989cf86d9da259faf5ad753d8166f2ee8a","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 & 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        values.append(cur)\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]), ([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None)], [([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2])], [([255, 255, 255, 255, 127], None), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([], []), ([256], None), ([-1], None)], [([129], None), ([200, 1, 2], [9217, 2]), ([], []), ([256], None), ([-1], None), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0])], [([129], None), ([-1], None), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0]), ([129, 0, 129, 0, 129, 0], [128, 128, 128]), ([1, 2, 3], [1, 2, 3]), ([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":"19b72e653580901491e104352a758c37f78f2f25f268671117e1d3348637cba9","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 & 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    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]), ([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None)], [([192, 0], [8192]), ([129, 128, 0], [16384]), ([255, 255, 255, 127], [268435455]), ([255, 255, 255, 255, 127], None), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2])], [([255, 255, 255, 255, 127], None), ([129], None), ([0, 129, 0, 5], [0, 128, 5]), ([129, 0, 0, 129, 0], [128, 0, 128]), ([200, 1, 2], [9217, 2]), ([], []), ([256], None), ([-1], None)], [([129], None), ([200, 1, 2], [9217, 2]), ([], []), ([256], None), ([-1], None), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0])], [([129], None), ([-1], None), ([131, 255, 127, 0], [65535, 0]), ([128, 128, 128, 0], [0]), ([128, 0], [0]), ([129, 0, 129, 0, 129, 0], [128, 128, 128]), ([1, 2, 3], [1, 2, 3]), ([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-truncated-tail","generated_at":"2026-09-29T14:50:02.492251+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":"The decoder does not check for an unfinished quantity after the last byte.","sha256":"71d8e80ff29efc716a90cfada1e6011a6933d2fe1b90189dd91bb7d84351d2ce","title":"Variable-length quantity stream decoder: truncated final quantity silently dropped · 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":39.212,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[127],"check":"oracle 1","expected":[127],"passed":true},{"actual":[128],"check":"oracle 2","expected":[128],"passed":true},{"actual":[8192],"check":"oracle 3","expected":[8192],"passed":true},{"actual":[16384],"check":"oracle 4","expected":[16384],"passed":true},{"actual":[268435455],"check":"oracle 5","expected":[268435455],"passed":true},{"actual":null,"check":"oracle 6","expected":null,"passed":true},{"actual":[1],"check":"oracle 7","expected":null,"passed":false}],"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\": [128], \"expected\": [128], \"passed\": true}, {\"check\": \"oracle 3\", \"actual\": [8192], \"expected\": [8192], \"passed\": true}, {\"check\": \"oracle 4\", \"actual\": [16384], \"expected\": [16384], \"passed\": true}, {\"check\": \"oracle 5\", \"actual\": [268435455], \"expected\": [268435455], \"passed\": true}, {\"check\": \"oracle 6\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 7\", \"actual\": [1], \"expected\": null, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.419,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[127],"check":"oracle 1","expected":[127],"passed":true},{"actual":[128],"check":"oracle 2","expected":[128],"passed":true},{"actual":[8192],"check":"oracle 3","expected":[8192],"passed":true},{"actual":[16384],"check":"oracle 4","expected":[16384],"passed":true},{"actual":[268435455],"check":"oracle 5","expected":[268435455],"passed":true},{"actual":null,"check":"oracle 6","expected":null,"passed":true},{"actual":[],"check":"oracle 7","expected":null,"passed":false}],"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\": [128], \"expected\": [128], \"passed\": true}, {\"check\": \"oracle 3\", \"actual\": [8192], \"expected\": [8192], \"passed\": true}, {\"check\": \"oracle 4\", \"actual\": [16384], \"expected\": [16384], \"passed\": true}, {\"check\": \"oracle 5\", \"actual\": [268435455], \"expected\": [268435455], \"passed\": true}, {\"check\": \"oracle 6\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oracle 7\", \"actual\": [], \"expected\": null, \"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."}}