{"abstract":"Delta 128 is written as [1, 0], which a reader decodes as two separate deltas 1 and 0.","category":"MIDI event timing","checks":8,"contract":"Input a delta-time integer 0..0x0FFFFFFF (booleans rejected). Encode as 7-bit groups, most significant group first, with bit 7 set on every byte except the last. Zero encodes as [0]. Out-of-range or non-integer input returns None.","contract_signature":"x","evaluation_group":"w2-midi-event-timing-vlq-encode","failed_approach":"Tagging without masking lets high bits of the remaining value leak into leading bytes for deltas of 16384 and above.","family":"w2-midi-event-timing-vlq-encode-continuation-mask","id":"FA-81341","implementations":{"attempt":{"sha256":"41547662132ca5d96de534c9397621fd2a90cc619f1c4aa4a10eabe78c677381","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    if not isinstance(x, int) or isinstance(x, bool) or x < 0 or x > 0x0FFFFFFF:\n        return None\n    out = [x & 0x7F]\n    x >>= 7\n    while x:\n        out.append(x | 0x80)\n        x >>= 7\n    return out[::-1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[(0, [0]), (1, [1]), (64, [64]), (127, [127]), (128, [129, 0]), (255, [129, 127]), (100000, [134, 141, 32]), (268435455, [255, 255, 255, 127])], [(127, [127]), (129, [129, 1]), (8192, [192, 0]), (2097151, [255, 255, 127]), (268435456, None), (-1, None), (True, None), (2097152, [129, 128, 128, 0])], [(128, [129, 0]), (129, [129, 1]), (255, [129, 127]), (16383, [255, 127]), (2097152, [129, 128, 128, 0]), (True, None), ('7', None), (1000000, [189, 132, 64])], [(129, [129, 1]), (255, [129, 127]), (8192, [192, 0]), (16383, [255, 127]), (16384, [129, 128, 0]), (100000, [134, 141, 32]), (2097151, [255, 255, 127]), (268435455, [255, 255, 255, 127])], [(16383, [255, 127]), (16384, [129, 128, 0]), (100000, [134, 141, 32]), (2097151, [255, 255, 127]), (2097152, [129, 128, 128, 0]), (268435455, [255, 255, 255, 127]), (480, [131, 96]), (2097152, [129, 128, 128, 0])]]\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":"8c16a726d1cca84dc8fcf30bcc0a9ee8cf5daaecd4bd5885bc2f1775f6ccb446","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x):\n    if not isinstance(x, int) or isinstance(x, bool) or x < 0 or x > 0x0FFFFFFF:\n        return None\n    out = [x & 0x7F]\n    x >>= 7\n    while x:\n        out.append(x & 0x7F)\n        x >>= 7\n    return out[::-1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[(0, [0]), (1, [1]), (64, [64]), (127, [127]), (128, [129, 0]), (255, [129, 127]), (100000, [134, 141, 32]), (268435455, [255, 255, 255, 127])], [(127, [127]), (129, [129, 1]), (8192, [192, 0]), (2097151, [255, 255, 127]), (268435456, None), (-1, None), (True, None), (2097152, [129, 128, 128, 0])], [(128, [129, 0]), (129, [129, 1]), (255, [129, 127]), (16383, [255, 127]), (2097152, [129, 128, 128, 0]), (True, None), ('7', None), (1000000, [189, 132, 64])], [(129, [129, 1]), (255, [129, 127]), (8192, [192, 0]), (16383, [255, 127]), (16384, [129, 128, 0]), (100000, [134, 141, 32]), (2097151, [255, 255, 127]), (268435455, [255, 255, 255, 127])], [(16383, [255, 127]), (16384, [129, 128, 0]), (100000, [134, 141, 32]), (2097151, [255, 255, 127]), (2097152, [129, 128, 128, 0]), (268435455, [255, 255, 255, 127]), (480, [131, 96]), (2097152, [129, 128, 128, 0])]]\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-encode-continuation-mask","generated_at":"2026-09-29T14:50:02.023933+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":"Leading groups are masked to seven bits but never tagged with the continuation bit.","sha256":"b0aa71f4db4c015713ca0c05940c4fa62bbbf183edbcccc9d6a181e5c74717e8","title":"Variable-length quantity delta encoder: leading bytes emitted without continuation flag · 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":40.051,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[1],"check":"oracle 1","expected":[1],"passed":true},{"actual":[64],"check":"oracle 2","expected":[64],"passed":true},{"actual":[127],"check":"oracle 3","expected":[127],"passed":true},{"actual":[129,0],"check":"oracle 4","expected":[129,0],"passed":true},{"actual":[129,127],"check":"oracle 5","expected":[129,127],"passed":true},{"actual":[134,909,32],"check":"oracle 6","expected":[134,141,32],"passed":false},{"actual":[255,16383,2097151,127],"check":"oracle 7","expected":[255,255,255,127],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"oracle 0\", \"actual\": [0], \"expected\": [0], \"passed\": true}, {\"check\": \"oracle 1\", \"actual\": [1], \"expected\": [1], \"passed\": true}, {\"check\": \"oracle 2\", \"actual\": [64], \"expected\": [64], \"passed\": true}, {\"check\": \"oracle 3\", \"actual\": [127], \"expected\": [127], \"passed\": true}, {\"check\": \"oracle 4\", \"actual\": [129, 0], \"expected\": [129, 0], \"passed\": true}, {\"check\": \"oracle 5\", \"actual\": [129, 127], \"expected\": [129, 127], \"passed\": true}, {\"check\": \"oracle 6\", \"actual\": [134, 909, 32], \"expected\": [134, 141, 32], \"passed\": false}, {\"check\": \"oracle 7\", \"actual\": [255, 16383, 2097151, 127], \"expected\": [255, 255, 255, 127], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":37.737,"exit_code":1,"observations":[{"actual":[0],"check":"oracle 0","expected":[0],"passed":true},{"actual":[1],"check":"oracle 1","expected":[1],"passed":true},{"actual":[64],"check":"oracle 2","expected":[64],"passed":true},{"actual":[127],"check":"oracle 3","expected":[127],"passed":true},{"actual":[1,0],"check":"oracle 4","expected":[129,0],"passed":false},{"actual":[1,127],"check":"oracle 5","expected":[129,127],"passed":false},{"actual":[6,13,32],"check":"oracle 6","expected":[134,141,32],"passed":false},{"actual":[127,127,127,127],"check":"oracle 7","expected":[255,255,255,127],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"oracle 0\", \"actual\": [0], \"expected\": [0], \"passed\": true}, {\"check\": \"oracle 1\", \"actual\": [1], \"expected\": [1], \"passed\": true}, {\"check\": \"oracle 2\", \"actual\": [64], \"expected\": [64], \"passed\": true}, {\"check\": \"oracle 3\", \"actual\": [127], \"expected\": [127], \"passed\": true}, {\"check\": \"oracle 4\", \"actual\": [1, 0], \"expected\": [129, 0], \"passed\": false}, {\"check\": \"oracle 5\", \"actual\": [1, 127], \"expected\": [129, 127], \"passed\": false}, {\"check\": \"oracle 6\", \"actual\": [6, 13, 32], \"expected\": [134, 141, 32], \"passed\": false}, {\"check\": \"oracle 7\", \"actual\": [127, 127, 127, 127], \"expected\": [255, 255, 255, 127], \"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."}}