FA-89356 / Instruction set emulation / Open access

CMP clears carry on equality · case 01

Comparing equal values clears carry, so a branch on carry set after CMP misses equal operands.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The compare sets carry only for strictly greater accumulator values.

THE FAILURE

The compare sets carry only for strictly greater accumulator values.

Unsuccessful approach: Deriving carry from the result sign is a signed test and breaks for large differences.

Case contract

Input [a, c, ops] for an 8-bit accumulator with carry c; V starts 0. adc m: s = a+m+c, A = s & 0xFF, C = s > 0xFF, V = signed overflow of the 8-bit add. sbc m is adc of (m xor 0xFF) with the same carry (carry set means no borrow). cmp m: C = a >= m (unsigned), N/Z from (a-m) & 0xFF, A and V unchanged. After each op report [A, N, V, Z, C] where N is bit 7 and Z is result == 0.

Why this case matters

CPU emulators live or die on flag semantics; carry-as-inverted-borrow and overflow are the classic 8-bit emulation bugs.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    a, c, ops = args
    v = 0
    out = []
    for op, m in ops:
        if op == 'cmp':
            r = (a - m) & 0xFF
            c = int(a > m)
            out.append([a, r >> 7, v, int(r == 0), c])
            continue
        if op == 'sbc':
            m = m ^ 0xFF
        s = a + m + c
        r = s & 0xFF
        v = int(((a ^ r) & (m ^ r) & 0x80) != 0)
        c = int(s > 0xFF)
        a = r
        out.append([a, r >> 7, v, int(r == 0), c])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('adc without carry', [17, 0, [['adc', 32], ['adc', 5]]], [[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 145]]], [[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 254]]], [[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 126]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [127, 0, [['adc', 128], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [56, 1, [['adc', 255]]], [[56, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [81, 0, [['sbc', 16], ['sbc', 63]]], [[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 62], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 193]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [18, 0, [['adc', 32], ['adc', 5]]], [[50, 0, 0, 0, 0], [55, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 146]]], [[160, 1, 1, 0, 0], [50, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 253]]], [[0, 0, 0, 1, 1], [254, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 125]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [242, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [126, 0, [['adc', 129], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [57, 1, [['adc', 255]]], [[57, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [82, 0, [['sbc', 16], ['sbc', 63]]], [[65, 0, 0, 0, 1], [2, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 61], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 194]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [19, 0, [['adc', 32], ['adc', 5]]], [[51, 0, 0, 0, 0], [56, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 147]]], [[160, 1, 1, 0, 0], [51, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 252]]], [[0, 0, 0, 1, 1], [253, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 124]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [243, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [125, 0, [['adc', 130], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [58, 1, [['adc', 255]]], [[58, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [83, 0, [['sbc', 16], ['sbc', 63]]], [[66, 0, 0, 0, 1], [3, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 60], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 195]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [20, 0, [['adc', 32], ['adc', 5]]], [[52, 0, 0, 0, 0], [57, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 148]]], [[160, 1, 1, 0, 0], [52, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 251]]], [[0, 0, 0, 1, 1], [252, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 123]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [244, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [124, 0, [['adc', 131], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [59, 1, [['adc', 255]]], [[59, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [84, 0, [['sbc', 16], ['sbc', 63]]], [[67, 0, 0, 0, 1], [4, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 59], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 196]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [21, 0, [['adc', 32], ['adc', 5]]], [[53, 0, 0, 0, 0], [58, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 149]]], [[160, 1, 1, 0, 0], [53, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 250]]], [[0, 0, 0, 1, 1], [251, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 122]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [245, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [123, 0, [['adc', 132], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [60, 1, [['adc', 255]]], [[60, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [85, 0, [['sbc', 16], ['sbc', 63]]], [[68, 0, 0, 0, 1], [5, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 58], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 197]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
adc without carry	`[[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]`	`[[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]`	Passed
adc signed overflow both ways	`[[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]`	`[[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]`	Passed
adc carry out to zero	`[[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]`	`[[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]`	Passed
sbc with carry set (no borrow)	`[[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]`	`[[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]`	Passed
sum of exactly 0xFF	`[[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]`	`[[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]`	Passed
carry in wraps operand	`[[56, 0, 0, 0, 1]]`	`[[56, 0, 0, 0, 1]]`	Passed
sbc with carry clear (borrow)	`[[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]`	`[[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]`	Passed
cmp orders and keeps accumulator	`[[64, 0, 0, 1, 0], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]`	`[[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]`	Failed
sbc to exactly zero	`[[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]]`	`[[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]]`	Passed

SHA-256 / 109accb8729ee51dea364c5b746ea33a07de785878d73266a1c45df654eddf80

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(*args):
    a, c, ops = args
    v = 0
    out = []
    for op, m in ops:
        if op == 'cmp':
            r = (a - m) & 0xFF
            c = int(r < 0x80)
            out.append([a, r >> 7, v, int(r == 0), c])
            continue
        if op == 'sbc':
            m = m ^ 0xFF
        s = a + m + c
        r = s & 0xFF
        v = int(((a ^ r) & (m ^ r) & 0x80) != 0)
        c = int(s > 0xFF)
        a = r
        out.append([a, r >> 7, v, int(r == 0), c])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('adc without carry', [17, 0, [['adc', 32], ['adc', 5]]], [[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 145]]], [[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 254]]], [[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 126]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [127, 0, [['adc', 128], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [56, 1, [['adc', 255]]], [[56, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [81, 0, [['sbc', 16], ['sbc', 63]]], [[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 62], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 193]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [18, 0, [['adc', 32], ['adc', 5]]], [[50, 0, 0, 0, 0], [55, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 146]]], [[160, 1, 1, 0, 0], [50, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 253]]], [[0, 0, 0, 1, 1], [254, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 125]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [242, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [126, 0, [['adc', 129], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [57, 1, [['adc', 255]]], [[57, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [82, 0, [['sbc', 16], ['sbc', 63]]], [[65, 0, 0, 0, 1], [2, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 61], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 194]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [19, 0, [['adc', 32], ['adc', 5]]], [[51, 0, 0, 0, 0], [56, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 147]]], [[160, 1, 1, 0, 0], [51, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 252]]], [[0, 0, 0, 1, 1], [253, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 124]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [243, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [125, 0, [['adc', 130], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [58, 1, [['adc', 255]]], [[58, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [83, 0, [['sbc', 16], ['sbc', 63]]], [[66, 0, 0, 0, 1], [3, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 60], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 195]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [20, 0, [['adc', 32], ['adc', 5]]], [[52, 0, 0, 0, 0], [57, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 148]]], [[160, 1, 1, 0, 0], [52, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 251]]], [[0, 0, 0, 1, 1], [252, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 123]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [244, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [124, 0, [['adc', 131], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [59, 1, [['adc', 255]]], [[59, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [84, 0, [['sbc', 16], ['sbc', 63]]], [[67, 0, 0, 0, 1], [4, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 59], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 196]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])], [('adc without carry', [21, 0, [['adc', 32], ['adc', 5]]], [[53, 0, 0, 0, 0], [58, 0, 0, 0, 0]]), ('adc signed overflow both ways', [80, 0, [['adc', 80], ['adc', 149]]], [[160, 1, 1, 0, 0], [53, 0, 1, 0, 1]]), ('adc carry out to zero', [255, 1, [['adc', 0], ['adc', 250]]], [[0, 0, 0, 1, 1], [251, 1, 0, 0, 0]]), ('sbc with carry set (no borrow)', [80, 1, [['sbc', 48], ['sbc', 176], ['sbc', 122]]], [[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [245, 1, 0, 0, 0]]), ('sum of exactly 0xFF', [123, 0, [['adc', 132], ['adc', 0]]], [[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]), ('carry in wraps operand', [60, 1, [['adc', 255]]], [[60, 0, 0, 0, 1]]), ('sbc with carry clear (borrow)', [85, 0, [['sbc', 16], ['sbc', 63]]], [[68, 0, 0, 0, 1], [5, 0, 0, 0, 1]]), ('cmp orders and keeps accumulator', [64, 0, [['cmp', 64], ['cmp', 65], ['cmp', 58], ['adc', 1]]], [[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]), ('sbc to exactly zero', [33, 1, [['sbc', 33], ['cmp', 197]]], [[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]])]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
adc without carry	`[[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]`	`[[49, 0, 0, 0, 0], [54, 0, 0, 0, 0]]`	Passed
adc signed overflow both ways	`[[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]`	`[[160, 1, 1, 0, 0], [49, 0, 1, 0, 1]]`	Passed
adc carry out to zero	`[[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]`	`[[0, 0, 0, 1, 1], [255, 1, 0, 0, 0]]`	Passed
sbc with carry set (no borrow)	`[[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]`	`[[32, 0, 0, 0, 1], [112, 0, 0, 0, 0], [241, 1, 0, 0, 0]]`	Passed
sum of exactly 0xFF	`[[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]`	`[[255, 1, 0, 0, 0], [255, 1, 0, 0, 0]]`	Passed
carry in wraps operand	`[[56, 0, 0, 0, 1]]`	`[[56, 0, 0, 0, 1]]`	Passed
sbc with carry clear (borrow)	`[[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]`	`[[64, 0, 0, 0, 1], [1, 0, 0, 0, 1]]`	Passed
cmp orders and keeps accumulator	`[[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]`	`[[64, 0, 0, 1, 1], [64, 1, 0, 0, 0], [64, 0, 0, 0, 1], [66, 0, 0, 0, 0]]`	Passed
sbc to exactly zero	`[[0, 0, 0, 1, 1], [0, 0, 0, 0, 1]]`	`[[0, 0, 0, 1, 1], [0, 0, 0, 0, 0]]`	Failed

SHA-256 / c223f55a674106c053142fb3b711cc42615ef8cb7b58c0710d7040d4a59284bd

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic bounded teaching model of one emulator rule; the instruction semantics are a stipulated contract inspired by common ISAs and are not a claim of cycle-exact or architectural conformance. 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.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:16.692361+00:00.

Case digest / 672689f0f7b6d3a3f673aadff5f4d625c85a3d772eab12477580802680a350ed