{"abstract":"Small conversions avoid most of the fee.","category":"Game economy crafting balance","checks":8,"contract":"rates map currency -> copper value. Same currency returns [amount, 0] without fee. Otherwise value = amount*rate[from]; fee = ceil(value*fee_bp/10000), at least 1 copper when value > 0 and fee_bp > 0 and 0 otherwise; net = value - fee; return [net // rate[to], net % rate[to]] (change in copper).","contract_signature":"amount, from_cur, to_cur, rates, fee_bp","evaluation_group":"w2-game-economy-crafting-balance-currency-exchange","failed_approach":"Round-to-nearest still undercharges fractional fees below one half.","family":"w2-game-economy-crafting-balance-currency-exchange-fee-rounding","id":"FA-86216","implementations":{"attempt":{"sha256":"5bacbf183d7111f42c2356fbc6bdbecb42e1ee96768a9f469d9c939d0e29cc02","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(amount, from_cur, to_cur, rates, fee_bp):\n    if from_cur == to_cur:\n        return [amount, 0]\n    value = amount * rates[from_cur]\n    fee = round(value * fee_bp / 10000)\n    if value > 0 and fee_bp > 0:\n        fee = max(fee, 1)\n    net = value - fee\n    return [net // rates[to_cur], net % rates[to_cur]]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncases = [[('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [7, 46]),\n  ('regression fee rounding #1',\n   [7, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [6, 89]),\n  ('regression fee rounding #2',\n   [40, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 3866]),\n  ('regression fee rounding #3',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('regression fee rounding #1',\n   [7, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [6, 89]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 25],\n   [748, 0]),\n  ('regression fee rounding #2',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('regression fee rounding #3',\n   [1468, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [0, 1445]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [7, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [17, 41]),\n  ('regression fee rounding #1',\n   [40, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 3866]),\n  ('regression fee rounding #2',\n   [7, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [17, 23]),\n  ('regression fee rounding #3',\n   [1, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [2, 48]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [7, 25]),\n  ('fault site fee rounding #2',\n   [1, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [0, 98]),\n  ('regression fee rounding #1',\n   [2921, 'token', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [292070, 0]),\n  ('regression fee rounding #2',\n   [2375, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [5936, 90]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [751, 'silver', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [751, 0])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('regression fee rounding #1',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('fault site fee rounding #1',\n   [1, 'silver', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [98, 0]),\n  ('regression fee rounding #2',\n   [40, 'copper', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 38]),\n  ('regression fee rounding #3',\n   [7, 'silver', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [2, 189]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [7, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [67669, 0])]]\nfor label, args, expected in cases[N-1]:\n    check(label, 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":"10abaf37b5b306303db0355c2627c8001a2b6317d2edc09fdf3662057b5e934a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(amount, from_cur, to_cur, rates, fee_bp):\n    if from_cur == to_cur:\n        return [amount, 0]\n    value = amount * rates[from_cur]\n    fee = value * fee_bp // 10000\n    if value > 0 and fee_bp > 0:\n        fee = max(fee, 1)\n    net = value - fee\n    return [net // rates[to_cur], net % rates[to_cur]]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncases = [[('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [7, 46]),\n  ('regression fee rounding #1',\n   [7, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [6, 89]),\n  ('regression fee rounding #2',\n   [40, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 3866]),\n  ('regression fee rounding #3',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('regression fee rounding #1',\n   [7, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [6, 89]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 25],\n   [748, 0]),\n  ('regression fee rounding #2',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('regression fee rounding #3',\n   [1468, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [0, 1445]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [7, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [17, 41]),\n  ('regression fee rounding #1',\n   [40, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 3866]),\n  ('regression fee rounding #2',\n   [7, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [17, 23]),\n  ('regression fee rounding #3',\n   [1, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [2, 48]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [2, 49])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('fault site fee rounding #1',\n   [3, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [7, 25]),\n  ('fault site fee rounding #2',\n   [1, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [0, 98]),\n  ('regression fee rounding #1',\n   [2921, 'token', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [292070, 0]),\n  ('regression fee rounding #2',\n   [2375, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [5936, 90]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [751, 'silver', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],\n   [751, 0])],\n [('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),\n  ('regression fee rounding #1',\n   [1, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],\n   [248, 0]),\n  ('fault site fee rounding #1',\n   [1, 'silver', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [98, 0]),\n  ('regression fee rounding #2',\n   [40, 'copper', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [0, 38]),\n  ('regression fee rounding #3',\n   [7, 'silver', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],\n   [2, 189]),\n  ('same currency no fee #1',\n   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],\n   [5, 0]),\n  ('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),\n  ('control #1',\n   [7, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],\n   [67669, 0])]]\nfor label, args, expected in cases[N-1]:\n    check(label, 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":"Deterministic toy contract stipulated for this model; integer or exact arithmetic only, not a reproduction of any specific game engine. 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-game-economy-crafting-balance-currency-exchange-fee-rounding","generated_at":"2026-09-29T14:50:47.590060+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Game economies leak or destroy currency when one crafting or pricing rule is off by one boundary, rounding stage or state update; the defect is observable in exact integer outcomes.","root_cause":"The fee is floored instead of rounded up.","sha256":"1c6f97a263ea61857d4ef494aeb9eacc05b276cbb290a686eb11716431c22a9e","title":"Currency exchange desk: Exchange fee truncates · 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":42.486,"exit_code":1,"observations":[{"actual":[7,48],"check":"fee rounds up #1","expected":[7,48],"passed":true},{"actual":[7,46],"check":"fault site fee rounding #1","expected":[7,46],"passed":true},{"actual":[6,90],"check":"regression fee rounding #1","expected":[6,89],"passed":false},{"actual":[0,3867],"check":"regression fee rounding #2","expected":[0,3866],"passed":false},{"actual":[249,0],"check":"regression fee rounding #3","expected":[248,0],"passed":false},{"actual":[5,0],"check":"same currency no fee #1","expected":[5,0],"passed":true},{"actual":[0,0],"check":"zero amount with fee #1","expected":[0,0],"passed":true},{"actual":[2,49],"check":"control #1","expected":[2,49],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fee rounds up #1\", \"actual\": [7, 48], \"expected\": [7, 48], \"passed\": true}, {\"check\": \"fault site fee rounding #1\", \"actual\": [7, 46], \"expected\": [7, 46], \"passed\": true}, {\"check\": \"regression fee rounding #1\", \"actual\": [6, 90], \"expected\": [6, 89], \"passed\": false}, {\"check\": \"regression fee rounding #2\", \"actual\": [0, 3867], \"expected\": [0, 3866], \"passed\": false}, {\"check\": \"regression fee rounding #3\", \"actual\": [249, 0], \"expected\": [248, 0], \"passed\": false}, {\"check\": \"same currency no fee #1\", \"actual\": [5, 0], \"expected\": [5, 0], \"passed\": true}, {\"check\": \"zero amount with fee #1\", \"actual\": [0, 0], \"expected\": [0, 0], \"passed\": true}, {\"check\": \"control #1\", \"actual\": [2, 49], \"expected\": [2, 49], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.395,"exit_code":1,"observations":[{"actual":[7,49],"check":"fee rounds up #1","expected":[7,48],"passed":false},{"actual":[7,47],"check":"fault site fee rounding #1","expected":[7,46],"passed":false},{"actual":[6,90],"check":"regression fee rounding #1","expected":[6,89],"passed":false},{"actual":[0,3867],"check":"regression fee rounding #2","expected":[0,3866],"passed":false},{"actual":[249,0],"check":"regression fee rounding #3","expected":[248,0],"passed":false},{"actual":[5,0],"check":"same currency no fee #1","expected":[5,0],"passed":true},{"actual":[0,0],"check":"zero amount with fee #1","expected":[0,0],"passed":true},{"actual":[2,49],"check":"control #1","expected":[2,49],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fee rounds up #1\", \"actual\": [7, 49], \"expected\": [7, 48], \"passed\": false}, {\"check\": \"fault site fee rounding #1\", \"actual\": [7, 47], \"expected\": [7, 46], \"passed\": false}, {\"check\": \"regression fee rounding #1\", \"actual\": [6, 90], \"expected\": [6, 89], \"passed\": false}, {\"check\": \"regression fee rounding #2\", \"actual\": [0, 3867], \"expected\": [0, 3866], \"passed\": false}, {\"check\": \"regression fee rounding #3\", \"actual\": [249, 0], \"expected\": [248, 0], \"passed\": false}, {\"check\": \"same currency no fee #1\", \"actual\": [5, 0], \"expected\": [5, 0], \"passed\": true}, {\"check\": \"zero amount with fee #1\", \"actual\": [0, 0], \"expected\": [0, 0], \"passed\": true}, {\"check\": \"control #1\", \"actual\": [2, 49], \"expected\": [2, 49], \"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."}}