FA-61891 / Currency rounding and FX conversion / Open access

A zero target rate yields a zero conversion instead of a bad-rate error · case 01

A corrupt zero rate for the target silently produces 0.00.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The validity test uses r < 0, admitting a zero rate.

VERIFIED REPAIR

Reject every rate that is zero or negative before converting.

Unsuccessful approach: Rejecting only a zero source rate avoids division by zero but still converts into a zero-rated target.

Case contract

solve(amount, frm, to, rates): rates maps a currency to units of that currency per 1 USD (decimal strings); USD is implicitly 1 when absent. Convert exactly as amount / rate[frm] * rate[to] with no intermediate rounding, then round half-even to the target exponent (USD/EUR/GBP/CHF/SEK/NOK 2, JPY/KRW 0, KWD 3, CLF 4) and return a plain string. A missing rate returns 'ERR:no-rate:<code>', a zero or negative rate 'ERR:bad-rate:<code>' (source checked first).

Why this case matters

Currency amounts must be rounded at the right stage and in the right unit, or ledgers, quotes and settlements drift by minor units.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, frm, to, rates):
    exps = {'USD': 2, 'EUR': 2, 'GBP': 2, 'CHF': 2, 'SEK': 2, 'NOK': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'CLF': 4}
    def rate(c):
        if c == 'USD' and c not in rates: return Decimal(1)
        if c not in rates: return None
        return Decimal(rates[c])
    rf, rt = rate(frm), rate(to)
    for c, r in ((frm, rf), (to, rt)):
        if r is None: return 'ERR:no-rate:' + c
        if r < 0: return 'ERR:bad-rate:' + c
    usd = Decimal(amount) / rf
    out = usd * rt
    return format(out.quantize(Decimal(1).scaleb(-exps[to]), rounding=ROUND_HALF_EVEN), 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')],
 [('regression nonpositive-rate 1', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('regression nonpositive-rate 2',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('control: zero rate target', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20'),
  ('control: usd absent', ('42.42', 'EUR', 'USD', {'EUR': '0.92'}), '46.11'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453')],
 [('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')]]
for label, args, expected in cases[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
regression nonpositive-rate 1	`0.00`	`ERR:bad-rate:CHF`	Failed
regression nonpositive-rate 2	`0`	`ERR:bad-rate:JPY`	Failed
control: euro to yen	`16453`	`16453`	Passed
control: usd to dinar	`30.710`	`30.710`	Passed
control: pound to usd	`6.33`	`6.33`	Passed
control: missing target	`ERR:no-rate:SEK`	`ERR:no-rate:SEK`	Passed

SHA-256 / 5097366d11f89d55a7abe9daa318d9541314d041ae845a917f106a0c0b246dfe

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, frm, to, rates):
    exps = {'USD': 2, 'EUR': 2, 'GBP': 2, 'CHF': 2, 'SEK': 2, 'NOK': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'CLF': 4}
    def rate(c):
        if c == 'USD' and c not in rates: return Decimal(1)
        if c not in rates: return None
        return Decimal(rates[c])
    rf, rt = rate(frm), rate(to)
    for c, r in ((frm, rf), (to, rt)):
        if r is None: return 'ERR:no-rate:' + c
        if r < 0 or (r == 0 and c == frm): return 'ERR:bad-rate:' + c
    usd = Decimal(amount) / rf
    out = usd * rt
    return format(out.quantize(Decimal(1).scaleb(-exps[to]), rounding=ROUND_HALF_EVEN), 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')],
 [('regression nonpositive-rate 1', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('regression nonpositive-rate 2',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('control: zero rate target', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20'),
  ('control: usd absent', ('42.42', 'EUR', 'USD', {'EUR': '0.92'}), '46.11'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453')],
 [('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')]]
for label, args, expected in cases[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
regression nonpositive-rate 1	`0.00`	`ERR:bad-rate:CHF`	Failed
regression nonpositive-rate 2	`0`	`ERR:bad-rate:JPY`	Failed
control: euro to yen	`16453`	`16453`	Passed
control: usd to dinar	`30.710`	`30.710`	Passed
control: pound to usd	`6.33`	`6.33`	Passed
control: missing target	`ERR:no-rate:SEK`	`ERR:no-rate:SEK`	Passed

SHA-256 / b8ee0377e2f59d0d5df439a0e6874a3da11359aba744716d85422ed571b4bac1

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, frm, to, rates):
    exps = {'USD': 2, 'EUR': 2, 'GBP': 2, 'CHF': 2, 'SEK': 2, 'NOK': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'CLF': 4}
    def rate(c):
        if c == 'USD' and c not in rates: return Decimal(1)
        if c not in rates: return None
        return Decimal(rates[c])
    rf, rt = rate(frm), rate(to)
    for c, r in ((frm, rf), (to, rt)):
        if r is None: return 'ERR:no-rate:' + c
        if r <= 0: return 'ERR:bad-rate:' + c
    usd = Decimal(amount) / rf
    out = usd * rt
    return format(out.quantize(Decimal(1).scaleb(-exps[to]), rounding=ROUND_HALF_EVEN), 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')],
 [('regression nonpositive-rate 1', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('regression nonpositive-rate 2',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('control: zero rate target', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20'),
  ('control: usd absent', ('42.42', 'EUR', 'USD', {'EUR': '0.92'}), '46.11'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453')],
 [('regression nonpositive-rate 1', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('regression nonpositive-rate 2', ('10', 'USD', 'JPY', {'JPY': '0'}), 'ERR:bad-rate:JPY'),
  ('control: euro to yen',
   ('100', 'EUR', 'JPY',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16453'),
  ('control: usd to dinar',
   ('100.00', 'USD', 'KWD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '30.710'),
  ('control: pound to usd',
   ('5', 'GBP', 'USD',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '6.33'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK')],
 [('regression nonpositive-rate 1',
   ('86062.42', 'USD', 'KRW', {'EUR': '0.92', 'KRW': '0', 'CLF': '0.02451', 'CHF': '0.8801', 'USD': '1'}),
   'ERR:bad-rate:KRW'),
  ('regression nonpositive-rate 2', ('10', 'EUR', 'CHF', {'EUR': '0.92', 'CHF': '0'}), 'ERR:bad-rate:CHF'),
  ('control: missing target',
   ('1', 'EUR', 'SEK',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   'ERR:no-rate:SEK'),
  ('control: won to franc',
   ('250000', 'KRW', 'CHF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '162.68'),
  ('control: yen to unit of account',
   ('99999', 'JPY', 'CLF',
    {'EUR': '0.92',
     'JPY': '151.37',
     'KRW': '1352.5',
     'KWD': '0.3071',
     'GBP': '0.7893',
     'CLF': '0.02451',
     'CHF': '0.8801'}),
   '16.1920'),
  ('control: explicit usd rate', ('10', 'USD', 'EUR', {'USD': '1', 'EUR': '0.92'}), '9.20')]]
for label, args, expected in cases[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
regression nonpositive-rate 1	`ERR:bad-rate:CHF`	`ERR:bad-rate:CHF`	Passed
regression nonpositive-rate 2	`ERR:bad-rate:JPY`	`ERR:bad-rate:JPY`	Passed
control: euro to yen	`16453`	`16453`	Passed
control: usd to dinar	`30.710`	`30.710`	Passed
control: pound to usd	`6.33`	`6.33`	Passed
control: missing target	`ERR:no-rate:SEK`	`ERR:no-rate:SEK`	Passed

SHA-256 / fe2efdb3ed9fcc2975e7cae03e2d04e92684c7484b654398bafbfcc17b99e976

Verification & scope

A deterministic, bounded teaching model with a stipulated toy contract; it makes no claim of conformance to any real regulation, standard, or institution's rules. 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 2026-09-29T14:46:59.407329+00:00.

Case digest / 33be8cc539883a4ba2a69e9ae0dfd23958922336460b830568dda21c7cde0dbf