FAILURE MAP
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FA-86221 / Game economy crafting balance / Open access

Currency exchange desk: Empty exchange charges the minimum fee · case 01

Exchanging nothing produces a negative balance.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The minimum fee applies even when no value is exchanged.

THE FAILURE

The minimum fee applies even when no value is exchanged.

Unsuccessful approach: Gating only on value charges a fee at a zero-fee desk.

Case 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).

Why this case matters

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.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(amount, from_cur, to_cur, rates, fee_bp):
    if from_cur == to_cur:
        return [amount, 0]
    value = amount * rates[from_cur]
    fee = -(-value * fee_bp // 10000)
    if fee_bp > 0:
        fee = max(fee, 1)
    net = value - fee
    return [net // rates[to_cur], net % rates[to_cur]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'gem', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'token', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('partial repair boundary #1',
   [1, 'gold', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [100, 0]),
  ('partial repair boundary #2',
   [3, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [3, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'token', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],
   [0, 0]),
  ('partial repair boundary #1',
   [40, 'token', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [40, 0]),
  ('partial repair boundary #2',
   [1, 'gold', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [100, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'copper', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [0, 0]),
  ('partial repair boundary #1',
   [40, 'gold', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [4000, 0]),
  ('partial repair boundary #2',
   [914, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [0, 914]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'copper', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('partial repair boundary #1',
   [939, 'token', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [375, 150]),
  ('partial repair boundary #2',
   [7, 'copper', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [0, 7]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [751, 'silver', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [751, 0])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('partial repair boundary #1',
   [7, 'gold', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [280, 0]),
  ('partial repair boundary #2',
   [2596, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [2596, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [7, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [67669, 0])]]
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 fixtureActualExpectedOutcome
zero amount with fee #1[-1, 99][0, 0]Failed
fault site minimum fee gate #1[-1, 9999][0, 0]Failed
fault site minimum fee gate #2[-1, 9999][0, 0]Failed
partial repair boundary #1[100, 0][100, 0]Passed
partial repair boundary #2[3, 0][3, 0]Passed
same currency no fee #1[5, 0][5, 0]Passed
fee rounds up #1[7, 48][7, 48]Passed
control #1[2, 49][2, 49]Passed

SHA-256 / 326f9fd0079d6bc553d18400c398e1557499cd8b5918d586a0c1402061fcb556

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(amount, from_cur, to_cur, rates, fee_bp):
    if from_cur == to_cur:
        return [amount, 0]
    value = amount * rates[from_cur]
    fee = -(-value * fee_bp // 10000)
    if value > 0:
        fee = max(fee, 1)
    net = value - fee
    return [net // rates[to_cur], net % rates[to_cur]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'gem', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'token', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('partial repair boundary #1',
   [1, 'gold', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [100, 0]),
  ('partial repair boundary #2',
   [3, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [3, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'token', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'silver', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],
   [0, 0]),
  ('partial repair boundary #1',
   [40, 'token', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [40, 0]),
  ('partial repair boundary #2',
   [1, 'gold', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [100, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'copper', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [0, 0]),
  ('partial repair boundary #1',
   [40, 'gold', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [4000, 0]),
  ('partial repair boundary #2',
   [914, 'copper', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [0, 914]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [1, 'gem', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [2, 49])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'copper', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 150],
   [0, 0]),
  ('partial repair boundary #1',
   [939, 'token', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [375, 150]),
  ('partial repair boundary #2',
   [7, 'copper', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [0, 7]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [751, 'silver', 'silver', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 1],
   [751, 0])],
 [('zero amount with fee #1', [0, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 50], [0, 0]),
  ('fault site minimum fee gate #1',
   [0, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 50],
   [0, 0]),
  ('fault site minimum fee gate #2',
   [0, 'gem', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [0, 0]),
  ('partial repair boundary #1',
   [7, 'gold', 'gem', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [280, 0]),
  ('partial repair boundary #2',
   [2596, 'silver', 'token', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 0],
   [2596, 0]),
  ('same currency no fee #1',
   [5, 'gold', 'gold', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250}, 150],
   [5, 0]),
  ('fee rounds up #1', [3, 'gem', 'silver', {'copper': 1, 'silver': 100, 'gem': 250}, 25], [7, 48]),
  ('control #1',
   [7, 'gold', 'copper', {'copper': 1, 'silver': 100, 'gold': 10000, 'gem': 250, 'token': 100}, 333],
   [67669, 0])]]
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 fixtureActualExpectedOutcome
zero amount with fee #1[0, 0][0, 0]Passed
fault site minimum fee gate #1[0, 0][0, 0]Passed
fault site minimum fee gate #2[0, 0][0, 0]Passed
partial repair boundary #1[99, 99][100, 0]Failed
partial repair boundary #2[2, 99][3, 0]Failed
same currency no fee #1[5, 0][5, 0]Passed
fee rounds up #1[7, 48][7, 48]Passed
control #1[2, 49][2, 49]Passed

SHA-256 / a4f3542ea922a75702ca8f4c21106ebe5d2c6757a7e838b364766054f99f0d5a

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 8 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.

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Verification & scope

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.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:47.587088+00:00.

Case digest / 09b921b4d89e0185a1ac2dcf69518f55108e19ad3510e8bd29fb8e12ec411236