FA-59806 / Subscription proration billing / Open access

Renewal price with lock and increase cap: increase cap base · case 01

Renewal increases exceed the promised percentage cap.

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

ROOT CAUSE

The cap is computed from the list price, so it never binds.

VERIFIED REPAIR

Restore the contract rule at the increase cap base step: use `ceiling = x['last_paid'] * (100 + x['cap_pct']) // 100`.

Unsuccessful approach: The attempt adds the percentage as cents to the last price.

Case contract

Input {last_paid, list_price, locked|None, lock_until, renewal_day, cap_pct}. While the lock is active (renewal_day <= lock_until) the target is min(list_price, locked); otherwise list_price. The renewal price is min(target, last_paid*(100+cap_pct)//100). Return cents.

Why this case matters

Grandfathered prices and increase caps protect renewing subscribers; their interplay sets the renewal amount.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(x):
    if x['locked'] is not None and x['renewal_day'] <= x['lock_until']:
        target = min(x['list_price'], x['locked'])
    else:
        target = x['list_price']
    ceiling = x['list_price'] * (100 + x['cap_pct']) // 100
    return min(target, ceiling)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'last_paid': 2000, 'list_price': 3312, 'locked': 2500, 'lock_until': 173, 'renewal_day': 173, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('partial-repair probe', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 328, 'renewal_day': 201, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': None, 'lock_until': 83, 'renewal_day': 100, 'cap_pct': 20}, 4900), ('normal control', {'last_paid': 222, 'list_price': 222, 'locked': 222, 'lock_until': 231, 'renewal_day': 231, 'cap_pct': 5}, 222), ('normal control', {'last_paid': 4217, 'list_price': 4172, 'locked': 4217, 'lock_until': 1, 'renewal_day': 2, 'cap_pct': 0}, 4172)], [('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('normal control', {'last_paid': 4900, 'list_price': 4441, 'locked': 4900, 'lock_until': 309, 'renewal_day': 310, 'cap_pct': 0}, 4441), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2000, 'lock_until': 91, 'renewal_day': 92, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 4900, 'lock_until': 26, 'renewal_day': 27, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1219, 'list_price': 1057, 'locked': 1119, 'lock_until': 293, 'renewal_day': 294, 'cap_pct': 10}, 1057)], [('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('partial-repair probe', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1000, 'lock_until': 85, 'renewal_day': 85, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 110, 'renewal_day': 262, 'cap_pct': 10}, 1000), ('normal control', {'last_paid': 7522, 'list_price': 7059, 'locked': 8022, 'lock_until': 19, 'renewal_day': 388, 'cap_pct': 20}, 7059), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 285, 'renewal_day': 285, 'cap_pct': 20}, 2000)], [('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('partial-repair probe', {'last_paid': 2000, 'list_price': 4561, 'locked': 1900, 'lock_until': 96, 'renewal_day': 97, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 6548, 'list_price': 6483, 'locked': 6448, 'lock_until': 196, 'renewal_day': 196, 'cap_pct': 5}, 6448), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 173, 'renewal_day': 263, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2500, 'lock_until': 167, 'renewal_day': 167, 'cap_pct': 10}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 208, 'renewal_day': 260, 'cap_pct': 5}, 4900)], [('regression', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('partial-repair probe', {'last_paid': 1000, 'list_price': 1465, 'locked': None, 'lock_until': 310, 'renewal_day': 310, 'cap_pct': 5}, 1050), ('partial-repair probe', {'last_paid': 4984, 'list_price': 7349, 'locked': 4984, 'lock_until': 94, 'renewal_day': 95, 'cap_pct': 20}, 5980), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 345, 'renewal_day': 345, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1000, 'list_price': 754, 'locked': 900, 'lock_until': 155, 'renewal_day': 206, 'cap_pct': 10}, 754), ('normal control', {'last_paid': 2000, 'list_price': 3042, 'locked': 1900, 'lock_until': 55, 'renewal_day': 55, 'cap_pct': 5}, 1900), ('normal control', {'last_paid': 2000, 'list_price': 1532, 'locked': 2000, 'lock_until': 313, 'renewal_day': 57, 'cap_pct': 20}, 1532)]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), 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 0	`2500`	`2400`	Failed
regression 1	`7407`	`5145`	Failed
partial-repair probe 2	`654`	`582`	Failed
partial-repair probe 3	`4394`	`4394`	Passed
normal control 4	`1000`	`1000`	Passed
normal control 5	`4900`	`4900`	Passed
normal control 6	`222`	`222`	Passed
normal control 7	`4172`	`4172`	Passed

SHA-256 / 0f9156ba88af9ab85d236579cd3a38d982e39bc5cd03baa6b2a87d7c91edc3f2

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    if x['locked'] is not None and x['renewal_day'] <= x['lock_until']:
        target = min(x['list_price'], x['locked'])
    else:
        target = x['list_price']
    ceiling = x['last_paid'] + x['cap_pct']
    return min(target, ceiling)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'last_paid': 2000, 'list_price': 3312, 'locked': 2500, 'lock_until': 173, 'renewal_day': 173, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('partial-repair probe', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 328, 'renewal_day': 201, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': None, 'lock_until': 83, 'renewal_day': 100, 'cap_pct': 20}, 4900), ('normal control', {'last_paid': 222, 'list_price': 222, 'locked': 222, 'lock_until': 231, 'renewal_day': 231, 'cap_pct': 5}, 222), ('normal control', {'last_paid': 4217, 'list_price': 4172, 'locked': 4217, 'lock_until': 1, 'renewal_day': 2, 'cap_pct': 0}, 4172)], [('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('normal control', {'last_paid': 4900, 'list_price': 4441, 'locked': 4900, 'lock_until': 309, 'renewal_day': 310, 'cap_pct': 0}, 4441), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2000, 'lock_until': 91, 'renewal_day': 92, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 4900, 'lock_until': 26, 'renewal_day': 27, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1219, 'list_price': 1057, 'locked': 1119, 'lock_until': 293, 'renewal_day': 294, 'cap_pct': 10}, 1057)], [('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('partial-repair probe', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1000, 'lock_until': 85, 'renewal_day': 85, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 110, 'renewal_day': 262, 'cap_pct': 10}, 1000), ('normal control', {'last_paid': 7522, 'list_price': 7059, 'locked': 8022, 'lock_until': 19, 'renewal_day': 388, 'cap_pct': 20}, 7059), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 285, 'renewal_day': 285, 'cap_pct': 20}, 2000)], [('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('partial-repair probe', {'last_paid': 2000, 'list_price': 4561, 'locked': 1900, 'lock_until': 96, 'renewal_day': 97, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 6548, 'list_price': 6483, 'locked': 6448, 'lock_until': 196, 'renewal_day': 196, 'cap_pct': 5}, 6448), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 173, 'renewal_day': 263, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2500, 'lock_until': 167, 'renewal_day': 167, 'cap_pct': 10}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 208, 'renewal_day': 260, 'cap_pct': 5}, 4900)], [('regression', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('partial-repair probe', {'last_paid': 1000, 'list_price': 1465, 'locked': None, 'lock_until': 310, 'renewal_day': 310, 'cap_pct': 5}, 1050), ('partial-repair probe', {'last_paid': 4984, 'list_price': 7349, 'locked': 4984, 'lock_until': 94, 'renewal_day': 95, 'cap_pct': 20}, 5980), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 345, 'renewal_day': 345, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1000, 'list_price': 754, 'locked': 900, 'lock_until': 155, 'renewal_day': 206, 'cap_pct': 10}, 754), ('normal control', {'last_paid': 2000, 'list_price': 3042, 'locked': 1900, 'lock_until': 55, 'renewal_day': 55, 'cap_pct': 5}, 1900), ('normal control', {'last_paid': 2000, 'list_price': 1532, 'locked': 2000, 'lock_until': 313, 'renewal_day': 57, 'cap_pct': 20}, 1532)]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), 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 0	`2020`	`2400`	Failed
regression 1	`4905`	`5145`	Failed
partial-repair probe 2	`505`	`582`	Failed
partial-repair probe 3	`4125`	`4394`	Failed
normal control 4	`1000`	`1000`	Passed
normal control 5	`4900`	`4900`	Passed
normal control 6	`222`	`222`	Passed
normal control 7	`4172`	`4172`	Passed

SHA-256 / 248672a0e0ba67b14f93c0a73f6715b8b2cafd7ab013fa21eb603a83261eea74

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(x):
    if x['locked'] is not None and x['renewal_day'] <= x['lock_until']:
        target = min(x['list_price'], x['locked'])
    else:
        target = x['list_price']
    ceiling = x['last_paid'] * (100 + x['cap_pct']) // 100
    return min(target, ceiling)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'last_paid': 2000, 'list_price': 3312, 'locked': 2500, 'lock_until': 173, 'renewal_day': 173, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('partial-repair probe', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 328, 'renewal_day': 201, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': None, 'lock_until': 83, 'renewal_day': 100, 'cap_pct': 20}, 4900), ('normal control', {'last_paid': 222, 'list_price': 222, 'locked': 222, 'lock_until': 231, 'renewal_day': 231, 'cap_pct': 5}, 222), ('normal control', {'last_paid': 4217, 'list_price': 4172, 'locked': 4217, 'lock_until': 1, 'renewal_day': 2, 'cap_pct': 0}, 4172)], [('regression', {'last_paid': 4900, 'list_price': 7407, 'locked': None, 'lock_until': 112, 'renewal_day': 113, 'cap_pct': 5}, 5145), ('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('partial-repair probe', {'last_paid': 4105, 'list_price': 4394, 'locked': 4005, 'lock_until': 133, 'renewal_day': 322, 'cap_pct': 20}, 4394), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('normal control', {'last_paid': 4900, 'list_price': 4441, 'locked': 4900, 'lock_until': 309, 'renewal_day': 310, 'cap_pct': 0}, 4441), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2000, 'lock_until': 91, 'renewal_day': 92, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 4900, 'lock_until': 26, 'renewal_day': 27, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1219, 'list_price': 1057, 'locked': 1119, 'lock_until': 293, 'renewal_day': 294, 'cap_pct': 10}, 1057)], [('regression', {'last_paid': 485, 'list_price': 654, 'locked': None, 'lock_until': 58, 'renewal_day': 58, 'cap_pct': 20}, 582), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 4900, 'list_price': 5180, 'locked': 4900, 'lock_until': 0, 'renewal_day': 66, 'cap_pct': 20}, 5180), ('partial-repair probe', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1000, 'lock_until': 85, 'renewal_day': 85, 'cap_pct': 20}, 1000), ('normal control', {'last_paid': 1000, 'list_price': 1000, 'locked': 1500, 'lock_until': 110, 'renewal_day': 262, 'cap_pct': 10}, 1000), ('normal control', {'last_paid': 7522, 'list_price': 7059, 'locked': 8022, 'lock_until': 19, 'renewal_day': 388, 'cap_pct': 20}, 7059), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 285, 'renewal_day': 285, 'cap_pct': 20}, 2000)], [('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('regression', {'last_paid': 2000, 'list_price': 3222, 'locked': 2500, 'lock_until': 57, 'renewal_day': 260, 'cap_pct': 0}, 2000), ('partial-repair probe', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('partial-repair probe', {'last_paid': 2000, 'list_price': 4561, 'locked': 1900, 'lock_until': 96, 'renewal_day': 97, 'cap_pct': 20}, 2400), ('normal control', {'last_paid': 6548, 'list_price': 6483, 'locked': 6448, 'lock_until': 196, 'renewal_day': 196, 'cap_pct': 5}, 6448), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': None, 'lock_until': 173, 'renewal_day': 263, 'cap_pct': 5}, 2000), ('normal control', {'last_paid': 2000, 'list_price': 2000, 'locked': 2500, 'lock_until': 167, 'renewal_day': 167, 'cap_pct': 10}, 2000), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 208, 'renewal_day': 260, 'cap_pct': 5}, 4900)], [('regression', {'last_paid': 2000, 'list_price': 3442, 'locked': 2000, 'lock_until': 83, 'renewal_day': 84, 'cap_pct': 5}, 2100), ('regression', {'last_paid': 2000, 'list_price': 2438, 'locked': 2500, 'lock_until': 146, 'renewal_day': 147, 'cap_pct': 20}, 2400), ('partial-repair probe', {'last_paid': 1000, 'list_price': 1465, 'locked': None, 'lock_until': 310, 'renewal_day': 310, 'cap_pct': 5}, 1050), ('partial-repair probe', {'last_paid': 4984, 'list_price': 7349, 'locked': 4984, 'lock_until': 94, 'renewal_day': 95, 'cap_pct': 20}, 5980), ('normal control', {'last_paid': 4900, 'list_price': 4900, 'locked': 5400, 'lock_until': 345, 'renewal_day': 345, 'cap_pct': 5}, 4900), ('normal control', {'last_paid': 1000, 'list_price': 754, 'locked': 900, 'lock_until': 155, 'renewal_day': 206, 'cap_pct': 10}, 754), ('normal control', {'last_paid': 2000, 'list_price': 3042, 'locked': 1900, 'lock_until': 55, 'renewal_day': 55, 'cap_pct': 5}, 1900), ('normal control', {'last_paid': 2000, 'list_price': 1532, 'locked': 2000, 'lock_until': 313, 'renewal_day': 57, 'cap_pct': 20}, 1532)]]
for i, (label, args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (label, i), 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 0	`2400`	`2400`	Passed
regression 1	`5145`	`5145`	Passed
partial-repair probe 2	`582`	`582`	Passed
partial-repair probe 3	`4394`	`4394`	Passed
normal control 4	`1000`	`1000`	Passed
normal control 5	`4900`	`4900`	Passed
normal control 6	`222`	`222`	Passed
normal control 7	`4172`	`4172`	Passed

SHA-256 / 71868d0262154afe8d45d1beb54ae58d1a1cfe024ecb2383bbde3a04cbe278a6

Verification & scope

A deterministic teaching model of a stipulated billing rule. It makes no claim to reproduce any billing provider's exact behaviour and is not billing software. 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 2026-09-29T14:46:39.790530+00:00.

Case digest / 9996de41cc6c7e9cfd7295e0e73d4a5ac05e36f02b8251466ade0a711cb3d242