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FA-59601 / Subscription proration billing / Open access

Dunning retry schedule and status: terminal status stop · case 01

Unpaid subscriptions keep counting failures or are silently reactivated.

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

ROOT CAUSE

Only the canceled status stops processing; unpaid is not treated as terminal.

VERIFIED REPAIR

Restore the contract rule at the terminal status stop step: use `if status in ('canceled', 'unpaid'): break`.

Unsuccessful approach: The attempt stops only on failures, so a later payment reactivates a terminated subscription.

Case contract

Input {events: [[day, fail|pay]], due, retry: offsets from due for retries, final canceled|unpaid, today}. Events up to today are processed by day (stable). Payment settles: status active, no retry, stop. Each failure increments a counter; after more failures than scheduled retries the status becomes final and processing stops; otherwise past_due with next retry at due + retry[failures-1]. Return [status, next_retry].

Why this case matters

Payment retries drive subscription status; off-by-one retry counting cancels customers early or never.

1 / The failure

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

N = 1
observations = []
def solve(x):
    status = 'active'
    fails = 0
    nxt = None
    for day, kind in sorted(x['events'], key=lambda e: e[0]):
        if day > x['today']:
            break
        if status == 'canceled':
            break
        if kind == 'pay':
            status = 'active'; nxt = None; break
        fails += 1
        if fails > len(x['retry']):
            status = x['final']; nxt = None
        else:
            status = 'past_due'; nxt = x['due'] + x['retry'][fails - 1]
    return [status, nxt]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 4}, ['active', None]), ('normal control', {'events': [[19, 'fail'], [32, 'fail'], [37, 'fail'], [29, 'fail'], [33, 'pay'], [42, 'fail']], 'due': 19, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 34}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [8, 'fail'], [4, 'fail'], [23, 'fail']], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 15}, ['past_due', 5]), ('normal control', {'events': [[18, 'fail'], [12, 'fail'], [21, 'fail'], [19, 'fail']], 'due': 10, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 23}, ['unpaid', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('normal control', {'events': [[24, 'pay'], [14, 'fail'], [13, 'pay'], [21, 'pay'], [16, 'fail'], [6, 'fail']], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 35}, ['active', None]), ('normal control', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('normal control', {'events': [], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 24}, ['active', None]), ('normal control', {'events': [[15, 'pay'], [8, 'pay'], [23, 'fail'], [23, 'fail']], 'due': 2, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 9}, ['active', None])], [('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('regression', {'events': [[20, 'fail'], [27, 'pay'], [16, 'fail'], [22, 'fail'], [23, 'fail'], [23, 'fail']], 'due': 6, 'retry': [1, 3], 'final': 'unpaid', 'today': 34}, ['unpaid', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('normal control', {'events': [[5, 'pay']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 18}, ['active', None]), ('normal control', {'events': [[17, 'fail'], [31, 'pay']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 16}, ['active', None]), ('normal control', {'events': [[5, 'pay'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 2}, ['active', None]), ('normal control', {'events': [[15, 'fail']], 'due': 1, 'retry': [1, 3], 'final': 'canceled', 'today': 14}, ['active', None])], [('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[21, 'fail'], [21, 'fail'], [28, 'fail'], [21, 'fail'], [21, 'pay'], [39, 'fail']], 'due': 14, 'retry': [5], 'final': 'unpaid', 'today': 25}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 13, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 26}, ['active', None]), ('normal control', {'events': [[22, 'fail'], [10, 'pay'], [11, 'fail'], [25, 'fail'], [15, 'fail'], [16, 'fail']], 'due': 10, 'retry': [1, 3], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [22, 'pay'], [30, 'fail'], [27, 'fail']], 'due': 16, 'retry': [5], 'final': 'canceled', 'today': 32}, ['active', None]), ('normal control', {'events': [[28, 'fail']], 'due': 17, 'retry': [1, 3], 'final': 'unpaid', 'today': 21}, ['active', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('normal control', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('normal control', {'events': [[27, 'pay'], [21, 'fail'], [28, 'fail'], [31, 'fail'], [19, 'pay'], [21, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 30}, ['active', None]), ('normal control', {'events': [[8, 'fail'], [9, 'fail'], [33, 'pay']], 'due': 8, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 8}, ['past_due', 11])]]
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 fixtureActualExpectedOutcome
regression 0['active', None]['unpaid', None]Failed
regression 1['active', None]['unpaid', None]Failed
partial-repair probe 2['canceled', None]['canceled', None]Passed
partial-repair probe 3['active', None]['unpaid', None]Failed
normal control 4['active', None]['active', None]Passed
normal control 5['active', None]['active', None]Passed
normal control 6['past_due', 5]['past_due', 5]Passed
normal control 7['unpaid', None]['unpaid', None]Passed

SHA-256 / a48d26521362bba834a930928803c2da58b2d39b2121a32a7f32f604cd2f1354

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    status = 'active'
    fails = 0
    nxt = None
    for day, kind in sorted(x['events'], key=lambda e: e[0]):
        if day > x['today']:
            break
        if status == x['final'] and kind == 'fail':
            break
        if kind == 'pay':
            status = 'active'; nxt = None; break
        fails += 1
        if fails > len(x['retry']):
            status = x['final']; nxt = None
        else:
            status = 'past_due'; nxt = x['due'] + x['retry'][fails - 1]
    return [status, nxt]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 4}, ['active', None]), ('normal control', {'events': [[19, 'fail'], [32, 'fail'], [37, 'fail'], [29, 'fail'], [33, 'pay'], [42, 'fail']], 'due': 19, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 34}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [8, 'fail'], [4, 'fail'], [23, 'fail']], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 15}, ['past_due', 5]), ('normal control', {'events': [[18, 'fail'], [12, 'fail'], [21, 'fail'], [19, 'fail']], 'due': 10, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 23}, ['unpaid', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('normal control', {'events': [[24, 'pay'], [14, 'fail'], [13, 'pay'], [21, 'pay'], [16, 'fail'], [6, 'fail']], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 35}, ['active', None]), ('normal control', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('normal control', {'events': [], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 24}, ['active', None]), ('normal control', {'events': [[15, 'pay'], [8, 'pay'], [23, 'fail'], [23, 'fail']], 'due': 2, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 9}, ['active', None])], [('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('regression', {'events': [[20, 'fail'], [27, 'pay'], [16, 'fail'], [22, 'fail'], [23, 'fail'], [23, 'fail']], 'due': 6, 'retry': [1, 3], 'final': 'unpaid', 'today': 34}, ['unpaid', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('normal control', {'events': [[5, 'pay']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 18}, ['active', None]), ('normal control', {'events': [[17, 'fail'], [31, 'pay']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 16}, ['active', None]), ('normal control', {'events': [[5, 'pay'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 2}, ['active', None]), ('normal control', {'events': [[15, 'fail']], 'due': 1, 'retry': [1, 3], 'final': 'canceled', 'today': 14}, ['active', None])], [('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[21, 'fail'], [21, 'fail'], [28, 'fail'], [21, 'fail'], [21, 'pay'], [39, 'fail']], 'due': 14, 'retry': [5], 'final': 'unpaid', 'today': 25}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 13, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 26}, ['active', None]), ('normal control', {'events': [[22, 'fail'], [10, 'pay'], [11, 'fail'], [25, 'fail'], [15, 'fail'], [16, 'fail']], 'due': 10, 'retry': [1, 3], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [22, 'pay'], [30, 'fail'], [27, 'fail']], 'due': 16, 'retry': [5], 'final': 'canceled', 'today': 32}, ['active', None]), ('normal control', {'events': [[28, 'fail']], 'due': 17, 'retry': [1, 3], 'final': 'unpaid', 'today': 21}, ['active', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('normal control', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('normal control', {'events': [[27, 'pay'], [21, 'fail'], [28, 'fail'], [31, 'fail'], [19, 'pay'], [21, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 30}, ['active', None]), ('normal control', {'events': [[8, 'fail'], [9, 'fail'], [33, 'pay']], 'due': 8, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 8}, ['past_due', 11])]]
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 fixtureActualExpectedOutcome
regression 0['active', None]['unpaid', None]Failed
regression 1['unpaid', None]['unpaid', None]Passed
partial-repair probe 2['active', None]['canceled', None]Failed
partial-repair probe 3['active', None]['unpaid', None]Failed
normal control 4['active', None]['active', None]Passed
normal control 5['active', None]['active', None]Passed
normal control 6['past_due', 5]['past_due', 5]Passed
normal control 7['unpaid', None]['unpaid', None]Passed

SHA-256 / 4c15b823d85f0d81db9ec8877500f8a44ba6a50f2482a6188fba7c3c034611e9

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    status = 'active'
    fails = 0
    nxt = None
    for day, kind in sorted(x['events'], key=lambda e: e[0]):
        if day > x['today']:
            break
        if status in ('canceled', 'unpaid'):
            break
        if kind == 'pay':
            status = 'active'; nxt = None; break
        fails += 1
        if fails > len(x['retry']):
            status = x['final']; nxt = None
        else:
            status = 'past_due'; nxt = x['due'] + x['retry'][fails - 1]
    return [status, nxt]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 4}, ['active', None]), ('normal control', {'events': [[19, 'fail'], [32, 'fail'], [37, 'fail'], [29, 'fail'], [33, 'pay'], [42, 'fail']], 'due': 19, 'retry': [3, 5, 7], 'final': 'canceled', 'today': 34}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [8, 'fail'], [4, 'fail'], [23, 'fail']], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 15}, ['past_due', 5]), ('normal control', {'events': [[18, 'fail'], [12, 'fail'], [21, 'fail'], [19, 'fail']], 'due': 10, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 23}, ['unpaid', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[13, 'fail'], [6, 'fail'], [27, 'fail'], [20, 'fail'], [6, 'fail'], [19, 'pay']], 'due': 2, 'retry': [5], 'final': 'unpaid', 'today': 28}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('normal control', {'events': [[24, 'pay'], [14, 'fail'], [13, 'pay'], [21, 'pay'], [16, 'fail'], [6, 'fail']], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 35}, ['active', None]), ('normal control', {'events': [[4, 'fail'], [11, 'fail']], 'due': 3, 'retry': [5], 'final': 'canceled', 'today': 8}, ['past_due', 8]), ('normal control', {'events': [], 'due': 5, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 24}, ['active', None]), ('normal control', {'events': [[15, 'pay'], [8, 'pay'], [23, 'fail'], [23, 'fail']], 'due': 2, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 9}, ['active', None])], [('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('regression', {'events': [[20, 'fail'], [27, 'pay'], [16, 'fail'], [22, 'fail'], [23, 'fail'], [23, 'fail']], 'due': 6, 'retry': [1, 3], 'final': 'unpaid', 'today': 34}, ['unpaid', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('normal control', {'events': [[5, 'pay']], 'due': 3, 'retry': [1, 3], 'final': 'canceled', 'today': 18}, ['active', None]), ('normal control', {'events': [[17, 'fail'], [31, 'pay']], 'due': 8, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 16}, ['active', None]), ('normal control', {'events': [[5, 'pay'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 2}, ['active', None]), ('normal control', {'events': [[15, 'fail']], 'due': 1, 'retry': [1, 3], 'final': 'canceled', 'today': 14}, ['active', None])], [('regression', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('regression', {'events': [[21, 'fail'], [21, 'fail'], [28, 'fail'], [21, 'fail'], [21, 'pay'], [39, 'fail']], 'due': 14, 'retry': [5], 'final': 'unpaid', 'today': 25}, ['unpaid', None]), ('partial-repair probe', {'events': [[33, 'pay'], [20, 'fail'], [22, 'fail'], [34, 'fail'], [35, 'fail'], [36, 'fail']], 'due': 15, 'retry': [5], 'final': 'canceled', 'today': 41}, ['canceled', None]), ('partial-repair probe', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('normal control', {'events': [], 'due': 13, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 26}, ['active', None]), ('normal control', {'events': [[22, 'fail'], [10, 'pay'], [11, 'fail'], [25, 'fail'], [15, 'fail'], [16, 'fail']], 'due': 10, 'retry': [1, 3], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [[21, 'fail'], [22, 'pay'], [30, 'fail'], [27, 'fail']], 'due': 16, 'retry': [5], 'final': 'canceled', 'today': 32}, ['active', None]), ('normal control', {'events': [[28, 'fail']], 'due': 17, 'retry': [1, 3], 'final': 'unpaid', 'today': 21}, ['active', None])], [('regression', {'events': [[32, 'pay'], [16, 'fail'], [17, 'fail']], 'due': 12, 'retry': [5], 'final': 'unpaid', 'today': 36}, ['unpaid', None]), ('regression', {'events': [[15, 'pay'], [6, 'fail'], [14, 'fail'], [22, 'fail'], [5, 'fail'], [15, 'fail']], 'due': 0, 'retry': [1, 3], 'final': 'unpaid', 'today': 19}, ['unpaid', None]), ('partial-repair probe', {'events': [[43, 'pay'], [34, 'fail'], [29, 'fail']], 'due': 20, 'retry': [5], 'final': 'canceled', 'today': 48}, ['canceled', None]), ('partial-repair probe', {'events': [[37, 'pay'], [38, 'fail'], [34, 'fail'], [27, 'fail'], [32, 'fail']], 'due': 14, 'retry': [1, 3], 'final': 'unpaid', 'today': 42}, ['unpaid', None]), ('normal control', {'events': [[25, 'fail'], [22, 'fail']], 'due': 19, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 41}, ['past_due', 23]), ('normal control', {'events': [[27, 'pay'], [21, 'fail'], [28, 'fail'], [31, 'fail'], [19, 'pay'], [21, 'fail']], 'due': 15, 'retry': [2, 4, 8, 16], 'final': 'unpaid', 'today': 39}, ['active', None]), ('normal control', {'events': [], 'due': 1, 'retry': [2, 4, 8, 16], 'final': 'canceled', 'today': 30}, ['active', None]), ('normal control', {'events': [[8, 'fail'], [9, 'fail'], [33, 'pay']], 'due': 8, 'retry': [3, 5, 7], 'final': 'unpaid', 'today': 8}, ['past_due', 11])]]
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 fixtureActualExpectedOutcome
regression 0['unpaid', None]['unpaid', None]Passed
regression 1['unpaid', None]['unpaid', None]Passed
partial-repair probe 2['canceled', None]['canceled', None]Passed
partial-repair probe 3['unpaid', None]['unpaid', None]Passed
normal control 4['active', None]['active', None]Passed
normal control 5['active', None]['active', None]Passed
normal control 6['past_due', 5]['past_due', 5]Passed
normal control 7['unpaid', None]['unpaid', None]Passed

SHA-256 / 13eb32799ddc0f51c829eebbb674023bcdb6b2f19c39af436b86dd187e997eb4

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 2026-09-29T14:46:37.851187+00:00.

Case digest / db2177ab5141b1a4087e26c8929af784d89a31db52a2106a7a7719a6903bb7bb