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Duplicate delivery changes an aggregate · case 01

A replayed event increases a total that should change once per event identity.

Verified by executionVariant 1 · 3 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Delivery identity was discarded before aggregation.

VERIFIED REPAIR

Deduplicate by event identity, preserving distinct events with equal amounts.

Unsuccessful approach: Deduplicating amounts collapses legitimate equal-valued events.

Case contract

Deduplicate by event identity, preserving distinct events with equal amounts.

Why this case matters

A compact reasoning and repair task with executable evidence.

1 / The failure

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

N = 1
observations = []
def solve(events):
    return sum(e['amount'] for e in events)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
events = [{'id': 'a', 'amount': N}, {'id': 'a', 'amount': N}, {'id': 'b', 'amount': N}]
check('replayed delivery', solve(events), 2*N)
check('empty stream', solve([]), 0)
check('distinct equal amounts', solve(events[1:]), 2*N)
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
replayed delivery32Failed
empty stream00Passed
distinct equal amounts22Passed

SHA-256 / 82649a60bba1130d37a14f4c26126733aebbb4c9098c20d5b7d4e8d09f9e1387

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(events):
    return sum(set(e['amount'] for e in events))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
events = [{'id': 'a', 'amount': N}, {'id': 'a', 'amount': N}, {'id': 'b', 'amount': N}]
check('replayed delivery', solve(events), 2*N)
check('empty stream', solve([]), 0)
check('distinct equal amounts', solve(events[1:]), 2*N)
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
replayed delivery12Failed
empty stream00Passed
distinct equal amounts12Failed

SHA-256 / e3474409f621b10e0fb1761e2c8f869b1e8a2e43e146dbd0f64d84eb3a30098b

3 / The verified repair

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

N = 1
observations = []
def solve(events):
    return sum({e['id']: e['amount'] for e in events}.values())
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
events = [{'id': 'a', 'amount': N}, {'id': 'a', 'amount': N}, {'id': 'b', 'amount': N}]
check('replayed delivery', solve(events), 2*N)
check('empty stream', solve([]), 0)
check('distinct equal amounts', solve(events[1:]), 2*N)
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
replayed delivery22Passed
empty stream00Passed
distinct equal amounts22Passed

SHA-256 / 7d2776c4e9d6f8fd0de632bd6c9e76d2c12d485dcff06b679d09d240b1184898

Verification & scope

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 2026-09-29T14:36:49.838454+00:00.

Case digest / 392ecea4c3b80d482671512f7aa82cc0029e5117b51cc864c2cb16ff250f7271