FAILURE MAP
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FA-361 / Consensus / Open access

Activate a joint voting configuration: The configuration entry is beyond the committed prefix · case 01

The joint configuration operation is admitted even though the configuration entry is beyond the committed prefix.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The admission path omits the configuration entry invariant while validating the other operation preconditions.

THE FAILURE

The admission path omits the configuration entry invariant while validating the other operation preconditions.

Unsuccessful approach: Adding the configuration entry check repairs the reported defect, but replacing the adjacent no pending change check loses that independent invariant.

Case contract

Return a Boolean admission decision for activate a joint voting configuration. The record r must satisfy all of: len(set(r['old_majority'][0]) & set(r['old_majority'][1])) * 2 > len(set(r['old_majority'][0])); len(set(r['new_majority'][0]) & set(r['new_majority'][1])) * 2 > len(set(r['new_majority'][0])); r['configuration_entry'][0] <= r['configuration_entry'][1]; r['no_pending_change'] is None; all(x >= r['learner_catchup'][0] for x in r['learner_catchup'][1]). Extra tracing fields are ignored; validation does not mutate the record.

Why this case matters

A deterministic local contract for consensus. Each negative fixture violates exactly one invariant. No transport timing, persistence, cryptographic verification, or full protocol implementation is claimed.

1 / The failure

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

N = 1
observations = []
def solve(r):
    return (len(set(r['old_majority'][0]) & set(r['old_majority'][1])) * 2 > len(set(r['old_majority'][0]))) and (len(set(r['new_majority'][0]) & set(r['new_majority'][1])) * 2 > len(set(r['new_majority'][0]))) and (r['no_pending_change'] is None) and (all(x >= r['learner_catchup'][0] for x in r['learner_catchup'][1]))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'old_majority': [[1, 2, 3], [1, 2]], 'new_majority': [[3, 4, 5], [3, 4]], 'configuration_entry': [8, 8], 'no_pending_change': None, 'learner_catchup': [8, [8, 10]]}
check('valid operation', solve(r), True)
check('The old configuration has only a minority', solve(dict(r, **{'old_majority': [[1, 2, 3], [1]]})), False)
check('The new configuration has only a minority', solve(dict(r, **{'new_majority': [[3, 4, 5], [3]]})), False)
check('The configuration entry is beyond the committed prefix', solve(dict(r, **{'configuration_entry': [9, 8]})), False)
check('A second membership change overlaps an unfinalized change', solve(dict(r, **{'no_pending_change': 'pending'})), False)
check('A promoted learner lacks the configuration entry', solve(dict(r, **{'learner_catchup': [8, [7, 10]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'old_majority': [[1, 2, 3], [1]], 'new_majority': [[3, 4, 5], [3]], 'configuration_entry': [9, 8], 'no_pending_change': 'pending', 'learner_catchup': [8, [7, 10]]}
keys = list(invalid)
pair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}
check('two independent violations in variant', solve(dict(r, **pair)), False)
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
valid operationTrueTruePassed
The old configuration has only a minorityFalseFalsePassed
The new configuration has only a minorityFalseFalsePassed
The configuration entry is beyond the committed prefixTrueFalseFailed
A second membership change overlaps an unfinalized changeFalseFalsePassed
A promoted learner lacks the configuration entryFalseFalsePassed
unrelated tracing metadataTrueTruePassed
repeat validation is pureTrueTruePassed
two independent violations in variantFalseFalsePassed

SHA-256 / 695972c383d7837357a891cec757ca770d8e3d7bb5c86dd1874345bf0d7b9f17

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(r):
    return (len(set(r['old_majority'][0]) & set(r['old_majority'][1])) * 2 > len(set(r['old_majority'][0]))) and (len(set(r['new_majority'][0]) & set(r['new_majority'][1])) * 2 > len(set(r['new_majority'][0]))) and (r['configuration_entry'][0] <= r['configuration_entry'][1]) and (all(x >= r['learner_catchup'][0] for x in r['learner_catchup'][1]))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'old_majority': [[1, 2, 3], [1, 2]], 'new_majority': [[3, 4, 5], [3, 4]], 'configuration_entry': [8, 8], 'no_pending_change': None, 'learner_catchup': [8, [8, 10]]}
check('valid operation', solve(r), True)
check('The old configuration has only a minority', solve(dict(r, **{'old_majority': [[1, 2, 3], [1]]})), False)
check('The new configuration has only a minority', solve(dict(r, **{'new_majority': [[3, 4, 5], [3]]})), False)
check('The configuration entry is beyond the committed prefix', solve(dict(r, **{'configuration_entry': [9, 8]})), False)
check('A second membership change overlaps an unfinalized change', solve(dict(r, **{'no_pending_change': 'pending'})), False)
check('A promoted learner lacks the configuration entry', solve(dict(r, **{'learner_catchup': [8, [7, 10]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'old_majority': [[1, 2, 3], [1]], 'new_majority': [[3, 4, 5], [3]], 'configuration_entry': [9, 8], 'no_pending_change': 'pending', 'learner_catchup': [8, [7, 10]]}
keys = list(invalid)
pair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}
check('two independent violations in variant', solve(dict(r, **pair)), False)
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
valid operationTrueTruePassed
The old configuration has only a minorityFalseFalsePassed
The new configuration has only a minorityFalseFalsePassed
The configuration entry is beyond the committed prefixFalseFalsePassed
A second membership change overlaps an unfinalized changeTrueFalseFailed
A promoted learner lacks the configuration entryFalseFalsePassed
unrelated tracing metadataTrueTruePassed
repeat validation is pureTrueTruePassed
two independent violations in variantFalseFalsePassed

SHA-256 / 91bd59f43b044d8a649156208ff3f2d62685e1a63d8346b24a26de2baa2fa526

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 9 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.

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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 2026-09-29T14:36:52.596199+00:00.

Case digest / 76894fc2ef8cfa98ba7645a3b85a6003d8439106fc9d687d299f90df0a57cc0f