FA-516 / Consensus / Open access

Accept a proposal value: An accept request bypasses the bounded value envelope · case 01

The acceptor accept operation is admitted even though an accept request bypasses the bounded value envelope.

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

ROOT CAUSE

The admission path omits the value length invariant while validating the other operation preconditions.

VERIFIED REPAIR

Require len(r['value_length'][0]) <= r['value_length'][1] together with every other stated precondition before accepting the operation.

Unsuccessful approach: Adding the value length check repairs the reported defect, but replacing the adjacent accept persisted check loses that independent invariant.

Case contract

Return a Boolean admission decision for accept a proposal value. The record r must satisfy all of: tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1]); r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]; r['slot_untrimmed'][0] > r['slot_untrimmed'][1]; len(r['value_length'][0]) <= r['value_length'][1]; r['accept_persisted'] is True. 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 (tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1])) and (r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]) and (r['slot_untrimmed'][0] > r['slot_untrimmed'][1]) and (r['accept_persisted'] is True)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'ballot_promised': [[6, 1], [5, 2]], 'ballot_value_unique': ['x', 'x'], 'slot_untrimmed': [11, 10], 'value_length': ['abc', 3], 'accept_persisted': True}
check('valid operation', solve(r), True)
check('A value is accepted below the promised ballot', solve(dict(r, **{'ballot_promised': [[5, 1], [5, 2]]})), False)
check('The same ballot accepts two different values', solve(dict(r, **{'ballot_value_unique': ['x', 'y']})), False)
check('A forgotten slot is reopened without its chosen evidence', solve(dict(r, **{'slot_untrimmed': [10, 10]})), False)
check('An accept request bypasses the bounded value envelope', solve(dict(r, **{'value_length': ['abcd', 3]})), False)
check('An accept acknowledgement precedes durable acceptance', solve(dict(r, **{'accept_persisted': False})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'ballot_promised': [[5, 1], [5, 2]], 'ballot_value_unique': ['x', 'y'], 'slot_untrimmed': [10, 10], 'value_length': ['abcd', 3], 'accept_persisted': False}
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 fixture	Actual	Expected	Outcome
valid operation	`True`	`True`	Passed
A value is accepted below the promised ballot	`False`	`False`	Passed
The same ballot accepts two different values	`False`	`False`	Passed
A forgotten slot is reopened without its chosen evidence	`False`	`False`	Passed
An accept request bypasses the bounded value envelope	`True`	`False`	Failed
An accept acknowledgement precedes durable acceptance	`False`	`False`	Passed
unrelated tracing metadata	`True`	`True`	Passed
repeat validation is pure	`True`	`True`	Passed
two independent violations in variant	`False`	`False`	Passed

SHA-256 / c51e8d33d90608b932d3ef818c0a48f4b63488ba4041c3dafef4b98eded95bcd

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1])) and (r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]) and (r['slot_untrimmed'][0] > r['slot_untrimmed'][1]) and (len(r['value_length'][0]) <= r['value_length'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'ballot_promised': [[6, 1], [5, 2]], 'ballot_value_unique': ['x', 'x'], 'slot_untrimmed': [11, 10], 'value_length': ['abc', 3], 'accept_persisted': True}
check('valid operation', solve(r), True)
check('A value is accepted below the promised ballot', solve(dict(r, **{'ballot_promised': [[5, 1], [5, 2]]})), False)
check('The same ballot accepts two different values', solve(dict(r, **{'ballot_value_unique': ['x', 'y']})), False)
check('A forgotten slot is reopened without its chosen evidence', solve(dict(r, **{'slot_untrimmed': [10, 10]})), False)
check('An accept request bypasses the bounded value envelope', solve(dict(r, **{'value_length': ['abcd', 3]})), False)
check('An accept acknowledgement precedes durable acceptance', solve(dict(r, **{'accept_persisted': False})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'ballot_promised': [[5, 1], [5, 2]], 'ballot_value_unique': ['x', 'y'], 'slot_untrimmed': [10, 10], 'value_length': ['abcd', 3], 'accept_persisted': False}
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 fixture	Actual	Expected	Outcome
valid operation	`True`	`True`	Passed
A value is accepted below the promised ballot	`False`	`False`	Passed
The same ballot accepts two different values	`False`	`False`	Passed
A forgotten slot is reopened without its chosen evidence	`False`	`False`	Passed
An accept request bypasses the bounded value envelope	`False`	`False`	Passed
An accept acknowledgement precedes durable acceptance	`True`	`False`	Failed
unrelated tracing metadata	`True`	`True`	Passed
repeat validation is pure	`True`	`True`	Passed
two independent violations in variant	`False`	`False`	Passed

SHA-256 / df1cc29bfcb93b82b612191f54593f5c36225de7cfd4b7eb8540c30c2539746e

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1])) and (r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]) and (r['slot_untrimmed'][0] > r['slot_untrimmed'][1]) and (len(r['value_length'][0]) <= r['value_length'][1]) and (r['accept_persisted'] is True)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'ballot_promised': [[6, 1], [5, 2]], 'ballot_value_unique': ['x', 'x'], 'slot_untrimmed': [11, 10], 'value_length': ['abc', 3], 'accept_persisted': True}
check('valid operation', solve(r), True)
check('A value is accepted below the promised ballot', solve(dict(r, **{'ballot_promised': [[5, 1], [5, 2]]})), False)
check('The same ballot accepts two different values', solve(dict(r, **{'ballot_value_unique': ['x', 'y']})), False)
check('A forgotten slot is reopened without its chosen evidence', solve(dict(r, **{'slot_untrimmed': [10, 10]})), False)
check('An accept request bypasses the bounded value envelope', solve(dict(r, **{'value_length': ['abcd', 3]})), False)
check('An accept acknowledgement precedes durable acceptance', solve(dict(r, **{'accept_persisted': False})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'ballot_promised': [[5, 1], [5, 2]], 'ballot_value_unique': ['x', 'y'], 'slot_untrimmed': [10, 10], 'value_length': ['abcd', 3], 'accept_persisted': False}
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 fixture	Actual	Expected	Outcome
valid operation	`True`	`True`	Passed
A value is accepted below the promised ballot	`False`	`False`	Passed
The same ballot accepts two different values	`False`	`False`	Passed
A forgotten slot is reopened without its chosen evidence	`False`	`False`	Passed
An accept request bypasses the bounded value envelope	`False`	`False`	Passed
An accept acknowledgement precedes durable acceptance	`False`	`False`	Passed
unrelated tracing metadata	`True`	`True`	Passed
repeat validation is pure	`True`	`True`	Passed
two independent violations in variant	`False`	`False`	Passed

SHA-256 / eb9d7bbe71755162b65014d96941fc643bc5e72b192956e4bf9414e06f003df2

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 2026-09-29T14:36:53.730926+00:00.

Case digest / 8b53dde9c86da0f1f56a1c8985209658dccdc865876c0ff3d16acac6d0e1e881