FA-746 / Queues / Open access

Accept a durable queue publication: A producer sequence gap is accepted as contiguous · case 01

The queue publish operation is admitted even though a producer sequence gap is accepted as contiguous.

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

ROOT CAUSE

The admission path omits the sequence next invariant while validating the other operation preconditions.

VERIFIED REPAIR

Require r['sequence_next'][0] == r['sequence_next'][1]+1 together with every other stated precondition before accepting the operation.

Unsuccessful approach: Adding the sequence next check repairs the reported defect, but replacing the adjacent message size check loses that independent invariant.

Case contract

Return a Boolean admission decision for accept a durable queue publication. The record r must satisfy all of: len(r['message_size'][0]) <= r['message_size'][1]; r['queue_capacity'][0]+r['queue_capacity'][1] <= r['queue_capacity'][2]; bool(r['routing_target']); r['producer_epoch'][0] == r['producer_epoch'][1]; r['sequence_next'][0] == r['sequence_next'][1]+1. Extra tracing fields are ignored; validation does not mutate the record.

Why this case matters

A deterministic local contract for queues. 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(r['message_size'][0]) <= r['message_size'][1]) and (r['queue_capacity'][0]+r['queue_capacity'][1] <= r['queue_capacity'][2]) and (bool(r['routing_target'])) and (r['producer_epoch'][0] == r['producer_epoch'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'message_size': ['abc', 3], 'queue_capacity': [8, 2, 10], 'routing_target': ['orders'], 'producer_epoch': [4, 4], 'sequence_next': [8, 7]}
check('valid operation', solve(r), True)
check('An oversized message bypasses broker frame limits', solve(dict(r, **{'message_size': ['abcd', 3]})), False)
check('Admission exceeds the queue retained-byte budget', solve(dict(r, **{'queue_capacity': [8, 3, 10]})), False)
check('A mandatory message has no matching queue', solve(dict(r, **{'routing_target': []})), False)
check('A fenced producer continues publishing', solve(dict(r, **{'producer_epoch': [3, 4]})), False)
check('A producer sequence gap is accepted as contiguous', solve(dict(r, **{'sequence_next': [9, 7]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'message_size': ['abcd', 3], 'queue_capacity': [8, 3, 10], 'routing_target': [], 'producer_epoch': [3, 4], 'sequence_next': [9, 7]}
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
An oversized message bypasses broker frame limits	`False`	`False`	Passed
Admission exceeds the queue retained-byte budget	`False`	`False`	Passed
A mandatory message has no matching queue	`False`	`False`	Passed
A fenced producer continues publishing	`False`	`False`	Passed
A producer sequence gap is accepted as contiguous	`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 / 56862abe192a25e17a5eba8eea095db65f90dd0a4bf699c822290f5ec63fb027

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (r['queue_capacity'][0]+r['queue_capacity'][1] <= r['queue_capacity'][2]) and (bool(r['routing_target'])) and (r['producer_epoch'][0] == r['producer_epoch'][1]) and (r['sequence_next'][0] == r['sequence_next'][1]+1)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'message_size': ['abc', 3], 'queue_capacity': [8, 2, 10], 'routing_target': ['orders'], 'producer_epoch': [4, 4], 'sequence_next': [8, 7]}
check('valid operation', solve(r), True)
check('An oversized message bypasses broker frame limits', solve(dict(r, **{'message_size': ['abcd', 3]})), False)
check('Admission exceeds the queue retained-byte budget', solve(dict(r, **{'queue_capacity': [8, 3, 10]})), False)
check('A mandatory message has no matching queue', solve(dict(r, **{'routing_target': []})), False)
check('A fenced producer continues publishing', solve(dict(r, **{'producer_epoch': [3, 4]})), False)
check('A producer sequence gap is accepted as contiguous', solve(dict(r, **{'sequence_next': [9, 7]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'message_size': ['abcd', 3], 'queue_capacity': [8, 3, 10], 'routing_target': [], 'producer_epoch': [3, 4], 'sequence_next': [9, 7]}
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
An oversized message bypasses broker frame limits	`True`	`False`	Failed
Admission exceeds the queue retained-byte budget	`False`	`False`	Passed
A mandatory message has no matching queue	`False`	`False`	Passed
A fenced producer continues publishing	`False`	`False`	Passed
A producer sequence gap is accepted as contiguous	`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 / 9c6da85016270438fc3d906c55127ca6cf93aabd4efa443f0daf6198eabd5be0

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (len(r['message_size'][0]) <= r['message_size'][1]) and (r['queue_capacity'][0]+r['queue_capacity'][1] <= r['queue_capacity'][2]) and (bool(r['routing_target'])) and (r['producer_epoch'][0] == r['producer_epoch'][1]) and (r['sequence_next'][0] == r['sequence_next'][1]+1)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'message_size': ['abc', 3], 'queue_capacity': [8, 2, 10], 'routing_target': ['orders'], 'producer_epoch': [4, 4], 'sequence_next': [8, 7]}
check('valid operation', solve(r), True)
check('An oversized message bypasses broker frame limits', solve(dict(r, **{'message_size': ['abcd', 3]})), False)
check('Admission exceeds the queue retained-byte budget', solve(dict(r, **{'queue_capacity': [8, 3, 10]})), False)
check('A mandatory message has no matching queue', solve(dict(r, **{'routing_target': []})), False)
check('A fenced producer continues publishing', solve(dict(r, **{'producer_epoch': [3, 4]})), False)
check('A producer sequence gap is accepted as contiguous', solve(dict(r, **{'sequence_next': [9, 7]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'message_size': ['abcd', 3], 'queue_capacity': [8, 3, 10], 'routing_target': [], 'producer_epoch': [3, 4], 'sequence_next': [9, 7]}
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
An oversized message bypasses broker frame limits	`False`	`False`	Passed
Admission exceeds the queue retained-byte budget	`False`	`False`	Passed
A mandatory message has no matching queue	`False`	`False`	Passed
A fenced producer continues publishing	`False`	`False`	Passed
A producer sequence gap is accepted as contiguous	`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 / 8ea93560e997352f0b1e768d5f01062994be9096bf0b28345ab9c60c3fe81bc2

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 2026-09-29T14:36:55.584473+00:00.

Case digest / 48d765f6da85edffd972d456d8a607a89a387e78b50d8ac541ab0f71df8f68ac