FA-726 / Queues / Open access

Accept a durable queue publication: An oversized message bypasses broker frame limits · case 01

The queue publish operation is admitted even though an oversized message bypasses broker frame limits.

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

ROOT CAUSE

The admission path omits the message size invariant while validating the other operation preconditions.

THE FAILURE

The admission path omits the message size invariant while validating the other operation preconditions.

Unsuccessful approach: Adding the message size check repairs the reported defect, but replacing the adjacent queue capacity 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 (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

2 / The unsuccessful fix

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 (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	`True`	`False`	Failed
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 / a3c8e8c1d65964f17cb76e2c85a6cf5925da247fa57937e934599d94ed74787b

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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 / 5af43651615538dfd80d3aaebe8d3a1f0c3f49ecd7dee024ae97258e958301f7