FA-756 / Queues / Open access

Reserve a queued message for delivery: A message is delivered after its expiration deadline · case 01

The queue reservation operation is admitted even though a message is delivered after its expiration deadline.

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

ROOT CAUSE

The admission path omits the not expired invariant while validating the other operation preconditions.

THE FAILURE

The admission path omits the not expired invariant while validating the other operation preconditions.

Unsuccessful approach: Adding the not expired check repairs the reported defect, but replacing the adjacent no live reservation check loses that independent invariant.

Case contract

Return a Boolean admission decision for reserve a queued message for delivery. The record r must satisfy all of: r['visible_now'][0] >= r['visible_now'][1]; r['not_expired'][0] < r['not_expired'][1]; r['no_live_reservation'][0] is None or r['no_live_reservation'][1] >= r['no_live_reservation'][0]; r['consumer_credit'][0] < r['consumer_credit'][1]; r['group_head'][0] == min(r['group_head'][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['visible_now'][0] >= r['visible_now'][1]) and (r['no_live_reservation'][0] is None or r['no_live_reservation'][1] >= r['no_live_reservation'][0]) and (r['consumer_credit'][0] < r['consumer_credit'][1]) and (r['group_head'][0] == min(r['group_head'][1]))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'visible_now': [10, 10], 'not_expired': [9, 10], 'no_live_reservation': [8, 8], 'consumer_credit': [2, 3], 'group_head': [3, [3, 4]]}
check('valid operation', solve(r), True)
check('A scheduled message is delivered before its visibility instant', solve(dict(r, **{'visible_now': [9, 10]})), False)
check('A message is delivered after its expiration deadline', solve(dict(r, **{'not_expired': [10, 10]})), False)
check('A second worker reserves a currently leased message', solve(dict(r, **{'no_live_reservation': [9, 8]})), False)
check('The broker exceeds consumer in-flight credit', solve(dict(r, **{'consumer_credit': [3, 3]})), False)
check('A FIFO message overtakes an earlier group member', solve(dict(r, **{'group_head': [4, [3, 4]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'visible_now': [9, 10], 'not_expired': [10, 10], 'no_live_reservation': [9, 8], 'consumer_credit': [3, 3], 'group_head': [4, [3, 4]]}
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 scheduled message is delivered before its visibility instant	`False`	`False`	Passed
A message is delivered after its expiration deadline	`True`	`False`	Failed
A second worker reserves a currently leased message	`False`	`False`	Passed
The broker exceeds consumer in-flight credit	`False`	`False`	Passed
A FIFO message overtakes an earlier group member	`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 / a6d0a29d42da4f9ccf8c52aba76f627c5276f0aaa5486a62ba8d68276f5e62bb

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (r['visible_now'][0] >= r['visible_now'][1]) and (r['not_expired'][0] < r['not_expired'][1]) and (r['consumer_credit'][0] < r['consumer_credit'][1]) and (r['group_head'][0] == min(r['group_head'][1]))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'visible_now': [10, 10], 'not_expired': [9, 10], 'no_live_reservation': [8, 8], 'consumer_credit': [2, 3], 'group_head': [3, [3, 4]]}
check('valid operation', solve(r), True)
check('A scheduled message is delivered before its visibility instant', solve(dict(r, **{'visible_now': [9, 10]})), False)
check('A message is delivered after its expiration deadline', solve(dict(r, **{'not_expired': [10, 10]})), False)
check('A second worker reserves a currently leased message', solve(dict(r, **{'no_live_reservation': [9, 8]})), False)
check('The broker exceeds consumer in-flight credit', solve(dict(r, **{'consumer_credit': [3, 3]})), False)
check('A FIFO message overtakes an earlier group member', solve(dict(r, **{'group_head': [4, [3, 4]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'visible_now': [9, 10], 'not_expired': [10, 10], 'no_live_reservation': [9, 8], 'consumer_credit': [3, 3], 'group_head': [4, [3, 4]]}
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 scheduled message is delivered before its visibility instant	`False`	`False`	Passed
A message is delivered after its expiration deadline	`False`	`False`	Passed
A second worker reserves a currently leased message	`True`	`False`	Failed
The broker exceeds consumer in-flight credit	`False`	`False`	Passed
A FIFO message overtakes an earlier group member	`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 / d4c6193a29f2c6b92304693ac7f8dc112db5e97546c999c4db29ce99efed41b9

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 2026-09-29T14:36:55.999365+00:00.

Case digest / abbd5c75b865fe495983c593f02fb634c5ad93d8a42d1fc8dcd3885cc0e5d79a