FA-831 / Queues / Open access

Redrive a previously dead-lettered message: Redrive races an updated dead-letter record · case 01

The queue redrive operation is admitted even though redrive races an updated dead-letter record.

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

ROOT CAUSE

The admission path omits the source version invariant while validating the other operation preconditions.

VERIFIED REPAIR

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

Unsuccessful approach: Adding the source version check repairs the reported defect, but replacing the adjacent destination schema check loses that independent invariant.

Case contract

Return a Boolean admission decision for redrive a previously dead-lettered message. The record r must satisfy all of: r['redrive_budget'][0] < r['redrive_budget'][1]; r['source_version'][0] == r['source_version'][1]; r['destination_schema'][0] in r['destination_schema'][1]; r['retention_remaining'][0] < r['retention_remaining'][1]; r['rate_tokens'][0] >= r['rate_tokens'][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['redrive_budget'][0] < r['redrive_budget'][1]) and (r['destination_schema'][0] in r['destination_schema'][1]) and (r['retention_remaining'][0] < r['retention_remaining'][1]) and (r['rate_tokens'][0] >= r['rate_tokens'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'redrive_budget': [2, 3], 'source_version': [7, 7], 'destination_schema': [2, [2, 3]], 'retention_remaining': [19, 20], 'rate_tokens': [3, 3]}
check('valid operation', solve(r), True)
check('Poison messages circulate past the redrive allowance', solve(dict(r, **{'redrive_budget': [3, 3]})), False)
check('Redrive races an updated dead-letter record', solve(dict(r, **{'source_version': [6, 7]})), False)
check('The target consumer cannot decode the original schema', solve(dict(r, **{'destination_schema': [1, [2, 3]]})), False)
check('Redrive revives a message past its absolute retention', solve(dict(r, **{'retention_remaining': [20, 20]})), False)
check('Redrive bypasses its recovery traffic budget', solve(dict(r, **{'rate_tokens': [2, 3]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'redrive_budget': [3, 3], 'source_version': [6, 7], 'destination_schema': [1, [2, 3]], 'retention_remaining': [20, 20], 'rate_tokens': [2, 3]}
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
Poison messages circulate past the redrive allowance	`False`	`False`	Passed
Redrive races an updated dead-letter record	`True`	`False`	Failed
The target consumer cannot decode the original schema	`False`	`False`	Passed
Redrive revives a message past its absolute retention	`False`	`False`	Passed
Redrive bypasses its recovery traffic budget	`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 / 0f36719aaa0b8108a1064ed59a21b1c56fc4f9aff201500a892f9932ddf2e49c

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (r['redrive_budget'][0] < r['redrive_budget'][1]) and (r['source_version'][0] == r['source_version'][1]) and (r['retention_remaining'][0] < r['retention_remaining'][1]) and (r['rate_tokens'][0] >= r['rate_tokens'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'redrive_budget': [2, 3], 'source_version': [7, 7], 'destination_schema': [2, [2, 3]], 'retention_remaining': [19, 20], 'rate_tokens': [3, 3]}
check('valid operation', solve(r), True)
check('Poison messages circulate past the redrive allowance', solve(dict(r, **{'redrive_budget': [3, 3]})), False)
check('Redrive races an updated dead-letter record', solve(dict(r, **{'source_version': [6, 7]})), False)
check('The target consumer cannot decode the original schema', solve(dict(r, **{'destination_schema': [1, [2, 3]]})), False)
check('Redrive revives a message past its absolute retention', solve(dict(r, **{'retention_remaining': [20, 20]})), False)
check('Redrive bypasses its recovery traffic budget', solve(dict(r, **{'rate_tokens': [2, 3]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'redrive_budget': [3, 3], 'source_version': [6, 7], 'destination_schema': [1, [2, 3]], 'retention_remaining': [20, 20], 'rate_tokens': [2, 3]}
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
Poison messages circulate past the redrive allowance	`False`	`False`	Passed
Redrive races an updated dead-letter record	`False`	`False`	Passed
The target consumer cannot decode the original schema	`True`	`False`	Failed
Redrive revives a message past its absolute retention	`False`	`False`	Passed
Redrive bypasses its recovery traffic budget	`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 / fa64b6790dcd7932d42a8bf7f1df909aa454faf1d6b96710e75892950e4b45bd

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (r['redrive_budget'][0] < r['redrive_budget'][1]) and (r['source_version'][0] == r['source_version'][1]) and (r['destination_schema'][0] in r['destination_schema'][1]) and (r['retention_remaining'][0] < r['retention_remaining'][1]) and (r['rate_tokens'][0] >= r['rate_tokens'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'redrive_budget': [2, 3], 'source_version': [7, 7], 'destination_schema': [2, [2, 3]], 'retention_remaining': [19, 20], 'rate_tokens': [3, 3]}
check('valid operation', solve(r), True)
check('Poison messages circulate past the redrive allowance', solve(dict(r, **{'redrive_budget': [3, 3]})), False)
check('Redrive races an updated dead-letter record', solve(dict(r, **{'source_version': [6, 7]})), False)
check('The target consumer cannot decode the original schema', solve(dict(r, **{'destination_schema': [1, [2, 3]]})), False)
check('Redrive revives a message past its absolute retention', solve(dict(r, **{'retention_remaining': [20, 20]})), False)
check('Redrive bypasses its recovery traffic budget', solve(dict(r, **{'rate_tokens': [2, 3]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'redrive_budget': [3, 3], 'source_version': [6, 7], 'destination_schema': [1, [2, 3]], 'retention_remaining': [20, 20], 'rate_tokens': [2, 3]}
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
Poison messages circulate past the redrive allowance	`False`	`False`	Passed
Redrive races an updated dead-letter record	`False`	`False`	Passed
The target consumer cannot decode the original schema	`False`	`False`	Passed
Redrive revives a message past its absolute retention	`False`	`False`	Passed
Redrive bypasses its recovery traffic budget	`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 / 09fa60df1708f7252fc6940f93fa9f61761b5dbc2bf134dc7399ccac9845b048

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 2026-09-29T14:36:56.132605+00:00.

Case digest / 5b135418dd07a369a4b2c7ca756d0fb9e3bfc48d4f4e0c25f3f3eae8e963f795