FA-1566 / Replication / Open access

Complete a streaming checkpoint barrier: Unaligned checkpoint omits messages already in transit · case 01

The checkpoint barrier operation is admitted even though unaligned checkpoint omits messages already in transit.

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

ROOT CAUSE

The admission path omits the inflight captured invariant while validating the other operation preconditions.

VERIFIED REPAIR

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

Unsuccessful approach: Adding the inflight captured check repairs the reported defect, but replacing the adjacent sink prepared check loses that independent invariant.

Case contract

Return a Boolean admission decision for complete a streaming checkpoint barrier. The record r must satisfy all of: set(r['all_inputs'][0]) == set(r['all_inputs'][1]); len(set(r['barrier_id'])) == 1; r['state_flushed'] is True; r['inflight_captured'][0] == r['inflight_captured'][1]; r['sink_prepared'] == 'prepared'. Extra tracing fields are ignored; validation does not mutate the record.

Why this case matters

A deterministic local contract for replication. 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 (set(r['all_inputs'][0]) == set(r['all_inputs'][1])) and (len(set(r['barrier_id'])) == 1) and (r['state_flushed'] is True) and (r['sink_prepared'] == 'prepared')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_inputs': [['a', 'b'], ['a', 'b']], 'barrier_id': [4, 4], 'state_flushed': True, 'inflight_captured': [8, 8], 'sink_prepared': 'prepared'}
check('valid operation', solve(r), True)
check('A checkpoint completes before every input channel reaches its barrier', solve(dict(r, **{'all_inputs': [['a', 'b'], ['a']]})), False)
check('Barriers from different checkpoint rounds are combined', solve(dict(r, **{'barrier_id': [4, 5]})), False)
check('A checkpoint is acknowledged while state exists only in memory', solve(dict(r, **{'state_flushed': False})), False)
check('Unaligned checkpoint omits messages already in transit', solve(dict(r, **{'inflight_captured': [5, 8]})), False)
check('Upstream progress commits before the transactional sink prepares', solve(dict(r, **{'sink_prepared': 'open'})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_inputs': [['a', 'b'], ['a']], 'barrier_id': [4, 5], 'state_flushed': False, 'inflight_captured': [5, 8], 'sink_prepared': 'open'}
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 checkpoint completes before every input channel reaches its barrier	`False`	`False`	Passed
Barriers from different checkpoint rounds are combined	`False`	`False`	Passed
A checkpoint is acknowledged while state exists only in memory	`False`	`False`	Passed
Unaligned checkpoint omits messages already in transit	`True`	`False`	Failed
Upstream progress commits before the transactional sink prepares	`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 / 0b610a1a0faade41caaef7ddf67ae8b61c5bf0a4ef72976888b39254097e93c0

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (set(r['all_inputs'][0]) == set(r['all_inputs'][1])) and (len(set(r['barrier_id'])) == 1) and (r['state_flushed'] is True) and (r['inflight_captured'][0] == r['inflight_captured'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_inputs': [['a', 'b'], ['a', 'b']], 'barrier_id': [4, 4], 'state_flushed': True, 'inflight_captured': [8, 8], 'sink_prepared': 'prepared'}
check('valid operation', solve(r), True)
check('A checkpoint completes before every input channel reaches its barrier', solve(dict(r, **{'all_inputs': [['a', 'b'], ['a']]})), False)
check('Barriers from different checkpoint rounds are combined', solve(dict(r, **{'barrier_id': [4, 5]})), False)
check('A checkpoint is acknowledged while state exists only in memory', solve(dict(r, **{'state_flushed': False})), False)
check('Unaligned checkpoint omits messages already in transit', solve(dict(r, **{'inflight_captured': [5, 8]})), False)
check('Upstream progress commits before the transactional sink prepares', solve(dict(r, **{'sink_prepared': 'open'})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_inputs': [['a', 'b'], ['a']], 'barrier_id': [4, 5], 'state_flushed': False, 'inflight_captured': [5, 8], 'sink_prepared': 'open'}
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 checkpoint completes before every input channel reaches its barrier	`False`	`False`	Passed
Barriers from different checkpoint rounds are combined	`False`	`False`	Passed
A checkpoint is acknowledged while state exists only in memory	`False`	`False`	Passed
Unaligned checkpoint omits messages already in transit	`False`	`False`	Passed
Upstream progress commits before the transactional sink prepares	`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 / f132605e63dbef8d15d67bde46da1fe2e881415c764b22a1bddf09e54ffc85d1

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (set(r['all_inputs'][0]) == set(r['all_inputs'][1])) and (len(set(r['barrier_id'])) == 1) and (r['state_flushed'] is True) and (r['inflight_captured'][0] == r['inflight_captured'][1]) and (r['sink_prepared'] == 'prepared')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'all_inputs': [['a', 'b'], ['a', 'b']], 'barrier_id': [4, 4], 'state_flushed': True, 'inflight_captured': [8, 8], 'sink_prepared': 'prepared'}
check('valid operation', solve(r), True)
check('A checkpoint completes before every input channel reaches its barrier', solve(dict(r, **{'all_inputs': [['a', 'b'], ['a']]})), False)
check('Barriers from different checkpoint rounds are combined', solve(dict(r, **{'barrier_id': [4, 5]})), False)
check('A checkpoint is acknowledged while state exists only in memory', solve(dict(r, **{'state_flushed': False})), False)
check('Unaligned checkpoint omits messages already in transit', solve(dict(r, **{'inflight_captured': [5, 8]})), False)
check('Upstream progress commits before the transactional sink prepares', solve(dict(r, **{'sink_prepared': 'open'})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'all_inputs': [['a', 'b'], ['a']], 'barrier_id': [4, 5], 'state_flushed': False, 'inflight_captured': [5, 8], 'sink_prepared': 'open'}
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 checkpoint completes before every input channel reaches its barrier	`False`	`False`	Passed
Barriers from different checkpoint rounds are combined	`False`	`False`	Passed
A checkpoint is acknowledged while state exists only in memory	`False`	`False`	Passed
Unaligned checkpoint omits messages already in transit	`False`	`False`	Passed
Upstream progress commits before the transactional sink prepares	`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 / 48c9c7fe09f33d1f5b31b9b62dc3af923959683f650e8242ce128d6996236799

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 2026-09-29T14:37:03.702373+00:00.

Case digest / 5fcfc6e6a0d7c41461da59267f6227a4ab993430b1ddd1945a0bb0465820c29a