FA-1571 / Replication / Open access

Complete a streaming checkpoint barrier: Upstream progress commits before the transactional sink prepares · case 01

The checkpoint barrier operation is admitted even though upstream progress commits before the transactional sink prepares.

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

ROOT CAUSE

The admission path omits the sink prepared invariant while validating the other operation preconditions.

THE FAILURE

The admission path omits the sink prepared invariant while validating the other operation preconditions.

Unsuccessful approach: Adding the sink prepared check repairs the reported defect, but replacing the adjacent all inputs 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['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

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (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	`True`	`False`	Failed
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 / 7e2a7a6be96d79df922a6555205d9a43e6e90962cd1aa3c9f63575a799e83b57

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 2026-09-29T14:37:03.702157+00:00.

Case digest / 26affa5131ea601c608add7ab6c32b74e33d3a9ab5d8580bc43ef135b19eb51b