FA-406 / Replication / Open access

Install a replicated state snapshot: An incomplete snapshot replaces the live state · case 01

The snapshot install operation is admitted even though an incomplete snapshot replaces the live state.

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

ROOT CAUSE

The admission path omits the complete chunks invariant while validating the other operation preconditions.

VERIFIED REPAIR

Require set(r['complete_chunks'][0]) == set(range(r['complete_chunks'][1])) together with every other stated precondition before accepting the operation.

Unsuccessful approach: Adding the complete chunks check repairs the reported defect, but replacing the adjacent checksum match check loses that independent invariant.

Case contract

Return a Boolean admission decision for install a replicated state snapshot. The record r must satisfy all of: r['newer_applied'][0] >= r['newer_applied'][1]; set(r['complete_chunks'][0]) == set(range(r['complete_chunks'][1])); r['checksum_match'][0] == r['checksum_match'][1]; bool(r['configuration_present']); r['index_term_pair'][0] == r['index_term_pair'][1]. 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 (r['newer_applied'][0] >= r['newer_applied'][1]) and (r['checksum_match'][0] == r['checksum_match'][1]) and (bool(r['configuration_present'])) and (r['index_term_pair'][0] == r['index_term_pair'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'newer_applied': [12, 10], 'complete_chunks': [[0, 1, 2], 3], 'checksum_match': ['abc', 'abc'], 'configuration_present': [1, 2, 3], 'index_term_pair': [[12, 3], [12, 3]]}
check('valid operation', solve(r), True)
check('A snapshot rolls back applied state', solve(dict(r, **{'newer_applied': [9, 10]})), False)
check('An incomplete snapshot replaces the live state', solve(dict(r, **{'complete_chunks': [[0, 2], 3]})), False)
check('Corrupt snapshot contents become authoritative', solve(dict(r, **{'checksum_match': ['bad', 'abc']})), False)
check('The snapshot omits its membership configuration', solve(dict(r, **{'configuration_present': []})), False)
check('Snapshot metadata refers to a different log term', solve(dict(r, **{'index_term_pair': [[12, 2], [12, 3]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'newer_applied': [9, 10], 'complete_chunks': [[0, 2], 3], 'checksum_match': ['bad', 'abc'], 'configuration_present': [], 'index_term_pair': [[12, 2], [12, 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
A snapshot rolls back applied state	`False`	`False`	Passed
An incomplete snapshot replaces the live state	`True`	`False`	Failed
Corrupt snapshot contents become authoritative	`False`	`False`	Passed
The snapshot omits its membership configuration	`False`	`False`	Passed
Snapshot metadata refers to a different log term	`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 / ce6fbac50cce90b6a7ec7878d0f286abfa115b16ac2db946cdc86a53f3e118bc

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(r):
    return (r['newer_applied'][0] >= r['newer_applied'][1]) and (set(r['complete_chunks'][0]) == set(range(r['complete_chunks'][1]))) and (bool(r['configuration_present'])) and (r['index_term_pair'][0] == r['index_term_pair'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'newer_applied': [12, 10], 'complete_chunks': [[0, 1, 2], 3], 'checksum_match': ['abc', 'abc'], 'configuration_present': [1, 2, 3], 'index_term_pair': [[12, 3], [12, 3]]}
check('valid operation', solve(r), True)
check('A snapshot rolls back applied state', solve(dict(r, **{'newer_applied': [9, 10]})), False)
check('An incomplete snapshot replaces the live state', solve(dict(r, **{'complete_chunks': [[0, 2], 3]})), False)
check('Corrupt snapshot contents become authoritative', solve(dict(r, **{'checksum_match': ['bad', 'abc']})), False)
check('The snapshot omits its membership configuration', solve(dict(r, **{'configuration_present': []})), False)
check('Snapshot metadata refers to a different log term', solve(dict(r, **{'index_term_pair': [[12, 2], [12, 3]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'newer_applied': [9, 10], 'complete_chunks': [[0, 2], 3], 'checksum_match': ['bad', 'abc'], 'configuration_present': [], 'index_term_pair': [[12, 2], [12, 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
A snapshot rolls back applied state	`False`	`False`	Passed
An incomplete snapshot replaces the live state	`False`	`False`	Passed
Corrupt snapshot contents become authoritative	`True`	`False`	Failed
The snapshot omits its membership configuration	`False`	`False`	Passed
Snapshot metadata refers to a different log term	`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 / db00e7e37ea792758580b87883551d5f795dadcac7e90bc2c6e4a3951efb8a72

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(r):
    return (r['newer_applied'][0] >= r['newer_applied'][1]) and (set(r['complete_chunks'][0]) == set(range(r['complete_chunks'][1]))) and (r['checksum_match'][0] == r['checksum_match'][1]) and (bool(r['configuration_present'])) and (r['index_term_pair'][0] == r['index_term_pair'][1])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
r = {'newer_applied': [12, 10], 'complete_chunks': [[0, 1, 2], 3], 'checksum_match': ['abc', 'abc'], 'configuration_present': [1, 2, 3], 'index_term_pair': [[12, 3], [12, 3]]}
check('valid operation', solve(r), True)
check('A snapshot rolls back applied state', solve(dict(r, **{'newer_applied': [9, 10]})), False)
check('An incomplete snapshot replaces the live state', solve(dict(r, **{'complete_chunks': [[0, 2], 3]})), False)
check('Corrupt snapshot contents become authoritative', solve(dict(r, **{'checksum_match': ['bad', 'abc']})), False)
check('The snapshot omits its membership configuration', solve(dict(r, **{'configuration_present': []})), False)
check('Snapshot metadata refers to a different log term', solve(dict(r, **{'index_term_pair': [[12, 2], [12, 3]]})), False)
check('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)
check('repeat validation is pure', solve(r), True)
invalid = {'newer_applied': [9, 10], 'complete_chunks': [[0, 2], 3], 'checksum_match': ['bad', 'abc'], 'configuration_present': [], 'index_term_pair': [[12, 2], [12, 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
A snapshot rolls back applied state	`False`	`False`	Passed
An incomplete snapshot replaces the live state	`False`	`False`	Passed
Corrupt snapshot contents become authoritative	`False`	`False`	Passed
The snapshot omits its membership configuration	`False`	`False`	Passed
Snapshot metadata refers to a different log term	`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 / bdbee3faa7735838124026847fc899ef34d8cf5bb1df90b992c5676216fdb7ea

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 2026-09-29T14:36:52.662628+00:00.

Case digest / 178c029e5d82da1f30ed2fb9daf7c2571a1e3796452ad064ec47e01c4038fb5e