FA-76096 / Chat ordering and read receipts / Open access

Apply create, edit and delete events to message state: version compare · case 01

A delayed older edit overwrites the newest text of a message.

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ROOT CAUSE

The version compare decision evaluates `if e['ver'] != state[i]['ver']:` where the contract requires `if e['ver'] > state[i]['ver']:`.

THE FAILURE

The version compare decision evaluates `if e['ver'] != state[i]['ver']:` where the contract requires `if e['ver'] > state[i]['ver']:`.

Unsuccessful approach: Accepting equal versions lets a conflicting duplicate-version edit replace the text that was applied first. The attempted `if e['ver'] > state[i]['ver'] - 1:` still disagrees with a fixture.

Case contract

events {op, id, ver, text} arrive in any order and are processed in arrival order. Per id the highest version wins and an edit that only equals the current version is ignored; an edit that arrives before its create is buffered (highest buffered version kept) and applied if it is newer than the create. Delete is terminal: the id shows None and later creates and edits are ignored whatever their version. Result: id -> text (None for deleted) for created or deleted ids, sorted by id.

Why this case matters

Message edits and deletions race with the original message across devices; tombstones must stay terminal.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(events):
    state = {}
    buffered = {}
    dead = set()
    for e in events:
        i = e['id']
        if e['op'] == 'delete':
            dead.add(i)
            state[i] = {'text': None, 'ver': e['ver']}
        elif i in dead:
            continue
        elif e['op'] == 'create':
            best = buffered.pop(i, None)
            state[i] = best if best and best['ver'] > e['ver'] else e
        elif i in state:
            if e['ver'] != state[i]['ver']:
                state[i] = e
        else:
            cur = buffered.get(i)
            if cur is None or e['ver'] > cur['ver']:
                buffered[i] = e
    return {i: v['text'] for i, v in sorted(state.items())}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 4, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 3, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 4, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 1, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}],), {'g0': 't0'})], 2: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 5, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 4, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 5, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 2, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}],), {'g0': 't0', 'g1': 't1'})], 3: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 6, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 5, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 6, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 3, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2'})], 4: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 7, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 6, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 7, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 4, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}, {'op': 'create', 'id': 'g3', 'ver': 1, 'text': 't3'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2', 'g3': 't3'})], 5: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 8, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 7, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 8, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 5, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}, {'op': 'create', 'id': 'g3', 'ver': 1, 'text': 't3'}, {'op': 'create', 'id': 'g4', 'ver': 1, 'text': 't4'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2', 'g3': 't3', 'g4': 't4'})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
edit after delete with higher version	`{'a': None}`	`{'a': None}`	Passed
edit arrives before create	`{'b': 'fixed typo'}`	`{'b': 'fixed typo'}`	Passed
stale buffered edit	`{'c': 'new'}`	`{'c': 'new'}`	Passed
late stale edit	`{'d': 'y'}`	`{'d': 'z'}`	Failed
two buffered edits out of order	`{'e': 'v3'}`	`{'e': 'v3'}`	Passed
two buffered edits in order	`{'h': 'w3'}`	`{'h': 'w3'}`	Passed
conflicting edit with equal version	`{'i': 'first'}`	`{'i': 'first'}`	Passed
create after delete	`{'f': None}`	`{'f': None}`	Passed
plain messages	`{'g0': 't0'}`	`{'g0': 't0'}`	Passed

SHA-256 / c7616c6225f3b7c60eb0e3067225a953d9897785287b2ff5313c0c16f4b99d40

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(events):
    state = {}
    buffered = {}
    dead = set()
    for e in events:
        i = e['id']
        if e['op'] == 'delete':
            dead.add(i)
            state[i] = {'text': None, 'ver': e['ver']}
        elif i in dead:
            continue
        elif e['op'] == 'create':
            best = buffered.pop(i, None)
            state[i] = best if best and best['ver'] > e['ver'] else e
        elif i in state:
            if e['ver'] > state[i]['ver'] - 1:
                state[i] = e
        else:
            cur = buffered.get(i)
            if cur is None or e['ver'] > cur['ver']:
                buffered[i] = e
    return {i: v['text'] for i, v in sorted(state.items())}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 4, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 3, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 4, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 1, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}],), {'g0': 't0'})], 2: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 5, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 4, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 5, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 2, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}],), {'g0': 't0', 'g1': 't1'})], 3: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 6, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 5, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 6, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 3, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2'})], 4: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 7, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 6, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 7, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 4, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}, {'op': 'create', 'id': 'g3', 'ver': 1, 'text': 't3'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2', 'g3': 't3'})], 5: [('edit after delete with higher version', ([{'op': 'create', 'id': 'a', 'ver': 1, 'text': 'hi'}, {'op': 'delete', 'id': 'a', 'ver': 2, 'text': None}, {'op': 'edit', 'id': 'a', 'ver': 8, 'text': 'again'}],), {'a': None}), ('edit arrives before create', ([{'op': 'edit', 'id': 'b', 'ver': 2, 'text': 'fixed typo'}, {'op': 'create', 'id': 'b', 'ver': 1, 'text': 'fixd'}],), {'b': 'fixed typo'}), ('stale buffered edit', ([{'op': 'edit', 'id': 'c', 'ver': 1, 'text': 'old'}, {'op': 'create', 'id': 'c', 'ver': 7, 'text': 'new'}],), {'c': 'new'}), ('late stale edit', ([{'op': 'create', 'id': 'd', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'd', 'ver': 3, 'text': 'z'}, {'op': 'edit', 'id': 'd', 'ver': 2, 'text': 'y'}],), {'d': 'z'}), ('two buffered edits out of order', ([{'op': 'edit', 'id': 'e', 'ver': 3, 'text': 'v3'}, {'op': 'edit', 'id': 'e', 'ver': 2, 'text': 'v2'}, {'op': 'create', 'id': 'e', 'ver': 1, 'text': 'v1'}],), {'e': 'v3'}), ('two buffered edits in order', ([{'op': 'edit', 'id': 'h', 'ver': 2, 'text': 'w2'}, {'op': 'edit', 'id': 'h', 'ver': 8, 'text': 'w3'}, {'op': 'create', 'id': 'h', 'ver': 1, 'text': 'w1'}],), {'h': 'w3'}), ('conflicting edit with equal version', ([{'op': 'create', 'id': 'i', 'ver': 1, 'text': 'x'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'first'}, {'op': 'edit', 'id': 'i', 'ver': 2, 'text': 'second'}],), {'i': 'first'}), ('create after delete', ([{'op': 'delete', 'id': 'f', 'ver': 1, 'text': None}, {'op': 'create', 'id': 'f', 'ver': 5, 'text': 'ghost'}],), {'f': None}), ('plain messages', ([{'op': 'create', 'id': 'g0', 'ver': 1, 'text': 't0'}, {'op': 'create', 'id': 'g1', 'ver': 1, 'text': 't1'}, {'op': 'create', 'id': 'g2', 'ver': 1, 'text': 't2'}, {'op': 'create', 'id': 'g3', 'ver': 1, 'text': 't3'}, {'op': 'create', 'id': 'g4', 'ver': 1, 'text': 't4'}],), {'g0': 't0', 'g1': 't1', 'g2': 't2', 'g3': 't3', 'g4': 't4'})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
edit after delete with higher version	`{'a': None}`	`{'a': None}`	Passed
edit arrives before create	`{'b': 'fixed typo'}`	`{'b': 'fixed typo'}`	Passed
stale buffered edit	`{'c': 'new'}`	`{'c': 'new'}`	Passed
late stale edit	`{'d': 'z'}`	`{'d': 'z'}`	Passed
two buffered edits out of order	`{'e': 'v3'}`	`{'e': 'v3'}`	Passed
two buffered edits in order	`{'h': 'w3'}`	`{'h': 'w3'}`	Passed
conflicting edit with equal version	`{'i': 'second'}`	`{'i': 'first'}`	Failed
create after delete	`{'f': None}`	`{'f': None}`	Passed
plain messages	`{'g0': 't0'}`	`{'g0': 't0'}`	Passed

SHA-256 / c88bd98bdf38c5ea63ff955c87c1c175a28db90aa86fe83b0ea26ad36fd2bfc8

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.

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Verification & scope

Stipulated offline chat model; not a complete messaging protocol, client or server implementation. 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 2026-09-29T14:49:13.236758+00:00.

Case digest / cc6184237f308f216290046e6542210a0a688acdb9a8b505f38a81ee3c9d15a1