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FA-76086 / Chat ordering and read receipts / Open access

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

A concurrent edit with a higher version resurrects a message that was deleted.

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ROOT CAUSE

The terminal delete decision evaluates `elif i in dead and e['op'] == 'create':` where the contract requires `elif i in dead:`.

THE FAILURE

The terminal delete decision evaluates `elif i in dead and e['op'] == 'create':` where the contract requires `elif i in dead:`.

Unsuccessful approach: Comparing versions against the tombstone still lets a newer edit undelete the message. The attempted `elif i in dead and e['ver'] <= state[i]['ver']:` 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 and e['op'] == 'create':
            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 fixtureActualExpectedOutcome
edit after delete with higher version{'a': 'again'}{'a': None}Failed
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': 'first'}{'i': 'first'}Passed
create after delete{'f': None}{'f': None}Passed
plain messages{'g0': 't0'}{'g0': 't0'}Passed

SHA-256 / 31bed4531edeef11f3847153f5758aeea32c252464abdd7b364d3252486de37a

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 and e['ver'] <= state[i]['ver']:
            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 fixtureActualExpectedOutcome
edit after delete with higher version{'a': 'again'}{'a': None}Failed
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': 'first'}{'i': 'first'}Passed
create after delete{'f': None}{'f': None}Passed
plain messages{'g0': 't0'}{'g0': 't0'}Passed

SHA-256 / 97be19b56fda9e7c51c057a84929e38fa394b37b235fcb5dcb40d7bf9e91ed40

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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.

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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 / 7620a7f6d87fe07e70fc4d53c6a8f2d21769beaffb4f47b3d3bbf9987b73017e