FAILURE MAP
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FA-75106 / CRDT convergence / Open access

Epoch-resettable counter: an older epoch overwrites a newer one · case 01

A replica that has not seen a reset undoes it when it syncs.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Adoption triggers on any epoch mismatch, including an incoming epoch that is older.

THE FAILURE

Adoption triggers on any epoch mismatch, including an incoming epoch that is older.

Unsuccessful approach: Also adopting equal epochs replaces the receiver's concurrent increments instead of merging them.

Case contract

Each replica holds an epoch and grow-only slots for that epoch. ["inc", r, k] grows r's slot; ["reset", r] increments r's epoch and clears all its slots. ["sync", s, d]: if s's epoch is higher, d adopts s's epoch and a copy of s's slots; if equal, slots merge by maximum; if lower, nothing changes. Return values (sum of slots) and epochs.

Why this case matters

Reset-wins counters need an epoch so a reset is not undone by increments that were concurrent with it.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events, replicas):
    E = {r: 0 for r in replicas}
    S = {r: {} for r in replicas}
    for ev in events:
        if ev[0] == 'inc':
            r = ev[1]
            S[r][r] = S[r].get(r, 0) + ev[2]
        elif ev[0] == 'reset':
            r = ev[1]
            E[r] += 1
            S[r] = {}
        else:
            s, d = ev[1], ev[2]
            if E[s] != E[d]:
                E[d] = E[s]
                S[d] = dict(S[s])
            elif E[s] == E[d]:
                for k, v in S[s].items():
                    S[d][k] = max(S[d].get(k, 0), v)
    return {'values': [sum(S[r].values()) for r in replicas], 'epochs': [E[r] for r in replicas]}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('reset wins over concurrent older increments', [[['inc', 'a', 1], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 6], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 6, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 1], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 3, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 1], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 1], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 3, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 1], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    2: [('reset wins over concurrent older increments', [[['inc', 'a', 2], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 7], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 7, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 2], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [4, 4, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 2], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 2], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 2], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [4, 4, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 2], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    3: [('reset wins over concurrent older increments', [[['inc', 'a', 3], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 8], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 8, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 3], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [5, 5, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 3], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 3], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 3], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [5, 5, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 3], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    4: [('reset wins over concurrent older increments', [[['inc', 'a', 4], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 9], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 9, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 4], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [6, 6, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 4], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 4], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [6, 6, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 4], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    5: [('reset wins over concurrent older increments', [[['inc', 'a', 5], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 10], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 10, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 5], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [7, 7, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 5], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 5], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 5], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [7, 7, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 5], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
}[N]
for label, args, expected in cases:
    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
reset wins over concurrent older increments{'epochs': [1, 1, 0], 'values': [0, 0, 0]}{'epochs': [1, 1, 0], 'values': [0, 0, 0]}Passed
stale epoch is ignored{'epochs': [0, 0, 0], 'values': [6, 6, 0]}{'epochs': [1, 0, 0], 'values': [3, 6, 0]}Failed
equal epochs merge by maximum{'epochs': [1, 1, 0], 'values': [3, 3, 0]}{'epochs': [1, 1, 0], 'values': [3, 3, 0]}Passed
second reset opens a new epoch{'epochs': [2, 0, 2], 'values': [1, 0, 1]}{'epochs': [2, 0, 2], 'values': [1, 0, 1]}Passed
reset clears every slot{'epochs': [1, 0, 0], 'values': [1, 3, 0]}{'epochs': [1, 0, 0], 'values': [1, 3, 0]}Passed
independent resets reach the same epoch{'epochs': [1, 1, 0], 'values': [3, 3, 0]}{'epochs': [1, 1, 0], 'values': [3, 3, 0]}Passed
epoch adoption copies the newer slots{'epochs': [1, 1, 1], 'values': [2, 2, 2]}{'epochs': [1, 1, 1], 'values': [2, 2, 2]}Passed
epoch is local knowledge{'epochs': [2, 1, 0], 'values': [0, 1, 0]}{'epochs': [2, 1, 0], 'values': [0, 1, 0]}Passed

SHA-256 / c2276af4b025935435609812203e501f9e7f04dff2450f0d54fd577b46969fe8

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events, replicas):
    E = {r: 0 for r in replicas}
    S = {r: {} for r in replicas}
    for ev in events:
        if ev[0] == 'inc':
            r = ev[1]
            S[r][r] = S[r].get(r, 0) + ev[2]
        elif ev[0] == 'reset':
            r = ev[1]
            E[r] += 1
            S[r] = {}
        else:
            s, d = ev[1], ev[2]
            if E[s] >= E[d]:
                E[d] = E[s]
                S[d] = dict(S[s])
            elif E[s] == E[d]:
                for k, v in S[s].items():
                    S[d][k] = max(S[d].get(k, 0), v)
    return {'values': [sum(S[r].values()) for r in replicas], 'epochs': [E[r] for r in replicas]}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('reset wins over concurrent older increments', [[['inc', 'a', 1], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 6], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 6, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 1], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 3, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 1], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 1], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 3, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 1], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    2: [('reset wins over concurrent older increments', [[['inc', 'a', 2], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 7], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 7, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 2], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [4, 4, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 2], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 2], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 2], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [4, 4, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 2], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    3: [('reset wins over concurrent older increments', [[['inc', 'a', 3], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 8], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 8, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 3], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [5, 5, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 3], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 3], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 3], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [5, 5, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 3], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    4: [('reset wins over concurrent older increments', [[['inc', 'a', 4], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 9], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 9, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 4], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [6, 6, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 4], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 4], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [6, 6, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 4], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
    5: [('reset wins over concurrent older increments', [[['inc', 'a', 5], ['sync', 'a', 'b'], ['inc', 'b', 2], ['reset', 'a'], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [0, 0, 0], 'epochs': [1, 1, 0]}), ('stale epoch is ignored', [[['reset', 'a'], ['inc', 'a', 3], ['inc', 'b', 10], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [3, 10, 0], 'epochs': [1, 0, 0]}), ('equal epochs merge by maximum', [[['reset', 'a'], ['sync', 'a', 'b'], ['inc', 'a', 5], ['inc', 'b', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [7, 7, 0], 'epochs': [1, 1, 0]}), ('second reset opens a new epoch', [[['inc', 'c', 4], ['reset', 'c'], ['inc', 'c', 5], ['reset', 'c'], ['inc', 'c', 1], ['sync', 'c', 'a']], ['a', 'b', 'c']], {'values': [1, 0, 1], 'epochs': [2, 0, 2]}), ('reset clears every slot', [[['inc', 'a', 5], ['inc', 'b', 3], ['sync', 'b', 'a'], ['reset', 'a'], ['inc', 'a', 1]], ['a', 'b', 'c']], {'values': [1, 3, 0], 'epochs': [1, 0, 0]}), ('independent resets reach the same epoch', [[['inc', 'a', 1], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 5], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'a']], ['a', 'b', 'c']], {'values': [7, 7, 0], 'epochs': [1, 1, 0]}), ('epoch adoption copies the newer slots', [[['inc', 'b', 5], ['reset', 'a'], ['inc', 'a', 2], ['sync', 'a', 'b'], ['sync', 'b', 'c']], ['a', 'b', 'c']], {'values': [2, 2, 2], 'epochs': [1, 1, 1]}), ('epoch is local knowledge', [[['reset', 'a'], ['reset', 'a'], ['reset', 'b'], ['inc', 'b', 1]], ['a', 'b', 'c']], {'values': [0, 1, 0], 'epochs': [2, 1, 0]})],
}[N]
for label, args, expected in cases:
    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
reset wins over concurrent older increments{'epochs': [1, 1, 0], 'values': [0, 0, 0]}{'epochs': [1, 1, 0], 'values': [0, 0, 0]}Passed
stale epoch is ignored{'epochs': [1, 0, 0], 'values': [3, 6, 0]}{'epochs': [1, 0, 0], 'values': [3, 6, 0]}Passed
equal epochs merge by maximum{'epochs': [1, 1, 0], 'values': [1, 1, 0]}{'epochs': [1, 1, 0], 'values': [3, 3, 0]}Failed
second reset opens a new epoch{'epochs': [2, 0, 2], 'values': [1, 0, 1]}{'epochs': [2, 0, 2], 'values': [1, 0, 1]}Passed
reset clears every slot{'epochs': [1, 0, 0], 'values': [1, 3, 0]}{'epochs': [1, 0, 0], 'values': [1, 3, 0]}Passed
independent resets reach the same epoch{'epochs': [1, 1, 0], 'values': [2, 2, 0]}{'epochs': [1, 1, 0], 'values': [3, 3, 0]}Failed
epoch adoption copies the newer slots{'epochs': [1, 1, 1], 'values': [2, 2, 2]}{'epochs': [1, 1, 1], 'values': [2, 2, 2]}Passed
epoch is local knowledge{'epochs': [2, 1, 0], 'values': [0, 1, 0]}{'epochs': [2, 1, 0], 'values': [0, 1, 0]}Passed

SHA-256 / 52469ed9490b6551fcdb30966ac682d7b7560194b901c71f81c61ce46b206adb

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The verified repair and its recorded checks are member-only.

This mechanism has 8 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

A deterministic, bounded teaching model of one replicated data type with stipulated operation and merge rules; it is not a production CRDT library and makes no claim of conformance to any specific published design. 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 2026-09-29T14:49:03.098844+00:00.

Case digest / 30b0ada537f12328a1bfd330363513501e4d0fe7158cfb20a66e0c05afea707f