FA-75274 / CRDT convergence / Member archive

Awareness presence table: a replayed update revives a timed-out client · case 04

A client removed by timeout reappears when an old update is redelivered.

Member previewVariant 4 · 3 implementations · 9 checks per implementation

Case contract

Presence updates ["update", client, clock, state|None, now] are accepted when clock exceeds the last accepted clock for that client, or when it equals it, the state is None and the client is present. Accepted updates record the clock; a None state removes the client (logging a removal only if it was present); otherwise [state, now] is stored. ["tick", now] removes, in client order, every client other than self_id whose last update is at least timeout old. Return present [client, state] pairs and the removal log.

Why this case matters

Ephemeral presence rides alongside document CRDTs and must neither resurrect departed peers nor expire the local user.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
stale update after timeout is rejected	`{"present": [["c1", "on"]], "removed": ["c1"]}`	`{"present": [], "removed": ["c1"]}`	Failed

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