FA-75284 / CRDT convergence / Member archive

Awareness presence table: a client exactly at the timeout is kept · case 04

A peer silent for exactly the timeout remains visible one tick too long.

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": []}`	`{"present": [], "removed": ["c1"]}`	Failed

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