FA-75032 / CRDT convergence / Member archive

Causal delivery buffer: delivery adopts the sender's whole vector · case 02

The delivered vector moves backwards and old messages are accepted again.

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Case contract

A receiver starts with an empty delivered vector. An arrival [sender, vector, payload] is a duplicate when its sender entry is at or below the delivered entry or the same (sender, entry) is already buffered. Otherwise it is buffered; then, repeatedly, the oldest buffered message whose sender entry is exactly delivered+1 and whose other entries are all <= delivered is delivered, setting only the sender entry. Return delivered payloads, sorted pending payloads, duplicate count and the delivered vector.

Why this case matters

Operation-based CRDTs converge only if operations are delivered exactly once and in causal order.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
receiver ahead of a dependency keeps its clock	`{"clock": [["a", 3]], "delivered": ["a1", "a2", "b1", "a2", "a3"], "duplicates": 0, "pending": []}`	`{"clock": [["a", 3], ["b", 1]], "delivered": ["a1", "a2", "b1", "a3"], "duplicates": 1, "pending": []}`	Failed

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