FA-75014 / CRDT convergence / Member archive

Causal delivery buffer: messages from one sender are delivered across a gap · case 04

A later message from a sender is applied before the earlier one it follows.

Member previewVariant 4 · 3 implementations · 10 checks per implementation

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
gap from one sender waits	`{"clock": [["a", 2], ["b", 5]], "delivered": ["a2", "b1", "b2", "b3", "b4", "b5"], "duplicates": 0, "pending": []}`	`{"clock": [["b", 5]], "delivered": ["b1", "b2", "b3", "b4", "b5"], "duplicates": 0, "pending": ["a2"]}`	Failed

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