FA-74992 / CRDT convergence / Member archive

Delta causal context join: the newest dot in the vector is treated as unseen · case 02

An element removed at the peer survives when its dot equals the peer's vector entry.

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Case contract

A state is {"dots": [[element, replica, n]], "vv": {replica: n}, "cloud": [[replica, n]]}. A context covers (r, n) when n <= vv[r] or [r, n] is in the cloud. Join keeps dots present in both states plus dots of one state not covered by the other's context; contexts join by vector maximum and cloud union, then the cloud is compacted: an entry equal to vv[r]+1 advances vv[r], entries at or below vv[r] are pruned. Return elements, dots, vector and cloud, all sorted.

Why this case matters

Delta-state add-wins sets rely on causal contexts to tell removals from unseen additions.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
dot at the vector boundary is covered	`{"cloud": [], "dots": [["x", "a", 2]], "elements": ["x"], "vv": [["a", 2]]}`	`{"cloud": [], "dots": [], "elements": [], "vv": [["a", 2]]}`	Failed

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