FA-75068 / CRDT convergence / Member archive

Two-phase graph: a vertex with incoming edges can be removed · case 03

Removing the target of an edge is accepted and the edge silently disappears.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Vertices and edges each have grow-only add and remove sets. A vertex is live when added and not removed; an edge is visible when added, not removed, and both endpoints are live. At the origin replica, adding an edge requires both endpoints live, removing a vertex requires no visible edge touching it in either direction, and removing an edge requires it visible; failed preconditions record the op index. ["merge", s, d] unions all four sets into d. Return sorted live vertices and visible edges per replica plus rejections.

Why this case matters

Graph CRDTs must keep edges consistent with vertex removals that happen concurrently on other replicas.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
vertex with incoming edge cannot be removed	`{"graphs": [[[], []], [[], []]], "rejected": []}`	`{"graphs": [[["u", "v"], [["u", "v"]]], [[], []]], "rejected": [3, 4]}`	Failed

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