FA-75314 / CRDT convergence / Member archive

State vector diff: the local vector reports the last clock instead of the next one · case 04

The advertised state vector is one behind, so peers resend the last clock of every client.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

The local store holds structs [client, clock, length] covering clocks clock..clock+length-1. The remote state vector maps client ids (decimal strings, as decoded from JSON) to the next clock it expects; absent clients expect 0. Send, sorted by client then clock, every struct part the remote lacks, slicing a partly known struct to start at the expected clock. Also return the local state vector.

Why this case matters

Delta sync in sequence CRDTs exchanges state vectors to ship only the structs the peer is missing.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
empty remote vector gets everything	`{"send": [[1, 0, 3], [1, 3, 2], [1, 5, 4], [2, 0, 5], [7, 0, 2], [7, 2, 1]], "state_vector": [["1", 8], ["2", 4], ["7", 2]]}`	`{"send": [[1, 0, 3], [1, 3, 2], [1, 5, 4], [2, 0, 5], [7, 0, 2], [7, 2, 1]], "state_vector": [["1", 9], ["2", 5], ["7", 3]]}`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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