FA-75162 / CRDT convergence / Member archive

Visible index translation: tombstones are counted as visible positions · case 02

Edits land on deleted characters or next to the wrong neighbour.

Member previewVariant 2 · 3 implementations · 9 checks per implementation

Case contract

A sequence CRDT holds [id, char, deleted]. Local edits use visible indices: ["insert", i, ch] (0 <= i <= visible length) references the visible element at i-1 (None at 0), is placed immediately after it, and gets id "L<k>" from a counter advanced only by accepted inserts; ["delete", i] (0 <= i < visible length) tombstones the visible element at i. Out-of-range edits yield ["reject", i]. Return the emitted ops and visible text.

Why this case matters

Editors translate cursor positions into identifier-based CRDT operations; tombstones make that translation error-prone.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
insert after tombstones uses the visible neighbour	`{"ops": [["ins", "L1", "e1"]], "text": "aXde"}`	`{"ops": [["ins", "L1", "e3"]], "text": "adXe"}`	Failed

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