FA-45985 / Bounded deques / Member archive

Cursor after an erased node retains its old index · case 05

Cursor after an erased node retains its old index.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

Erase a selected position while updating independent stable cursors. A cursor at the erased element moves to its successor, or end; later cursors shift left, earlier cursors stay. Return values, cursor positions, and cursor-observed values; None denotes end.

Why this case matters

Controlled bounded deque implementation model with explicit storage and lifecycle observations.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
interior cursors	`[[5, 7, 8], [0, 1, 2, 3, null], [5, 7, 8, null, null]]`	`[[5, 7, 8], [0, 1, 1, 2, null], [5, 7, 7, 8, null]]`	Failed

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

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