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Invalid gathered lanes disappear instead of retaining a null slot · case 02

Invalid gathered lanes disappear instead of retaining a null slot.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Compose a sliced child selection with its parent selection, gather base values, and consult base validity. Preserve child order and repeated indices; invalid entries produce None.

Why this case matters

A bounded deterministic data engine model makes representation and changelog faults reproducible.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
validity moves with address	`[4, 2]`	`[4, 2, null]`	Failed

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

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