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Dense union decoding exposes a child under a null parent · case 04

Dense union decoding exposes a child under a null parent.

Member previewVariant 4 · 3 implementations · 6 checks per implementation

Case contract

Decode a dense tagged union. Tags select named child buffers through a tag map; offsets address those buffers independently of output position. Parent and selected child validity both apply. Emit [child-name,value] for valid parents, None for null parents.

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
parent null	`[["a", 4]]`	`[null]`	Failed

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