FA-4374 / Container mutation / Member archive

List extend expands one level · case 04

The operation returns a result or retained state that violates this contract: Extend by the iterable elements, without recursively flattening nested elements.

Member previewVariant 4 · 3 implementations · 4 checks per implementation

Case scope

A controlled failure with recorded boundary checks.

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
flat extension	`["a", ["b", "c"]]`	`["a", "b", "c"]`	Failed

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

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