FA-4118 / Sequence semantics / Member archive

First element default · case 03

The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.

Member previewVariant 3 · 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
two distinct elements	`"b"`	`"a"`	Failed

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

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