FA-4129 / Sequence semantics / Member archive

Second element not second distinct · case 04

The operation returns a result or retained state that violates this contract: Return the second positional element or None if fewer than two elements exist.

Member previewVariant 4 · 3 implementations · 5 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
singleton collection	`"a"`	`null`	Failed

MEMBER ARCHIVE

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

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