FA-12958 / Numerical aggregation / Member archive

Merge central moment 2: Incoming scatter replaces rather than combines prior within-block scatter. · case 03

The reduction disagrees with its explicit aggregation oracle.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Merge disjoint integer observation blocks into [count, exact mean, unnormalised central moments through order 2]. Empty blocks are identities; moments are Fraction strings, empty summary is zero.

Why this case matters

Exact bounded examples isolate a reduction defect without floating-point or external-service effects.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 2	`[3, "4", "24"]`	`[3, "4", "26"]`	Failed

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