FA-13487 / Numerical aggregation / Member archive

Retractable central summary: The retraction correction squares the residual about the old center. · case 02

The reduction disagrees with its explicit aggregation oracle.

Member previewVariant 2 · 3 implementations · 10 checks per implementation

Case contract

Process add/remove integer observations; each removal names one active equal-valued observation. Maintain [count, exact mean, unnormalised squared central scatter]. Empty state is [0,"0","0"].

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 1	`[1, "8", "121/4"]`	`[1, "8", "0"]`	Failed

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