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O'Brien-Fleming type alpha spending: The spending boundary uses a one-sided quantile · case 02

The total alpha spent by the final look is double the design alpha.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Cumulative alpha spent at information fraction t is 2 - 2 Phi(z_{1-alpha/2} / sqrt(t)) (t capped at 1). Information fractions must strictly increase from 0, otherwise return None. Return the incremental alpha spent at each look rounded to 6.

Why this case matters

Spending functions let teams peek at experiments without inflating the false positive rate.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
single final look spends all alpha	`[0.1]`	`[0.05]`	Failed

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