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Learned missingness indicators uses held-out rows while fitting · case 03

Learned missingness indicators uses held-out rows while fitting.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Train and rows are nonempty rectangular rows. Fit the output feature list as columns containing at least one None in training; emit a 0/1 missing flag for each such column in the same order.

Why this case matters

A small deterministic preprocessing contract makes the fit boundary and transform behavior directly inspectable.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
heldout cannot add column	`[[1]]`	`[[]]`	Failed

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