Translate distillation cost into expected-loss terms

[orgoca]

Problem

We report the distillation cost as "about 2% of the teacher's Gini." That is honest and precise, and it is also not the unit anyone approves budget in.

A CRO asks: what does that cost in expected loss on a book of this size? Without that translation, the trade-off cannot be evaluated against the alternative — which is usually not "no model" but "deploy the teacher with a full MLOps stack."

Proposed approach

A helper that turns a Gini delta into portfolio economics under stated assumptions:

loss_impact(artifact, teacher_latent, y, X, exposure, approval_rate, lgd=...) →

• bad rate at the same approval rate, teacher vs artifact
• incremental expected loss per year at a given book size
• swap-set analysis: which accounts the artifact approves that the teacher declines, and vice versa

Assumptions must be explicit and caller-supplied. This is a calculator, not a claim.

Acceptance criteria

• Every assumption is a named parameter with no silent default
• Output states the assumptions alongside the numbers
• Documented with an explicit caveat that this is a planning estimate, not a forecast

Files

New helper in compileml.tune or a small compileml.economics, plus docs

Scope

Small to medium. Straightforward analytics; the care goes into not overclaiming.