Status from artifacts — the roll-up that can't lie, and the not-ready call — step 4 of 8

The only honest aggregate is worst-of: a workstream is exactly as healthy as its sickest task. With severity ranked green < amber < red, "worst" is the max by severity.

Fill in the one-liner: the rag from rags with the highest SEV value.

Expected output:

amber
green
red