This question evaluates a data scientist's competency in designing and analyzing A/B experiments for a homepage recommendation carousel, including selection of primary and secondary metrics, assessment of statistical power and practical significance, and the setup of guardrails.

A product team has shipped an A/B test for a new recommendation carousel placed on the app's homepage. Users are randomly assigned at the user level to Control (no carousel) or Treatment (homepage shows the carousel). The goal is to improve user engagement and downstream conversions without harming overall experience or performance.
Assume a standard 50/50 split, sticky assignment, and at least one weekly cycle of traffic.
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