Your question is Choose Randomization Unit for Referrals. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You work on a consumer fintech app and want to test a growth change in the referral and invite experience. The treatment could affect not just the exposed user, but also the friends they invite and the households they belong to, so you are worried that a naive user-level split may contaminate results.
How would you think about the right unit of randomization for this growth experiment? Walk through how your choice would affect metric definition, power, and the validity of the test.