Referral & Word-of-Mouth Growth System.

### Input
Business, customer base, CAC, what customers love

### Task
Design a referral program structure: the incentive model (double-sided vs. one-sided, discount vs. cash vs. credit vs. gift), the trigger moment (when in the customer journey to ask — peak happiness moment), the ask mechanism (in-app, email, post-purchase), and the referral flow (how referee learns, how referrer tracks). Calculate: break-even referral reward based on current CAC.

### Output
Referral program design: incentive model + trigger moment + ask mechanism + referral flow + break-even reward calculation