How to evaluate emoji reactions?

A messaging app plans to launch an **emoji reactions** feature. Users can react to a message by **long-pressing the message for 5 seconds** and selecting an emoji. The company wants to know whether this feature creates value and whether it should be launched broadly. Describe how you would evaluate this feature from a product analytics and experimentation perspective. Your answer should address: 1. **Product objective:** What user or business problem might emoji reactions solve? 2. **Success metrics:** What primary, secondary, and guardrail metrics would you track? Consider both sender-side and receiver-side behavior, short-term engagement, and potential negative effects. 3. **Experiment design:** How would you design an A/B test for this feature? Specify the unit of randomization, treatment definition, likely sources of interference/network effects, experiment duration, and how you would think about power and minimum detectable effect. 4. **Measurement details:** What events would you instrument? How would you define adoption, active usage, retention impact, and quality of conversations? 5. **Risks and confounding:** What biases or pitfalls could make the feature appear better or worse than it really is? Consider novelty effects, heterogeneous treatment effects, long-press friction, message volume differences, and power-user concentration. 6. **Decision framework:** Under what conditions would you recommend full launch, iteration, or rollback? 7. **Executive communication:** How would you summarize the results for a C-level audience that cares about growth, engagement, and user experience rather than statistical detail? Assume the app is consumer-facing, has an existing messaging product, and can run a randomized experiment.