Finishing the build is the moment the legal work starts, not the moment it ends. This guide tracks a mobile app across the gap between "feature-complete" and "live in the store," in roughly the order the risks bite: forming an entity that can absorb a lawsuit, proving you actually own your code, surviving Apple's and Google's developer agreements after Epic v. Apple and the EU Digital Markets Act, and writing a EULA, terms of service, and privacy policy that courts and regulators will honor. It then walks the consumer-protection gauntlet that governs money and subscriptions (ROSCA and the state automatic-renewal laws), accessibility (the ADA and WCAG), children's data (COPPA), advertising truthfulness, open-source license compliance, and the export and encryption rules that quietly attach when an app ships worldwide. A running hypothetical, a sleep-and-focus app called Nocturne, keeps the doctrine concrete. Because privacy law, platform economics, and negative-option rulemaking are all in motion, treat this as a detailed map rather than a substitute for counsel.