You launch your Flutter app. It performs great in beta. Onboarding goes well. Then, somewhere between 50K and 150K users, things start breaking in ways your local tests never predicted. API responses slow down. State updates trigger unnecessary widget rebuilds. App size complaints start showing up in reviews. Your CI pipeline begins to feel like it is held together with tape. This is not a Flutter problem. It is an architecture and discipline problem. Flutter is fully capable of scaling,but only if your codebase is built with growth in mind from an early stage. Most teams do not plan for that, and they pay for it later. Here is what actually goes wrong, and what you can do about it.…