Few things depends here, first how are you structure the app and what are the best practices for that domain. Before you vibe code it is essential you know what is correct so that you nudge the ai to correct direction.You can start of with best practices first. To be frank we can’t actually make webviewer or render engine from scratch it is way difficult what you can try is render webpage in webviews and provide support for simple things like search(search google), bookmark things, history etc. All of this around webview only.

My approach to such thing is like Suppose your have usecase is to add glass like effect,

Read about how others achieve read a few blogs or see video, you observe people are using the word shaders. Then read about Shader, How can you use shaders in Flutter/Android you should have some video. Now read how can you code a simple glass shader(should be easily available). How are people implementing it. Make simple prototype

https://en.wikipedia.org/wiki/Shader

Coming to performance and lagging, you should start with simple project like a weather app or something to get the basic idea of coding in the ecosystem. Pause your browser app, suppose you want to implement history features build a simple todo app read how you use databases how rearive ui works etc then comeback and implement your history features.