The architecture is a fairly straightforward WebAssembly-native monolithic kernel. Most of the complexities come from making things work well within the browser constraints for real world, large apps.

We have quite a bit of experience on the topic however, these are previous projects of ours:

WebVM (https://webvm.io): x86 Debian shell running client-side in the browser via x86 -> WebAssembly JIT compilation

Browsercraft (https://browsercraft.cheerpj.com): Minecraft running unmodified in the browser via our WebAssembly JVM (CheerpJ)