The architecture of SiYuan, as I’ve learned from chatting with the author, is based on a Go-lang “kernel” process, which is responsible for parsing the markdown files, and indexing them. The electron app communicates with the “kernel” process via WebSocket and is used solely for input and display, using an HTML-based WYSIWYG editor they started working on a few years ago for their forum software.
This is quite different from Obsidian’s architecture, which is pretty easy to understand if you’ve participated in plugin creation. The entire app runs inside an electron window, and there is no inter-process communications. In fact, you can infer much of the architecture from our public plugin API.