Lexical also treat its own EditorState as the source of truth. We use DOM MutationObservers to ensure the DOM matches the EditorState at all times. We do allow external mutations from things like spellcheckers update Lexical – otherwise people wouldn't be able to use Grammarly and other tools with Lexical. However, that's really constrained so that they don't overreach.

Lexical also has the notion of double-buffering. When you update Lexical, or use a node transform, you're actually mutating the "work in progress" EditorState. Once Lexical feels that the EditorState is ready, it will commit it to the DOM, and that EditorState will become immutable and will reflect what you see on the page.