An LLM's output streaming into a window — renders incrementally, no tearing macOS Quick Look opening a 5 KB note and a 1 MB doc — both effectively instant Conventional wisdom is that React is the wrong tool for a text editor — every keystroke changes state, state re-renders, and re-rendering a whole document per character is too slow, so editors lean on ProseMirror / Lexical / Slate that run their own DOM and keep React as a thin shell. I wanted to see how far idiomatic React actually goes. The editing core ended up entirely in React, no editor framework underneath: 20 KB gzipped kernel，no runtime deps beyond React Opens a 1 MB Markdown doc instantly，— a 5 KB note and a 1 MB file open at basically the same perceptual speed No per-keystroke lag — cursor stays steady, no flicker Streaming text in (e.g. piping an LLM's output) renders incrementally without tearing Here's how it stays in that budget. Short version: Immer structural sharing + a ~99% memo hit rate, without bypassing reconciliation.…