I build NestMux, a desktop app that runs Claude Code, Codex, Gemini CLI, Copilot and OpenCode in a grid of real terminals, each with its own account and its own git worktree. This is how it works inside, including the parts that are heuristics wearing a confident UI and the parts that do not survive a restart. If you are building something similar, most of this transfers. If you are deciding whether to use it, this is the honest version of what it does. Thirty-five seconds of it running, s...