Real-time streaming with the nex CLI

Build a terminal chat UX that streams tokens as they arrive. Combines the official `nex` CLI with stdin pipes for unix-style composability.

Outline

• Installing the nex CLI via curl -fsSL https://nextoken.biz/install.sh | sh
• One-shot streaming: nex chat "explain X" --stream
• Stdin pipes: git log --oneline | nex chat "summarise recent work" --stream
• Building an interactive REPL on top: 50 lines of bash + readline
• Persisting conversation history to ~/.nex/history/<session>.jsonl
• Killing a stream gracefully with Ctrl+C without leaving the request half-billed

Ship-date guess

Sprint 2, after CLI binaries publish.