Persistent memory and governance for AI coding agents. Local-first .brain/ directory with engrams, audit log, and hypervisor file protection. Optional remote sync to relay.nucleusos.dev. Works across Cursor, Claude Code, Windsurf, and Gemini via Streamable HTTP or stdio. Features: persistent memory, governance, local-first, multi-client, remote sync. Install: pip install nucleus-mcp && nucleus-init --scan