The unauthenticated REPL server started in --multi-user mode whenever DEVENV or REPL_ENABLE was set, unlike developer tools which are already blocked there. Gate its creation behind shouldStartReplServer, mirroring the developer tools policy, so it never starts with --multi-user. Give it a dedicated PENPOT_MCP_REPL_HOST knob defaulting to localhost so it no longer inherits the main server 0.0.0.0 bind in Docker, keep the devenv script on 0.0.0.0, and document and test the new behavior. Closes#11631 AI-assisted-by: muse-spark-1.3-contributor
