Persistent MCP servers (opt-in via `persistent: true`) survive host disconnects — they appear as offline in mcp_list and auto-restore when the host reconnects. Ephemeral servers (default) still clean up on disconnect. Offline servers return a clear error on mcp_call with time-since-disconnect info. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>