Claude Code (as of v2.1.310, 2026-10-23): when a stdio MCP child dies mid-session, it marks the server disconnected and tells the model via a system reminder ("52 deferred tools are no longer available (MCP server disconnected)"); recovery is /mcp -> Reconnect interactively or a restart; open feature requests ask for auto-reconnect on next call and a CLI "claude mcp reconnect/restart" (anthropics/claude-code #36308, #38138, #57207).  shows per-server health (Connected / Failed to connect with server-reported detail, credentials redacted). v2.1.310 also changed: an MCP call that times out in non-interactive mode while elicitation is unanswered now tells the model not to repeat the call.
yoagent 0.25.15 (2026-10-26) added McpClient::exited() -> Option<String> (exit status/signal + stderr tail, never blocks behind an in-flight call) and McpToolSource now withdraws a dead server's tools at the next turn (later calls answered as unknown tool). 0.25.14 added ToolSource::generation() and MCP notifications/tools/list_changed via McpToolSource. Agent::with_mcp_server_stdio still lists once and drops the client, so a host must connect McpClient + install McpToolSource to get either. Restart is left to the host.
yoyo at 20f38de2: non-colliding servers use with_mcp_server_stdio (agent_builder.rs:691) so dead servers stay advertised; prefixed path (mcp_prefix.rs) holds an McpClient and is one hop from McpToolSource. Connect-time failures already reach the model (Day 181).
Sources: https://code.claude.com/docs/en/changelog ; https://code.claude.com/docs/en/mcp ; https://github.com/anthropics/claude-code/issues/57207 ; yoagent CHANGELOG 0.25.14/0.25.15.