MCP Client — manages MCP server child processes via rmcp.

Uses rmcp (1.4.x) RunningService<RoleClient, AgentBlockClientHandler> internally. AgentBlockClientHandler provides custom notification handling via Lua callbacks (wired in Subtask 2/3). For Subtask 1, all notification methods are default no-ops.

All rmcp round-trips are wrapped in a per-call timeout so a hung child cannot block a Lua coroutine indefinitely.

Concurrency contract

list_tools and call_tool take &self, so the manager can be held under tokio::sync::RwLock and multiple RPCs — including against the same server — can proceed in parallel via read guards. Request/response multiplexing on a single server is handled by rmcp's Peer, which pairs each outbound request with a oneshot receiver keyed by request ID. connect and disconnect are mutating (&mut self) and must take the write guard.

This contract is covered by in-process unit tests in #[cfg(test)] at the bottom of this file. If rmcp alters its Peer concurrency model, or if this module is refactored to re-serialize RPCs, those tests fail.

Child environment

Stdio servers are spawned as child processes and inherit the host's environment, minus the host's own credential variables ([agent_block_types::creds::OWN_CREDENTIAL_ENV_VARS]), which [McpManager::connect] removes — the same set sh.exec strips. A server that legitimately needs one of those keys must be handed it explicitly via the env argument (mcp.connect(name, cmd, args, { env = {...} }) from Lua), which is applied after the removals.

Usage from Lua

mcp.connect("outline", "outline-mcp", {})
local tools = mcp.list_tools("outline")
local result = mcp.call("outline", "shelf", {})
mcp.disconnect("outline")