feat(rmcp): Move MCP server builder from core to rmcp crate

Author: benbrandt

Cargo.lock

@@ -2,11 +2,11 @@
 members = [
     "src/agent-client-protocol",
     "src/agent-client-protocol-derive",
-    # Keep polyfill before conductor: release-plz currently ignores versioned
+    # Keep polyfill and rmcp before conductor: release-plz currently ignores versioned
     # dev-dependency edges, but cargo publish still validates them.
     "src/agent-client-protocol-polyfill",
-    "src/agent-client-protocol-conductor",
     "src/agent-client-protocol-rmcp",
+    "src/agent-client-protocol-conductor",
     "src/agent-client-protocol-test",
     "src/agent-client-protocol-trace-viewer",
     "src/yopo",

Cargo.toml

@@ -14,7 +14,7 @@ The core SDK. Provides:
 - **Connection builders** (`builder()`, `connect_to()`, `connect_with()`)
 - **Message handling** (`on_receive_request`, `on_receive_notification`, `on_receive_dispatch`)
 - **Protocol types** (`agent_client_protocol::schema::*`) - all ACP message types
-- **MCP server builder** - for adding tools to proxies
+- **MCP server attachment** - runtime-agnostic interfaces for wiring MCP servers into ACP sessions
 
 ### agent-client-protocol-tokio
 
@@ -27,6 +27,7 @@ Tokio-specific utilities:
 
 Integration with the [rmcp](https://docs.rs/rmcp) crate:
 
+- **`McpServer::builder()`** - define MCP tools in Rust code
 - **`McpServer::from_rmcp()`** - wrap an rmcp server as an ACP MCP server
 
 ## Role System
@@ -156,7 +157,7 @@ stateDiagram-v2
 | `src/agent-client-protocol/src/component.rs` | ConnectTo and Builder traits          |
 | `src/agent-client-protocol/src/handler.rs`   | Connection builder implementation     |
 | `src/agent-client-protocol/src/typed.rs`     | Dispatch type and handler matching    |
-| `src/agent-client-protocol/src/mcp_server/`  | MCP server builder                    |
+| `src/agent-client-protocol/src/mcp_server/`  | Runtime-agnostic MCP server attachment |
 | `src/agent-client-protocol/src/concepts/`    | Rustdoc concept explanations          |
 
 ## Design Decisions

md/design.md

@@ -37,6 +37,7 @@ uuid.workspace = true
 
 [dev-dependencies]
 agent-client-protocol = { workspace = true, features = ["unstable_mcp_over_acp"] }
+agent-client-protocol-rmcp.workspace = true
 agent-client-protocol-test.workspace = true
 yopo.workspace = true
 expect-test.workspace = true

src/agent-client-protocol-conductor/Cargo.toml

@@ -2,6 +2,7 @@
 
 use agent_client_protocol::mcp_server::McpServer;
 use agent_client_protocol::{Conductor, ConnectTo, Proxy};
+use agent_client_protocol_rmcp::McpServerExt as _;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 

src/agent-client-protocol-conductor/tests/mcp_integration/proxy.rs

@@ -12,6 +12,7 @@ use agent_client_protocol::schema::{
 };
 use agent_client_protocol::{Agent, Client, Conductor, ConnectTo, DynConnectTo, Proxy};
 use agent_client_protocol_conductor::{ConductorImpl, ProxiesAndAgent};
+use agent_client_protocol_rmcp::McpServerExt as _;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::path::PathBuf;

src/agent-client-protocol-conductor/tests/mcp_server_handler_chain.rs

@@ -8,6 +8,7 @@ use agent_client_protocol::mcp_server::McpServer;
 use agent_client_protocol::{Agent, Conductor, ConnectTo, Proxy, Role, RunWithConnectionTo};
 use agent_client_protocol_conductor::{ConductorImpl, ProxiesAndAgent};
 use agent_client_protocol_polyfill::mcp_over_acp::McpOverAcpPolyfill;
+use agent_client_protocol_rmcp::McpServerExt as _;
 use agent_client_protocol_test::testy::{Testy, TestyCommand};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};

src/agent-client-protocol-conductor/tests/scoped_mcp_server.rs

@@ -6,6 +6,7 @@
 use agent_client_protocol::{
     ByteStreams, ConnectTo, RunWithConnectionTo, mcp_server::McpServer, role::mcp, util::run_until,
 };
+use agent_client_protocol_rmcp::McpServerExt as _;
 use rmcp::{ClientHandler, ServiceExt, model::ClientInfo};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};

src/agent-client-protocol-conductor/tests/standalone_mcp_server.rs

@@ -7,6 +7,7 @@ use agent_client_protocol::mcp_server::McpServer;
 use agent_client_protocol::{Conductor, ConnectTo, DynConnectTo, Proxy, RunWithConnectionTo};
 use agent_client_protocol_conductor::{ConductorImpl, ProxiesAndAgent};
 use agent_client_protocol_polyfill::mcp_over_acp::McpOverAcpPolyfill;
+use agent_client_protocol_rmcp::McpServerExt as _;
 use agent_client_protocol_test::testy::{Testy, TestyCommand};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};

src/agent-client-protocol-conductor/tests/test_mcp_tool_output_types.rs

@@ -13,6 +13,7 @@ use agent_client_protocol::mcp_server::McpServer;
 use agent_client_protocol::{Conductor, ConnectTo, DynConnectTo, Proxy};
 use agent_client_protocol_conductor::{ConductorImpl, ProxiesAndAgent};
 use agent_client_protocol_polyfill::mcp_over_acp::McpOverAcpPolyfill;
+use agent_client_protocol_rmcp::McpServerExt as _;
 use agent_client_protocol_test::testy::{Testy, TestyCommand};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};