feat(rmcp)!: upgrade integration to rmcp 3.4

.release-plz.toml

@@ -35,7 +35,9 @@ version_group = "acp"
 # major release here. Keep it outside the `acp` version group because its
 # version need not equal the core version, but verify dependency-only release
 # proposals manually: core 1.x -> 2.x requires rmcp 2.x -> 3.x even if
-# release-plz initially classifies the manifest update as a patch.
+# release-plz initially classifies the manifest update as a patch. Upgrading
+# the public rmcp dependency from 2.x -> 3.x similarly requires this integration
+# crate to move from 3.x -> 4.x; it does not require a core ACP major release.
 [[package]]
 name = "agent-client-protocol-rmcp"
 

Cargo.toml

@@ -58,7 +58,7 @@ tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
 
 # MCP SDK
-rmcp = { version = "2.1.0", features = ["server", "transport-io", "schemars"] }
+rmcp = { version = "3.4.0", features = ["server", "transport-io", "schemars"] }
 
 # CLI parsing
 clap = { version = "4.5", features = ["derive"] }

md/SUMMARY.md

@@ -31,6 +31,7 @@
 
 # Reference
 
+- [Migrating the rmcp Integration to v4](./migration-rmcp-v4.md)
 - [Migrating to v2.0](./migration_v2.0.md)
 - [Migrating to v0.11](./migration_v0.11.x.md)
 

md/migration-rmcp-v4.md

@@ -0,0 +1,61 @@
+# Migrating the rmcp Integration to v4
+
+The next major release of `agent-client-protocol-rmcp` upgrades its public
+`rmcp` dependency from 2.x to 3.4. This is a breaking change for integrations
+that pass rmcp services or types across the crate boundary. The core
+`agent-client-protocol` SDK remains on 2.x, and the minimum supported Rust
+version remains 1.88.
+
+| Integration crate | Core ACP SDK | MCP SDK |
+| --- | --- | --- |
+| `agent-client-protocol-rmcp` 4.x (unreleased) | 2.x | `rmcp` 3.x |
+| `agent-client-protocol-rmcp` 3.x | 2.x | `rmcp` 2.x |
+
+Upgrade the application's rmcp dependency together with the integration crate.
+A service implementing rmcp 2.x's `Service` cannot be passed to the new
+`McpServer::from_rmcp`, even when it provides the same tools.
+
+## Custom services and tools
+
+- Use `ServerConfig` and `ClientConfig` instead of the deprecated `ServerInfo`
+  and `ClientInfo` aliases.
+- A manual `ServerHandler::call_tool` implementation now returns
+  `Result<CallToolResponse, ErrorData>`. Convert a completed `CallToolResult`
+  with `.into()`. The response enum also represents MRTR input-required
+  results and task-extension results; do not assume every response is a
+  completed tool result.
+- Functions registered with rmcp's `#[tool]` macro can still return
+  `CallToolResult`. The ACP integration's `tool` and `tool_fn` builder APIs also
+  remain available, and their results become completed tool responses.
+- `ToolExecution` and `Tool::with_execution` are no longer part of the tool
+  model. Do not add the old task-execution marker to tool definitions.
+
+For example, a manual handler that previously returned
+`Ok(CallToolResult::structured(value))` returns
+`Ok(CallToolResult::structured(value).into())` under its new
+`CallToolResponse` return type.
+
+## Modern MCP is now available to supplied services
+
+rmcp 3.4 implements discovery, per-request metadata, modern result shapes,
+MRTR, and subscription APIs for MCP 2026-07-28. The adapter preserves those
+requests and results when using `McpServer::from_rmcp`; a supplied service is
+still responsible for its advertised capabilities and handlers.
+
+The integration tests exercise both the built-in tool server and a supplied
+rmcp service with actual 2026-07-28 requests, without sending `initialize`.
+They cover direct tool calls before discovery, discovery itself, per-request
+version errors, and an MRTR retry with fresh request metadata.
+
+Do not treat the version-string constant or dependency upgrade alone as
+protocol selection. rmcp 3.4's `ProtocolVersion::LATEST` still defaults to
+2025-11-25. A modern client must select 2026-07-28 explicitly and include
+the required request metadata.
+
+## MCP-over-ACP remains a separate draft
+
+This upgrade does not change ACP's unstable `mcp/connect`, `mcp/message`, or
+`mcp/disconnect` envelopes. Redesigning that transport around stateless,
+server-addressed requests is separate work. The new transport's latest-only
+target does not require removing existing rmcp behavior from this prerequisite
+dependency upgrade.

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

@@ -39,7 +39,7 @@ async fn test_scoped_mcp_server_through_proxy() -> Result<(), agent_client_proto
     .await?;
 
     expect_test::expect![[r#"
-        "OK: CallToolResult { content: [Text(TextContent { text: \"2\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
+        "OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"2\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
     "#]].assert_debug_eq(&result);
 
     Ok(())
@@ -84,7 +84,7 @@ async fn test_scoped_mcp_server_through_session() -> Result<(), agent_client_pro
                     .await?;
 
                 expect_test::expect![[r#"
-                    "OK: CallToolResult { content: [Text(TextContent { text: \"2\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
+                    "OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"2\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
                 "#]].assert_debug_eq(&result);
 
                 Ok(())

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

@@ -7,7 +7,7 @@ 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 rmcp::{ClientHandler, ServiceExt, model::ClientConfig};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use tokio_util::compat::{TokioAsyncReadCompatExt, TokioAsyncWriteCompatExt};
@@ -64,8 +64,8 @@ fn create_test_server() -> McpServer<mcp::Client, impl RunWithConnectionTo<mcp::
 struct MinimalClientHandler;
 
 impl ClientHandler for MinimalClientHandler {
-    fn get_info(&self) -> ClientInfo {
-        ClientInfo::default()
+    fn get_info(&self) -> ClientConfig {
+        ClientConfig::default()
     }
 }
 

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

@@ -74,7 +74,7 @@ async fn test_tool_fn_greet() -> Result<(), agent_client_protocol::Error> {
     .await?;
 
     expect_test::expect![[r#"
-        "OK: CallToolResult { content: [Text(TextContent { text: \"\\\"Hello, World!\\\"\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
+        "OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"\\\"Hello, World!\\\"\", meta: None, annotations: None })], structured_content: None, is_error: Some(false), meta: None }"
     "#]].assert_debug_eq(&result);
 
     Ok(())

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

@@ -500,7 +500,7 @@ async fn test_trace_client_mcp_server() -> Result<(), agent_client_protocol::Err
                             "sessionUpdate": String("agent_message_chunk"),
                             "content": Object {
                                 "type": String("text"),
-                                "text": String("OK: CallToolResult { content: [Text(TextContent { text: \"{\\\"echoed\\\":\\\"Client echoes: Hello from client test!\\\",\\\"call_number\\\":1}\", meta: None, annotations: None })], structured_content: Some(Object {\"echoed\": String(\"Client echoes: Hello from client test!\"), \"call_number\": Number(1)}), is_error: Some(false), meta: None }"),
+                                "text": String("OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"{\\\"echoed\\\":\\\"Client echoes: Hello from client test!\\\",\\\"call_number\\\":1}\", meta: None, annotations: None })], structured_content: Some(Object {\"echoed\": String(\"Client echoes: Hello from client test!\"), \"call_number\": Number(1)}), is_error: Some(false), meta: None }"),
                             },
                             "messageId": String("testy-message-end-turn-1"),
                         },

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

@@ -670,7 +670,7 @@ async fn test_trace_mcp_tool_call() -> Result<(), agent_client_protocol::Error>
                         "capabilities": Object {},
                         "clientInfo": Object {
                             "name": String("rmcp"),
-                            "version": String("2.2.0"),
+                            "version": String("3.4.0"),
                         },
                     },
                 },
@@ -689,7 +689,7 @@ async fn test_trace_mcp_tool_call() -> Result<(), agent_client_protocol::Error>
                         },
                         "serverInfo": Object {
                             "name": String("rmcp"),
-                            "version": String("2.2.0"),
+                            "version": String("3.4.0"),
                         },
                         "instructions": String("A simple test MCP server with an echo tool"),
                     },
@@ -761,7 +761,7 @@ async fn test_trace_mcp_tool_call() -> Result<(), agent_client_protocol::Error>
                             "sessionUpdate": String("agent_message_chunk"),
                             "content": Object {
                                 "type": String("text"),
-                                "text": String("OK: CallToolResult { content: [Text(TextContent { text: \"{\\\"result\\\":\\\"Echo: Hello from trace test!\\\"}\", meta: None, annotations: None })], structured_content: Some(Object {\"result\": String(\"Echo: Hello from trace test!\")}), is_error: Some(false), meta: None }"),
+                                "text": String("OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"{\\\"result\\\":\\\"Echo: Hello from trace test!\\\"}\", meta: None, annotations: None })], structured_content: Some(Object {\"result\": String(\"Echo: Hello from trace test!\")}), is_error: Some(false), meta: None }"),
                             },
                             "messageId": String("testy-message-end-turn-1"),
                         },
@@ -794,7 +794,7 @@ async fn test_trace_mcp_tool_call() -> Result<(), agent_client_protocol::Error>
                             "sessionUpdate": String("agent_message_chunk"),
                             "content": Object {
                                 "type": String("text"),
-                                "text": String("OK: CallToolResult { content: [Text(TextContent { text: \"{\\\"result\\\":\\\"Echo: Hello from trace test!\\\"}\", meta: None, annotations: None })], structured_content: Some(Object {\"result\": String(\"Echo: Hello from trace test!\")}), is_error: Some(false), meta: None }"),
+                                "text": String("OK: CallToolResult { result_type: None, content: [Text(TextContent { text: \"{\\\"result\\\":\\\"Echo: Hello from trace test!\\\"}\", meta: None, annotations: None })], structured_content: Some(Object {\"result\": String(\"Echo: Hello from trace test!\")}), is_error: Some(false), meta: None }"),
                             },
                             "messageId": String("testy-message-end-turn-1"),
                         },

src/agent-client-protocol-cookbook/src/lib.rs

@@ -720,8 +720,8 @@ pub mod global_mcp_server {
     //!
     //! #[tool_handler]
     //! impl ServerHandler for MyMcpServer {
-    //!     fn get_info(&self) -> ServerInfo {
-    //!         ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
+    //!     fn get_info(&self) -> ServerConfig {
+    //!         ServerConfig::new(ServerCapabilities::builder().enable_tools().build())
     //!             .with_protocol_version(ProtocolVersion::V_2024_11_05)
     //!             .with_server_info(Implementation::from_build_env())
     //!     }

src/agent-client-protocol-rmcp/CHANGELOG.md

@@ -7,6 +7,22 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Breaking changes
+
+- Upgrade the public `rmcp` dependency from 2.x to 3.4. This requires the next
+  major release of `agent-client-protocol-rmcp` (4.x), while the core ACP SDK
+  remains on 2.x. Services supplied to `McpServer::from_rmcp` must use rmcp 3.x.
+- Adapt tool handlers to rmcp's `CallToolResponse`, use `ServerConfig` in place
+  of the deprecated `ServerInfo` alias, and remove legacy tool-execution
+  metadata. See the [migration guide](https://agentclientprotocol.github.io/rust-sdk/migration-rmcp-v4.html).
+
+### Added
+
+- Integration coverage for MCP 2026-07-28 requests without initialization,
+  discovery, per-request metadata/version validation, and MRTR results from
+  caller-supplied rmcp services. This dependency upgrade does not replace the
+  current unstable MCP-over-ACP wire lifecycle.
+
 ## [3.1.1](https://github.com/agentclientprotocol/rust-sdk/compare/agent-client-protocol-rmcp-v3.1.0...agent-client-protocol-rmcp-v3.1.1) - 2026-09-18
 
 ### Other

src/agent-client-protocol-rmcp/README.md

@@ -67,10 +67,17 @@ release of either dependency therefore requires a major release of this crate.
 
 | agent-client-protocol-rmcp | agent-client-protocol | rmcp |
 | -------------------------- | --------------------- | ---- |
+| 4.x (unreleased)           | 2.x                   | 3.x  |
 | 3.x                        | 2.x                   | 2.x  |
 | 2.x                        | 1.x                   | 2.x  |
 | 1.x                        | 1.x                   | 1.x  |
 
+See the [rmcp 4.x integration migration guide](https://agentclientprotocol.github.io/rust-sdk/migration-rmcp-v4.html)
+for adapting services to rmcp 3.x. The minimum supported Rust version remains
+1.88. The dependency upgrade does not itself change the unstable ACP transport
+envelopes or require applications to use modern MCP instead of rmcp's default
+protocol version.
+
 ## Related Crates
 
 - **[agent-client-protocol](../agent-client-protocol/)** — Core ACP protocol types and traits

src/agent-client-protocol-rmcp/examples/with_mcp_server.rs

@@ -66,8 +66,8 @@ impl ExampleMcpServer {
 #[allow(unknown_lints, clippy::unused_async_trait_impl)]
 #[tool_handler]
 impl ServerHandler for ExampleMcpServer {
-    fn get_info(&self) -> ServerInfo {
-        ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
+    fn get_info(&self) -> ServerConfig {
+        ServerConfig::new(ServerCapabilities::builder().enable_tools().build())
             .with_server_info(Implementation::new("example-mcp-server", "0.1.0"))
             .with_protocol_version(ProtocolVersion::V_2024_11_05)
             .with_instructions("A simple example MCP server with an echo tool")