feat!: add MRTR behavior support (SEP-2322) (#929)

* feat!: add MRTR behavior support

* feat: harden SEP-2322 MRTR support

* ci: diff public API only on features common to base and head

cargo public-api builds both revisions with the same feature set, so a
feature introduced (or removed) by a PR broke the build of the other
revision. Restrict the all-features diff to features present in both the
base and head revisions.

Author: DaleSeo

.github/workflows/ci.yml

@@ -170,18 +170,32 @@ jobs:
 
       - name: Check rmcp (all features except local)
         run: |
-          FEATURES=$(cargo metadata --no-deps --format-version 1 \
-            | jq -r '[.packages[] | select(.name == "rmcp") | .features | keys[]
-                      | select(startswith("__") | not)
-                      | select(. != "local")] | join(",")')
+          BASE_SHA=${{ github.event.pull_request.base.sha }}
+          # `cargo public-api diff` builds both revisions with the same feature
+          # set, so a feature that exists on only one side (e.g. a feature added
+          # or removed by this PR) would fail to build the other revision. Diff
+          # only the features present in BOTH the base and the head; features
+          # unique to one side are necessarily pure additions/removals, which the
+          # release-type deny flags already govern.
+          list_features() {
+            cargo metadata --no-deps --format-version 1 --manifest-path "$1/Cargo.toml" \
+              | jq -r '.packages[] | select(.name == "rmcp") | .features | keys[]
+                       | select(startswith("__") | not)
+                       | select(. != "local")'
+          }
+          list_features "." | sort -u > "$RUNNER_TEMP/head_features"
+          git worktree add --detach "$RUNNER_TEMP/rmcp-base" "$BASE_SHA"
+          list_features "$RUNNER_TEMP/rmcp-base" | sort -u > "$RUNNER_TEMP/base_features"
+          git worktree remove --force "$RUNNER_TEMP/rmcp-base"
+          FEATURES=$(comm -12 "$RUNNER_TEMP/head_features" "$RUNNER_TEMP/base_features" | paste -sd, -)
           cargo public-api \
             --package rmcp \
             --features "$FEATURES" \
             -ss \
             diff \
             $DENY \
             --force \
-            ${{ github.event.pull_request.base.sha }}..${{ github.sha }}
+            "$BASE_SHA"..${{ github.sha }}
 
   spelling:
     name: spell check with typos

conformance/src/bin/server.rs

@@ -213,9 +213,9 @@ impl ServerHandler for ConformanceServer {
         &self,
         request: CallToolRequestParams,
         cx: RequestContext<RoleServer>,
-    ) -> Result<CallToolResult, ErrorData> {
+    ) -> Result<CallToolResponse, ErrorData> {
         let args = request.arguments.unwrap_or_default();
-        match request.name.as_ref() {
+        let result = match request.name.as_ref() {
             "test_simple_text" => Ok(CallToolResult::success(vec![ContentBlock::text(
                 "This is a simple text response for testing.",
             )])),
@@ -530,7 +530,8 @@ impl ServerHandler for ConformanceServer {
                 format!("Unknown tool: {}", request.name),
                 None,
             )),
-        }
+        };
+        result.map(Into::into)
     }
 
     async fn list_resources(
@@ -555,9 +556,9 @@ impl ServerHandler for ConformanceServer {
         &self,
         request: ReadResourceRequestParams,
         _cx: RequestContext<RoleServer>,
-    ) -> Result<ReadResourceResult, ErrorData> {
+    ) -> Result<ReadResourceResponse, ErrorData> {
         let uri = request.uri.as_str();
-        match uri {
+        let result = match uri {
             "test://static-text" => Ok(ReadResourceResult::new(vec![
                 ResourceContents::TextResourceContents {
                     uri: uri.into(),
@@ -598,7 +599,8 @@ impl ServerHandler for ConformanceServer {
                     ))
                 }
             }
-        }
+        };
+        result.map(Into::into)
     }
 
     async fn list_resource_templates(
@@ -679,8 +681,8 @@ impl ServerHandler for ConformanceServer {
         &self,
         request: GetPromptRequestParams,
         _cx: RequestContext<RoleServer>,
-    ) -> Result<GetPromptResult, ErrorData> {
-        match request.name.as_str() {
+    ) -> Result<GetPromptResponse, ErrorData> {
+        let result = match request.name.as_str() {
             "test_simple_prompt" => Ok(GetPromptResult::new(vec![PromptMessage::new_text(
                 Role::User,
                 "This is a simple test prompt.",
@@ -721,7 +723,8 @@ impl ServerHandler for ConformanceServer {
                 format!("Unknown prompt: {}", request.name),
                 None,
             )),
-        }
+        };
+        result.map(Into::into)
     }
 
     async fn complete(

crates/rmcp-macros/src/prompt_handler.rs

@@ -35,7 +35,7 @@ pub fn prompt_handler(attr: TokenStream, input: TokenStream) -> syn::Result<Toke
             &self,
             request: rmcp::model::GetPromptRequestParams,
             context: rmcp::service::RequestContext<rmcp::RoleServer>,
-        ) -> Result<rmcp::model::GetPromptResult, rmcp::ErrorData> {
+        ) -> Result<rmcp::model::GetPromptResponse, rmcp::ErrorData> {
             let prompt_context = rmcp::handler::server::prompt::PromptContext::new(
                 self,
                 request.name,

crates/rmcp-macros/src/task_handler.rs

@@ -77,7 +77,16 @@ pub fn task_handler(attr: TokenStream, input: TokenStream) -> syn::Result<TokenS
 
                 let task_result_id = task_id.clone();
                 let future = Box::pin(async move {
-                    let result = server.call_tool(future_request, future_context).await;
+                    let result = server
+                        .call_tool(future_request, future_context)
+                        .await
+                        .and_then(|response| match response {
+                            rmcp::model::CallToolResponse::Complete(result) => Ok(result),
+                            _ => Err(rmcp::ErrorData::internal_error(
+                                "input_required is not supported for task-based tool calls",
+                                None,
+                            )),
+                        });
                     Ok(
                         Box::new(ToolCallTaskResult::new(task_result_id, result))
                             as Box<dyn OperationResultTransport>,

crates/rmcp-macros/src/tool_handler.rs

@@ -47,7 +47,7 @@ pub fn tool_handler(attr: TokenStream, input: TokenStream) -> syn::Result<TokenS
                 &self,
                 request: rmcp::model::CallToolRequestParams,
                 context: rmcp::service::RequestContext<rmcp::RoleServer>,
-            ) -> Result<rmcp::model::CallToolResult, rmcp::ErrorData> {
+            ) -> Result<rmcp::model::CallToolResponse, rmcp::ErrorData> {
                 let tcc = rmcp::handler::server::tool::ToolCallContext::new(self, request, context);
                 #router.call(tcc).await
             }

crates/rmcp/Cargo.toml

@@ -22,6 +22,7 @@ features = [
   "client-side-sse",
   "elicitation",
   "macros",
+  "request-state",
   "reqwest",
   "reqwest-native-tls",
   "reqwest-tls-no-provider",
@@ -64,6 +65,10 @@ schemars = { version = "1.0", optional = true, features = ["chrono04"] }
 # for image encoding
 base64 = { version = "0.22", optional = true }
 
+# for SEP-2322 requestState integrity sealing (opt-in via the `request-state` feature)
+hmac = { version = "0.12", optional = true }
+sha2 = { version = "0.10", optional = true }
+
 # for HTTP client
 reqwest = { version = "0.13.2", default-features = false, features = [
   "json",
@@ -120,6 +125,9 @@ server = ["transport-async-rw", "schemars", "dep:pastey"]
 macros = ["dep:rmcp-macros", "dep:pastey"]
 elicitation = ["dep:url"]
 
+# SEP-2322 requestState integrity helper (HMAC-SHA256 seal/open codec)
+request-state = ["dep:hmac", "dep:sha2", "base64"]
+
 # reqwest http client
 __reqwest = ["dep:reqwest"]
 
@@ -315,6 +323,11 @@ name = "test_trace_context"
 required-features = ["server", "client"]
 path = "tests/test_trace_context.rs"
 
+[[test]]
+name = "test_mrtr_behavior"
+required-features = ["server", "client"]
+path = "tests/test_mrtr_behavior.rs"
+
 [[test]]
 name = "test_prompt_macros"
 required-features = ["server", "client"]

crates/rmcp/src/handler/server.rs

@@ -27,6 +27,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
     ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
         // `context` is moved into the dispatch below, so read the negotiated version first.
         let protocol_version = context.protocol_version();
+        let mrtr_supported = protocol_version
+            .as_ref()
+            .is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
         let result = match request {
             ClientRequest::InitializeRequest(request) => self
                 .initialize(request.params, context)
@@ -46,7 +49,7 @@ impl<H: ServerHandler> Service<RoleServer> for H {
             ClientRequest::GetPromptRequest(request) => self
                 .get_prompt(request.params, context)
                 .await
-                .map(ServerResult::GetPromptResult),
+                .map(ServerResult::from),
             ClientRequest::ListPromptsRequest(request) => self
                 .list_prompts(request.params, context)
                 .await
@@ -62,7 +65,7 @@ impl<H: ServerHandler> Service<RoleServer> for H {
             ClientRequest::ReadResourceRequest(request) => self
                 .read_resource(request.params, context)
                 .await
-                .map(ServerResult::ReadResourceResult),
+                .map(ServerResult::from),
             ClientRequest::SubscribeRequest(request) => self
                 .subscribe(request.params, context)
                 .await
@@ -105,7 +108,7 @@ impl<H: ServerHandler> Service<RoleServer> for H {
                 } else {
                     self.call_tool(request.params, context)
                         .await
-                        .map(ServerResult::CallToolResult)
+                        .map(ServerResult::from)
                 }
             }
             ClientRequest::ListToolsRequest(request) => self
@@ -133,6 +136,17 @@ impl<H: ServerHandler> Service<RoleServer> for H {
                 .await
                 .map(ServerResult::CancelTaskResult),
         };
+        let result = result.and_then(|result| {
+            if matches!(result, ServerResult::InputRequiredResult(_)) && !mrtr_supported {
+                Err(McpError::invalid_request(
+                    "InputRequiredResult requires negotiated protocol version 2026-07-28 or newer",
+                    None,
+                ))
+            } else {
+                Ok(result)
+            }
+        });
+
         // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
         // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
         // compare lexically the same as chronologically.
@@ -229,7 +243,7 @@ macro_rules! server_handler_methods {
             &self,
             request: GetPromptRequestParams,
             context: RequestContext<RoleServer>,
-        ) -> impl Future<Output = Result<GetPromptResult, McpError>> + MaybeSendFuture + '_ {
+        ) -> impl Future<Output = Result<GetPromptResponse, McpError>> + MaybeSendFuture + '_ {
             std::future::ready(Err(McpError::method_not_found::<GetPromptRequestMethod>()))
         }
         fn list_prompts(
@@ -259,7 +273,7 @@ macro_rules! server_handler_methods {
             &self,
             request: ReadResourceRequestParams,
             context: RequestContext<RoleServer>,
-        ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + MaybeSendFuture + '_ {
+        ) -> impl Future<Output = Result<ReadResourceResponse, McpError>> + MaybeSendFuture + '_ {
             std::future::ready(Err(
                 McpError::method_not_found::<ReadResourceRequestMethod>(),
             ))
@@ -312,7 +326,7 @@ macro_rules! server_handler_methods {
             &self,
             request: CallToolRequestParams,
             context: RequestContext<RoleServer>,
-        ) -> impl Future<Output = Result<CallToolResult, McpError>> + MaybeSendFuture + '_ {
+        ) -> impl Future<Output = Result<CallToolResponse, McpError>> + MaybeSendFuture + '_ {
             std::future::ready(Err(McpError::method_not_found::<CallToolRequestMethod>()))
         }
         fn list_tools(
@@ -485,7 +499,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: GetPromptRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<GetPromptResult, McpError>> + MaybeSendFuture + '_ {
+            ) -> impl Future<Output = Result<GetPromptResponse, McpError>> + MaybeSendFuture + '_ {
                 (**self).get_prompt(request, context)
             }
 
@@ -518,7 +532,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: ReadResourceRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + MaybeSendFuture + '_ {
+            ) -> impl Future<Output = Result<ReadResourceResponse, McpError>> + MaybeSendFuture + '_ {
                 (**self).read_resource(request, context)
             }
 
@@ -542,7 +556,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CallToolRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CallToolResult, McpError>> + MaybeSendFuture + '_ {
+            ) -> impl Future<Output = Result<CallToolResponse, McpError>> + MaybeSendFuture + '_ {
                 (**self).call_tool(request, context)
             }