feat(mcp): migrate to Streamable HTTP transport (MCP spec 2025-03-26)

- Upgrade mcp-spring-webmvc from 0.10.0 to 0.18.1 (adds
  WebMvcStreamableServerTransportProvider alongside the legacy SSE provider)
- Add mcp-json-jackson2 0.18.1 for JacksonMcpJsonMapper adapter
- Exclude McpWebMvcServerAutoConfiguration (SSE transport) via
  spring.autoconfigure.exclude; register WebMvcStreamableServerTransportProvider
  and its RouterFunction manually in McpConfig so Spring AI's
  McpServerAutoConfiguration picks up the correct transport bean
- Remove sse-message-endpoint / sse-endpoint from application.yml;
  all MCP traffic now flows through POST+GET /mcp
- Remove McpSseMethodNotAllowed workaround from WebConfig and drop
  'sse' from SPA fallback exclusions (no longer needed)

Clients should connect with type: http at https://trueref.sal.giize.com/mcp

trueref-adapters/pom.xml

@@ -44,12 +44,27 @@
             <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
         </dependency>
 
-        <!-- Spring AI MCP server (Streamable HTTP) -->
+        <!-- Spring AI MCP server — tool/resource registration and McpSyncServer wiring.
+             McpWebMvcServerAutoConfiguration (SSE transport) is excluded in application.yml;
+             the Streamable HTTP transport is wired manually in McpConfig. -->
         <dependency>
             <groupId>org.springframework.ai</groupId>
             <artifactId>spring-ai-starter-mcp-server-webmvc</artifactId>
         </dependency>
 
+        <!-- MCP Java SDK 0.18.1: provides WebMvcStreamableServerTransportProvider.
+             Overrides the 0.10.0 version pulled in by spring-ai-starter-mcp-server-webmvc. -->
+        <dependency>
+            <groupId>io.modelcontextprotocol.sdk</groupId>
+            <artifactId>mcp-spring-webmvc</artifactId>
+            <version>0.18.1</version>
+        </dependency>
+        <dependency>
+            <groupId>io.modelcontextprotocol.sdk</groupId>
+            <artifactId>mcp-json-jackson2</artifactId>
+            <version>0.18.1</version>
+        </dependency>
+
         <!-- H2 + Flyway -->
         <dependency>
             <groupId>com.h2database</groupId>

trueref-adapters/src/main/java/com/trueref/adapter/in/mcp/McpConfig.java

@@ -1,22 +1,47 @@
 package com.trueref.adapter.in.mcp;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
+import io.modelcontextprotocol.json.jackson2.JacksonMcpJsonMapper;
+import io.modelcontextprotocol.server.transport.WebMvcStreamableServerTransportProvider;
 import org.springframework.ai.tool.ToolCallbackProvider;
 import org.springframework.ai.tool.method.MethodToolCallbackProvider;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.function.RouterFunction;
+import org.springframework.web.servlet.function.ServerResponse;
 
 /**
- * Registers the trueref MCP tool callbacks with Spring AI's MCP WebMVC auto-configuration. The
+ * Wires the MCP Streamable HTTP transport (2025-03-26 spec) and registers trueref tool callbacks.
- * {@link MethodToolCallbackProvider} scans {@link TrueRefMcpTools} for methods annotated with
+ *
- * {@link org.springframework.ai.tool.annotation.Tool} and publishes them on the MCP endpoint
+ * <p>Spring AI 1.0.0 only ships {@link io.modelcontextprotocol.server.transport.WebMvcSseServerTransportProvider}
- * configured in {@code application.yml} (POST {@code /mcp} via
+ * (legacy SSE). We exclude {@code McpWebMvcServerAutoConfiguration} in {@code application.yml} and
- * {@code spring.ai.mcp.server.sse-message-endpoint}).
+ * register {@link WebMvcStreamableServerTransportProvider} directly — Spring AI's
+ * {@code McpServerAutoConfiguration} accepts any {@code McpServerTransportProvider} bean.
+ *
+ * <p>Clients connect with {@code type: http} at {@code POST /mcp} (JSON-RPC) and optionally open
+ * a long-poll GET {@code /mcp} stream for server-initiated notifications.
  */
 @Configuration
 @EnableConfigurationProperties(McpProperties.class)
 public class McpConfig {
 
+    /** Streamable HTTP transport — handles both POST (JSON-RPC) and GET (SSE stream) on /mcp. */
+    @Bean
+    public WebMvcStreamableServerTransportProvider streamableTransportProvider(ObjectMapper objectMapper) {
+        return WebMvcStreamableServerTransportProvider.builder()
+                .jsonMapper(new JacksonMcpJsonMapper(objectMapper))
+                .mcpEndpoint("/mcp")
+                .build();
+    }
+
+    /** Registers the transport's GET+POST routes with Spring MVC. */
+    @Bean
+    public RouterFunction<ServerResponse> mcpStreamableRoutes(
+            WebMvcStreamableServerTransportProvider transport) {
+        return transport.getRouterFunction();
+    }
+
     @Bean
     public ToolCallbackProvider trueRefMcpToolCallbacks(TrueRefMcpTools tools) {
         return MethodToolCallbackProvider.builder().toolObjects(tools).build();

trueref-adapters/src/main/java/com/trueref/adapter/in/rest/WebConfig.java

@@ -5,11 +5,6 @@ import java.util.Set;
 import org.jspecify.annotations.Nullable;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.Resource;
-import org.springframework.http.HttpHeaders;
-import org.springframework.http.HttpStatus;
-import org.springframework.http.ResponseEntity;
-import org.springframework.web.bind.annotation.PostMapping;
-import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 import org.springframework.web.servlet.resource.PathResourceResolver;
@@ -20,26 +15,11 @@ import org.springframework.web.servlet.resource.PathResourceResolver;
  * explicitly excluded — Spring routes those first anyway, but we exclude them defensively so the
  * resource resolver does not attempt a fallback for them.
  */
-/**
- * Explicit POST handler for the SSE endpoint. Modern MCP clients (e.g. Claude Code) probe for
- * Streamable HTTP transport by POSTing to the server URL first. Returning 405 here tells them this
- * server uses the legacy HTTP+SSE transport, triggering the correct GET-based SSE fallback.
- */
-@RestController
-class McpSseMethodNotAllowed {
-    @PostMapping("/sse")
-    ResponseEntity<Void> rejectPost() {
-        HttpHeaders headers = new HttpHeaders();
-        headers.add(HttpHeaders.ALLOW, "GET");
-        return ResponseEntity.status(HttpStatus.METHOD_NOT_ALLOWED).headers(headers).build();
-    }
-}
-
 @Configuration
 public class WebConfig implements WebMvcConfigurer {
 
     private static final Set<String> EXCLUDED_PREFIXES =
-            Set.of("api/", "mcp", "sse", "swagger-ui/", "v3/api-docs", "actuator/");
+            Set.of("api/", "mcp", "swagger-ui/", "v3/api-docs", "actuator/");
 
     @Override
     public void addResourceHandlers(ResourceHandlerRegistry registry) {

trueref-bootstrap/src/main/resources/application.yml

@@ -19,12 +19,13 @@ spring:
     locations: classpath:db/migration
   mvc:
     async:
-      request-timeout: 0   # SSE streams must not time out
+      request-timeout: 0   # MCP GET streams must not time out
-  # Spring AI MCP server. In Spring AI 1.0.0 the WebMVC transport is SSE-based
+  # Spring AI MCP server — Streamable HTTP transport (MCP spec 2025-03-26).
-  # (WebMvcSseServerTransportProvider) — the closest available transport to the 2025-03-26
+  # McpWebMvcServerAutoConfiguration (SSE transport) is excluded below;
-  # "Streamable HTTP" spec; there is no separate "protocol: streamable" property in this
+  # WebMvcStreamableServerTransportProvider is wired manually in McpConfig.
-  # starter. JSON-RPC POSTs land on `sse-message-endpoint` (/mcp); server-initiated
+  # Clients connect with type: http at POST /mcp.
-  # notifications stream over `sse-endpoint` (/sse). See com.trueref.adapter.in.mcp.
+  autoconfigure:
+    exclude: org.springframework.ai.mcp.server.autoconfigure.McpWebMvcServerAutoConfiguration
   ai:
     mcp:
       server:
@@ -32,8 +33,6 @@ spring:
         name: trueref
         version: 0.1.0
         type: SYNC
-        sse-message-endpoint: /mcp
-        sse-endpoint: /sse
 
 server:
   port: 8080