feat: Enhance MCP roots implementation and test coverage

- Add proper ListRootsResult wrapping in async client
- Implement paginated listRoots methods in server components
- Fix roots notification handling in async server
- Add roots integration tests
- Update architecture diagram and documentation layout

The changes improve the roots feature implementation with proper result
types,  and robust notification handling. Adds thorough
test coverage for roots functionality including async notifications and
root addition/removal scenarios.

Resolves #46

mcp/src/test/java/org/springframework/ai/mcp/MockMcpTransport.java

@@ -30,9 +30,10 @@ import org.springframework.ai.mcp.spec.ClientMcpTransport;
 import org.springframework.ai.mcp.spec.McpSchema;
 import org.springframework.ai.mcp.spec.McpSchema.JSONRPCNotification;
 import org.springframework.ai.mcp.spec.McpSchema.JSONRPCRequest;
+import org.springframework.ai.mcp.spec.ServerMcpTransport;
 
 @SuppressWarnings("unused")
-public class MockMcpTransport implements ClientMcpTransport {
+public class MockMcpTransport implements ClientMcpTransport, ServerMcpTransport {
 
 	private final AtomicInteger inboundMessageCount = new AtomicInteger(0);
 

mcp/src/test/java/org/springframework/ai/mcp/client/McpAsyncClientResponseHandlerTests.java

@@ -100,7 +100,8 @@ class McpAsyncClientResponseHandlerTests {
 
 		McpSchema.JSONRPCResponse response = (McpSchema.JSONRPCResponse) sentMessage;
 		assertThat(response.id()).isEqualTo("test-id");
-		assertThat(response.result()).isEqualTo(List.of(new Root("file:///test/path", "test-root")));
+		assertThat(response.result())
+			.isEqualTo(new McpSchema.ListRootsResult(List.of(new Root("file:///test/path", "test-root"))));
 		assertThat(response.error()).isNull();
 
 		asyncMcpClient.closeGracefully();

mcp/src/test/java/org/springframework/ai/mcp/server/SseAsyncIntegrationTests.java

@@ -15,8 +15,10 @@
 */
 package org.springframework.ai.mcp.server;
 
+import java.time.Duration;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -37,12 +39,14 @@ import org.springframework.ai.mcp.spec.McpSchema.CreateMessageRequest;
 import org.springframework.ai.mcp.spec.McpSchema.CreateMessageResult;
 import org.springframework.ai.mcp.spec.McpSchema.InitializeResult;
 import org.springframework.ai.mcp.spec.McpSchema.Role;
+import org.springframework.ai.mcp.spec.McpSchema.Root;
 import org.springframework.http.server.reactive.HttpHandler;
 import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
 import org.springframework.web.reactive.function.client.WebClient;
 import org.springframework.web.reactive.function.server.RouterFunctions;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.awaitility.Awaitility.await;
 
 public class SseAsyncIntegrationTests {
 
@@ -156,4 +160,60 @@ public class SseAsyncIntegrationTests {
 		}).verifyComplete();
 	}
 
+	// ---------------------------------------
+	// Roots Tests
+	// ---------------------------------------
+	@Test
+	void testRootsSuccess() {
+
+		List<Root> roots = List.of(new Root("uri1://", "root1"), new Root("uri2://", "root2"));
+
+		AtomicReference<List<Root>> rootsRef = new AtomicReference<>();
+		var mcpServer = McpServer.using(mcpServerTransport)
+			.rootsChangeConsumer(rootsUpdate -> rootsRef.set(rootsUpdate))
+			.sync();
+
+		// HttpHandler httpHandler =
+		// RouterFunctions.toHttpHandler(mcpServerTransport.getRouterFunction());
+		// ReactorHttpHandlerAdapter adapter = new ReactorHttpHandlerAdapter(httpHandler);
+		// HttpServer httpServer = HttpServer.create().port(8080).handle(adapter);
+		// DisposableServer d = httpServer.bindNow();
+
+		var mcpClient = clientBuilder.capabilities(ClientCapabilities.builder().roots(true).build())
+			.roots(roots)
+			.sync();
+
+		InitializeResult initResult = mcpClient.initialize();
+		assertThat(initResult).isNotNull();
+
+		assertThat(rootsRef.get()).isNull();
+
+		assertThat(mcpServer.listRoots().roots()).containsAll(roots);
+
+		mcpClient.rootsListChangedNotification();
+
+		await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
+			assertThat(rootsRef.get()).containsAll(roots);
+		});
+
+		// Remove a root
+		mcpClient.removeRoot(roots.get(0).uri());
+
+		await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
+			assertThat(rootsRef.get()).containsAll(List.of(roots.get(1)));
+		});
+
+		// Add a new root
+		var root3 = new Root("uri3://", "root3");
+		mcpClient.addRoot(root3);
+
+		await().atMost(Duration.ofSeconds(5)).untilAsserted(() -> {
+			assertThat(rootsRef.get()).containsAll(List.of(roots.get(1), root3));
+		});
+
+		mcpClient.close();
+
+		mcpServer.close();
+	}
+
 }