Return void from McpStatelessSyncServer#closeGracefully instead of Mono (#1019)

Co-authored-by: Dariusz Jędrzejczyk <2554306+chemicL@users.noreply.github.com>
Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

MIGRATION-2.0.md

@@ -9,6 +9,7 @@ The changes fall into these areas:
 - [JSON serialization behaviour](#json-serialization-behaviour) — wire-format changes.
 - [Server-side validation](#server-side-validation) — runtime validation of tool arguments and embedded schemas.
 - [Transport changes](#transport-changes) — removed methods and the SSE deprecation.
+- [Server API changes](#server-api-changes) — sync server method signature corrections.
 - [New features](#new-features) — additive, backward-compatible capabilities.
 
 ---
@@ -220,6 +221,18 @@ The HTTP+SSE client and server transports (and their supporting validator/except
 
 ---
 
+## Server API changes
+
+### `McpStatelessSyncServer#closeGracefully` returns `void`
+
+In 1.x, `McpStatelessSyncServer.closeGracefully()` accidentally leaked the reactive signature from the underlying async server and returned `Mono<Void>`. The sync API is intentionally blocking, so returning a `Mono` was an oversight — callers had to call `.block()` themselves to get any actual shutdown behaviour.
+
+In 2.0 the return type is corrected to `void`; the blocking call is performed internally.
+
+**Action:** Remove any `.block()` (or `.subscribe()`) call you had appended to `closeGracefully()`. The method now blocks until the server has shut down and returns normally.
+
+---
+
 ## New features
 
 These are additive and backward-compatible.

mcp-core/src/main/java/io/modelcontextprotocol/server/McpStatelessSyncServer.java

@@ -50,10 +50,10 @@ public class McpStatelessSyncServer {
 
 	/**
 	 * Gracefully closes the server, allowing any in-progress operations to complete.
-	 * @return A Mono that completes when the server has been closed
+	 *
 	 */
-	public Mono<Void> closeGracefully() {
-		return this.asyncServer.closeGracefully();
+	public void closeGracefully() {
+		this.asyncServer.closeGracefully().block();
 	}
 
 	/**

mcp-test/src/main/java/io/modelcontextprotocol/AbstractStatelessIntegrationTests.java

@@ -4,8 +4,6 @@
 
 package io.modelcontextprotocol;
 
-import static io.modelcontextprotocol.util.ToolsUtils.EMPTY_JSON_SCHEMA;
-
 import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
@@ -31,9 +29,9 @@ import io.modelcontextprotocol.spec.McpSchema.Tool;
 import net.javacrumbs.jsonunit.core.Option;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
-import org.junit.jupiter.params.provider.ValueSource;
 import reactor.core.publisher.Mono;
 
+import static io.modelcontextprotocol.util.ToolsUtils.EMPTY_JSON_SCHEMA;
 import static net.javacrumbs.jsonunit.assertj.JsonAssertions.assertThatJson;
 import static net.javacrumbs.jsonunit.assertj.JsonAssertions.json;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -128,7 +126,7 @@ public abstract class AbstractStatelessIntegrationTests {
 			assertThat(response).isNotNull().isEqualTo(callResponse);
 		}
 		finally {
-			mcpServer.closeGracefully().block();
+			mcpServer.closeGracefully();
 		}
 	}