feat: add integration tests and post-processor for handling Flux return types in MCP tools

Signed-off-by: liugddx <[email protected]>

Author: liugddx

auto-configurations/mcp/spring-ai-autoconfigure-mcp-server-common/src/main/java/org/springframework/ai/mcp/server/common/autoconfigure/annotations/StatelessServerSpecificationFactoryAutoConfiguration.java

@@ -127,8 +127,12 @@ public List<McpStatelessServerFeatures.AsyncCompletionSpecification> completionS
 		@Bean
 		public List<McpStatelessServerFeatures.AsyncToolSpecification> toolSpecs(
 				ServerMcpAnnotatedBeans beansWithMcpMethodAnnotations) {
-			return AsyncMcpAnnotationProviders
-				.statelessToolSpecifications(beansWithMcpMethodAnnotations.getBeansByAnnotation(McpTool.class));
+			List<Object> toolBeans = beansWithMcpMethodAnnotations.getBeansByAnnotation(McpTool.class);
+			List<McpStatelessServerFeatures.AsyncToolSpecification> originalSpecs = AsyncMcpAnnotationProviders
+				.statelessToolSpecifications(toolBeans);
+
+			// Apply post-processing to handle Flux return types (Issue #4542)
+			return FluxToolSpecificationPostProcessor.processToolSpecifications(originalSpecs, toolBeans);
 		}
 
 	}