Document ideal pattern for use of MCP with CommandLineRunner

[codefromthecrypt]

Expected Behavior

I would like to use CommandLineRunner with an MCP stdio server without thinking about it and without a hang.

Current Behavior

Currently, if I use an MCP stdio server it hangs after the CommandLineRunner completes

If I use the approach of SpringApplication.close(), it errs then hangs

OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended [otel.javaagent 2025-04-16 00:41:36:711 +0000] [main] INFO io.opentelemetry.javaagent.tooling.VersionLogger - opentelemetry-javaagent - version: 1.3.0 2025-04-16T00:42:05.032Z ERROR 1 --- [ main] [ ] o.s.boot.SpringApplication : Application run failed

reactor.core.Exceptions$ReactiveException: java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'source(MonoCreate)' (and no fallback has been configured)
at reactor.core.Exceptions.propagate(Exceptions.java:410) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:102) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.publisher.Mono.block(Mono.java:1779) ~[reactor-core-3.7.4.jar!/:3.7.4]
at io.modelcontextprotocol.client.McpSyncClient.callTool(McpSyncClient.java:200) ~[mcp-0.9.0.jar!/:0.9.0]
at org.springframework.ai.mcp.SyncMcpToolCallback.call(SyncMcpToolCallback.java:115) ~[spring-ai-mcp-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.mcp.SyncMcpToolCallback.call(SyncMcpToolCallback.java:125) ~[spring-ai-mcp-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.model.tool.DefaultToolCallingManager.executeToolCall(DefaultToolCallingManager.java:227) ~[spring-ai-model-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.model.tool.DefaultToolCallingManager.executeToolCalls(DefaultToolCallingManager.java:139) ~[spring-ai-model-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.azure.openai.AzureOpenAiChatModel.internalCall(AzureOpenAiChatModel.java:265) ~[spring-ai-azure-openai-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.azure.openai.AzureOpenAiChatModel.call(AzureOpenAiChatModel.java:240) ~[spring-ai-azure-openai-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultChatClientRequestSpec$1.aroundCall(DefaultChatClient.java:680) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.advisor.DefaultAroundAdvisorChain.lambda$nextAroundCall$1(DefaultAroundAdvisorChain.java:98) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at io.micrometer.observation.Observation.observe(Observation.java:564) ~[micrometer-observation-1.14.5.jar!/:1.14.5]
at org.springframework.ai.chat.client.advisor.DefaultAroundAdvisorChain.nextAroundCall(DefaultAroundAdvisorChain.java:98) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetChatResponse(DefaultChatClient.java:493) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.lambda$doGetObservableChatResponse$1(DefaultChatClient.java:482) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at io.micrometer.observation.Observation.observe(Observation.java:564) ~[micrometer-observation-1.14.5.jar!/:1.14.5]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetObservableChatResponse(DefaultChatClient.java:482) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetChatResponse(DefaultChatClient.java:466) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.content(DefaultChatClient.java:516) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
at example.VersionAgent.run(VersionAgent.java:34) ~[!/:0.0.1-SNAPSHOT]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:359) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:196) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:89) ~[spring-aop-6.2.5.jar!/:6.2.5]
at io.micrometer.tracing.annotation.SpanAspectMethodInvocation.proceed(SpanAspectMethodInvocation.java:47) ~[micrometer-tracing-1.4.4.jar!/:1.4.4]
at io.micrometer.tracing.annotation.ImperativeMethodInvocationProcessor.proceedUnderSynchronousSpan(ImperativeMethodInvocationProcessor.java:91) ~[micrometer-tracing-1.4.4.jar!/:1.4.4]
at io.micrometer.tracing.annotation.ImperativeMethodInvocationProcessor.process(ImperativeMethodInvocationProcessor.java:73) ~[micrometer-tracing-1.4.4.jar!/:1.4.4]
at io.micrometer.tracing.annotation.SpanAspect.newSpanMethod(SpanAspect.java:59) ~[micrometer-tracing-1.4.4.jar!/:1.4.4]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:642) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:632) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:71) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:173) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184) ~[spring-aop-6.2.5.jar!/:6.2.5]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:727) ~[spring-aop-6.2.5.jar!/:6.2.5]
at example.VersionAgent$$SpringCGLIB$$0.run() ~[!/:0.0.1-SNAPSHOT]
at org.springframework.boot.SpringApplication.lambda$callRunner$5(SpringApplication.java:788) ~[spring-boot-3.4.4.jar!/:3.4.4]
at org.springframework.util.function.ThrowingConsumer$1.acceptWithException(ThrowingConsumer.java:82) ~[spring-core-6.2.5.jar!/:6.2.5]
at org.springframework.util.function.ThrowingConsumer.accept(ThrowingConsumer.java:60) ~[spring-core-6.2.5.jar!/:6.2.5]
at org.springframework.util.function.ThrowingConsumer$1.accept(ThrowingConsumer.java:86) ~[spring-core-6.2.5.jar!/:6.2.5]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:796) ~[spring-boot-3.4.4.jar!/:3.4.4]
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:787) ~[spring-boot-3.4.4.jar!/:3.4.4]
at org.springframework.boot.SpringApplication.lambda$callRunners$3(SpringApplication.java:772) ~[spring-boot-3.4.4.jar!/:3.4.4]
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source) ~[na:na]
at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(Unknown Source) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source) ~[na:na]
at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source) ~[na:na]
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source) ~[na:na]
at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source) ~[na:na]
at java.base/java.util.stream.ReferencePipeline.forEach(Unknown Source) ~[na:na]
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:772) ~[spring-boot-3.4.4.jar!/:3.4.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:325) ~[spring-boot-3.4.4.jar!/:3.4.4]
at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:149) ~[spring-boot-3.4.4.jar!/:3.4.4]
at example.Main.run(Main.java:66) ~[!/:0.0.1-SNAPSHOT]
at example.McpClientAgent.main(Mcp.java:90) ~[!/:0.0.1-SNAPSHOT]
at example.Main.main(Main.java:44) ~[!/:0.0.1-SNAPSHOT]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
at org.springframework.boot.loader.launch.Launcher.launch(Launcher.java:102) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
at org.springframework.boot.loader.launch.Launcher.launch(Launcher.java:64) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
at org.springframework.boot.loader.launch.PropertiesLauncher.main(PropertiesLauncher.java:580) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
Suppressed: java.lang.Exception: #block terminated with an error
at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104) ~[reactor-core-3.7.4.jar!/:3.7.4]
... 65 common frames omitted
Caused by: java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'source(MonoCreate)' (and no fallback has been configured)
at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420) ~[reactor-core-3.7.4.jar!/:3.7.4]
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.TracingSubscriber.onNext(TracingSubscriber.java:68) ~[elastic-otel-javaagent.jar:na]
at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162) ~[reactor-core-3.7.4.jar!/:3.7.4]
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.TracingSubscriber.onNext(TracingSubscriber.java:68) ~[elastic-otel-javaagent.jar:na]
at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285) ~[reactor-core-3.7.4.jar!/:3.7.4]
at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.ContextPropagationOperator$RunnableWrapper.run(ContextPropagationOperator.java:373) ~[elastic-otel-javaagent.jar:na]
at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68) ~[reactor-core-3.7.4.jar!/:3.7.4]
at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28) ~[reactor-core-3.7.4.jar!/:3.7.4]
at java.base/java.util.concurrent.FutureTask.run(Unknown Source) ~[na:na]
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) ~[na:na]
at java.base/java.lang.Thread.run(Unknown Source) ~[na:na]

The only way that I can get the process to exit without hanging or erring is to use the same pattern as the examples show: Inject a ConfigurableApplicationContext to your CommandLineRunner and then close it before exiting its function.

Context

I want to showcase Spring AI in simplest form, and it is simple unless I use an MCP server, which introduces a curious workaround. Even if in spring boot there are concerns we can't address for all use cases, possibly Spring AI can have some decoration of a CommandLineRunner that integrates with and closes its MCP servers.

Even if ConfigurableApplicationContext.close() is the only viable way out, I appreciate your attention.

cc @tzolov @philwebb @ThomasVitale

[tzolov]

Hey @codefromthecrypt ,

Using SpringApplication.run(Application.class, args).close() seems to work fine (using 1.0.0-SNAPSHOT):

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args).close();
	}

	@Value("${ai.user.input}")
	private String userInput;

	@Bean
	public CommandLineRunner predefinedQuestions(ChatClient.Builder chatClientBuilder, ToolCallbackProvider tools) {

		return args -> {
				var chatClient = chatClientBuilder
						.defaultTools(tools)
						.build();

				System.out.println("\n>>> QUESTION: " + userInput);
				System.out.println("\n>>> ASSISTANT: " + chatClient.prompt(userInput).call().content());
		};
	}
}

runs and prints this:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

 :: Spring Boot ::                (v3.3.6)

2025-04-29T10:23:11.667+03:00  INFO 19810 --- [mcp] [           main] o.s.ai.mcp.samples.client.Application    : Starting Application using Java 17.0.12 with PID 19810 (/Users/christiantzolov/Dev/projects/spring-ai-examples/model-context-protocol/client-starter/starter-default-client/target/classes started by christiantzolov in /Users/christiantzolov/Dev/projects/spring-ai-examples)
2025-04-29T10:23:11.669+03:00  INFO 19810 --- [mcp] [           main] o.s.ai.mcp.samples.client.Application    : No active profile set, falling back to 1 default profile: "default"
2025-04-29T10:23:12.795+03:00  INFO 19810 --- [mcp] [           main] o.s.ai.mcp.samples.client.Application    : Started Application in 1.259 seconds (process running for 1.377)

>>> QUESTION: What tools are available?

>>> ASSISTANT: I can help you explore the tools available in this environment. There are two search tools at your disposal:

1. **Brave Web Search** - This is a general web search tool that can help you find information about almost any topic online. It's ideal for:
   - General queries
   - News and articles
   - Online content
   - Recent events
   - Broad information gathering

2. **Brave Local Search** - This tool is specialized for finding information about physical locations and businesses. It's best for:
   - Finding nearby businesses
   - Restaurants and services
   - Places with physical addresses
   - Getting business details like phone numbers, ratings, and opening hours

Would you like me to demonstrate how either of these tools works with a specific query? Or do you have a particular question you'd like to search for?

Are you seeing something different?

[codefromthecrypt]

I'm not sure if this is apple/apples or not. Maybe invoking the tool may help? First, I need to define my runner as a component as otherwise I can't identify it in a trace (I'm not using bean for this reason).

So, maybe 1/5 times I get the least amount of error (using runner.close() instead of the explicit context close()
Next, only once was I able to get this to stop without a stack trace, and then I got this log:

2025-04-30T02:32:18.410Z  WARN 1 --- [onPool-worker-1] [                                                 ] i.m.c.transport.StdioClientTransport     : Process terminated with code 143

The other times I get a harder to interpret stack trace like this:

2025-04-30T02:32:51.196Z ERROR 1 --- [           main] [                                                 ] o.s.boot.SpringApplication               : Application run failed

reactor.core.Exceptions$ReactiveException: java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'source(MonoCreate)' (and no fallback has been configured)
        at reactor.core.Exceptions.propagate(Exceptions.java:410) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:102) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.publisher.Mono.block(Mono.java:1779) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at io.modelcontextprotocol.client.McpSyncClient.callTool(McpSyncClient.java:200) ~[mcp-0.9.0.jar!/:0.9.0]
        at org.springframework.ai.mcp.SyncMcpToolCallback.call(SyncMcpToolCallback.java:115) ~[spring-ai-mcp-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.mcp.SyncMcpToolCallback.call(SyncMcpToolCallback.java:125) ~[spring-ai-mcp-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.model.tool.DefaultToolCallingManager.executeToolCall(DefaultToolCallingManager.java:227) ~[spring-ai-model-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.model.tool.DefaultToolCallingManager.executeToolCalls(DefaultToolCallingManager.java:139) ~[spring-ai-model-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.openai.OpenAiChatModel.internalCall(OpenAiChatModel.java:242) ~[spring-ai-openai-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.openai.OpenAiChatModel.call(OpenAiChatModel.java:180) ~[spring-ai-openai-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultChatClientRequestSpec$1.aroundCall(DefaultChatClient.java:680) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.advisor.DefaultAroundAdvisorChain.lambda$nextAroundCall$1(DefaultAroundAdvisorChain.java:98) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at io.micrometer.observation.Observation.observe(Observation.java:564) ~[micrometer-observation-1.14.6.jar!/:1.14.6]
        at org.springframework.ai.chat.client.advisor.DefaultAroundAdvisorChain.nextAroundCall(DefaultAroundAdvisorChain.java:98) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetChatResponse(DefaultChatClient.java:493) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.lambda$doGetObservableChatResponse$1(DefaultChatClient.java:482) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at io.micrometer.observation.Observation.observe(Observation.java:564) ~[micrometer-observation-1.14.6.jar!/:1.14.6]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetObservableChatResponse(DefaultChatClient.java:482) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.doGetChatResponse(DefaultChatClient.java:466) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at org.springframework.ai.chat.client.DefaultChatClient$DefaultCallResponseSpec.content(DefaultChatClient.java:516) ~[spring-ai-client-chat-1.0.0-M7.jar!/:1.0.0-M7]
        at example.VersionAgent.run(VersionAgent.java:34) ~[!/:0.0.1-SNAPSHOT]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:359) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:196) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:89) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at io.micrometer.tracing.annotation.SpanAspectMethodInvocation.proceed(SpanAspectMethodInvocation.java:47) ~[micrometer-tracing-1.4.5.jar!/:1.4.5]
        at io.micrometer.tracing.annotation.ImperativeMethodInvocationProcessor.proceedUnderSynchronousSpan(ImperativeMethodInvocationProcessor.java:91) ~[micrometer-tracing-1.4.5.jar!/:1.4.5]
        at io.micrometer.tracing.annotation.ImperativeMethodInvocationProcessor.process(ImperativeMethodInvocationProcessor.java:73) ~[micrometer-tracing-1.4.5.jar!/:1.4.5]
        at io.micrometer.tracing.annotation.SpanAspect.newSpanMethod(SpanAspect.java:59) ~[micrometer-tracing-1.4.5.jar!/:1.4.5]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
        at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:642) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:632) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:71) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:173) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:728) ~[spring-aop-6.2.6.jar!/:6.2.6]
        at example.VersionAgent$$SpringCGLIB$$0.run(<generated>) ~[!/:0.0.1-SNAPSHOT]
        at org.springframework.boot.SpringApplication.lambda$callRunner$5(SpringApplication.java:789) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at org.springframework.util.function.ThrowingConsumer$1.acceptWithException(ThrowingConsumer.java:82) ~[spring-core-6.2.6.jar!/:6.2.6]
        at org.springframework.util.function.ThrowingConsumer.accept(ThrowingConsumer.java:60) ~[spring-core-6.2.6.jar!/:6.2.6]
        at org.springframework.util.function.ThrowingConsumer$1.accept(ThrowingConsumer.java:86) ~[spring-core-6.2.6.jar!/:6.2.6]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:797) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:788) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at org.springframework.boot.SpringApplication.lambda$callRunners$3(SpringApplication.java:773) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source) ~[na:na]
        at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(Unknown Source) ~[na:na]
        at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source) ~[na:na]
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source) ~[na:na]
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source) ~[na:na]
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source) ~[na:na]
        at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source) ~[na:na]
        at java.base/java.util.stream.ReferencePipeline.forEach(Unknown Source) ~[na:na]
        at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:773) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:325) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:149) ~[spring-boot-3.4.5.jar!/:3.4.5]
        at example.Main.run(Main.java:66) ~[!/:0.0.1-SNAPSHOT]
        at example.McpClientAgent.main(Mcp.java:90) ~[!/:0.0.1-SNAPSHOT]
        at example.Main.main(Main.java:44) ~[!/:0.0.1-SNAPSHOT]
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source) ~[na:na]
        at java.base/java.lang.reflect.Method.invoke(Unknown Source) ~[na:na]
        at org.springframework.boot.loader.launch.Launcher.launch(Launcher.java:102) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
        at org.springframework.boot.loader.launch.Launcher.launch(Launcher.java:64) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
        at org.springframework.boot.loader.launch.PropertiesLauncher.main(PropertiesLauncher.java:580) ~[genai-function-calling.jar:0.0.1-SNAPSHOT]
        Suppressed: java.lang.Exception: #block terminated with an error
                at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104) ~[reactor-core-3.7.5.jar!/:3.7.5]
                ... 65 common frames omitted
Caused by: java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'source(MonoCreate)' (and no fallback has been configured)
        at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.TracingSubscriber.onNext(TracingSubscriber.java:68) ~[elastic-otel-javaagent.jar:na]
        at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.TracingSubscriber.onNext(TracingSubscriber.java:68) ~[elastic-otel-javaagent.jar:na]
        at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at io.opentelemetry.javaagent.shaded.instrumentation.reactor.v3_1.ContextPropagationOperator$RunnableWrapper.run(ContextPropagationOperator.java:373) ~[elastic-otel-javaagent.jar:na]
        at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28) ~[reactor-core-3.7.5.jar!/:3.7.5]
        at java.base/java.util.concurrent.FutureTask.run(Unknown Source) ~[na:na]
        at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) ~[na:na]
        at java.base/java.lang.Thread.run(Unknown Source) ~[na:na]

My guess is that the reason someone added the context close here was indeterministic lifecycle handling? https://github.com/spring-projects/spring-ai-examples/blob/main/model-context-protocol/client-starter/starter-default-client/src/main/java/org/springframework/ai/mcp/samples/client/Application.java#L50

The example code is here and also isolated in docker. so it is very repeatable. not using snapshot but using latest milestone https://github.com/elastic/observability-examples/tree/main/genai-function-calling/spring-ai