JAVA SDK connectto streamablehttptransport raise "Client failed to initialize by explicit API call"

JAVA SDK connectto streamablehttptransport raise "Client failed to initialize by explicit API call".
sse is fine.
I searched on issuses, Some similar issues were found, but they were all marked as resolved.

Bug description
JAVA SDK connectto streamablehttptransport raise "Client failed to initialize by explicit API call"

Environment
Please provide as many details as possible: Spring MCP version, Java version, which vector store you use if any, etc
java 17 , main brunch 2026-03-25； v1.1.0

Steps to reproduce

    public static void testmcphttp() {
        String mcpUrl = "http://192.168.190.51:31603/api/mcp/mcpserver/mcp";
        String tk = "gtk849416ca3e3b44a28b9956046895fafe";
        mcpUrl = "http://127.0.0.1:8702/api/mcp/mcpserver/mcp";
        tk = "gtkba06f61af36f4cf597624c73cc23abbc";
        HttpClientStreamableHttpTransport transport = HttpClientStreamableHttpTransport
                .builder("http://127.0.0.1:8702")
                .endpoint("/api/mcp/mcpserver/mcp?tk=" + tk)
                .build();
        McpSyncClient mcpSyncClient = McpClient
                .sync(transport)
                .clientInfo(new McpSchema.Implementation("Sample client", "0.0.0"))
                .build();

        mcpSyncClient.initialize();
    }

Expected behavior

Exception in thread "main" java.lang.RuntimeException: Client failed to initialize by explicit API call
	at io.modelcontextprotocol.client.LifecycleInitializer.lambda$withInitialization$2(LifecycleInitializer.java:288)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:94)
	at reactor.core.publisher.SerializedSubscriber.onError(SerializedSubscriber.java:124)
	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296)
	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281)
	at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420)
	at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162)
	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270)
	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28)
	at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
		at reactor.core.publisher.Mono.block(Mono.java:1779)
		at io.modelcontextprotocol.client.McpSyncClient.initialize(McpSyncClient.java:189)
		at io.modelcontextprotocol.TLCMCP.testmcphttp(TLCMCP.java:33)
		at io.modelcontextprotocol.TLCMCP.main(TLCMCP.java:57)
Caused by: java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'map' (and no fallback has been configured)
	... 14 more

Minimal Complete Reproducible example

    public static void testmcphttp() {
        String mcpUrl = "http://192.168.190.51:31603/api/mcp/mcpserver/mcp";
        String tk = "gtk849416ca3e3b44a28b9956046895fafe";
        mcpUrl = "http://127.0.0.1:8702/api/mcp/mcpserver/mcp";
        tk = "gtkba06f61af36f4cf597624c73cc23abbc";
        HttpClientStreamableHttpTransport transport = HttpClientStreamableHttpTransport
                .builder("http://127.0.0.1:8702")
                .endpoint("/api/mcp/mcpserver/mcp?tk=" + tk)
                .build();
        McpSyncClient mcpSyncClient = McpClient
                .sync(transport)
                .clientInfo(new McpSchema.Implementation("Sample client", "0.0.0"))
                .build();

        mcpSyncClient.initialize();
    }

从提供的 HttpClientStreamableHttpTransport builder 示例开始，并使用 mcpSyncClient.initialize() 重现失败。阅读 LifecycleInitializer.java 第 288 行附近的内容以及导致 20 秒超时的初始化路径，然后将 streamable HTTP 的行为与报告中可正常工作的 SSE 情况进行比较。完成的标准是 Java SDK 能够针对提供的 streamable HTTP endpoint 成功初始化，并且有一个覆盖该行为的回归测试。