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();
    }

Bắt đầu với ví dụ builder HttpClientStreamableHttpTransport được cung cấp và tái hiện lỗi bằng mcpSyncClient.initialize(). Đọc LifecycleInitializer.java quanh dòng 288 và đường dẫn khởi tạo dẫn đến timeout 20 giây, sau đó so sánh hành vi của streamable HTTP với trường hợp SSE được báo cáo là hoạt động. Công việc được hoàn tất khi Java SDK khởi tạo thành công cho streamable HTTP endpoint được cung cấp và có một regression test cho hành vi này.