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

從提供的 HttpClientStreamableHttpTransport builder 範例開始，並使用 mcpSyncClient.initialize() 重現失敗。閱讀 LifecycleInitializer.java 第 288 行附近的內容以及導致 20 秒逾時的初始化路徑，然後將 streamable HTTP 的行為與回報中可正常運作的 SSE 情況進行比較。完成的標準是 Java SDK 能夠針對提供的 streamable HTTP endpoint 成功初始化，並且有一個涵蓋此行為的回歸測試。

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();
    }