MCP server to be able to return custom http codes

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I am writing a custom MCP server. I am using an existing HttpServletStatelessServerTransport but mine is a stateful server with multiple pods. But since I do not have control on the session Id generation & validation & moreover, the validation in stateful transport is based on memory, I have chosen a stateless transport. But now on validating the sessionId in every MCP request, I want to be able to return an 404, if session id is not found or return 500 or other status codes. But I do not have this control now.

I was looking if there is a way in HttpServletStatelessServerTransport by which the MCP Error message can be passed by the McpStatelessServerHandler in the exception thrown by it

Current Behavior
In the below code, we can see that even if handleRequest method of McpStatelessServerHandler throws IllegalArgumentException, a customized error message cannot be returned to the client.

			logger.error("Failed to deserialize message: {}", e.getMessage());
			this.responseError(response, HttpServletResponse.SC_BAD_REQUEST, new McpError("Invalid message format"));
		}
		catch (Exception e) {
			logger.error("Unexpected error handling message: {}", e.getMessage());
			this.responseError(response, HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
					new McpError("Unexpected error: " + e.getMessage()));
		}```

**Context**

The only work around is to find the MCP request method before calling the transport's service method and return appropriate http code with required message. This is not ideal though

從 HttpServletStatelessServerTransport 和 McpStatelessServerHandler 開始，重點關注 handleRequest 和 transport 的 service 方法。追蹤例外如何到達 responseError，以及目前的 workaround 如何在呼叫 transport 前檢查 MCP 請求方法。完成的標準是 handler 失敗時可以回傳由呼叫方選擇的 HTTP 狀態和 MCP 錯誤訊息，包括工作階段驗證失敗。