[Regression] Stateless Mode renders ClientInfo null, breaking multi-instance cloud deployments

[TianqiZhang]

Describe the bug
In the latest SDK (v0.4.0-preview.2+), the McpServer.ClientInfo property is always null when the server is configured in Stateless mode. This is a regression from previous behavior where session context was encoded into the mcp-session-id.

While the release notes mention this as a change, it functionally breaks the ability to host MCP servers on load-balanced platforms (like Azure App Service or AWS Lambda) where:

1. In-memory state is impossible (due to round-robin routing).
2. ClientInfo is required for logging.

To Reproduce
As stated in release notes.

Expected behavior
The SDK should preserve a mechanism to retain ClientInfo across requests in Stateless mode.

Logging ClientInfo is critical for many MCP servers. Since standard "Sticky Sessions" are not reliable on many serverless/PaaS platforms, the previous implementation (encoding session state into the Session ID) was the only viable "Cloud Native" solution.

We request that the SDK restores this "round-tripped Session" strategy (or adds a specific flag for it) to preserve basic logging functionality without forcing developers to implement complex workarounds just to read the Client Name/Version.

[mikekistler]

I think the reason ClientInfo is not retained across requests to a stateless server is that "stateless" means that each request is independent of all other requests to the server. ClientInfo is sent in the Initialize request, but once that request is completed that info is irrelevant to subsequent requests.

If you want ClientInfo to be retained and available to subsequent requests, this is not a stateless server, so configure it as such and you will get the behaviour you are asking for.