Local MCP client sends server/discover but then initializes with an incompatible legacy protocol version

Short summary

No response

Affected version or release

1.1.15

Installation context

No response

What happened?

Summary

Copilot App cannot connect to a local MCP server that supports only the current MCP protocol (2026-07-28).

The client successfully sends server/discover, but then sends a legacy initialize request using protocol version 2025-11-25. A server correctly implementing the stateless 2026-07-28 protocol rejects that request because initialize is not part of that lifecycle.

Reproduction

1. Configure a local MCP server built with a current MCP SDK and supporting only 2026-07-28.
2. Add it in Copilot App as a Local/stdio MCP server.
3. Observe that Copilot sends server/discover.
4. Copilot then sends initialize with protocolVersion: "2025-11-25".

Actual result

Connection fails with:

JSON-RPC error: -32022: connection is serving the 2026-07-28 protocol; the initialize handshake is not accepted
({"supported":["2026-07-28"],"requested":"2025-11-25"})

### Steps to reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

Start by tracing the local/stdio MCP connection after the server/discover request and inspect how the client selects the protocol version and lifecycle. Reproduce with a server supporting only 2026-07-28; done means the client connects without sending the incompatible legacy initialize request while preserving supported older-protocol behavior.