Changes the error status code from 400 to 404 in the documentation's TypeScript example.

Motivation and Context

The error status code returned by the server should be 404, not 400, so that the client starts a new session.

When a client receives HTTP 404 in response to a request containing an MCP-Session-Id, it MUST start a new session by sending a new InitializeRequest without a session ID attached.

https://modelcontextprotocol.io/specification/draft/basic/transports#session-management

How Has This Been Tested?

Tested with Claude. Claude returns an error when receiving a 400 status code error after sending an invalid MCP-Session-Id, but with the 404 status code, it initializes a new session, as it should.

Breaking Changes

No breaking changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context