fix sampling and elicitation calls for streamable http

[evalstate]

Send Sampling and Elicitation requests via the associated POST channel for the Tool Call.

Description

Server Details

• Server: Everything
• Changes to: Sampling and Elicitation Tools

Motivation and Context

Sampling and Elicitation Requests were being issued through the GET channel rather than associated with corresponding Tool Call. Causes hanging behaviour in clients.

How Has This Been Tested?

Tested STDIO and StreamableHTTP behavior. Suspect this hasn't been spotted in e.g. Inspector as the sampling request happens - just dissociated.

That yellow spot shows the new behavior - request received on the POST SSE stream.

Breaking Changes

No - this fixing things!

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 Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

[ochafik]

Thanks @evalstate !