feat(everything): add trigger-agentic-sampling tool

[olaservo]

Description

Adds support for SEP-1577 (Sampling With Tools) to the Everything server by introducing a new trigger-agentic-sampling tool that demonstrates the agentic sampling loop pattern.

This tool:

• Sends a prompt to the client's LLM with tools available
• Handles tool_use responses and executes tools locally
• Loops until a final text response is received or max iterations reached
• Only registers if the client supports sampling.tools capability

Server Details

• Server: everything
• Changes to: tools

Motivation and Context

Issue: #3040

SEP-1577 adds tool calling support to the MCP sampling API, enabling servers to provide tools that the LLM can use during sampling requests. This creates an "agentic loop" where:

1. Server sends sampling/createMessage with a tools array
2. If the LLM returns stopReason: "toolUse", the server executes the tools
3. Server sends tool results back and continues until final response

The Everything server is a reference implementation that demonstrates all MCP features, so it should include this capability.

How Has This Been Tested?

• Build passes successfully
• Tool registration is conditional on sampling.tools capability check
• Follows the same pattern as existing conditional tools (trigger-sampling-request, trigger-elicitation-request)
• Tested with custom client using local build of Typescript SDK (see also: Client-side sampling validation doesn't use CreateMessageResultWithToolsSchema when tools are present typescript-sdk#1346 )

(We can wait to merge until I've had a chance to add a screengrab if that's preferred.)

Breaking Changes

No

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

References

• SEP-1577 Proposal
• Specification changes
• TypeScript SDK changes
• Inspector support

Implementation Notes

The tool includes simple local implementations of echo and add tools for demonstration purposes. In a production scenario, tools could likely be reused via:

• Internal server.server.callTool() calls
• Connecting to other MCP servers as a client
• Shared business logic functions

I thought about trying to re-use existing tools already defined in the everything server, but then decided to keep it self-contained instead.