Implement SEP-1577 - Sampling With Tools)

[ochafik]

Implement types from modelcontextprotocol/modelcontextprotocol#1577 (accepted)

Spec PR: modelcontextprotocol/modelcontextprotocol#1796 (under review)

cc/ @bhosmer-ant

Follow up PRs may include more code from #991:

• Examples
• ToolRegistry, runToolLoop helpers

Motivation and Context

Allows using tools in sampling.

How Has This Been Tested?

#991 has examples + backfill support

Breaking Changes

Yes: any code that uses the result of sampling will now need to check whether CreateMessageResult.content is an array or not (if the server is on a previous spec version, the content returned cannot be an array, but the static types now allow both)

const response = await options.server.server.createMessage({ messages, maxTokens: 4000 });

// BEFORE:
// const contentText = response.content.type === 'text' ? response.content.text : '';

// AFTER:
const contentArray = Array.isArray(response.content) ? response.content : [response.content];
const contentText = contentArray.filter(c => c.type === 'text').map(c => c.text).join('\n');

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