Implement SEP-1319: Decouple Request Payload from RPC Methods

[felixweinberger]

This is a tracking issue for implementation of SEP-1319.

Summary

This SEP proposes a structural refactoring to separate data payload definitions from RPC method definitions in the MCP specification. The TypeScript SDK needs to restructure its internal type definitions to define payload structures as independent, top-level schemas that RPC method definitions reference, decoupling the data model from the transport mechanism. This refactoring improves code clarity, maintainability, and enables future support for alternative transports like gRPC while maintaining backward compatibility.

Related Issues & PRs

• Implementation PRs: n/a
• Related PRs: n/a
• Related Issues: n/a

[KKonstantinov]

Could take this one on if not assigned to anyone else.

[KKonstantinov]

Opened a draft: #1086