MCP draft spec: MRTR breaking change — server-initiated requests pattern deprecated

[claude-yolo]

WHY this matters

The MCP draft spec landed a breaking change: servers MUST now use the MRTR (Multi Round-Trip Request) pattern for server-to-client requests. The old server-initiated request pattern is no longer supported.

Servers MUST send server-to-client requests (such as `roots/list`, `sampling/createMessage`, or `elicitation/create`) using the MRTR pattern. The previous pattern of server-initiated requests is no longer supported. This is a breaking change.

What else changed

• MCP is now explicitly stateless — servers MUST NOT rely on prior requests over the same connection to establish context. Every request must be self-contained via _meta.
• versioning.md replaces "Lifecycle" — protocol version is now declared per-request, no handshake
• New pattern pages: MRTR, subscriptions, cancellation, progress
• Removed: "LLM Sampling Controls" from security requirements, "Logging" from client features

Impact

Any MCP server implementation that currently uses server-initiated requests directly needs to migrate to the MRTR pattern.

Source

PR #1009 — docs/mcp-spec-stateless-patterns-20260603-1942

Assign: @lroolle