Update AsyncRw standard method registry for MCP 2026-07-28

[DaleSeo]

Summary

is_standard_method and is_standard_notification in crates/rmcp/src/transport/async_rw.rs are still documented as being based on MCP 2025-06-18 and do not include all methods in the stable 2026-07-28 protocol.

The missing current methods are:

• elicitation/create
• server/discover
• subscriptions/listen
• notifications/subscriptions/acknowledged

Legacy method names should remain recognized for backward compatibility.

Impact

The compatibility parser consults this registry after deserialization fails. A malformed current standard notification such as notifications/subscriptions/acknowledged is therefore classified as non-MCP and silently ignored instead of surfacing the parse failure. The request omissions do not currently trigger that drop path because requests carry an ID, but the registry and its documentation are still incomplete.

Expected changes

• Update the registry and its specification reference for MCP 2026-07-28.
• Preserve legacy methods supported by the SDK.
• Add focused tests showing that current standard notifications are not treated as ignorable unknown notifications.
• Keep genuinely unknown notifications ignored for compatibility.

Stable schema: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2026-07-28/schema.ts