MCP protocol version now recorded per request

0.11.3

Patch Changes

• #4465 9ffdb00 Thanks @gesh! - Record the protocol version for 2025-11-25 traffic served by a per-request server.

  That revision carries the negotiated version at the initialize handshake, so an MCP SDK v2 server built per HTTP request has no way to know it: the instance handling a later tools/call never saw the handshake, and a legacy-era request carries no _meta envelope for the identity chain to read. Those events went out with no $mcp_protocol_version.

  The chain gains the one carrier that era does have — the MCP-Protocol-Version request header, which 2025-11-25 requires a client to send on every request after initialize. It is read after the protocol-level envelope and params._meta and before the server's own accessors, so a modern-era request still prefers the value the protocol gives it, and no era is branched on. (2026-08-10)