MCP protocol version now captured on every event

0.10.0

Minor Changes

• #4210 e732595 Thanks @gesh! - feat(mcp): capture the negotiated MCP protocol version as $mcp_protocol_version

  The SDK now stamps $mcp_protocol_version — the MCP spec version negotiated at initialize (read off the server's initialize response) — on the $mcp_initialize event and on every subsequent event for the session (tool calls, listings, and the $exception sibling). It's persisted in per-server session info and, on stateless / multi-pod deployments, recovered on other pods from the session token, which now carries the client's requested version in a new pv field. Use it to track MCP spec-revision adoption and to break event metrics (error rate, latency) down by spec version.

  SessionTokenPayload gains an optional protocolVersion, and PostHogMCP.captureInitialize accepts an optional protocolVersion. (2026-07-21) (2026-07-22)