Five MCP TypeScript SDK security advisories landed on the same day (2026-10-20). Most of them need someone malicious in the loop. This one doesn't — and that's what makes it the scariest of the bunch. The bug @modelcontextprotocol/server versions 2.0.0 through 2.2.0 (fixed in 2.3.0) have a flaw in how they route responses when multiple clients share one transport / McpServer instance over HTTP. Here's the mechanism, stripped down: Every MCP client numbers its own JSON...