X_MCP_HOST_REFUSED
Means
an MCP request named a Host that is not this machine
Typical cause
x mcp serve answered a request whose Host is not localhost, a *.localhost name or a loopback address — the shape of a DNS-rebinding page, whose Host and Origin agree. Answered 421 before the bearer token is read
Fix
curl -X POST http://localhost:9229/mcp -H 'authorization: Bearer <token>'