The supervisor's MCP HTTP handler was answering every parsed request,
including notifications (messages with no id field). Per JSON-RPC 2.0,
notifications must not receive a response. The Apr-29 incident saw
Claude Code's MCP client receive a -32601 error for the standard
notifications/initialized handshake step and disconnect immediately
after a successful initialize.
Skip writing the response when req.ID == nil. Cover both the
known-method (notifications/initialized) and unknown-method paths
with tests.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
