The SSE endpoint event advertised the absolute path /mcp/messages, which drops the /server prefix when clients connect through the bundled nginx proxy on port 20211. Clients then POST to /mcp/messages, nginx serves it as a static file and returns 404, so MCP clients can't connect via the proxy. A relative path resolves against whichever SSE URL the client used, so it works both directly and behind the prefix.
Jonas Friedmann
68aaeaf527