Codex Streamable HTTP MCP startup failed after initialize because Netdata returned 200 with an SSE complete event for notifications/initialized. Per MCP Streamable HTTP transport semantics, notification-only POSTs should return 202 Accepted with no body.

• Handshake semantics fix (SSE adapter)

  • Updated src/web/mcp/adapters/mcp-sse.c (mcp_sse_serialize_response) to detect requests that produce no JSON-RPC responses (responses_used == 0) and return:
    • HTTP 202 Accepted
    • empty body
    • no SSE complete envelope

• Behavior preserved for response-bearing requests

  • Requests that produce one or more JSON-RPC responses keep existing SSE behavior:
    • HTTP 200 OK
    • text/event-stream
    • message event(s) + trailing complete event

if (!responses_used) {
    buffer_flush(w->response.data);
    mcp_http_disable_compression(w);
    buffer_flush(w->response.header);
    w->response.code = HTTP_RESP_ACCEPTED;
    freez(responses);
    return w->response.code;
}