MCP OAuth succeeds (token + initialize OK) but ChatGPT web still re-opens auth on tool call

We are debugging a reproducible re-auth loop on ChatGPT web with a custom MCP server.

Environment

• MCP server behind OAuth endpoints authorize/token/register

• * Transport: streamable HTTP (stateless)
  

• Observed behavior

• 1. Connector setup succeeds in ChatGPT (OAuth completes and connector appears active).
  

• 2. In chat, invoking a tool triggers Connect/auth again.
  

• 3. This repeats even though backend logs show successful auth + MCP handshake.
  

What server logs confirm

• register returns 201 (public client, token_endpoint_auth_method=none)

• * authorize issues code (302)
  

  •   * token returns 200 with refresh token
    

    •     * api/mcp receives and authorizes bearer token
      

      •       * initialize, notifications/initialized, tools/list, resources/list return 200
        

        •         * Mcp-Session-Id is returned and later