Establish the legacy HTTP+SSE (2024-11-05) two-endpoint transport:
open the GET SSE stream at the server URL, read the first endpoint
event to learn the message-POST URI, then keep the stream open in a
background task to receive JSON-RPC responses and server notifications.
Throws if the endpoint event is not received. Called by
McpClient.connect once a modern POST has been rejected with 400/404/405.
Establish the legacy HTTP+SSE (2024-11-05) two-endpoint transport: open the GET SSE stream at the server URL, read the first endpoint event to learn the message-POST URI, then keep the stream open in a background task to receive JSON-RPC responses and server notifications. Throws if the endpoint event is not received. Called by McpClient.connect once a modern POST has been rejected with 400/404/405.