This issue proposes adding the following text as the second paragraph in 7.2

The first event returned by a server in response to a message/stream method MUST contain either a Message or Task. If a Message is returned, then the server MUST end the SSE stream immediately after. Alternatively, if a Task is returned, then subsequent events MAY include either TaskStatusUpdateEvent or TaskArtifactUpdateEvent. The server MUST end the SSE stream after sending a TaskStatusUpdateEvent with a terminal status.

@pstephengoogle Rather than try and address these issues in a single PR, I am planning to break them down into smaller issues/PRs.