Establishes a unidirectional event stream. The server sends events as lines
formatted per the SSE spec. Clients should set Accept: text/event-stream
and keep the connection open.

The server sends a task.completed event whenever a requested task run reaches
any terminal state (completed, failed, or canceled).
The status field of the payload indicates which state was reached.

The server automatically closes the stream in the following cases:

• All requested task runs have reached a terminal state.
• The stream has not sent any events for 30 minutes.

For tasks with a timeout higher than 30 minutes, waiting clients should fall back
to polling with the Retrieve task run
endpoint.