post
https://flow.seekr.com/v1/threads//runs/stream
Calls the agent's /runs/stream endpoint, returning an SSE stream.
We 'peek' at the generator to ensure there's no immediate HTTP error before sending a 200 status code to the client. We do this because response headers, and status code are sent in the beginning (before processing the stream). We can't start streaming with a 2xx and then return a 4xx status code.