streamSession
GET
/api/v1/sessions/{sessionId}/stream
WebSocket. The server sends every event after after as a JSON text
message (a SessionEvent), then live events as they happen. After a
reconnect, pass the last seq received to continue without gaps.
{"type":"status","running":bool} messages report whether a turn runs;
{"type":"presence","viewers":[{id,name,avatarUrl,role}]} lists who is watching.