Reconnects to an in-progress stream from a given offset. Replays buffered chunks from Redis, then subscribes to live chunks. If the message is already completed, returns the stored parts as JSON.
Authentication via JWT token or API key. JWT: Get from Veryfront dashboard. API Key: Format "vf_
Chunk index to resume from (0-based)
x >= 0SSE event stream (resumed) or JSON (completed)
The response is of type string.