Sync Sandbox Workspace Files

Sync partial workspace files so the UI can show progress mid-run.

Args: run_id: Run UUID from the path. body: Optional fields deliverables_json, final_report, curation_report — missing fields preserve the existing value. callback_token: One-time token issued at run creation.

Raises: HTTPException 401: Token invalid or run already finalized. HTTPException 404: Run not found.