Convert NeMo Gym to ATIF

Purpose

NeMo Gym's stored rollouts use its Responses-style format, not ATIF. This does not mean the rollout must run outside NeMo Gym. NeMo Gym's Harbor bridge can run the user's Harbor agent and then project its ATIF into a NeMo Gym response. Keep the user's agent and harness; choose the best retained evidence for downstream processing. The bundled script writes owner-private files and prints only a content-free summary.

For native ng_trajectory evidence, the optional shared NeMo Compass loader is available alongside this ATIF adapter. Read NeMo Compass ingestion before using scripts/load_gym_trace.py. It retains normalized evidence without claiming that the attachment is ATIF or changing the ATIF conversion boundary.