NeMo-RL E2E Testing

Validate a Megatron-Bridge model or training API change through NeMo-RL's Megatron backend. This catches integration issues that Bridge-only tests miss: NeMo-RL-owned rollout scheduling, reward handling, policy/reference setup, HF import/export through Bridge, optimizer setup, checkpoint ownership, and policy-to-generation weight transfer.

Use this as an external compatibility smoke test after the focused Bridge tests for the model/provider change pass.

This is not a replacement for Bridge model parity tests. A NeMo-RL GRPO or SFT run proves that Bridge can survive an external RL training loop; architecture correctness still comes from Bridge import/export, logits, roundtrip, and model-specific inference tests.

Scope

Think in coverage levels. Start with Level 0 and add only the levels justified by the change.