chore(dtensor): move remaining DTensor v1 configs to v2

[yuki-97]

DTensor v1 removal stack — merge in order:

1. chore(dtensor): move remaining DTensor v1 configs to v2 #4196 (this PR) — move the remaining v1 configs to v2
2. feat(dtensor): reject dtensor_cfg._v2=false #4207 — reject dtensor_cfg._v2=false
3. refactor(dtensor): remove the DTensor v1 policy worker #4198 — delete the v1 policy worker

Follow-ups:
4. delete the dtensor_cfg._v2 key itself
5. other cleanups, TBD

What does this PR do ?

Moves every remaining DTensor v1 config in the repo onto the v2 (Automodel) backend, so that the v1 worker can be deleted in a follow-up PR (#4198).

policy.dtensor_cfg._v2 defaults to False (nemo_rl/models/policy/lm_policy.py), so a config that
never mentions _v2 silently runs the v1 DTensorPolicyWorker. Between that default and 6 files
pinning _v2: false explicitly, 20 resolved dtensor_cfg blocks were still on v1.

What changed

8 root files were edited; everything else inherits via defaults:.
checkpoint.model_save_format was added wherever it was missing or null —
build_checkpoint_config (nemo_rl/models/automodel/checkpoint.py) requires it on the v2 path.

Exemplar configs (covered by CI:L1 functional tests)

• examples/configs/dpo.yaml
• examples/configs/rm.yaml
• examples/configs/grpo_math_1B_dynamo.yaml

Roots for the nightly / release recipes

• examples/configs/recipes/llm/grpo-deepscaler-1.5b-8K.yaml
• examples/configs/recipes/llm/grpo-gspo-deepscaler-1.5b-8K.yaml
• examples/configs/recipes/llm/grpo-gemma3-27b-it-8n8g-fsdp2tp8-actckpt-long.yaml
• examples/configs/recipes/llm/dapo-qwen2.5-7b.v2.yaml
• examples/nemo_gym/grpo_workplace_assistant_nemotron_nano_v2_9b.yaml

Inherited via defaults: — not edited, but flipped to v2

• recipes/llm/grpo-deepscaler-1.5b-16K.yaml (nightly)
• recipes/llm/grpo-deepscaler-1.5b-24K.yaml (nightly)
• recipes/llm/grpo-deepscaler-1.5b-8K-tq_simple.yaml (nightly)
• recipes/llm/grpo-deepscaler-1.5b-1n4g-8K.yaml (nightly_gb200)
• recipes/llm/grpo-gspo-deepscaler-1.5b-8K-tq_simple.yaml (nightly)
• recipes/llm/grpo-gemma3-27b-it-8n4g-fsdp2tp4-actckpt-long.yaml (release_gb200)
• recipes/llm/dapo-qwen2.5-7b-16n4g-fsdp2cp2.v2.yaml (release_gb200)
• recipes/llm/dpo-llama3.2-1b-instruct-1n8g-fsdp2tp1.v2.yaml (nightly)
• recipes/llm/dpo-mistral-nemo-instruct-2407-1n8g-fsdp2tp8-actckpt-long.yaml (nightly)
• recipes/llm/dpo-llama3.2-1b-instruct-1n4g-fsdp2tp1.v2.yaml (nightly_gb200)
• recipes/llm/dpo-llama3.1-8b-instruct-4n8g-fsdp2tp4.yaml (release)
• recipes/llm/dpo-llama3.1-8b-tulu3-1n8g-fsdp2tp1.yaml (release)
• recipes/llm/gdpo-qwen2.5-1.5b-1n8g-gym-multireward.yaml (nightly)

Also in the diff

• tests/test_suites/llm/dapo-qwen2.5-7b.v2.sh and dapo-qwen2.5-7b-16n4g-fsdp2cp2.v2.sh — drop the flaky terminal-step token_mult_prob_error["20"] < 1.05 check; the median(...) < 1.1 bound in the same file stays.
• tests/unit/test_config_validation.py — test_all_config_dtensor_selects_v2 walks every config with defaults: resolved and fails on _v2: false, or on a missing _v2 when dtensor_cfg is enabled.
• tests/unit/reference_configs/{dpo,rm}.yaml — updated to match the exemplar edits above.

Verification

Only the recipes below were run (roots, or the ones most likely to be affected), all pass -- the other nightly / release recipes were not run:

• grpo-deepscaler-1.5b-8K (root)
• grpo-deepscaler-1.5b-16K (inherited)
• grpo-gspo-deepscaler-1.5b-8K (root)
• grpo-gemma3-27b-it-8n8g-fsdp2tp8-actckpt-long (root)
• dapo-qwen2.5-7b.v2 (root)
• gdpo-qwen2.5-1.5b-1n8g-gym-multireward (inherited)

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[yuki-97]

/ok to test f201ac1

[yuki-97]

/ok to test 49a5f85

[yuki-97]

/ok to test 85dc155

[yuki-97]

/ok to test 6bc8577

[yuki-97]

Team review of the v1 to v2 config flip: 4 agents (RL/config expert, bug-finder, test reviewer, devil's advocate) plus a leader verification pass.

The mechanical core of this PR checks out. Verified independently:

• defaults: inheritance is an OmegaConf deep merge (nemo_rl/utils/config.py:46), so the partial checkpoint: overrides on the deepscaler recipes keep the parent's save_consolidated / single_rank_consolidation / consolidation_timeout_minutes.
• All 7 tests/unit/reference_configs/ pairs pass test_config_v2.py::test_reference_configs_up_to_date (missing=[] different=[] re-run by hand); comments and key order are irrelevant to that test, and no other twin needed updating.
• Every config that resolves to _v2: true and enabled: true carries a legal model_save_format, so nothing hits the build_checkpoint_config ValueError.
• The torch_save vs safetensors split is correct: the only 4 live convert_dcp_to_hf callers are the deepscaler scripts, and all of their recipes inherit torch_save through defaults:.
• Per-config v2 feature compatibility was checked against the pinned Automodel submodule and came back clean — the gemma3 tp=8 parallel plan (Automodel carries an identical _parallelize_gemma3 registered for Gemma3ForConditionalGeneration), the RM score. head path, context_parallel_size: 4, cpu_offload, and the dynamo path.

Two comments below, neither blocking. Several candidate findings were investigated and dropped as unfounded, including a suspected convert_dcp_to_hf breakage across the flipped configs and a suspected v1 residue in the vlm_mpo family.

One status note rather than a finding: no functional test has run on 6bc8577 yet — the green checks are lint/release/semantic, and the test approval queue entry is still waiting.

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[yuki-97]

/ok to test 84dcc5f

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[terrykong]

The migration itself is complete and correct, and that is most of this PR.

A recursive walk over every dtensor_cfg in examples/**, tests/unit/reference_configs/ and research/ — 417 blocks — finds nothing that resolves to _v2: false, and no enabled v2 block missing a legal model_save_format. The torch_save / safetensors split is right: every deepscaler recipe whose .sh runs convert_dcp_to_hf.py resolves to torch_save, which it needs, since it reads a DCP .metadata file that safetensors does not write. All 7 reference-config pairs were compared key by key: no missing keys, no differences, and the dpo/rm twin updates were required. The key deletions all resolve correctly through their parents, and no doc tells users to set _v2: false.

The stack order is right, too: flip the values here so CI stays green, then turn on the guard in #4207. There is no commit in the stack where the repo's own configs fail its own check.

One thing worth knowing before merge: no unit or functional lane has run on the current head b243070a. The last /ok to test named 84dcc5f, which was force-pushed away, so only the DCO, copyright, secrets, semantic and submodule checks are green. test_all_config_dtensor_selects_v2 has never executed in CI on this head. An /ok to test b243070a would cover that.

The findings below come from 7 agents plus a leader verification pass. The first adversarial pass went silent and was stopped; a second independent adversarial pass then reviewed the full set, and several candidate findings were dropped as unfounded.

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[yuki-97]

/ok to test 9546acb