[DanialTaheri]

What

_patch_vllm_radio_layerscale_loader matches RadioModel.load_weights as a
single 20-line snippet. The super_vl_rl_v0.25.1
fork that the nemo-ci rl-gym images ship reshaped that body in three ways:

1. the legacy branch is gated on is_legacy
2. an elif not is_legacy: native-mapping branch was inserted before the
   if vllm_key ... tail (it maps layer_scale{1,2}.lambda1 -> ls{1,2})
3. the loader call became shard-aware

Any one of those breaks the match, so the patch takes its logger.warning path
and returns without applying.

Why it matters

The failure is silent and expensive:

• Super Omni checkpoints are folded exports carrying no ls1/ls2 tensors
• megatron_cfg.freeze_vision_model: true keeps the vision tower out of the refit
• NeMo-RL forces load_format=dummy (overriding the recipe's auto)

So this patch's initializer_factor fill is the only code path that ever sets
LayerScale. When it no-ops, every residual branch of the RADIO tower is scaled
by dummy-init noise — with unchanged step time and no exception. The sole
evidence is one line in ray-driver.log:

WARNING:vllm_patch:patches.py:580: Could not apply vLLM RADIO LayerScale loader
patch: expected vLLM 0.25.1 source shape was not found in .../radio.py

Measured on a 16-node Super Omni GRPO run — identical recipe, data and
checkpoint, step 1:

	reward	train/token_mult_prob_error	mean_seq_mult_prob_error	masked seqs
patch applies (stock 0.25.1)	0.574	1.0305	1.141	11 / 2048
patch no-ops (fork)	0.216	1.4503	16,906,104	1775 / 2048
after this change (fork)	0.556	1.0305	1.057	6 / 2048

87% of the batch was being masked out by the logprob-error threshold.

How

Split the rewrite into two independent edits anchored on text stable across
both variants, so a future reshape of one branch cannot silently disable the
other:

• Edit 1 (optional) — drop the legacy ls1/ls2 skip, so explicit
  LayerScale weights load rather than only being backfilled.
• Edit 2 (required) — insert the initializer_factor fill before
  return loaded_params, anchored on
  loaded_params.add(vllm_key)\n\n return loaded_params (unique in both
  variants).

The required edit now warns and refuses to write a half-applied patch rather
than returning quietly, so the next drift is diagnosable from one log line.
self.config.initializer_factor also became
getattr(self.config, "initializer_factor", 1.0) — the checkpoint configs omit
the field and currently rely on RadioConfig's default.

Test plan

Applied against both stock vLLM 0.25.1 and the fork's radio.py, asserting
that it applies, the result parses, the fill loop lands inside load_weights
before its return, the fork's native-mapping branch and shard-aware
weight_loader survive, and a second application is a no-op. All pass on both.

End-to-end: 16-node Super Omni GRPO run on the fork-based container with
load_format=dummy unchanged — Could not apply ... went from 40+ occurrences
across the cluster to 0, and step-1 metrics match the stock-vLLM baseline to
five decimal places (see table above).

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