LLaVA-OneVision-2: Skill for OpenCode

Purpose / 用途

Use this skill when you set up or debug training-side sample packing for LLaVA-OneVision2 — i.e. when you need to decide which env vars to export in a training shell script (Stage-1 / Stage-1.5 / Stage-2) and want to understand why both OFFLINE_PACKING_BMR and OFFLINE_PACKED_DATA must be 1 to actually get padding-free attention.

在配置或调试 LLaVA-OneVision2 训练侧的样本 packing 时使用——比如要决定在训练 shell 脚本（Stage-1 / Stage-1.5 / Stage-2）中导出哪些环境变量，以及为什么必须 OFFLINE_PACKING_BMR=1 和 OFFLINE_PACKED_DATA=1 同时打开才能真正获得 padding-free 的 attention。

This skill is specifically for:

• Choosing the correct env var combination in training scripts
• Diagnosing cross-sample attention leakage in packed runs
• Understanding why cu_lengths is a dummy [[0]] in some runs and a real [B, P+1] tensor in others
• Avoiding the well-known OFFLINE_PACKING_VQA red herring (it is dead code)

Companion skill: cu-lengths-attention-flow covers the consumer side (how cu_lengths is fed into ViT/LLM attention). This skill covers the producer + gate side.

姊妹 skill：cu-lengths-attention-flow 讲消费端（cu_lengths 如何送入 ViT/LLM attention）。本 skill 讲生产端 + 开关。

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TL;DR / 一句话总结

For packed training to work end-to-end, both env vars must be 1:

export OFFLINE_PACKING_BMR='1'   # data-layer gate: build real cu_lengths
export OFFLINE_PACKED_DATA='1'   # batch-layer gate: forward real cu_lengths to model

Setting only one is a silent bug. OFFLINE_PACKING_VQA is dead code; do not rely on it.

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The Three Env Vars / 三个环境变量真相表

Env var	Status	Default	Read at	Effect
OFFLINE_PACKING_BMR	ALIVE	0	aiak_training_llm/data/multimodal/task_encoder.py:194	Inside PackedCaptioningSample handling, unroll each packed entry into a MultiMixQASample (BMR-style, with full prompt/caption messages). When 0, falls through to the legacy CaptioningSample branch which loses the multi-turn structure.
OFFLINE_PACKED_DATA	ALIVE	0	aiak_training_llm/data/multimodal/task_encoder.py:363	Inside batch(), replace dummy cu_lengths = [[0]] with the real per-sample s.cu_lengths stacked across the batch. Without this, the consumer side cannot construct PackedSeqParams.
OFFLINE_PACKING_VQA	DEAD	n/a	nowhere in aiak_training_llm/	Mentioned in README + several legacy shells under examples/llava_onevision1_5/ and examples/llava_onevision2/quick_start_video_2b/, but no source file reads it. Setting it has zero runtime effect. Treat as documentation noise.