v4: ROOT CAUSE FIX — use standard PEFT not Unsloth get_peft_model (fused LoRA kernels have dtype bug #4891). Revert to load_in_4bit=True, dtype=None matching V3.

v4: fix NF4 fp16/bf16 dtype bug (unsloth #4891) — load_in_4bit=False, 0.5B fits in full bf16 on 24GB

v4: fix fp16/bf16 mismatch — disable Unsloth gradient checkpointing (causes dtype conflict in LoRA QKV kernels at 0.5B)

v4 notebook: fix dtype Half/BFloat16 mismatch (explicit bf16), fix tied embeddings path, fix max_length warning

v4 notebook: fix TypeError crash, suppress warnings, update paths to CWD, add V3 task-aware system prompts

Fix total_mem → total_memory in V4 notebook (PyTorch API)

Add V4 Instruct-Only GRPO notebook implementing ADR-002