adding failure-modes

trl/SKILL.md

@@ -388,6 +388,56 @@ See `references/training_patterns.md` for detailed examples including:
 - DPO training (preference learning)
 - GRPO training (online RL)
 
+## Common Failure Modes
+
+### Out of Memory (OOM)
+
+**Fix (try in order):**
+1. Reduce batch size: `per_device_train_batch_size=1`, increase `gradient_accumulation_steps=8`. Effective batch size is `per_device_train_batch_size` x `gradient_accumulation_steps`. For best performance keep effective batch size close to 128. 
+2. Enable: `gradient_checkpointing=True`
+3. Upgrade hardware: t4-small → l4x1, a10g-small → a10g-large etc. 
+
+### Dataset Misformatted
+
+**Fix:**
+1. Validate first: `python scripts/validate_dataset.py --dataset name --method sft`
+2. Check required columns:
+   - SFT: `messages` OR `text` OR `prompt`+`completion`
+   - DPO: `prompt`, `chosen`, `rejected`
+   - GRPO: `prompt` only
+3. Apply formatting if needed:
+   ```python
+   dataset = dataset.map(lambda x: {"text": f"User: {x['input']}\nBot: {x['output']}"})
+   ```
+
+### Job Timeout
+
+**Fix:**
+1. Check logs for actual runtime: `hf_jobs("logs", {"job_id": "..."})`
+2. Increase timeout with buffer: `"timeout": "3h"` (add 30% to estimated time)
+3. Or reduce training: lower `num_train_epochs`, use smaller dataset, enable `max_steps`
+4. Save checkpoints: `save_strategy="steps"`, `save_steps=500`, `hub_strategy="every_save"`
+
+**Note:** Default 30min is insufficient for real training. Minimum 1-2 hours.
+
+### Hub Push Failures
+
+**Fix:**
+1. Add to job: `secrets={"HF_TOKEN": "$HF_TOKEN"}`
+2. Add to config: `push_to_hub=True`, `hub_model_id="username/model-name"`
+3. Verify auth: `mcp__huggingface__hf_whoami()`
+4. Check token has write permissions and repo exists (or set `hub_private_repo=True`)
+
+### Missing Dependencies
+
+**Fix:**
+Add to PEP 723 header:
+```python
+# /// script
+# dependencies = ["trl>=0.12.0", "peft>=0.7.0", "trackio", "missing-package"]
+# ///
+```
+
 ## Troubleshooting
 
 **Common issues:**