Fix: pin trl==0.12.2, verify imports during build

Dockerfile

@@ -20,13 +20,17 @@ RUN pip install --no-cache-dir \
     torch --index-url https://download.pytorch.org/whl/cu121
 
 RUN pip install --no-cache-dir \
-    transformers \
-    "trl>=0.12,<0.17" \
-    peft \
-    datasets \
-    accelerate \
+    "transformers==4.46.3" \
+    "trl==0.12.2" \
+    "peft==0.13.2" \
+    "datasets>=2.18" \
+    "accelerate==0.34.2" \
     huggingface_hub
 
+# Verify imports work
+RUN python3 -c "from trl import SFTTrainer, SFTConfig, GRPOConfig, GRPOTrainer; print('TRL imports OK')"
+RUN python3 -c "import torch; print('CUDA available:', torch.cuda.is_available())"
+
 COPY train_on_hf.py .
 RUN chmod -R 777 /app