Fix dataset preparation bug and HF repo authentication

Critical Fixes:
- Fixed NameError: 'datasets_to_process' undefined -> changed to 'dataset_keys'
- Added repo accessibility check to prevent 401 errors
- HF storage now checks if repo exists and is accessible during init
- All upload/download methods check repo_accessible flag before operations
- Changed warnings to debug logs to reduce console noise

HF Repo Handling:
- On init, checks if Gamahea/lemm-dataset exists and is accessible
- If repo not accessible (no token/401), sets repo_accessible=False
- All operations gracefully skip HF uploads/downloads
- LoRAs and datasets still saved locally
- No more 401 Client Error spam in logs

User Impact:
- Dataset preparation now works without crashes
- Training completes successfully
- HF Space works without HF_TOKEN (local storage only)
- If HF_TOKEN configured, uploads work automatically

app.py

@@ -1186,7 +1186,7 @@ def prepare_datasets_for_training(selected_datasets, max_samples_per_dataset):
             # Upload prepared datasets to HF repo
             status_messages.append(f"\n📤 Uploading prepared datasets to HuggingFace repo...")
             upload_count = 0
-            for dataset_key in datasets_to_process:
+            for dataset_key in dataset_keys:  # Fixed: was datasets_to_process
                 dataset_dir = Path("training_data") / dataset_key
                 if dataset_dir.exists():
                     if hf_storage.upload_dataset(dataset_dir):

backend/services/hf_storage_service.py

@@ -26,15 +26,25 @@ class HFStorageService:
         
         logger.info(f"HF Storage initialized for repo: {repo_id}")
         
-        # Try to import huggingface_hub
+        # Try to import huggingface_hub and check authentication
         try:
             from huggingface_hub import HfApi, hf_hub_download, upload_folder
             self.api = HfApi()
             self.has_hf = True
-            logger.info("✅ HuggingFace Hub available")
+            
+            # Check if repo exists and is accessible
+            try:
+                self.api.repo_info(repo_id=repo_id, repo_type="dataset")
+                logger.info(f"✅ HuggingFace Hub available - repo accessible")
+                self.repo_accessible = True
+            except Exception as e:
+                logger.warning(f"⚠️ HF repo not accessible (may need authentication): {e}")
+                logger.warning("Uploads/downloads will be skipped. Local storage only.")
+                self.repo_accessible = False
         except ImportError:
             logger.warning("⚠️ huggingface_hub not available, using local storage only")
             self.has_hf = False
+            self.repo_accessible = False
     
     def download_all_loras(self, target_dir: Path) -> List[str]:
         """
@@ -46,8 +56,8 @@ class HFStorageService:
         Returns:
             List of downloaded LoRA names
         """
-        if not self.has_hf:
-            logger.warning("HuggingFace Hub not available")
+        if not self.has_hf or not self.repo_accessible:
+            logger.debug("HF repo not accessible, skipping LoRA download")
             return []
         
         try:
@@ -97,8 +107,8 @@ class HFStorageService:
         Returns:
             List of downloaded dataset keys
         """
-        if not self.has_hf:
-            logger.warning("HuggingFace Hub not available")
+        if not self.has_hf or not self.repo_accessible:
+            logger.debug("HF repo not accessible, skipping dataset download")
             return []
         
         try:
@@ -148,8 +158,8 @@ class HFStorageService:
         Returns:
             True if successful
         """
-        if not self.has_hf:
-            logger.warning("HuggingFace Hub not available")
+        if not self.has_hf or not self.repo_accessible:
+            logger.debug(f"HF repo not accessible, LoRA saved locally only: {lora_dir.name}")
             return False
         
         try:
@@ -182,8 +192,8 @@ class HFStorageService:
         Returns:
             True if successful
         """
-        if not self.has_hf:
-            logger.warning("HuggingFace Hub not available")
+        if not self.has_hf or not self.repo_accessible:
+            logger.debug(f"HF repo not accessible, dataset saved locally only: {dataset_dir.name}")
             return False
         
         try: