fix: validate target_dir in detect_objects before processing

- Add early return if target_dir is None or invalid
- Handle reconstruct() error return properly
- Show clear error message when no video/images uploaded

mvp.py

@@ -1131,6 +1131,10 @@ def detect_objects(text_labels, target_dir, conf_thres, *viz_args):
     """
     Detect objects from text labels and return the detected objects.
     """
+    # Validate target_dir first
+    if not target_dir or target_dir == "None" or not os.path.isdir(target_dir):
+        return None, "Please upload a video or images first."
+
     # Require non-empty text labels
     if not text_labels or not isinstance(text_labels, str) or len([l.strip() for l in text_labels.split(";") if l.strip()]) == 0:
         return None, "Please enter at least one text label (separated by ';')."
@@ -1141,12 +1145,15 @@ def detect_objects(text_labels, target_dir, conf_thres, *viz_args):
             check_weights()
         except Exception as e:
             print(f"Warning: could not ensure Mask2Former weights: {e}")
-    
+
     # 1. Run reconstruction first if needed (checking if predictions exist)
     predictions_path = os.path.join(target_dir, "predictions.npz")
     if not os.path.exists(predictions_path):
         print("Predictions not found, running reconstruction first...")
-        reconstruct(target_dir, 50.0, *viz_args, text_labels=text_labels)
+        result = reconstruct(target_dir, 50.0, *viz_args, text_labels=text_labels)
+        # Check if reconstruction failed
+        if result and len(result) >= 2 and result[0] is None:
+            return None, result[1]  # Return error message from reconstruct
     
     
     # Extract text features if provided