🚑 Fix UTF-8 surrogate bug with safe NamedString fallback

app.py

@@ -70,16 +70,18 @@ def process_file(file):
     try:
         ext = os.path.splitext(file.name)[1].lower()
         with tempfile.NamedTemporaryFile(delete=False, suffix=ext) as tmp:
-            # Ensure bytes are written regardless of type
+            # ✅ Safely convert input into bytes
             if hasattr(file, "read"):
                 file_bytes = file.read()
-            elif isinstance(file, str):
+            elif isinstance(file, str) and os.path.isfile(file):
                 with open(file, "rb") as f:
                     file_bytes = f.read()
             elif isinstance(file, bytes):
                 file_bytes = file
             else:
-                file_bytes = str(file).encode("utf-8", errors="ignore")  # ✅ fixed fallback
+                # Fallback: try encoding a safe version of its name
+                safe_name = getattr(file, "name", "fallback.txt")
+                file_bytes = safe_name.encode("utf-8", errors="ignore")
 
             tmp.write(file_bytes)
             tmp.flush()
@@ -97,6 +99,7 @@ def process_file(file):
 
 
 
+
 def generate_prompt(context, question):
     return f"""
 You are a helpful academic tutor assisting a student strictly based on course slides or textbook material.