Fix Gradio validation and empty history errors

- Filter invalid alt_text fields in _clean_history_for_display to prevent Pydantic validation errors
- Add empty history check before apply_chat_template to prevent IndexError
- Add early return when no valid input exists

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

app.py

@@ -274,15 +274,28 @@ def _clean_history_for_display(history: list[dict[str, Any]]) -> list[dict[str,
             cleaned_content = []
             for item in content:
                 if isinstance(item, dict):
-                    # Remove _pil_image but keep other fields
-                    cleaned_item = {k: v for k, v in item.items() if k != "_pil_image"}
+                    # Remove _pil_image and ensure alt_text is string or absent
+                    cleaned_item = {}
+                    for k, v in item.items():
+                        if k == "_pil_image":
+                            continue
+                        if k == "alt_text" and not isinstance(v, str):
+                            continue
+                        cleaned_item[k] = v
                     cleaned_content.append(cleaned_item)
                 else:
                     cleaned_content.append(item)
             cleaned_message["content"] = cleaned_content
         elif isinstance(content, dict):
-            # Remove _pil_image but keep other fields
-            cleaned_message["content"] = {k: v for k, v in content.items() if k != "_pil_image"}
+            # Remove _pil_image and ensure alt_text is string or absent
+            cleaned_item = {}
+            for k, v in content.items():
+                if k == "_pil_image":
+                    continue
+                if k == "alt_text" and not isinstance(v, str):
+                    continue
+                cleaned_item[k] = v
+            cleaned_message["content"] = cleaned_item
         else:
             cleaned_message["content"] = content
 
@@ -312,18 +325,26 @@ def bot(
 
     text_history = _prepare_text_history(history)
 
-    input_text: str = tokenizer.apply_chat_template(
-        text_history,
-        tokenize=False,
-        add_generation_prompt=True,
-        # enable_thinking=True,
-    )
-
-    if tokenizer.bos_token:
+    # Handle empty history case
+    if not text_history:
+        input_text = ""
+    else:
+        input_text: str = tokenizer.apply_chat_template(
+            text_history,
+            tokenize=False,
+            add_generation_prompt=True,
+            # enable_thinking=True,
+        )
+
+    if input_text and tokenizer.bos_token:
         input_text = input_text.replace(tokenizer.bos_token, "", 1)
     print(input_text)
     model_inputs = None
 
+    # Early return if no input
+    if not input_text and not any(_message_contains_image(msg) for msg in history):
+        return
+
     if processor is not None and any(_message_contains_image(msg) for msg in history):
         try:
             processor_history = _prepare_processor_history(history)