fix: support Cursor IDE tool_choice format {"type": "auto"} (#12168)

* fix: support Cursor IDE tool_choice format {"type": "auto"}

- Update validate_chat_completion_tool_choice to normalize {"type": "auto"} to "auto"
- Handles Cursor IDE sending non-standard tool_choice format
- Add comprehensive tests for tool choice validation

Fixes #12098

* fix: return full tool_choice object for Cursor IDE format

Based on PR feedback, updated validate_chat_completion_tool_choice to return
the full tool_choice dictionary instead of just extracting the type string.
This maintains consistency with downstream code that expects the full object
structure.

- Changed behavior: {"type": "auto"} now returns {"type": "auto"} instead of "auto"
- Updated tests to reflect the new expected behavior
- Ensures compatibility with code that passes tool_choice to optional_params

Addresses feedback from PR #12168

litellm/utils.py

@@ -6571,6 +6571,14 @@ def validate_chat_completion_tool_choice(
     elif isinstance(tool_choice, str):
         return tool_choice
     elif isinstance(tool_choice, dict):
+        # Handle Cursor IDE format: {"type": "auto"} -> return as-is
+        if (
+            tool_choice.get("type") in ["auto", "none", "required"]
+            and "function" not in tool_choice
+        ):
+            return tool_choice
+        
+        # Standard OpenAI format: {"type": "function", "function": {...}}
         if tool_choice.get("type") is None or tool_choice.get("function") is None:
             raise Exception(
                 f"Invalid tool choice, tool_choice={tool_choice}. Please ensure tool_choice follows the OpenAI spec"

tests/litellm_utils_tests/test_validate_tool_choice.py

@@ -0,0 +1,63 @@
+import pytest
+import sys
+import os
+
+sys.path.insert(0, os.path.abspath("../.."))
+
+from litellm.utils import validate_chat_completion_tool_choice
+
+
+def test_validate_tool_choice_none():
+    """Test that None is returned as-is."""
+    result = validate_chat_completion_tool_choice(None)
+    assert result is None
+
+
+def test_validate_tool_choice_string():
+    """Test that string values are returned as-is."""
+    assert validate_chat_completion_tool_choice("auto") == "auto"
+    assert validate_chat_completion_tool_choice("none") == "none"
+    assert validate_chat_completion_tool_choice("required") == "required"
+
+
+def test_validate_tool_choice_standard_dict():
+    """Test standard OpenAI format with function."""
+    tool_choice = {"type": "function", "function": {"name": "my_function"}}
+    result = validate_chat_completion_tool_choice(tool_choice)
+    assert result == tool_choice
+
+
+def test_validate_tool_choice_cursor_format():
+    """Test Cursor IDE format: {"type": "auto"} -> {"type": "auto"}."""
+    assert validate_chat_completion_tool_choice({"type": "auto"}) == {"type": "auto"}
+    assert validate_chat_completion_tool_choice({"type": "none"}) == {"type": "none"}
+    assert validate_chat_completion_tool_choice({"type": "required"}) == {"type": "required"}
+
+
+def test_validate_tool_choice_invalid_dict():
+    """Test that invalid dict formats raise exceptions."""
+    # Missing both type and function
+    with pytest.raises(Exception) as exc_info:
+        validate_chat_completion_tool_choice({})
+    assert "Invalid tool choice" in str(exc_info.value)
+    
+    # Invalid type value
+    with pytest.raises(Exception) as exc_info:
+        validate_chat_completion_tool_choice({"type": "invalid"})
+    assert "Invalid tool choice" in str(exc_info.value)
+    
+    # Has type but missing function when type is "function"
+    with pytest.raises(Exception) as exc_info:
+        validate_chat_completion_tool_choice({"type": "function"})
+    assert "Invalid tool choice" in str(exc_info.value)
+
+
+def test_validate_tool_choice_invalid_type():
+    """Test that invalid types raise exceptions."""
+    with pytest.raises(Exception) as exc_info:
+        validate_chat_completion_tool_choice(123)
+    assert "Got=<class 'int'>" in str(exc_info.value)
+    
+    with pytest.raises(Exception) as exc_info:
+        validate_chat_completion_tool_choice([])
+    assert "Got=<class 'list'>" in str(exc_info.value)