fix(volcengine): handle thinking disabled parameter properly (#13598)

* fix(volcengine): handle thinking disabled parameter properly

When thinking is set to {"type": "disabled"} in volcengine provider config,
skip adding the parameter to extra_body entirely instead of passing it through.
This prevents "thinking: undefined" from appearing in request logs.

Fixes #13039

* test(volcengine): fix and enhance thinking parameter tests

- Fixed existing test that expected broken behavior
- Added comprehensive test coverage for all thinking parameter scenarios:
  * thinking disabled → omitted from extra_body
  * thinking enabled → included in extra_body
  * thinking None → included in extra_body as None
  * custom thinking values → included in extra_body
  * no thinking parameter → empty result

All tests passing, verifying the fix for issue #13039

litellm/llms/volcengine.py

@@ -81,8 +81,18 @@ class VolcEngineConfig(OpenAILikeChatConfig):
         )
 
         if "thinking" in optional_params:
-            optional_params.setdefault("extra_body", {})["thinking"] = (
-                optional_params.pop("thinking")
-            )
+            thinking_value = optional_params.pop("thinking")
+            
+            # Handle disabled thinking case - don't add to extra_body if disabled
+            if (
+                thinking_value is not None 
+                and isinstance(thinking_value, dict) 
+                and thinking_value.get("type") == "disabled"
+            ):
+                # Skip adding thinking parameter when it's disabled
+                pass
+            else:
+                # Add thinking parameter to extra_body for all other cases
+                optional_params.setdefault("extra_body", {})["thinking"] = thinking_value
 
         return optional_params

tests/test_litellm/llms/test_volcengine.py

@@ -14,6 +14,7 @@ class TestVolcEngineConfig:
         supported_params = config.get_supported_openai_params(model="doubao-seed-1.6")
         assert "thinking" in supported_params
 
+        # Test thinking disabled - should NOT appear in extra_body
         mapped_params = config.map_openai_params(
             non_default_params={
                 "thinking": {"type": "disabled"},
@@ -23,11 +24,8 @@ class TestVolcEngineConfig:
             drop_params=False,
         )
 
-        assert mapped_params == {
-            "extra_body": {
-                "thinking": {"type": "disabled"},
-            }
-        }
+        # Fixed: thinking disabled should be omitted from extra_body
+        assert mapped_params == {}
 
         e2e_mapped_params = get_optional_params(
             model="doubao-seed-1.6",
@@ -42,6 +40,61 @@ class TestVolcEngineConfig:
             "type": "enabled",
         }
 
+    def test_thinking_parameter_handling(self):
+        """Test comprehensive thinking parameter handling scenarios"""
+        config = VolcEngineConfig()
+        
+        # Test 1: thinking enabled - should appear in extra_body
+        result_enabled = config.map_openai_params(
+            non_default_params={"thinking": {"type": "enabled"}},
+            optional_params={},
+            model="doubao-seed-1.6",
+            drop_params=False,
+        )
+        assert result_enabled == {
+            "extra_body": {"thinking": {"type": "enabled"}}
+        }
+        
+        # Test 2: thinking None - should appear in extra_body as None
+        result_none = config.map_openai_params(
+            non_default_params={"thinking": None},
+            optional_params={},
+            model="doubao-seed-1.6", 
+            drop_params=False,
+        )
+        assert result_none == {
+            "extra_body": {"thinking": None}
+        }
+        
+        # Test 3: thinking with custom value - should appear in extra_body
+        result_custom = config.map_openai_params(
+            non_default_params={"thinking": "custom_mode"},
+            optional_params={},
+            model="doubao-seed-1.6",
+            drop_params=False,
+        )
+        assert result_custom == {
+            "extra_body": {"thinking": "custom_mode"}
+        }
+        
+        # Test 4: thinking disabled - should NOT appear in extra_body
+        result_disabled = config.map_openai_params(
+            non_default_params={"thinking": {"type": "disabled"}},
+            optional_params={},
+            model="doubao-seed-1.6",
+            drop_params=False,
+        )
+        assert result_disabled == {}
+        
+        # Test 5: No thinking parameter - should return empty dict
+        result_no_thinking = config.map_openai_params(
+            non_default_params={},
+            optional_params={},
+            model="doubao-seed-1.6",
+            drop_params=False,
+        )
+        assert result_no_thinking == {}
+
     def test_e2e_completion(self):
         from openai import OpenAI
 
@@ -78,6 +131,5 @@ class TestVolcEngineConfig:
 
             mock_create.assert_called_once()
             print(mock_create.call_args.kwargs)
-            assert mock_create.call_args.kwargs["extra_body"] == {
-                "thinking": {"type": "disabled"},
-            }
+            # Fixed: thinking disabled should NOT appear in extra_body
+            assert "extra_body" not in mock_create.call_args.kwargs or "thinking" not in mock_create.call_args.kwargs.get("extra_body", {})