fix: set include_thoughts=False when thinking_budget is 0

When thinking_budget is set to 0 (disabling thinking), include_thoughts
was hardcoded to True, causing a 400 INVALID_ARGUMENT error from the
Vertex AI API. Now include_thoughts is set based on whether thinking
is actually enabled (thinking_budget != 0).

Closes deepset-ai/haystack#2845

Author: yaowubarbara

integrations/google_genai/src/haystack_integrations/components/generators/google_genai/chat/chat_generator.py

@@ -901,7 +901,10 @@ def _process_thinking_config(generation_kwargs: dict[str, Any]) -> dict[str, Any
                 thinking_budget = -1
 
             # Create thinking config
-            thinking_config = types.ThinkingConfig(thinking_budget=thinking_budget, include_thoughts=True)
+            # When thinking_budget is 0, thinking is disabled so include_thoughts must be False
+            thinking_config = types.ThinkingConfig(
+                thinking_budget=thinking_budget, include_thoughts=thinking_budget != 0
+            )
             generation_kwargs["thinking_config"] = thinking_config
 
         if "thinking_level" in generation_kwargs:

integrations/google_genai/tests/test_chat_generator.py

@@ -1508,23 +1508,27 @@ def test_process_thinking_budget(monkeypatch):
     assert "thinking_budget" not in result
     assert "thinking_config" in result
     assert result["thinking_config"].thinking_budget == 1024
+    assert result["thinking_config"].include_thoughts is True
     # Other kwargs should be preserved
     assert result["temperature"] == 0.7
 
     # Test dynamic allocation (-1)
     generation_kwargs = {"thinking_budget": -1}
     result = GoogleGenAIChatGenerator._process_thinking_config(generation_kwargs.copy())
     assert result["thinking_config"].thinking_budget == -1
+    assert result["thinking_config"].include_thoughts is True
 
     # Test zero (disable thinking)
     generation_kwargs = {"thinking_budget": 0}
     result = GoogleGenAIChatGenerator._process_thinking_config(generation_kwargs.copy())
     assert result["thinking_config"].thinking_budget == 0
+    assert result["thinking_config"].include_thoughts is False
 
     # Test large value
     generation_kwargs = {"thinking_budget": 24576}
     result = GoogleGenAIChatGenerator._process_thinking_config(generation_kwargs.copy())
     assert result["thinking_config"].thinking_budget == 24576
+    assert result["thinking_config"].include_thoughts is True
 
     # Test when thinking_budget is not present
     generation_kwargs = {"temperature": 0.5}