fix(gemini): Add skip thought signature

src/strands/models/gemini.py

@@ -141,12 +141,16 @@ def _format_request_content_part(self, content: ContentBlock) -> genai.types.Par
             )
 
         if "toolUse" in content:
+            # Use skip_thought_signature_validator to bypass Gemini 3 Pro's strict validation
+            # This is a temporary workaround until we implement proper thought signature preservation
+            # See: https://ai.google.dev/gemini-api/docs/thought-signatures
             return genai.types.Part(
                 function_call=genai.types.FunctionCall(
                     args=content["toolUse"]["input"],
                     id=content["toolUse"]["toolUseId"],
                     name=content["toolUse"]["name"],
                 ),
+                thought_signature=b"skip_thought_signature_validator",
             )
 
         raise TypeError(f"content_type=<{next(iter(content))}> | unsupported type")

tests/strands/models/test_gemini.py

@@ -289,6 +289,8 @@ async def test_stream_request_with_tool_use(gemini_client, model, model_id):
                             "id": "c1",
                             "name": "calculator",
                         },
+                        # Skip validator is used as a temporary workaround for Gemini 3 Pro
+                        "thought_signature": "c2tpcF90aG91Z2h0X3NpZ25hdHVyZV92YWxpZGF0b3I=",
                     },
                 ],
                 "role": "model",
@@ -299,6 +301,35 @@ async def test_stream_request_with_tool_use(gemini_client, model, model_id):
     gemini_client.aio.models.generate_content_stream.assert_called_with(**exp_request)
 
 
+@pytest.mark.asyncio
+async def test_stream_request_with_tool_use_includes_thought_signature_skip(gemini_client, model, model_id):
+    """Test that toolUse includes skip_thought_signature_validator for Gemini 3 Pro compatibility."""
+    messages = [
+        {
+            "role": "assistant",
+            "content": [
+                {
+                    "toolUse": {
+                        "toolUseId": "tool1",
+                        "name": "get_weather",
+                        "input": {"city": "Seattle"},
+                    },
+                },
+            ],
+        },
+    ]
+    await anext(model.stream(messages))
+
+    call_args = gemini_client.aio.models.generate_content_stream.call_args
+    contents = call_args.kwargs["contents"]
+
+    # Verify the thought_signature is set to skip validator
+    part = contents[0]["parts"][0]
+    assert "thought_signature" in part
+    # Base64 encoded "skip_thought_signature_validator"
+    assert part["thought_signature"] == "c2tpcF90aG91Z2h0X3NpZ25hdHVyZV92YWxpZGF0b3I="
+
+
 @pytest.mark.asyncio
 async def test_stream_request_with_tool_results(gemini_client, model, model_id):
     messages = [

tests_integ/models/test_model_gemini.py

@@ -175,3 +175,28 @@ def test_agent_structured_output_image_input(assistant_agent, yellow_img, yellow
     tru_color = assistant_agent.structured_output(type(yellow_color), content)
     exp_color = yellow_color
     assert tru_color == exp_color
+
+
+@pytest.mark.parametrize("model_id", ["gemini-2.5-flash", "gemini-3-pro-preview"])
+def test_agent_multiturn_tool_use(model_id, tools, system_prompt):
+    """Test multi-turn conversation with tool use.
+
+    Gemini 3 Pro requires thought_signature in multi-turn function calling.
+    Without skip_thought_signature_validator, this fails with:
+    "Function call is missing a thought_signature in functionCall parts"
+
+    Validates fix for issue #1199.
+    """
+    model = GeminiModel(
+        client_args={"api_key": os.getenv("GOOGLE_API_KEY")},
+        model_id=model_id,
+        params={"temperature": 0.15},
+    )
+    agent = Agent(model=model, tools=tools, system_prompt=system_prompt)
+
+    result1 = agent("What is the current time in New York?")
+    assert "12:00" in result1.message["content"][0]["text"].lower()
+
+    # Second turn with tool use history - this is where Gemini 3 Pro would fail
+    result2 = agent("And what is the weather there?")
+    assert "sunny" in result2.message["content"][0]["text"].lower()