Python: fix(bedrock): don't send toolChoice when no tools are configured

python/packages/bedrock/agent_framework_bedrock/_chat_client.py

@@ -411,10 +411,14 @@ def _prepare_options(
                     # Omit toolConfig entirely so the model won't attempt tool calls.
                     tool_config = None
                 case "auto":
-                    tool_config = tool_config or {}
-                    tool_config["toolChoice"] = {"auto": {}}
+                    if tool_config and "tools" in tool_config:
+                        tool_config["toolChoice"] = {"auto": {}}
                 case "required":
-                    tool_config = tool_config or {}
+                    if not (tool_config and "tools" in tool_config):
+                        raise ValueError(
+                            "tool_choice='required' requires at least one tool to be configured, "
+                            "but no tools were provided."
+                        )
                     if required_name := tool_mode.get("required_function_name"):
                         tool_config["toolChoice"] = {"tool": {"name": required_name}}
                     else:

python/packages/bedrock/tests/test_bedrock_client.py

@@ -137,3 +137,36 @@ def test_prepare_options_tool_choice_required_includes_any() -> None:
 
     assert "toolConfig" in request
     assert request["toolConfig"]["toolChoice"] == {"any": {}}
+
+
+
+def test_prepare_options_tool_choice_auto_without_tools_omits_tool_config() -> None:
+    """When tool_choice='auto' but no tools are provided, toolConfig must be omitted.
+
+    Without tools, setting toolChoice would cause a ParamValidationError from Bedrock.
+    """
+    client = _make_client()
+    messages = [Message(role="user", contents=[Content.from_text(text="hello")])]
+
+    options: dict[str, Any] = {
+        "tool_choice": "auto",
+    }
+
+    request = client._prepare_options(messages, options)
+
+    assert "toolConfig" not in request, (
+        f"toolConfig should be omitted when no tools are provided, got: {request.get('toolConfig')}"
+    )
+
+
+def test_prepare_options_tool_choice_required_without_tools_raises() -> None:
+    """When tool_choice='required' but no tools are provided, a ValueError must be raised."""
+    client = _make_client()
+    messages = [Message(role="user", contents=[Content.from_text(text="hello")])]
+
+    options: dict[str, Any] = {
+        "tool_choice": "required",
+    }
+
+    with pytest.raises(ValueError, match="tool_choice='required' requires at least one tool"):
+        client._prepare_options(messages, options)