fix: mcp tool with array type should include items

# What does this PR do?


## Test Plan

tests/unit/providers/inline/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/unit/providers/inline/agents/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/unit/providers/inline/agents/meta_reference/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/unit/providers/inline/agents/meta_reference/responses/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/unit/providers/inline/agents/meta_reference/responses/test_streaming.py

@@ -0,0 +1,42 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from llama_stack.apis.tools import ToolDef, ToolParameter
+from llama_stack.providers.inline.agents.meta_reference.responses.streaming import (
+    convert_tooldef_to_chat_tool,
+)
+
+
+def test_convert_tooldef_to_chat_tool_preserves_items_field():
+    """Test that array parameters preserve the items field during conversion.
+
+    This test ensures that when converting ToolDef with array-type parameters
+    to OpenAI ChatCompletionToolParam format, the 'items' field is preserved.
+    Without this fix, array parameters would be missing schema information about their items.
+    """
+    tool_def = ToolDef(
+        name="test_tool",
+        description="A test tool with array parameter",
+        parameters=[
+            ToolParameter(
+                name="tags",
+                parameter_type="array",
+                description="List of tags",
+                required=True,
+                items={"type": "string"},
+            )
+        ],
+    )
+
+    result = convert_tooldef_to_chat_tool(tool_def)
+
+    assert result["type"] == "function"
+    assert result["function"]["name"] == "test_tool"
+
+    tags_param = result["function"]["parameters"]["properties"]["tags"]
+    assert tags_param["type"] == "array"
+    assert "items" in tags_param, "items field should be preserved for array parameters"
+    assert tags_param["items"] == {"type": "string"}