fix(agentgateway): guard list_tools None response in LoB flow

When MCP instrumentation returns None from list_tools(), skip the fragment
with a clear warning instead of raising AttributeError on result.tools.

Author: tiagoek

src/sap_cloud_sdk/agentgateway/_lob.py

@@ -325,6 +325,15 @@ async def list_server_tools(
                     else fragment_name
                 )
                 result = await session.list_tools()
+                if result is None or result.tools is None:
+                    logger.warning(
+                        "MCP server '%s' at '%s' returned no tools from list_tools() "
+                        "(response was None — often caused by OpenTelemetry MCP "
+                        "instrumentation swallowing errors). Skipping fragment.",
+                        fragment_name,
+                        dest_url,
+                    )
+                    return []
                 return [
                     MCPTool(
                         name=t.name,

tests/agentgateway/unit/test_lob.py

@@ -21,6 +21,7 @@
     fetch_user_auth,
     get_ias_client_id_lob,
     get_mcp_tools_lob,
+    list_server_tools,
     get_agent_cards_lob,
     _fetch_agent_card,
     call_mcp_tool_lob,
@@ -600,6 +601,91 @@ async def mock_list_tools_fn(*args, **kwargs):
             assert result[0].name == "tool2"
 
 
+# ============================================================
+# Test: list_server_tools
+# ============================================================
+
+
+class TestListServerTools:
+    """Tests for list_server_tools async function."""
+
+    @pytest.mark.asyncio
+    async def test_returns_empty_when_list_tools_returns_none(self, caplog):
+        """Return empty list when MCP list_tools response is None (OTel instrumentation)."""
+        import logging
+
+        caplog.set_level(logging.WARNING, logger="sap_cloud_sdk.agentgateway._lob")
+
+        with (
+            patch("sap_cloud_sdk.agentgateway._lob.httpx.AsyncClient") as mock_http,
+            patch(
+                "sap_cloud_sdk.agentgateway._lob.streamable_http_client"
+            ) as mock_stream,
+            patch("sap_cloud_sdk.agentgateway._lob.ClientSession") as mock_session,
+        ):
+            mock_http_instance = AsyncMock()
+            mock_http.return_value.__aenter__.return_value = mock_http_instance
+
+            mock_stream.return_value.__aenter__.return_value = (
+                AsyncMock(),
+                AsyncMock(),
+                None,
+            )
+
+            mock_session_instance = AsyncMock()
+            mock_init = MagicMock()
+            mock_init.serverInfo.name = "test-server"
+            mock_session_instance.initialize = AsyncMock(return_value=mock_init)
+            mock_session_instance.list_tools = AsyncMock(return_value=None)
+            mock_session.return_value.__aenter__.return_value = mock_session_instance
+
+            result = await list_server_tools(
+                "https://example.com/mcp", "auth-token", "frag-a", 60.0
+            )
+
+            assert result == []
+            assert "returned no tools from list_tools()" in caplog.text
+
+    @pytest.mark.asyncio
+    async def test_returns_empty_when_tools_attribute_is_none(self, caplog):
+        """Return empty list when list_tools result has tools=None."""
+        import logging
+
+        caplog.set_level(logging.WARNING, logger="sap_cloud_sdk.agentgateway._lob")
+
+        with (
+            patch("sap_cloud_sdk.agentgateway._lob.httpx.AsyncClient") as mock_http,
+            patch(
+                "sap_cloud_sdk.agentgateway._lob.streamable_http_client"
+            ) as mock_stream,
+            patch("sap_cloud_sdk.agentgateway._lob.ClientSession") as mock_session,
+        ):
+            mock_http_instance = AsyncMock()
+            mock_http.return_value.__aenter__.return_value = mock_http_instance
+
+            mock_stream.return_value.__aenter__.return_value = (
+                AsyncMock(),
+                AsyncMock(),
+                None,
+            )
+
+            mock_session_instance = AsyncMock()
+            mock_init = MagicMock()
+            mock_init.serverInfo.name = "test-server"
+            mock_session_instance.initialize = AsyncMock(return_value=mock_init)
+            mock_list_result = MagicMock()
+            mock_list_result.tools = None
+            mock_session_instance.list_tools = AsyncMock(return_value=mock_list_result)
+            mock_session.return_value.__aenter__.return_value = mock_session_instance
+
+            result = await list_server_tools(
+                "https://example.com/mcp", "auth-token", "frag-a", 60.0
+            )
+
+            assert result == []
+            assert "returned no tools from list_tools()" in caplog.text
+
+
 # ============================================================
 # Test: call_mcp_tool_lob
 # ============================================================