feat(go-agent): Ported retrieval node, added Keenable web search tool (#16396)

Ported retrieval node, added Keenable web search tool
- [x] New Feature (non-breaking change which adds functionality)

test/unit_test/api/db/services/test_tenant_model_service_instance_fallback.py

@@ -0,0 +1,48 @@
+#
+#  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+from types import SimpleNamespace
+
+from common.constants import ActiveStatusEnum
+from api.db.joint_services import tenant_model_service as module
+
+
+def test_resolve_instance_for_model_falls_back_from_default_to_single_active_instance(monkeypatch):
+    provider = SimpleNamespace(id="provider-1", provider_name="SILICONFLOW")
+    resolved = SimpleNamespace(
+        id="instance-1",
+        instance_name="yy2",
+        status=ActiveStatusEnum.ACTIVE.value,
+    )
+
+    monkeypatch.setattr(
+        module.TenantModelInstanceService,
+        "get_by_provider_id_and_instance_name",
+        lambda provider_id, instance_name: None,
+    )
+    monkeypatch.setattr(
+        module.TenantModelInstanceService,
+        "get_all_by_provider_id",
+        lambda provider_id: [resolved],
+    )
+
+    got = module._resolve_instance_for_model(
+        provider,
+        "default",
+        "Qwen/Qwen3-8B@default@SILICONFLOW",
+    )
+
+    assert got is resolved