feat: Persist Variables for Enhanced Debugging Workflow (#20699)

This pull request introduces a feature aimed at improving the debugging experience during workflow editing. With the addition of variable persistence, the system will automatically retain the output variables from previously executed nodes. These persisted variables can then be reused when debugging subsequent nodes, eliminating the need for repetitive manual input.

By streamlining this aspect of the workflow, the feature minimizes user errors and significantly reduces debugging effort, offering a smoother and more efficient experience.

Key highlights of this change:

- Automatic persistence of output variables for executed nodes.
- Reuse of persisted variables to simplify input steps for nodes requiring them (e.g., `code`, `template`, `variable_assigner`).
- Enhanced debugging experience with reduced friction.

Closes #19735.

api/tests/integration_tests/controllers/console/app/test_workflow_draft_variable.py

@@ -0,0 +1,47 @@
+import uuid
+from unittest import mock
+
+from controllers.console.app import workflow_draft_variable as draft_variable_api
+from controllers.console.app import wraps
+from factories.variable_factory import build_segment
+from models import App, AppMode
+from models.workflow import WorkflowDraftVariable
+from services.workflow_draft_variable_service import WorkflowDraftVariableList, WorkflowDraftVariableService
+
+
+def _get_mock_srv_class() -> type[WorkflowDraftVariableService]:
+    return mock.create_autospec(WorkflowDraftVariableService)
+
+
+class TestWorkflowDraftNodeVariableListApi:
+    def test_get(self, test_client, auth_header, monkeypatch):
+        srv_class = _get_mock_srv_class()
+        mock_app_model: App = App()
+        mock_app_model.id = str(uuid.uuid4())
+        test_node_id = "test_node_id"
+        mock_app_model.mode = AppMode.ADVANCED_CHAT
+        mock_load_app_model = mock.Mock(return_value=mock_app_model)
+
+        monkeypatch.setattr(draft_variable_api, "WorkflowDraftVariableService", srv_class)
+        monkeypatch.setattr(wraps, "_load_app_model", mock_load_app_model)
+
+        var1 = WorkflowDraftVariable.new_node_variable(
+            app_id="test_app_1",
+            node_id="test_node_1",
+            name="str_var",
+            value=build_segment("str_value"),
+            node_execution_id=str(uuid.uuid4()),
+        )
+        srv_instance = mock.create_autospec(WorkflowDraftVariableService, instance=True)
+        srv_class.return_value = srv_instance
+        srv_instance.list_node_variables.return_value = WorkflowDraftVariableList(variables=[var1])
+
+        response = test_client.get(
+            f"/console/api/apps/{mock_app_model.id}/workflows/draft/nodes/{test_node_id}/variables",
+            headers=auth_header,
+        )
+        assert response.status_code == 200
+        response_dict = response.json
+        assert isinstance(response_dict, dict)
+        assert "items" in response_dict
+        assert len(response_dict["items"]) == 1