fix: workflow end node validate error (#29473)

Co-authored-by: Novice <novice12185727@gmail.com>

api/tests/unit_tests/core/workflow/graph_engine/test_end_node_without_value_type.py

@@ -0,0 +1,60 @@
+"""
+Test case for end node without value_type field (backward compatibility).
+
+This test validates that end nodes work correctly even when the value_type
+field is missing from the output configuration, ensuring backward compatibility
+with older workflow definitions.
+"""
+
+from core.workflow.graph_events import (
+    GraphRunStartedEvent,
+    GraphRunSucceededEvent,
+    NodeRunStartedEvent,
+    NodeRunStreamChunkEvent,
+    NodeRunSucceededEvent,
+)
+
+from .test_table_runner import TableTestRunner, WorkflowTestCase
+
+
+def test_end_node_without_value_type_field():
+    """
+    Test that end node works without explicit value_type field.
+
+    The fixture implements a simple workflow that:
+    1. Takes a query input from start node
+    2. Passes it directly to end node
+    3. End node outputs the value without specifying value_type
+    4. Should correctly infer the type and output the value
+
+    This ensures backward compatibility with workflow definitions
+    created before value_type became a required field.
+    """
+    fixture_name = "end_node_without_value_type_field_workflow"
+
+    case = WorkflowTestCase(
+        fixture_path=fixture_name,
+        inputs={"query": "test query"},
+        expected_outputs={"query": "test query"},
+        expected_event_sequence=[
+            # Graph start
+            GraphRunStartedEvent,
+            # Start node
+            NodeRunStartedEvent,
+            NodeRunStreamChunkEvent,  # Start node streams the input value
+            NodeRunSucceededEvent,
+            # End node
+            NodeRunStartedEvent,
+            NodeRunSucceededEvent,
+            # Graph end
+            GraphRunSucceededEvent,
+        ],
+        description="End node without value_type field should work correctly",
+    )
+
+    runner = TableTestRunner()
+    result = runner.run_test_case(case)
+    assert result.success, f"Test failed: {result.error}"
+    assert result.actual_outputs == {"query": "test query"}, (
+        f"Expected output to be {{'query': 'test query'}}, got {result.actual_outputs}"
+    )