fix: fixed workflow as tool files field return empty problem (#27925)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: QuantumGhost <obelisk.reg+git@gmail.com>

api/core/workflow/nodes/tool/tool_node.py

@@ -329,7 +329,15 @@ class ToolNode(Node):
                     json.append(message.message.json_object)
             elif message.type == ToolInvokeMessage.MessageType.LINK:
                 assert isinstance(message.message, ToolInvokeMessage.TextMessage)
-                stream_text = f"Link: {message.message.text}\n"
+
+                # Check if this LINK message is a file link
+                file_obj = (message.meta or {}).get("file")
+                if isinstance(file_obj, File):
+                    files.append(file_obj)
+                    stream_text = f"File: {message.message.text}\n"
+                else:
+                    stream_text = f"Link: {message.message.text}\n"
+
                 text += stream_text
                 yield StreamChunkEvent(
                     selector=[node_id, "text"],