feat: add variable selector mapping

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

@@ -137,4 +137,8 @@ class ToolNode(BaseNode):
         """
         Extract variable selector to variable mapping
         """
-        pass
+        return {
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+            k.value_selector: k.variable
+            for k in cast(ToolNodeData, node_data).tool_parameters
+            if k.variable_type == 'selector'
+        }
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