refactor: simplify variable pool key structure and improve type safety (#23732)

Signed-off-by: -LAN- <laipz8200@outlook.com>

api/core/workflow/variable_loader.py

@@ -3,9 +3,8 @@ from collections.abc import Mapping, Sequence
 from typing import Any, Protocol
 
 from core.variables import Variable
-from core.variables.consts import MIN_SELECTORS_LENGTH
+from core.variables.consts import SELECTORS_LENGTH
 from core.workflow.entities.variable_pool import VariablePool
-from core.workflow.utils import variable_utils
 
 
 class VariableLoader(Protocol):
@@ -78,7 +77,7 @@ def load_into_variable_pool(
             variables_to_load.append(list(selector))
     loaded = variable_loader.load_variables(variables_to_load)
     for var in loaded:
-        assert len(var.selector) >= MIN_SELECTORS_LENGTH, f"Invalid variable {var}"
-        variable_utils.append_variables_recursively(
-            variable_pool, node_id=var.selector[0], variable_key_list=list(var.selector[1:]), variable_value=var
-        )
+        assert len(var.selector) >= SELECTORS_LENGTH, f"Invalid variable {var}"
+        # Add variable directly to the pool
+        # The variable pool expects 2-element selectors [node_id, variable_name]
+        variable_pool.add([var.selector[0], var.selector[1]], var)