fix(api): adding variable to variable pool recursively while loading draft variables. (#21478)

This PR fix the issue that `ObjectSegment` are not recursively added to the draft variable pool while loading draft variables from database. It also fixes an issue about loading variables with more than two elements in the its selector.

Enhances #19735.
Closes #21477.

api/core/workflow/variable_loader.py

@@ -3,7 +3,9 @@ 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.workflow.entities.variable_pool import VariablePool
+from core.workflow.utils import variable_utils
 
 
 class VariableLoader(Protocol):
@@ -76,4 +78,7 @@ def load_into_variable_pool(
             variables_to_load.append(list(selector))
     loaded = variable_loader.load_variables(variables_to_load)
     for var in loaded:
-        variable_pool.add(var.selector, var)
+        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
+        )