feat(workflow): support retrieving variables wrapped in {{}} from variable pool

api/app/core/workflow/variable_pool.py

@@ -10,6 +10,7 @@
 """
 
 import logging
+import re
 from typing import Any, TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -114,7 +115,9 @@ class VariablePool:
         """
         # 转换为 VariableSelector
         if isinstance(selector, str):
-            selector = VariableSelector.from_string(selector).path
+            pattern = r"\{\{\s*(.*?)\s*\}\}"
+            variable_literal = re.sub(pattern, r"\1", selector).strip()
+            selector = VariableSelector.from_string(variable_literal).path
 
         if not selector or len(selector) < 1:
             raise ValueError("变量选择器不能为空")