refactor(variables): clarify base vs union type naming (#30634)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

api/tests/unit_tests/core/variables/test_segment.py

@@ -35,7 +35,6 @@ from core.variables.variables import (
     SecretVariable,
     StringVariable,
     Variable,
-    VariableUnion,
 )
 from core.workflow.runtime import VariablePool
 from core.workflow.system_variable import SystemVariable
@@ -96,7 +95,7 @@ class _Segments(BaseModel):
 
 
 class _Variables(BaseModel):
-    variables: list[VariableUnion]
+    variables: list[Variable]
 
 
 def create_test_file(
@@ -194,7 +193,7 @@ class TestSegmentDumpAndLoad:
         # Create one instance of each variable type
         test_file = create_test_file()
 
-        all_variables: list[VariableUnion] = [
+        all_variables: list[Variable] = [
             NoneVariable(name="none_var"),
             StringVariable(value="test string", name="string_var"),
             IntegerVariable(value=42, name="int_var"),

api/tests/unit_tests/core/variables/test_variables.py

@@ -11,7 +11,7 @@ from core.variables import (
     SegmentType,
     StringVariable,
 )
-from core.variables.variables import Variable
+from core.variables.variables import VariableBase
 
 
 def test_frozen_variables():
@@ -76,7 +76,7 @@ def test_object_variable_to_object():
 
 
 def test_variable_to_object():
-    var: Variable = StringVariable(name="text", value="text")
+    var: VariableBase = StringVariable(name="text", value="text")
     assert var.to_object() == "text"
     var = IntegerVariable(name="integer", value=42)
     assert var.to_object() == 42

api/tests/unit_tests/core/workflow/test_variable_pool.py

@@ -24,7 +24,7 @@ from core.variables.variables import (
     IntegerVariable,
     ObjectVariable,
     StringVariable,
-    VariableUnion,
+    Variable,
 )
 from core.workflow.constants import CONVERSATION_VARIABLE_NODE_ID, ENVIRONMENT_VARIABLE_NODE_ID, SYSTEM_VARIABLE_NODE_ID
 from core.workflow.runtime import VariablePool
@@ -160,7 +160,7 @@ class TestVariablePoolSerialization:
         )
 
         # Create environment variables with all types including ArrayFileVariable
-        env_vars: list[VariableUnion] = [
+        env_vars: list[Variable] = [
             StringVariable(
                 id="env_string_id",
                 name="env_string",
@@ -182,7 +182,7 @@ class TestVariablePoolSerialization:
         ]
 
         # Create conversation variables with complex data
-        conv_vars: list[VariableUnion] = [
+        conv_vars: list[Variable] = [
             StringVariable(
                 id="conv_string_id",
                 name="conv_string",