refactor(api): Separate SegmentType for Integer/Float to Enable Pydantic Serialization (#22025)

refactor(api): Separate SegmentType for Integer/Float to Enable Pydantic Serialization (#22025)

This PR addresses serialization issues in the VariablePool model by separating the `value_type` tags for `IntegerSegment`/`FloatSegment` and `IntegerVariable`/`FloatVariable`. Previously, both Integer and Float types shared the same `SegmentType.NUMBER` tag, causing conflicts during serialization.

Key changes:
- Introduce distinct `value_type` tags for Integer and Float segments/variables
- Add `VariableUnion` and `SegmentUnion` types for proper type discrimination
- Leverage Pydantic's discriminated union feature for seamless serialization/deserialization
- Enable accurate serialization of data structures containing these types

Closes #22024.

api/models/workflow.py

@@ -12,6 +12,7 @@ from sqlalchemy import orm
 from core.file.constants import maybe_file_object
 from core.file.models import File
 from core.variables import utils as variable_utils
+from core.variables.variables import FloatVariable, IntegerVariable, StringVariable
 from core.workflow.constants import CONVERSATION_VARIABLE_NODE_ID, SYSTEM_VARIABLE_NODE_ID
 from core.workflow.nodes.enums import NodeType
 from factories.variable_factory import TypeMismatchError, build_segment_with_type
@@ -347,7 +348,7 @@ class Workflow(Base):
         )
 
     @property
-    def environment_variables(self) -> Sequence[Variable]:
+    def environment_variables(self) -> Sequence[StringVariable | IntegerVariable | FloatVariable | SecretVariable]:
         # TODO: find some way to init `self._environment_variables` when instance created.
         if self._environment_variables is None:
             self._environment_variables = "{}"
@@ -367,11 +368,15 @@ class Workflow(Base):
         def decrypt_func(var):
             if isinstance(var, SecretVariable):
                 return var.model_copy(update={"value": encrypter.decrypt_token(tenant_id=tenant_id, token=var.value)})
-            else:
+            elif isinstance(var, (StringVariable, IntegerVariable, FloatVariable)):
                 return var
+            else:
+                raise AssertionError("this statement should be unreachable.")
 
-        results = list(map(decrypt_func, results))
-        return results
+        decrypted_results: list[SecretVariable | StringVariable | IntegerVariable | FloatVariable] = list(
+            map(decrypt_func, results)
+        )
+        return decrypted_results
 
     @environment_variables.setter
     def environment_variables(self, value: Sequence[Variable]):