fix: message sorting in playground (#3293)

src/backend/base/langflow/services/database/models/vertex_builds/model.py

@@ -2,7 +2,7 @@
 from typing import TYPE_CHECKING, Optional
 from uuid import UUID, uuid4
 
-from pydantic import field_validator, BaseModel
+from pydantic import field_serializer, field_validator, BaseModel
 from sqlmodel import JSON, Column, Field, Relationship, SQLModel
 
 
@@ -32,6 +32,13 @@ def validate_flow_id(cls, value):
             value = UUID(value)
         return value
 
+    @field_serializer("timestamp")
+    @classmethod
+    def serialize_timestamp(cls, value):
+        if value.tzinfo is None:
+            value = value.replace(tzinfo=timezone.utc)
+        return value
+
 
 class VertexBuildTable(VertexBuildBase, table=True):  # type: ignore
     __tablename__ = "vertex_build"