fix: fixes date time issue, which was blocking run flow execution of agent flows (#5866)

* fixes PydanticSerializationError

fixes:
    PydanticSerializationError: Error calling function `serialize_model`: TypeError: tz_convert() takes exactly 2 positional arguments (1 given)

* format

* [autofix.ci] apply automated fixes

* Update src/backend/base/langflow/api/v1/schemas.py

Co-authored-by: Gabriel Luiz Freitas Almeida <gabriel@langflow.org>

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Gabriel Luiz Freitas Almeida <gabriel@langflow.org>

src/backend/base/langflow/api/v1/schemas.py

@@ -287,7 +287,7 @@ class ResultDataResponse(BaseModel):
                 return f"{obj[:max_length]}... [truncated]"
             return obj
         if isinstance(obj, datetime):
-            return obj.astimezone().isoformat()
+            return obj.replace(tzinfo=timezone.utc).isoformat()
         if isinstance(obj, Decimal):
             return float(obj)
         if isinstance(obj, UUID):

src/backend/base/langflow/graph/utils.py

@@ -86,6 +86,9 @@ def serialize_field(value):
         if hasattr(value, "to_json"):
             return value.to_json()
         return value.dict()
+    # Handle datetime objects
+    if hasattr(value, "isoformat"):
+        return value.isoformat()
     return str(value)
 
 
@@ -182,10 +185,10 @@ async def log_vertex_build(
             id=vertex_id,
             valid=valid,
             params=str(params) if params else None,
-            # ugly hack to get the model dump with weird datatypes
-            data=json.loads(data.model_dump_json()),
-            # ugly hack to get the model dump with weird datatypes
-            artifacts=json.loads(json.dumps(artifacts, default=str)),
+            # Serialize data using our custom serializer
+            data=serialize_field(data),
+            # Serialize artifacts using our custom serializer
+            artifacts=serialize_field(artifacts) if artifacts else None,
         )
         async with session_getter(get_db_service()) as session:
             inserted = await crud_log_vertex_build(session, vertex_build)