diff --git a/agentex/src/adapters/crud_store/adapter_postgres.py b/agentex/src/adapters/crud_store/adapter_postgres.py
index 8a794ce..027ea16 100644
--- a/agentex/src/adapters/crud_store/adapter_postgres.py
+++ b/agentex/src/adapters/crud_store/adapter_postgres.py
@@ -21,6 +21,7 @@
     select,
     update,
 )
+from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm.interfaces import LoaderOption
 from sqlalchemy.sql import Select
@@ -167,15 +168,25 @@ async def start_async_db_session(
             yield session
 
     async def create(self, item: T) -> T:
+        """Create an item using INSERT ... RETURNING for single query efficiency.
+
+        Uses RETURNING with explicit columns to avoid lazy-loading relationship
+        attributes on the returned ORM object, which would fail outside async context.
+        """
         async with (
             self.start_async_db_session(True) as session,
             async_sql_exception_handler(),
         ):
-            orm = self.orm(**item.to_dict())
-            session.add(orm)
+            # Exclude None values to allow server defaults (e.g., created_at) to apply
+            values = {k: v for k, v in item.to_dict().items() if v is not None}
+            # Return only columns (not full ORM) to avoid lazy-loading relationships
+            stmt = (
+                insert(self.orm).values(**values).returning(*self.orm.__table__.columns)
+            )
+            result = await session.execute(stmt)
+            row = result.one()
             await session.commit()
-            await session.refresh(orm)
-            return self.entity.model_validate(orm)
+            return self.entity.model_validate(dict(row._mapping))
 
     async def batch_create(self, items: list[T]) -> list[T]:
         async with (
diff --git a/agentex/src/domain/repositories/event_repository.py b/agentex/src/domain/repositories/event_repository.py
index 28715f1..1aa750c 100644
--- a/agentex/src/domain/repositories/event_repository.py
+++ b/agentex/src/domain/repositories/event_repository.py
@@ -2,6 +2,7 @@
 
 from fastapi import Depends
 from sqlalchemy import and_
+from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.future import select
 from src.adapters.crud_store.adapter_postgres import (
     PostgresCRUDRepository,
@@ -32,7 +33,6 @@ def __init__(
             EventEntity,
         )
 
-    # Have to do this because the sequence_id is automatically generated by the ORM
     async def create(
         self,
         id: str,
@@ -40,20 +40,25 @@ async def create(
         agent_id: str,
         content: TaskMessageContentEntity | None = None,
     ) -> EventEntity:
+        """Create an event using INSERT ... RETURNING to get sequence_id in one query."""
         async with (
             self.start_async_db_session(True) as session,
             async_sql_exception_handler(),
         ):
-            orm = EventORM(
-                id=id,
-                task_id=task_id,
-                agent_id=agent_id,
-                content=content.model_dump(mode="json") if content else None,
+            stmt = (
+                insert(EventORM)
+                .values(
+                    id=id,
+                    task_id=task_id,
+                    agent_id=agent_id,
+                    content=content.model_dump(mode="json") if content else None,
+                )
+                .returning(EventORM)
             )
-            session.add(orm)
+
+            result = await session.execute(stmt)
+            orm = result.scalar_one()
             await session.commit()
-            # Refresh the ORM object to get the auto-generated sequence_id
-            await session.refresh(orm)
             return self.entity.model_validate(orm)
 
     async def list_events_after_last_processed(