diff --git a/backend/packages/harness/deerflow/persistence/postgres_schema.py b/backend/packages/harness/deerflow/persistence/postgres_schema.py
index f7457b654..ba8ff5a8c 100644
--- a/backend/packages/harness/deerflow/persistence/postgres_schema.py
+++ b/backend/packages/harness/deerflow/persistence/postgres_schema.py
@@ -22,6 +22,8 @@ from __future__ import annotations
 import re
 from urllib.parse import parse_qsl, quote, urlencode, urlsplit, urlunsplit
 
+from deerflow.utils.file_io import await_drained
+
 
 def build_asyncpg_connect_args(schema: str) -> dict:
     """Return SQLAlchemy ``connect_args`` that pin asyncpg's search_path.
@@ -254,4 +256,4 @@ async def ensure_postgres_schema_async(conn_string: str, schema: str, *, install
     try:
         await conn.execute(statement)
     finally:
-        await conn.close()
+        await await_drained(conn.close())
diff --git a/backend/tests/test_postgres_schema_helper.py b/backend/tests/test_postgres_schema_helper.py
index 589ca097a..bf25ec229 100644
--- a/backend/tests/test_postgres_schema_helper.py
+++ b/backend/tests/test_postgres_schema_helper.py
@@ -1,5 +1,8 @@
 """Tests for the PostgreSQL schema helpers (Issue #3380)."""
 
+import asyncio
+import sys
+from types import SimpleNamespace
 from urllib.parse import parse_qs, urlsplit
 
 import pytest
@@ -9,6 +12,7 @@ from deerflow.persistence.postgres_schema import (
     build_psycopg_options,
     create_schema_sql,
     dsn_with_search_path,
+    ensure_postgres_schema_async,
     normalize_libpq_dsn,
 )
 
@@ -176,3 +180,64 @@ class TestNormalizeLibpqDsn:
     def test_rejects_non_postgres_scheme(self):
         with pytest.raises(ValueError, match="Unsupported PostgreSQL DSN scheme"):
             normalize_libpq_dsn("mysql://localhost/db")
+
+
+@pytest.mark.asyncio
+async def test_async_schema_close_drains_across_repeated_cancellation(monkeypatch) -> None:
+    class _BlockingConnection:
+        def __init__(self) -> None:
+            self.execute_started = asyncio.Event()
+            self.allow_execute = asyncio.Event()
+            self.close_started = asyncio.Event()
+            self.allow_close = asyncio.Event()
+            self.close_finished = asyncio.Event()
+
+        async def execute(self, _statement: str) -> None:
+            self.execute_started.set()
+            await self.allow_execute.wait()
+
+        async def close(self) -> None:
+            self.close_started.set()
+            await self.allow_close.wait()
+            self.close_finished.set()
+
+    conn = _BlockingConnection()
+
+    class _AsyncConnection:
+        @staticmethod
+        async def connect(_dsn: str, *, autocommit: bool):
+            assert autocommit is True
+            return conn
+
+    monkeypatch.setitem(sys.modules, "psycopg", SimpleNamespace(AsyncConnection=_AsyncConnection))
+    task: asyncio.Task[None] | None = None
+
+    try:
+        task = asyncio.create_task(
+            ensure_postgres_schema_async(
+                "postgresql://user:pass@localhost/deerflow",
+                "deerflow",
+                install_hint="install postgres extras",
+            )
+        )
+        await asyncio.wait_for(conn.execute_started.wait(), timeout=1)
+
+        task.cancel()
+        await asyncio.wait_for(conn.close_started.wait(), timeout=1)
+
+        task.cancel()
+        for _ in range(5):
+            await asyncio.sleep(0)
+        assert not task.done(), "schema setup returned before psycopg connection close finished"
+        assert not conn.close_finished.is_set()
+
+        conn.allow_close.set()
+        with pytest.raises(asyncio.CancelledError):
+            await task
+        assert conn.close_finished.is_set()
+    finally:
+        conn.allow_execute.set()
+        conn.allow_close.set()
+        if task is not None and not task.done():
+            task.cancel()
+            await asyncio.gather(task, return_exceptions=True)