wip(handoff): restore backend suite to green

Co-Authored-By: Codex <noreply@openai.com>

backend/tests/conftest.py

@@ -5,6 +5,7 @@ Provides test database setup, client fixtures, and authentication helpers.
 """
 
 import os
+import asyncio
 from typing import AsyncGenerator
 import pytest
 import sqlalchemy as sa
@@ -73,6 +74,20 @@ def pytest_collection_modifyitems(config, items):
         items[:] = selected
 
 
+@pytest.hookimpl(trylast=True, hookwrapper=True)
+def pytest_runtest_teardown(item, nextitem):
+    """Close pytest-asyncio's post-test clean loop before warnings collect it."""
+    yield
+    policy = asyncio.get_event_loop_policy()
+    try:
+        loop = policy.get_event_loop()
+    except RuntimeError:
+        return
+    if not loop.is_running() and not loop.is_closed():
+        loop.close()
+        policy.set_event_loop(None)
+
+
 @pytest.fixture
 async def test_db() -> AsyncGenerator[AsyncSession, None]:
     """
@@ -137,6 +152,7 @@ async def test_db() -> AsyncGenerator[AsyncSession, None]:
     # Dispose engine first so all pooled connections are released,
     # then reconnect to perform the schema teardown cleanly.
     await engine.dispose()
+    await asyncio.sleep(0.01)
 
     # Drop all tables after test (CASCADE for circular FKs)
     teardown_engine = create_async_engine(
@@ -150,6 +166,7 @@ async def test_db() -> AsyncGenerator[AsyncSession, None]:
             await conn.execute(sa.text("CREATE SCHEMA public"))
     finally:
         await teardown_engine.dispose()
+        await asyncio.sleep(0.01)
 
 
 @pytest.fixture