fix(memory): add thread-safe singleton initialization

- Add threading.Lock with double-check locking to ScopeManager
- Add asyncio.Lock with double-check locking to MemoryReflection
- Make reset_memory_metrics async with proper locking
- Update test fixtures to handle async reset functions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/unit/services/memory/metrics/test_collector.py

@@ -21,9 +21,9 @@ def metrics() -> MemoryMetrics:
 
 
 @pytest.fixture(autouse=True)
-def reset_singleton() -> None:
+async def reset_singleton() -> None:
     """Reset singleton before each test."""
-    reset_memory_metrics()
+    await reset_memory_metrics()
 
 
 class TestMemoryMetrics:
@@ -333,7 +333,7 @@ class TestSingleton:
         metrics1 = await get_memory_metrics()
         await metrics1.inc_operations("get", "working", None, True)
 
-        reset_memory_metrics()
+        await reset_memory_metrics()
 
         metrics2 = await get_memory_metrics()
         summary = await metrics2.get_summary()

backend/tests/unit/services/memory/reflection/test_service.py

@@ -59,9 +59,9 @@ def create_mock_episode(
 
 
 @pytest.fixture(autouse=True)
-def reset_singleton() -> None:
+async def reset_singleton() -> None:
     """Reset singleton before each test."""
-    reset_memory_reflection()
+    await reset_memory_reflection()
 
 
 @pytest.fixture
@@ -757,7 +757,7 @@ class TestSingleton:
     ) -> None:
         """Should create new instance after reset."""
         r1 = await get_memory_reflection(mock_session)
-        reset_memory_reflection()
+        await reset_memory_reflection()
         r2 = await get_memory_reflection(mock_session)
 
         assert r1 is not r2