feat(statehub): add offline write buffer relay

tests/conftest.py

@@ -98,10 +98,17 @@ async def client(test_engine):
         async with factory() as session:
             yield session
 
+    from api.services import write_idempotency as _write_idempotency
+
+    old_session_factory = _write_idempotency.async_session_factory
+    _write_idempotency.async_session_factory = factory
     app.dependency_overrides[get_session] = _override
-    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
-        yield ac
-    app.dependency_overrides.clear()
+    try:
+        async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as ac:
+            yield ac
+    finally:
+        app.dependency_overrides.clear()
+        _write_idempotency.async_session_factory = old_session_factory
 
 
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