background-work-and-hosted-serviceslisted

# Background Work and Hosted Services ## The loop that must not die `ExecuteAsync` is called once. An unhandled exception ends the service silently for the rest of the process lifetime (pre-.NET 8) or tears down the whole host (.NET 8+ default `BackgroundServiceExceptionBehavior.StopHost`). Neither is what a polling loop wants - it wants to log and continue: ```csharp // WRONG: first transient DB blip permanently stops processing (or kills the app) protected override async Task ExecuteAsync(CancellationToken stoppingToken) { while (!stoppingToken.IsCancellationRequested) { await ProcessBatchAsync(stoppingToken); await Task.Delay(_interval, stoppingToken); } } // RIGHT: failure of one iteration is logged, backed off, and survived protected override async Task ExecuteAsync(CancellationToken stoppingToken) { while (!stoppingToken.IsCancellationRequested) { try { await ProcessBatchAsync(stoppingToken); } catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested) { break; } catch (Exception ex) { _logger.LogError(ex, "Batch failed, retrying after backoff"); } await Task.Delay(_interval, stoppingToken); } } ``` This loop is one of the three sanctioned homes of `catch (Exception)`. The `OperationCanceledException` filter matters: cancellation during shutdown exits cleanly instead of logging a spurious error. ## Scoped services in a singleton world Hosted services are singletons; `DbCon