What this playbook covers This seven-page field guide is designed for senior .NET backend interview preparation. It connects dependency injection lifetimes to ownership and disposal, explains end-to-end cancellation and timeout budgets, provides an evidence-first EF Core query diagnosis playbook, and treats idempotency, retries, outbox delivery, and transaction boundaries as correctness decisions. How to use it Read one deep-dive chapter, answer its scenario questions aloud in 30 to 60 seconds, then take the linked production assessment in the Production-Grade .NET Backend Interview Path. The final pages contain 16 scenario checks, a concise answer key, and a scoring rubric. Quality note The C# and SQL patterns were manually reviewed, every page was rendered for visual inspection, and the guidance explicitly identifies trade-offs instead of presenting one-size-fits-all rules.