The "deletion test" is a thought experiment: imagine deleting your entire codebase and regenerating it from scratch. If that's terrifying, it reveals that critical knowledge lives only in the code itself, not in specifications, tests, or contracts. As code generation becomes cheaper through AI, the bottleneck shifts from production to validation. Systems should be built around durable oracles (property-based tests, invariants, contracts) that can mechanically verify correctness without referencing old implementations. When you have strong evaluation mechanisms, code becomes disposable and regeneration becomes safe.