Runes of protection: tests, structure, and clarity that keep corruption from returning. By the time a team reaches the stage I call Slaying the Unnatural, the work has changed from chasing noise to preserving order. A bug may have been found, understood, reproduced, and removed, but that does not mean the system is safe. Many younger engineers learn this the hard way because they think the hunt ends when the failing line is corrected. I have learned to treat that moment as the turning of the key in a dungeon door, not the return to daylight. The creature may be dead, but the chamber that summoned it still deserves inspection.…