Principal engineering Overview Check what the system actually does rather than recalling a pattern for it. Ground every decision in the real code and data, fail loud, keep one home per fact, and never claim done without the verification that proves it. Sibling skills carry the depth: , , , , , , , , , . Load the matching one on top of this. When to invoke | The task is | Also load | |---|---| | Starting a change, a debug, or work in unfamiliar code | | | Writing or touching any error path, fallback, or default | | | Adding data, config, state, or a second copy of anything | | | Claiming "done…