Use when the user wants a Pivotal-Labs-style XP pairing workflow — refining an epic, slicing it into stories, writing EARS specifications from Gherkin acceptance criteria, or doing strict per-spec TDD with developer approval at every gate. Also use when the user mentions epics, story slicing, EARS, or "pair with me on this."
Use when implementing any feature or bugfix in code — guides the strict RED-GREEN-REFACTOR cycle: write one failing test, confirm it fails for the right reason, write the minimal code to pass, refactor while the context is fresh.
Use when writing formal specifications using the EARS (Easy Approach to Requirements Syntax) patterns — converting natural-language requirements, Gherkin scenarios, or user stories into testable, atomic specs with stable semantic IDs.