Build-an-X workflow that produces a test-case matrix from a **live, undocumented feature** - running app at a URL, screen recording, screenshot, or verbal brief - by combining structured exploration (Playwright trace / DevTools / accessibility tree) with the heuristic models in `heuristic-test-design-reference` (SFDPOT, Whittaker attacks, FEW HICCUPPS, ISO 25010). Output is a structured case matrix, not an exploratory session charter. Use when there is no story, no AC, and no documentation - only a live feature.