Model, review, and refactor application state so source state stays minimal, derived state is computed instead of synchronized, impossible states are not representable, and each piece of state lives in the right place. Use this whenever the user mentions state management, reducers, stores, Redux, Zustand, React state, Vue state, Pinia, selectors, derived state, duplicated state, boolean flags, invalid states, async status, useEffect soup, forms, wizards, filters, URL state, server state, or confusing UI logic, even if they do not explicitly ask for a "state model."
Design, implement, review, and migrate XState v5 state machines and statecharts in TypeScript using modern v5 patterns. Use this whenever the user mentions XState, actors, state machines, statecharts, guards, transitions, workflows, or Stately, or is modeling non-trivial UI/app/process logic in a codebase that uses XState. Prefer a short machine sketch before code when requirements are fuzzy. If the problem is too simple for a state machine, say so and recommend @xstate/store instead.
Keep README files in sync with the repo using symbolic HTML comments. Use this skill whenever making a repo change that could affect documentation — code (exported APIs, configuration, examples, CLI commands, dependencies), repo structure (adding/removing/renaming files, directories, packages, or other sibling entries referenced by a listing comment), or metadata (package.json, manifests). Also use when authoring or editing README files to add or update symbolic comments. Trigger on any change — code or structural — that touches a construct referenced by an HTML comment in a markdown file.