# Frontend

- Ship a Ladle story alongside any new UI component, but only when the story would teach something a reader can't see from the component's source or the design system's existing stories. Run with `pnpm dev:ladle` from `frontend/`. Existing example: [src/app/runner-pool-error-popover.stories.tsx](src/app/runner-pool-error-popover.stories.tsx).
  - **Story the integration unit, not the wrapper.** If a component is a thin wrapper over a primitive (e.g. a `<Badge>` with three label variants), do not write a story for it — story the parent that combines it with other state. The interesting states live where data shapes interact: row + cell + tooltip, form + validation + submit. A trivial wrapper's "three near-identical renders" is noise, not coverage.
  - **Drive stories from realistic data fixtures, not prop permutations.** Build fixtures that mirror real API responses (empty result, single item, multi-region, partial failure, mixed kinds). Each story should answer "what does this look like when the backend returns X?" Listing every prop combination produces stories that pass design review but miss bugs like an empty endpoint set falling through to "Multiple endpoints".
  - **Cover the states that produced real bugs in this component.** When you fix a visual bug, the regression case becomes a story. If you can't articulate a state that would change behavior, you don't need another story.
  - **Skip the story if it would require mocking route loaders, auth, or the full data-provider stack.** Either refactor the component to accept its inputs as props (preferred — the story falls out for free), or test it through the parent route in the running dashboard. Do not stub `useLoaderData` / `useRouteContext` inside a story; that path rots fast.
- HTTP responses can be mocked end-to-end in dev via MSW. Append `?mock=1` to any dashboard URL (dev only, gated by `import.meta.env.DEV` in [src/lib/agent-mocks.ts](src/lib/agent-mocks.ts)) to boot the worker. Then in DevTools / agent-browser console: `window.__rivetMock("*/actors/:id/kv/keys/*", { status: 503, body: { group: "guard", code: "service_unavailable", message: "..." } })`. Mocks persist across reloads via sessionStorage; `window.__rivetClearMocks()` resets. Use this to exercise error UIs without standing up real engine state. Prod bundle is unaffected (dynamic `import("msw/browser")` behind the dev gate). To inspect a loading skeleton, add `delayMs` to hold the response open and keep the query pending: `window.__rivetMock("*/actors/names", { status: 200, body: { names: {} }, delayMs: 10000 })`.
